Aims. This study aimed to evaluate if total knee arthroplasty (TKA) femoral components aligned in either mechanical alignment (MA) or kinematic alignment (KA) are more biomimetic concerning trochlear sulcus orientation and restoration of trochlear height. Methods. Bone surfaces from 1,012 CT scans of non-arthritic femora were segmented using a modelling and analytics system. TKA femoral components (Triathlon; Stryker) were virtually implanted in both MA and KA. Trochlear sulcus orientation was assessed by measuring the distal trochlear sulcus angle (DTSA) in native femora and in KA and MA prosthetic femoral components. Trochlear anatomy restoration was evaluated by measuring the differences in medial, lateral, and sulcus trochlear height between native femora and KA and MA prosthetic femoral components. Results. Femoral components in both MA and KA alignments exhibited a more valgus DTSA compared to native femora. However, DTSA deviation from native was significantly less in KA than in MA (4.8° (SD 2.2°) vs 8.8° (SD 1.8°); p < 0.001). DTSA deviation from native orientation correlated positively with the mechanical lateral distal femoral angle (mLDFA) in KA and negatively in MA (r = 0.53, p < 0.001; r = -0.18, p < 0.001). Medial trochlear height was not restored with either MA or KA, with MA resulting in lower medial trochlear height than KA in the proximal 20% of the trochlea. Lateral and sulcus trochlear height was not restored with either alignment in the proximal 80% of the trochlea. At the terminal arc point, KA replicated sulcus and lateral trochlear height, while MA led to over-restoration. Conclusion. Femoral components aligned in KA demonstrated greater biomimetic qualities than those in MA regarding trochlear sulcus orientation and trochlear height restoration, particularly in valgus femora. Variability across knees was observed, warranting further research to evaluate the clinical implications of these findings. Cite this article: Bone Joint J 2024;106-B(8):817–825

The cause of dissatisfaction following total knee arthroplasty (TKA) remains elusive. Much attention has been focused on static mechanical alignment as a basis for surgical success and optimising outcomes. More recently, research on both normal and osteoarthritic knees, as well as kinematically aligned TKAs, has suggested that other specific and dynamic factors may be more important than a generic target of 0 ± 3º of a neutral axis. Consideration of these other variables is necessary to understand ideal targets and move beyond generic results. . Cite this article: Bone Joint J 2016;98-B(1 Suppl A):81–3

There has been a renewed interest in the importance of achievement of a neutral, mechanical alignment in total knee arthroplasty (TKA). The purpose of this presentation is to argue the merits behind questioning a neutral, mechanical alignment following TKA, and why the concepts of “constitutional varus” and “kinematic alignment” deserve further investigation. The impact of alignment on outcomes following TKA has been questioned for a number of reasons. First, recent investigations have highlighted that approximately 20% of patients are not satisfied with their outcome following TKA. Second, recent studies have shown that achievement of a mechanical axis within 3 degrees of neutral does not necessarily improve survivorship or clinical outcomes. Third, as patients requiring TKA have a wide array of morphologies and alignment, targeting the exact same alignment for each patient has been questioned. Lastly, despite the advent of new implant designs with proposed benefits of improved kinematics, few studies have shown a clinical improvement with their use. The concept of “constitutional varus” has suggested that restoration of a neutral, mechanical alignment may not be desirable and unnatural as 32% of men and 17% of women have a natural mechanical alignment of greater than 3 degrees at skeletal maturity. The “kinematic alignment” technique focuses on restoration of the joint line of the distal femur, posterior femur, and tibia to those of the non-arthritic, native knee. The kinematic alignment technique has shown promising results. However, while these concepts have merit, questions still remain regarding the optimal alignment target for each, individual patient

Introduction. Functional outcomes of mechanically aligned (MA) total knee arthroplasty have plateaued. The aim of this study is to find an alternative technique for implant positioning that improves functional outcomes of TKA. Methods. We prospectively randomized 100 consecutive patients undergoing TKA into two groups: in the group A an intramedullary femoral guide and an extramedullary tibial guide were used with aim to obtain a neutral traditional mechanical alignment; in the group B an extramedullary femoral guide set on distal femoral condyles and an extramedullary tibial guide neutrally aligned were used to obtain an adaptation of the conventional MA technique. Patients were followed-up clinically with the Short Form Health Survey (SF-12), Oxford Knee Score (OKS) and Visual Analogue Score (VAS) questionnaires pre-operatively and then at 1 year post-operatively. Mechanical alignment was calculated on standing weight bearing Xray pre- and post-operatively. T-test was used to compare the results between groups. Results. Both groups showed an improvement of clinical scores. At 1 year of follow-up OKS and SF-12 were significantly higher in group B: 47,6 ±0.75 and 46.5 ±0.76 respectively; VAS was similar in both groups. Values of mechanical alignment changed from 6.45 ±8.45 to 0.25 ±0.91 for group A and from 6.8 ±7.94 to 2.5 ±4.7 for group B. Conclusion. This study shows that adjusted mechanical alignment (AMA) with a small under-correction of frontal deformity lead to improved functional scores following total knee replacement compared to conventional technique of neutral alignment. These results are satisfactory at short follow-up but long-term studies are needed to evaluate the difference in the rate of wear of the prosthetic components

Restoring the overall mechanical alignment to neutral has been the gold standard since the 1970s and remains the current standard of knee arthroplasty today. Recently, there has been renewed interest in alternative alignment goals that place implants in a more “physiologic” position with the hope of improving clinical outcomes. Anywhere from 10 – 20% of patients are dissatisfied after knee replacement surgery and while the cause is multifactorial, some believe that it is related to changing native alignment and an oblique joint line (the concept of constitutional varus) to a single target of mechanical neutral alignment. In addition, recent studies have challenged the long held belief that total knee placed outside the classic “safe zone” of +/− 3 degrees increases the risk of mechanical failure which theoretically supports investigating alternative, more patient specific, alignment targets. From a biomechanical, implant retrieval, and clinical outcomes perspective, mechanical alignment should remain the gold standard for TKA. Varus tibias regardless of overall alignment pattern show increased polyethylene wear and varus loading increases the risk of posteromedial collapse. While recently questioned, the evidence states that alignment does matter. When you combine contemporary knee designs placed in varus with an overweight population (which is the majority of TKA patients) the failure rate increases exponentially when compared to neutral alignment. A recent meta-analysis on mechanical alignment and survivorship clearly demonstrated reduced survivorship for varus-aligned total knees. The only way to justify the biomechanical risks associated with placing components in an alternative alignment target is a significant clinical outcome benefit but the evidence is lacking. A randomised control trial comparing mechanical alignment (MA) and kinematic alignment (KA) found a significant improvement in clinical outcomes and knee function in KA patients at 2 year follow-up. In contrast, Young et al. recently published a randomised control trial comparing PSI KA and computer assisted mechanical TKA and found no difference in any clinical outcome measure. Why were the clinical outcomes scores in the MA patients so different: One potential explanation is that different surgical techniques were used. In the Dosset study, the femur was cut at 5 degrees valgus in all patients and femoral component rotation was always set at 3 degrees externally rotated to the posterior condylar axis. We know from several studies that this method leads to inaccuracies in both coronal plane and axial plane in some patients. Young et al. used computer assisted navigation to align his distal femur cut with the mechanical axis and adjusted femoral component rotation to the transepicondylar axis. The results suggest that a well performed mechanical aligned total knee replacement has excellent clinical performance equal to that of kinematic alignment without any of the long term risks of implant failure. Most contemporary TKA implants are designed to be loaded perpendicular to the polyethylene surface and placing them in shear without extensive biomechanical testing to support this alignment target may put patients at long term risk for an unproven benefit. Have we not learned our lesson?

The aim of mechanical alignment in total knee arthroplasty is to align all knees into a fixed neutral position, even though not all knees are the same. As a result, mechanical alignment often alters a patient’s constitutional alignment and joint line obliquity, resulting in soft-tissue imbalance. This annotation provides an overview of how the Coronal Plane Alignment of the Knee (CPAK) classification can be used to predict imbalance with mechanical alignment, and then offers practical guidance for bone balancing, minimizing the need for soft-tissue releases. Cite this article: Bone Joint J 2024;106-B(6):525–531

Mechanical alignment (MA) in total knee arthroplasty (TKA), although considered the gold standard, reportedly has up to 25% of patients expressing post-operative dissatisfaction. Biomechanical outcomes following kinematic alignment (KA) in TKA, developed to restore native joint alignment, remain unclear. Without a clear consensus for the optimal alignment strategy during TKA, the purpose of this study was to conduct a paired biomechanical comparison of MA and KA in TKA by experimentally quantifying joint laxity and medial collateral ligament (MCL) strain. 14 bilateral native fresh-frozen cadaveric lower limbs underwent medially-stabilised TKA (GMK Sphere, Medacta, Switzerland) using computed CT-based subject-specific guides, with KA and MA performed on left and right legs, respectively. Each specimen was subjected to sensor-controlled mediolateral laxity tests. A handheld force sensor (Mark-10, USA) was used to generate an abduction-adduction moment of 10Nm at the knee at fixed flexion angles (0°, 30°, 60°, 90°). A digital image correlation system was used to compute the strain on the superficial medial collateral ligament. A six-camera optical motion capture system (Vicon MX+, UK) was used to acquire kinematics using a pre-defined CT-based anatomical coordinate system. A linear mixed model and Tukey's posthoc test were performed to compare native, KA and MA conditions (p<0.05). Unlike MA, medial joint laxity in KA was similar to the native condition; however, no significant difference was found at any flexion angle (p>0.08). Likewise, KA was comparable with the native condition for lateral joint laxity, except at 30°, and no statistical difference was observed. Although joint laxity in MA seemed lower than the native condition, this difference was significant only for 30° flexion (p=0.01). Both KA and MA exhibited smaller MCL strain at 0° and 30°; however, all conditions were similar at 60° and 90°. Medial and lateral joint laxity seemed to have been restored better following KA than MA; however, KA did not outperform MA in MCL strain, especially after mid-flexion. Although this study provides only preliminary indications regarding the optimal alignment strategy to restore native kinematics following TKA, further research in postoperative joint biomechanics for load bearing conditions is warranted

Abstract. Background. Conventional TKR aims for neutral mechanical alignment which may result in a smaller lateral distal femoral condyle resection than the implant thickness. We aim to explore the mismatch between implant thickness and bone resection using 3D planning software used for Patient Specific Instrumentation (PSI) TKR. Methods. This is a retrospective anatomical study from pre-operative MRI 3D models for PSI TKR. Cartilage mapping allowed us to recreate the native anatomy, enabling us to quantify the mismatch between the distal lateral femoral condyle resection and the implant thickness. Results. We modelled 292 knees from PSI TKR performed between 2012 and 2015. There were 225 varus knees and 67 valgus knees, with mean supine hip-knee-angle of 5.6±3.1 degrees and 3.6±4.6 degrees, respectively. In varus knees, the mean cartilage loss from medial and lateral femoral condyle was 2.3±0.7mm and 1.1±0.8mm respectively; the mean overstuffing of the lateral condyle 1.9±2.2mm. In valgus knees, the mean cartilage loss from medial and lateral condyle was 1.4±0.8mm and 1.5±0.9mm respectively; the mean overstuffing of the lateral condyle was 4.1±1.9mm. Conclusions. Neutral alignment TKR often results in overstuffing of the lateral condyle. This may increase the patello-femoral pressure at the lateral facet in flexion. Anterior knee pain may be persistent even after patellar resurfacing due to tight lateral retinacular structures. An alternative method of alignment such as anatomic alignment may minimise this problem

Introduction: I always aim for neutral mechanical axis alignment. My principles of a successful TKA are proper alignment in all 3 planes, soft tissue balance in extension first, flexion gap balancing by parallel to tibial cut technique, maintenance of joint line, correct sizing of femoral component, and proper cement fixation. Long-term Survivorship: There is long-term data that supports the efficacy and durability of the neutral position of the proximal tibial cut. Over a 20-year follow-up there was a 92.6% success rate in my study. Other authors have found similarly successful survivorship for mechanical failure. Balance Technique in TKR: My technique to balance the knee is a balance extension gap first, which requires medial soft tissue balancing. Next, I balance the flexion gap parallel to the tibial cut. Our Results: In one study, I examined the clinical and radiographic data of 68 varus knees. Average post-operative mechanical alignment was 0 ± 3 degrees. There were no outliers which displays the reproducibility of the technique. This is the method of choice in the hands of most surgeons

No, Neutral mechanical axis has never been regarded as “necessary” to the success of TKA. In fact it has never been established as “ideal” with published data. Tibial femoral alignment after TKA is important, but it is also an issue that we do not understand completely. Neutral mechanical alignment refers to the relationship between the mechanical axes of the femur and tibia as shown on full length radiographs. “Neutral” means that these axes are collinear, i.e. that a line may be drawn from the center of the hip to the center of the ankle and it will intersect the center of the knee joint. The allure of the “straight line” has led many surgeons to regard a neutral mechanical axis as “perfection” for TKA surgery, but indeed, it is not the usual “normal” alignment for most human knees, nor is it the target for many conventional knee replacements. The “neutral mechanical axis” represents OVERCORRECTION for most knees. Moreland demonstrated in 1987 that few human knee joints are naturally aligned “in neutral”, but with the line from center of hip to center of ankle passing through the medial compartment. This tendency to relative varus mechanical axis in most human knees was corroborated by Bellemans et al in 2012. They substituted the word “constitutional varus” for what would otherwise be known as “normal alignment”. In general, patients with pathologic or significant varus alignment, whose arthroplasties have been performed competently, are at greatest risk for failure by wear, osteolysis and loosening. This is the prototypical failure mechanism that pre-occupied the surgeons responsible for making knee arthroplasty successful in the 1970s. The first paper to identify varus TKA alignment and failure due to loosening was Lotke and Ecker in 1977. They worked from short radiographs and ushered in an era of careful attention to valgus TKA alignment-not neutral alignment. Correction of varus deformity combined with ligament balancing was probably responsible for making condylar type knee arthroplasties work durably in the early days. Full length radiographs, used by Kennedy and White in 1987 to study alignment in unicompartmental arthroplasties, provide a more sophisticated method of evaluating knee alignment. These studies must be aligned with correct rotation to be valid. Computerised navigation was probably responsible for some surgeon's dedication to the neutral mechanical axis. The study of Parratte et al from Mayo has received much attention and argued that a neutral mechanical axis did NOT improve success rates at 15 years. It should be noted that these TKA's were expertly performed and even the less well-aligned cases were not “excessively” malaligned. This study does not state that alignment is irrelevant to the success of TKA, but rather that a range of alignments (with stability) might be expected to produce a durable arthroplasty. Concurrent with these developments has been an interest in “under-correcting” knee deformity or allowing osseous anatomy (with compensation for cartilage loss) guide component position. In truth, it is inaccurate to describe conventional “align and balance” techniques as necessarily seeking a neutral mechanical axis. Most classical alignment techniques do, however, alter the angle of component position from the original articular surface angles and theoretically may not function as well with the native soft tissue environment. Surgeons who would align the TKA identically to the arthritic knee may credit previous generations with improving the technology such that this is a possibility. If every patient is to be aligned with this technique, however, this suggests that soft tissue pathology does not exist. As with all complex issues, glib answers are to be avoided and deep analysis is appropriate

Conventional total knee arthroplasty aims to place the joint line perpendicular to the mechanical axis resulting in an overall neutral mechanical alignment. This objective is promulgated despite the fact healthy adult populations are on average in varus with few proximal tibias being neutral to the mechanical axis. The goal of a neutral mechanical axis is based largely on historical studies and the fact that it is easier to make a neutral tibial cut with conventional jigs and the eye. In order to balance the flexion and extension gap to accommodate a neutral tibial cut, in most patients, asymmetrical distal and posterior femoral cuts are required. The resulting position of the femoral component could be considered to be “mal-rotated” with respect to the patient's soft tissue envelope. Soft tissue releases are often required to “balance” the knee. Planning and execution of the surgery are largely based off 2-dimensional radiographs which grossly oversimplifies the concept of alignment to the coronal plane, largely ignoring what happens to the knee in 3 dimensions through range of motion and 4 dimensions with respect to gait, stair climbing, etc. Subsequently, sticking with neutral mechanical for all engenders the “looks' good, feels bad” phenomenon seen in many patients that may in part drive the higher dissatisfaction rates seen in knee arthroplasty globally compared to hip arthroplasty. New imaging and surgical techniques allow for the identification of patient specific alignment targets and the ability to more precisely execute the surgical plan with respect to 3-dimensional placement of the components. Long-term outcomes studies as well as more recent studies on “kinematic” positioning suggest that deviation away from a neutral mechanical target may in fact be safe with respect to survivorship and provide better function with a more “natural” feeling knee

Aims. Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement. Patients and Methods. A total of 47 patients due to undergo TKA were randomized to KA+PSI (n = 24) or MA+CAS (n = 23). In the KA+PSI group, there were 16 female and eight male patients with a mean age of 64 years (. sd. 8). In the MA+CAS group, there were 17 female and six male patients with a mean age of 63 years (. sd. 7). Surgery was performed using cemented, cruciate-retaining Triathlon total knees with patellar resurfacing, and patients were followed up for two years. The effect of alignment on tibial component migration and inducible displacement was analyzed irrespective of study group. Results. There was no difference over two years in longitudinal migration of the tibial component between the KA+PSI and MA+CAS groups (reaching median maximum total point motion migration at two years of 0.40 mm for the KA+PSI group and 0.37 mm for the MA+CAS group, p = 0.82; p = 0.68 adjusted for age, sex, and body mass index (BMI) for all follow-ups). Both groups had mean migrations below acceptable thresholds. There was no difference in inducible displacement (p = 0.34) or PROMS (p = 0.61 for the Oxford Knee Score) between groups. There was no correlation between alignment and tibial component migration or alignment and inducible displacement. These findings support non-neutral alignment as a viable option with this component, with no evidence that it compromises fixation. Conclusion. Kinematic alignment using patient-specific instrumentation in TKA was associated with acceptable tibial component migration, indicating stable fixation. These results are supportive of future investigations of kinematic alignment. Cite this article: Bone Joint J 2019;101-B:929–940

Introduction. Neutral mechanical alignment in TKA has been shown to be an important consideration for survivorship, wear, and aseptic loosening. However, native knee anatomy is described by a joint line in 3° of varus, 2–3° of mechanical distal femoral valgus, and 2–3° of proximal tibia varus. Described kinematic planning methods replicate native joint alignment in extension without changing tibiofemoral alignment, but do not account for native alignment through a range of motion. An asymmetric TKA femoral component with a thicker medial femoral condyle and posterior condylar internal rotation paired with an asymmetric polyethylene insert aligns the joint line in 3° of varus while maintaining distal femoral and proximal tibial cuts perpendicular to mechanical axis. The asymmetric components recreate an anatomic varus joint line while avoiding tibiofemoral malalignment or femoral component internal rotation, a risk factor for patellofemoral maltracking. The study seeks to determine how many patients would be candidates for a kinematically planned knee without violating the principle of a neutral mechanical axis (0° ± 3°). Methods. A cohort comprised of 55 consecutive preoperative THA patients with asymptomatic knees and 55 consecutive preoperative primary unilateral TKA patients underwent simultaneous biplanar radiographic imaging. Full length coronal images from the thoracolumbar junction to the ankles were measured by two independent observers for the following: mechanical tibiofemoral angle (mTFA), mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA). Patients who met the following conditions: mTFA 0°±3°; mLDFA 87°±3°; and mMPTA 87°±3°, were considered candidates for TKA with an asymmetric implant that would achieve a kinematic joint line and neutral mechanical axis. Similarly, patients with the following conditions: mTFA 0°±3°; mLDFA 90°±3°; and mMPTA 90°±3°, were considered candidates for TKA with a symmetric implant that would achieve a kinematic joint line and neutral mechanical axis. Results. In this cohort of 110 patients, the mean mTFA was 1° varus ± 5°, the mean mLDFA was 87° ± 3°, mMPTA 87°± 2°. The comparison of patients meeting each of the three conditions required for a TKA with a neutral mechanical axis and a kinematic joint line are outlined in Table 1. Conclusion. A TKA with kinematic 3° varus joint line and neutral mechanical axis was possible in 52% of patients using an asymmetric implant and 23% of patients using a symmetric implant. Previous descriptions of kinematic planning using standard TKA components required compromise of neutral mechanical axis alignment with detrimental effects on overall survivorship. Knee arthroplasty using an asymmetric implant may achieve the best of both worlds, neutral mechanical axis and a kinematic joint line, in a large percentage of patients

Introduction. Debate over appropriate alignment in total knee arthroplasty has become a topical subject as technology allows planned alignments that differ from a neutral mechanical axis. These surgical techniques employ patient-specific cutting blocks derived from 3D reconstructions of pre-operative imaging, commonly MRI or CT. The patient-specific OtisMed system uses a detailed MRI scan of the knee for 3D reconstruction to estimate the kinematic axis, dictating the cutting planes in the custom-fit cutting blocks machined for each patient [1, 2]. The purpose of this study was to evaluate the correlation between post-operative limb alignment and implant migration in subjects receiving shape match derived kinematic alignment. Methods. In a randomized controlled trial comparing patient-specific cutting blocks to navigated surgery, seventeen subjects in the patient specific group had complete 1 year data. They received cruciate retaining cemented total knee replacements (Triathlon, Stryker) using patient-specific cutting blocks (OtisMed custom-fit blocks, Stryker). Intra-operatively, 6–8 tantalum markers (1 mm diameter) were inserted in the proximal tibia. Radiostereometric analysis (RSA) [3, 4] exams were performed with subjects supine on post-operative day 1 and at 6 week, 3, 6, and 12 month follow-ups with dual overhead tubes (Rad 92, Varian Medical Systems, Inc., Palo Alto, CA, USA), digital detectors (CXDI-55C, Canon Inc., Tokyo, Japan), and a uniplanar calibration box (Halifax Biomedical Inc., Mabou, NS, Canada). RSA exams were analyzed in Model-based RSA (Version 3.32, RSAcore, Leiden, The Netherlands. Post-operative limb alignment was evaluated from weight-bearing long-leg films. Results. Post-operative limb alignments ranged from 5 degrees of varus to 5 degrees of valgus. Comparing implant migration to post-operative alignment did not demonstrate a relationship between deviation from neutral mechanical alignment and increased migration (Pearson correlation coefficient = 0.25, P = 0.33) (Figure 1). Conclusions. Previous studies have suggested that alignment of greater than 3 degrees from neutral may have adverse effects on implant survivorship [5], but this early data does not suggest increased migration with non-neutral alignment. Continued evaluation with RSA to 2 years will be performed to monitor these subjects over the longer term

INTRODUCTION. While standard instrumentation tries to reproduce mechanical axes based on mechanical alignment guides, a new “shape matching” system derives its plan from kinematic measurements using pre-operative MRIs. The current study aimed to compare the resultant alignment in a matched pair cadaveric study between the Shape Match and a standard mechanical system. METHODS. A prospective series of Twelve (12) eviscerated torso's were acquired for a total of twenty four (24) limb specimens that included intact pelvises, femoral heads, knees, and ankles. The cadavers received MRI-scans, which were used to manufacture the Shape Match cutting guides. Additionally all specimen received “pre-operative” CT-scans to determine leg axes. Two (2) investigating surgeons performed total knee arthroplasties on randomly chosen sides by following the surgical technique using conventional instruments. On the contralateral sides, implantation of the same prosthesis was done using the Kinematic Shape Match Cutting Guides. A navigation system was used to check for leg alignement. Implant alignement was determined using post-operative CT-scans. For statistical analysis SPSS was used. RESULTS. In measurements using the navigation system, the overall alignment of the leg showed no significant differences between the two tested systems. This was also found in the CT-Measurements. In the Shape Match group the difference between the planned and the final implantation regarding overall limb alignment ranged between −0,5° (valgus) and 6° varus (p=0,518; CI −1,97°/1,05°). The leg alignement in the conventional group ranged between −2,5° and 13° varus (p=0,176; CI −4,93°/1,02). DISCUSSION AND CONCLUSION. As expected, the two compared system employ different alignment strategies, which reflected in variations of the combinations of the three-dimensional component position on the femur and the tibia. These different strategies result in overall leg alignment that compares well between the two different methods, with fewer outliers in the Shape Match group

Non-invasive assessment of lower limb mechanical alignment and assessment of knee laxity using navigation technology is now possible during knee flexion owing to recent software developments. We report a comparison of this new technology with a validated commercially available invasive navigation system. We tested cadaveric lower limbs (n=12) with a commercial invasive navigation system against the non-invasive system. Mechanical femorotibial angle (MFTA) was measured with no stress, then with 15Nm of varus and valgus moment. MFTA was recorded at 10° intervals from full knee extension to 90° flexion. The investigator was blinded to all MFTA measurements. Repeatability coefficient was calculated to reflect each system's level of precision, and agreement between the systems; 3° was chosen as the upper limit of precision and agreement when measuring MFTA in the clinical setting based on current literature. Precision of the invasive system was superior and acceptable in all conditions of stress throughout flexion (repeatability coefficient <2°). Precision of the non-invasive system was acceptable from extension until 60° flexion (repeatability coefficient <3°), beyond which precision was unacceptable. Agreement between invasive and non-invasive systems was within 1.7° from extension to 50° flexion when measuring MFTA with no varus / valgus applied. When applying varus / valgus stress agreement between the systems was acceptable from full extension to 20° & 30° knee flexion respectively (repeatability coefficient <3°). Beyond this the systems did not demonstrate sufficient agreement. These results indicate that the non-invasive system can provide reliable quantitative data on MFTA and laxity in the range relevant to knee examination

Non-invasive assessment of lower limb mechanical alignment and assessment of knee laxity using navigation technology is now possible during knee flexion owing to recent software developments. We report a comparison of this new technology with a validated commercially available invasive navigation system. We tested cadaveric lower limbs (n=12) with a commercial invasive navigation system against the non-invasive system. Mechanical femorotibial angle (MFTA) was measured with no stress, then with 15 Nm of varus and valgus moment. MFTA was recorded at 10° intervals from full knee extension to 90° flexion. The investigator was blinded to all MFTA measurements. Repeatability coefficient was calculated to reflect each system's level of precision, and agreement between the systems; 3° was chosen as the upper limit of precision and agreement when measuring MFTA in the clinical setting based on current literature. Precision of the invasive system was superior and acceptable in all conditions of stress throughout flexion (repeatability coefficient <2°). Precision of the non-invasive system was acceptable from extension until 60° flexion (repeatability coefficient <3°), beyond which precision was unacceptable. Agreement between invasive and non-invasive systems was within 1.7° from extension to 50° flexion when measuring MFTA with no varus / valgus applied. When applying varus / valgus stress agreement between the systems was acceptable from full extension to 30° knee flexion (repeatability coefficient <3°). Beyond this the systems did not demonstrate sufficient agreement. These results indicate that the non-invasive system can provide reliable quantitative data on MFTA and laxity in the range relevant to knee examination

In total knee replacement (TKR), neutral mechanical alignment (NMA) is targeted in prosthetic component implantation. A novel implantation approach, referred to as kinematic alignment (KA), has been recently proposed (Eckhoff et al. 2005). This is based on the pre-arthritic lower limb alignment which is reconstructed using suitable image-based techniques, and is claimed to allow better soft-tissue balance (Eckhoff et al. 2005) and restoration of physiological joint function. Patient-specific instrumentation (PSI) introduced in TKR to execute personalized prosthesis component implantation are used for KA. The aim of this study was to report knee kinematics and electromyography (EMG) for a number lower limb muscles from two TKR patient groups, i.e. operated according to NMA via conventional instrumentation, or according to KA via PSI. 20 patients affected by primary gonarthrosis were implanted with a cruciate-retaining fixed-bearing prosthesis with patella resurfacing (Triathlon® by Stryker®, Kalamazoo, MI-USA). 17 of these patients, i.e. 11 operated targeting NMA (group A) via convention instrumentation and 6 targeting KA (group B) via PSI (ShapeMatch® by Stryker®, Kalamazoo, MI-USA), were assessed clinically using the International Knee Society Scoring (IKSS) System and biomechanically at 6-month follow-up. Knee kinematics during stair-climbing, chair-rising and extension-against-gravity was analysed by means of 3D video-fluoroscopy (CAT® Medical System, Monterotondo, Italy) synchronized with 4-channel EMG analysis (EMG Mate, Cometa®, Milan, Italy) of the main knee ad/abductor and flexor/extensor muscles. Knee joint motion was calculated in terms of flex/extension (FE), ad/abduction (AA), and internal/external rotation (IE), together with axial rotation of condyle contact point line (CLR). Postoperative knee and functional IKSS scores in group A were 78±20 and 80±23, worse than in group B, respectively 91±12 and 90±15. Knee motion patterns were much more consistent over patients in group B than A. In both groups, normal ranges were found for FE, IE and AA, the latter being generally smaller than 3°. Average IE ranges in the three motor tasks were respectively 8.2°±3.2°, 10.1°±3.9° and 7.9°±4.0° in group A, and 6.6°±4.0°, 10.5°±2.5° and 11.0°±3.9° in group B. Relevant CLRs were 8.2°±3.2°, 10.2°±3.7° and 8.8°±5.3° in group A, and 7.3°±3.5°, 12.6°±2.6° and 12.5°±4.2° in group B. EMG analysis revealed prolonged activation of the medial/lateral vasti muscles in group A. Such muscle co-contraction was not generally observed in all patients in group B, this perhaps proving more stability in the knee replaced following the KA approach. These results reveal that KA results in better function than NMA in TKR. Though small differences were observed between groups, the higher data consistency and the less prolonged muscle activations detected using KA support indirectly the claim of a more natural knee soft tissue balance. References

INTRODUCTION. In total knee arthroplasty (TKA), the effectiveness of the mechanical alignment (MA) within 0°±3° has been recently questioned. A novel implantation approach, i.e. the kinematic alignment (KA), emerged recently, this being based on the pre-arthritic lower-limb alignment. In KA, the trans-cylindrical axis is used as the reference, instead of the trans-epicondylar one, for femoral component alignment. This axis is defined as the line passing through the centres of the posterior femoral condyles modeled as cylinders. Recently, patient specific instrumentation (PSI) has been introduced in TKA as an alternative to conventional instrumentation. This provides a tool for preoperative implant planning also via KA. Particularly, KA using PSI seems to be more effective in restoring normal joint kinematics and muscle activity. The purpose of this study was to report preliminarily joint kinematic and electromyography results of two patient groups operated via conventional MA or KA, the latter using PSI. PATIENT AND METHODS. Twenty patients recruited for TKA were implanted with Triathlon® prosthesis (Stryker®-Orthopaedics, Mahwah, NJ-USA). Seventeen patients, eleven operated targeting MA using the convention instrumentation (group A) and six targeting KA (group B) using PSI (Stryker®-Orthopaedics), were assessed at 6 month follow-up clinically via IKSS and biomechanically. Knee kinematics during stair-climbing, chair-rising, and extension-against-gravity were evaluated using three-dimensional mono-planar video-fluoroscopy (CAT® Medical-System, Monterotondo, Italy) synchronised with electromyography (Wave-Wireless, Cometa®, Milan, Italy). Component pose was reconstructed to calculate knee flexion/extension (FE), ad/abduction (AA), internal/external-rotation (IE), together with the rotation of the contact-line (CLR), i.e. line connecting the medial (MCP) and lateral (LCP) tibio-femoral contact points. MCP and LCP antero-posterior translations were calculated and reported in percentage (%) of the tibial base-plate length. RESULTS. Postoperative clinical scores were better in group B. Knee/functional scores were 78±20/80±23 in group A and 91±12/90±15 in group B. AA range was found smaller than 3°, and physiological ranges of FE and IE were found in both groups. From extension to flexion, MCP translations were all anterior of about 13.8±5.6% anterior, 17.0±6.6% posterior and 15.4±6.6.9% posterior in group A, and 13.0±3.4%, 16.6±5.3% and 16.6±5.6% in group B; corresponding values for LCP were all posterior of about 9.5±3.6%, 11.1±4.3% and 8.7±2.6% in group A, and 102±2.1%, 13.7±8.6% and 14.6±9.8% in group B. These resulted in a CLR equal to 8.2°±3.2°, 10.2°±3.7° and 8.8°±5.3° in group A, and 7.3°±3.5°, 12.6°±2.6° and 12.5°±4.2° group B. Much more consistent patterns of motion were observed in group B. A prolonged activation of the vastus medialis and lateralis was observed in group A. DISCUSSION. These preliminary results show that better scores can be expected using PSI via KA. Although not relevant kinematic differences were observed between groups, more consistent patterns were observed in using PSI via KA. Furthermore, the observed less prolonged activation of the knee extensor muscles suggest that a more natural soft tissue balance is experienced in this group. These findings show a good efficacy of KA using PSI in TKA. The clinical/functional analysis of more patients and a longer follow-up are necessary to establish the claimed superiority of the novel approach

It is clear in 2013 that there is a substantial opportunity to improve patient outcomes after total knee replacement. Much attention in the last decade has focused on the apparent satisfaction gap between patients who have had total hip arthroplasty and those who have had total knee arthroplasty. Most authors note that a higher proportion of total hip patients claim to have complete satisfaction or note that they have forgotten that they had the joint replaced. The concept of “the forgotten joint replacement” is an interesting one because as surgeons and researchers we all recognise that neither total hip replacement nor total knee replacement will completely restore the native hip or knee joint's dynamic 3D biomechanics or kinematics. What the concept of the forgotten joint does tell us however is that there is a level of kinematic function above which humans cannot detect a difference with normal function. The inherent simplicity of the ball-and-socket design of the hip joint means we can achieve this level of function more reliably and reproducibly than we do in the knee joint. The knee joint presents a more difficult challenge.

Recent data suggests that there is a definable trade-off in total knee prosthesis design, and likely with component position and limb alignment, between those optimised for the best kinematics and those optimised for the best durability using contemporary biomaterials (namely metal, ceramic and ultra-high molecular weight polyethylene). Given this inherent trade-off then there will be an almost never-ending debate about what constitutes “the best” overall knee implant design because that will inevitably require an individual value-judgement about the relative merit of better kinematics or better durability. Currently, we have some insights into this trade-off when we consider the role of unicompartmental knee replacement in 2013. There is little debate that unicompartmental knee replacement results in closer-to-normal knee kinematics than does total knee replacement and that many patients seem to benefit from a quicker recovery and easier rehabilitation. Data from multiple national joint registries however shows that UKR is not quite as durable as total knee replacement (mean yearly failure rate 1.53% for UKR versus 1.26% for TKR). Different surgeons and different surgeons will look at that data however and come to markedly different conclusions about how to act — some will discount the difference in durability and favor the better function/quicker recovery of UKR while other equally intelligent persons will discount the difference in function and prefer the demonstrated better durability of TKR. Like any value-judgement there is no right answer or wrong answer.

As surgeons and researchers we do have opportunities in regard to surgical technique that remain unexplored. We have been limited over the past several decades by thinking primarily in terms of 2D static analyses of alignment, rotation and ligament balance. This is primarily because most assessments have been done using plain radiographs. The last decade however has seen a marked improvement in our capabilities for 3D imaging and dynamic assessment of knee joint function. The promise of computer-navigated and robotic-assisted surgery has largely remained unfulfilled as the limitations of 2D targets have come into focus. It is my belief that tomorrow's gains in total knee replacement will not involve dramatic changes in prosthesis design but instead on defining and then hitting more precise 3D targets for alignment, rotation and ligament balance in surgery. For surgeons and researchers this is an exciting time as there is a distinct opportunity to improve outcomes for millions of total knee replacement patients over the coming decades.

Most discussions of alignment after TKA focus on defining “malalignment”; the prefix mal- is derived from Latin and refers to bad, abnormal or defective and thus by definition malalignment is bad, abnormal or defective alignment. No one then wants a “malaligned” knee. The intellectually curious, however, might switch the focus to the other end of the spectrum and ask what does an ideally aligned knee look like in 2015? Is there really one simple target value for alignment in all patients undergoing TKA? Is that target broad (zero +/−3 degrees mechanical axis) or is it a narrow target in which a penalty, in regard to durability or function, is incurred as soon as you deviate even 1 degree? Is that ideal target the same if we are evaluating the functional performance of the TKA versus the durability of the TKA or could there be 2 different targets, one that maximises function and one that maximises durability? Is that target adequately described by a single 2-dimensional value (varus/valgus alignment in the frontal plane) as measured on a static radiograph? Is that value the same if the patient has a fixed pelvic obliquity, a varus thrust in the contralateral knee or an abnormal foot progression angle?

It is revealing to ask “do we understand TKA alignment better in 2015 than in 1979…?” Maybe not. We allowed ourselves over the past 2 decades to be intellectually complacent in regard to questions of ideal alignment after TKA. The constraints on accuracy imposed by our standard total knee instruments and the constraints on assessment imposed by 2-dimensional radiographs made broad, simple targets like a mechanical axis +/− 3 degrees reasonable starting points yet we have not further worked to verify if we can do better. It is naïve to think that the complex motion at the knee occurring in 6-dimensions over time can be reduced to a single static target value like a neutral mechanical axis and have strong predictive value in regard to the success or failure of an individual TKA. We assessed 399 knees of 3 different modern cemented designs at 15 years and found that factors other than alignment were more important than alignment in determining the 15-year survival.

Until more precise alignment targets can be identified for individual patients or sub-groups of patients then a neutral mechanical axis remains a reasonable surgical goal. However, the traditional description of TKA alignment as a dichotomous variable (aligned versus malaligned) defined around the broad, generic target value of 0 +/− 3 degrees relative to the mechanical axis is of little practical value in predicting the durability or function of modern TKA.

This study evaluates the effect of lower limb post-operative mechanical axis on the long term risk of revision surgery following primary total knee arthroplasty (TKA). The study is relevant because many recent clinical trials have evaluated the optimal surgical technique for accurately aligning components in TKA, despite little evidence that alignment may effect the long-term clinical outcome. The data used in this study was collected prospectively as part of a randomized control trial comparing the long term survival of cemented versus uncemented TKA. The trial included 501 press-fit condylar posterior cruciate ligament-retaining prostheses performed by the senior author (PJG) or under his direct supervision. The post-operative mechanical axis alignment of the lower limb was measured following TKA using standard AP weight-bearing long leg alignment radiographs. A comparison was made between a well-aligned group with a mechanical axis alignment within 3° of neutral; and a poorly-aligned group whose mechanical axis alignment deviated greater than 3° from neutral. Survival analysis used revision surgery, with exchange of any of the three originally inserted components (femoral, tibial, polyethylene insert), as the endpoint. There was no loss to follow-up in this study. The minimum follow-up of TKAs in this study was 5.8 years. In the population of TKAs that were followed up at 10 years, 6% (17/270) required revision surgery. There was a significant difference in the rate of revision surgery between the well-aligned group 5% (11/227) and the poorly-aligned group 14% (6/43 p< 0.05). This study shows that post-operative lower limb mechanical axis alignment is an important determinant of the need for revision surgery at 10 years. Surgeons performing TKA should pay particular attention to the placement of the tibial and femoral components, so that a mechanical axis within 3° of neutral is achieved

Purpose: To determine if use of CAS in TKA improves postoperative mechanical axis alignment and component position as compared to use of standard surgical instrumentation. Method: 200 patients were prospectively randomized to TKA utilizing CAS navigation vs. standard surgical technique. Two surgeons performed all procedures utilizing a subvastus approach, the BrainLab navigation system and posterior cruciate substituting implants. Postoperative mechanical axis alignment was measured on full length standing radiographs and component placement on CT (Perth protocol). Two independent raters measured radiographic angles. The variation in mechanical axis measures were compared between the two treatment groups using a two-sided permutation test. Results: Surgery has been completed on all 200 patients with patient demographics similar among the two treatment groups. Median tourniquet time was increased in the navigation group (82 mins versus 57 mins, p < 0.001). Radiographic analysis of the first 100 patients showed the standard deviation of the post-operative mechanical axis measurements to be 22% lower in the navigation group than the standard surgical instrumentation group (2.4 vs. 3.0), marginally significant (p = 0.055). Optimal mechanical axis alignment (to within 3 degrees or less) was achieved in 75% of patients with navigation and in 68% of patients with standard surgical instrumentation. Analysis of all 200 pts will be completed shortly as well as results of component placement based on postoperative CT. Conclusion: Based on analysis of the first 100 patients, use of CAS in TKA marginally statistically improved mechanical axis alignment precision compared to standard surgical technique

Correct positioning and alignment of components during primary total knee replacement (TKR) is widely accepted to be an important predictor of patient satisfaction and implant durability. This retrospective study reports the effect of the post-operative mechanical axis of the lower limb in the coronal plane on implant survival following primary TKR. A total of 501 TKRs in 396 patients were divided into an aligned group with a neutral mechanical axis (± 3°) and a malaligned group where the mechanical axis deviated from neutral by > 3°. At 15 years’ follow-up, 33 of 458 (7.2%) TKRs were revised for aseptic loosening. Kaplan-Meier survival analysis showed a weak tendency towards improved survival with restoration of a neutral mechanical axis, but this did not reach statistical significance (p = 0.47). We found that the relationship between survival of a primary TKR and mechanical axis alignment is weaker than that described in a number of previous reports

Significant concerns remain in computer navigated surgery regarding potential errors due to inadequate tracker or array fixation, cutting guide block movements, saw blade deviation, variable component seating and standardisation and validity of radiographic measurements of alignment for outcome assessment. There are no studies in the literature comparing computer generated axes at different steps of operation as well as radiographic axes using scanograms to our knowledge. Long leg films involve significant radiation, which can be minimised by the use of scanograms. A prospective study was performed to compare the per-operative and post-operative alignment of the lower limbs after navigated total knee replacements. All consecutive patients who underwent navigated total knee replacement between May 2006 and November 2006 were included in the study. Patients with inadequate data, patients who refused to participate in the study or lost contact, obvious measurement errors and patients having had recent operations were excluded. The intra-operative initial, trial and the final axes were recorded from the navigation system. Post-operatively a CT (Computer Tomogram) scanogram of the lower limbs was performed as per the scanogram protocol. Measurement of the mechanical hip-knee-ankle axis of the lower limb was performed on the computer. Results were analysed using appropriate statistical methods and comparison made between initial, trial, final and scanogram axes with assessment of their correlation coefficients. Twenty-five patients were initially recruited in the study, of which, 15 were available with completed data. There were four males and 11 females with the age ranging from 57–80 (average 70) years. The right knee was replaced in 12 and the left knee in three patients. The average initial alignment was 0.09° valgus (0.5° varus to 1° valgus), trial alignment 0.59° varus (2° varus to 1° valgus), final alignment 0.56° varus (4° varus to 1.5° valgus) and average radiographic alignment was 0.52° varus (3.1° varus to 1.8° valgus) in maximum possible extension. Average deviation from initial to trial alignment was 0.69° varus, trial to final was 0.03° varus and final to radiographic alignment was 0.12° valgus. Correlation co-efficient of 0.62 between the initial and final axes with average difference of 0.72° varus (p= 0.11, unequal variance 2 tailed) demonstrates reasonable reproducibility of the alignment with computer-guided surgery, also confirming the fact that there is some variation between the initial cut angles and final mechanical axes. Correlation co-efficient of 0.92 between final axes and radiographic axes suggests that scanogram is an imaging modality with reasonable accuracy for measuring mechanical limb alignment despite significantly low radiation and relatively low resolution. Potential errors in radiographic measurements due to rotational malposition combined with flexion deformity is highlighted

Aims. Alternative alignment concepts, including kinematic and restricted kinematic, have been introduced to help improve clinical outcomes following total knee arthroplasty (TKA). The purpose of this study was to evaluate the clinical results, along with patient satisfaction, following TKA using the concept of restricted kinematic alignment. Methods. A total of 121 consecutive TKAs performed between 11 February 2018 to 11 June 2019 with preoperative varus deformity were reviewed at minimum one-year follow-up. Three knees were excluded due to severe preoperative varus deformity greater than 15°, and a further three due to requiring revision surgery, leaving 109 patients and 115 knees to undergo primary TKA using the concept of restricted kinematic alignment with advanced technology. Patients were stratified into three groups based on the preoperative limb varus deformity: Group A with 1° to 5° varus (43 knees); Group B between 6° and 10° varus (56 knees); and Group C with varus greater than 10° (16 knees). This study group was compared with a matched cohort of 115 TKAs and 115 patients using a neutral mechanical alignment target with manual instruments performed from 24 October 2016 to 14 January 2019. Results. Mean overall patient satisfaction for the entire cohort was 4.7 (SE 0.1) on a 5-point Likert scale, with 93% being either very satisfied or satisfied compared with a Likert of 4.3 and patient satisfaction of 81% in the mechanical alignment group (p < 0.001 and p < 0.006 respectively). At mean follow-up of 17 months (11 to 27), the mean overall Likert, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, Western Ontario and McMaster Universities Osteoarthritis Index, Forgotten Joint Score, and Knee Society Knee and Function Scores were significantly better in the kinematic group than in the neutral mechanical alignment group. The most common complication in both groups was contracture requiring manipulation under anaesthesia, involving seven knees (6.1%) in the kinematic group and nine knees (7.8%) in the mechanical alignment group. Conclusion. With the advent of advanced technology, and the ability to obtain accurate bone cuts, the target limb alignment, and soft-tissue balance within millimetres, using a restricted kinematic alignment concept demonstrated excellent patient satisfaction following primary TKA. Longer-term analysis is required as to the durability of this method. Cite this article: Bone Joint J 2021;103-B(6 Supple A):59–66

The February 2023 Knee Roundup. 360. looks at: Machine-learning models: are all complications predictable?; Positive cultures can be safely ignored in revision arthroplasty patients that do not meet the 2018 International Consensus Meeting Criteria; Spinal versus general anaesthesia in contemporary primary total knee arthroplasty; Preoperative pain and early arthritis are associated with poor outcomes in total knee arthroplasty; Risk factors for infection and revision surgery following patellar tendon and quadriceps tendon repairs; Supervised versus unsupervised rehabilitation following total knee arthroplasty; Kinematic alignment has similar outcomes to mechanical alignment: a systematic review and meta-analysis; Lifetime risk of revision after knee arthroplasty influenced by age, sex, and indication; Risk factors for knee osteoarthritis after traumatic knee injury

The June 2024 Research Roundup. 360. looks at: Do the associations of daily steps with mortality and incident cardiovascular disease differ by sedentary time levels?; Large-scale assessment of ChatGPT in benign and malignant bone tumours imaging report diagnosis and its potential for clinical applications; Long-term effects of diffuse idiopathic skeletal hyperostosis on physical function: a longitudinal analysis; Effect of intramuscular fat in the thigh muscles on muscle architecture and physical performance in the middle-aged females with knee osteoarthritis; Preoperative package of care for osteoarthritis an opportunity not to be missed?; Superiority of kinematic alignment over mechanical alignment in total knee arthroplasty during medium- to long-term follow-up: a meta-analysis and trial sequential analysis

Aims. While mechanical alignment (MA) is the traditional technique in total knee arthroplasty (TKA), its potential for altering constitutional alignment remains poorly understood. This study aimed to quantify unintentional changes to constitutional coronal alignment and joint line obliquity (JLO) resulting from MA. Methods. A retrospective cohort study was undertaken of 700 primary MA TKAs (643 patients) performed between 2014 and 2017. Lateral distal femoral and medial proximal tibial angles were measured pre- and postoperatively to calculate the arithmetic hip-knee-ankle angle (aHKA), JLO, and Coronal Plane Alignment of the Knee (CPAK) phenotypes. The primary outcome was the magnitude and direction of aHKA, JLO, and CPAK alterations. Results. The mean aHKA and JLO increased by 0.1° (SD 3.4°) and 5.8° (SD 3.5°), respectively, from pre- to postoperatively. The most common phenotypes shifted from 76.3% CPAK Types I, II, or III (apex distal JLO) preoperatively to 85.0% IV, V, or VI (apex horizontal JLO) postoperatively. The proportion of knees with apex proximal JLO increased from 0.7% preoperatively to 11.1% postoperatively. Among all MA TKAs, 60.0% (420 knees) were changed from their constitutional alignments into CPAK Type V, while 40.0% (280 knees) either remained in constitutional Type V (5.0%, 35 knees) or were unintentionally aligned into other CPAK types (35.0%; 245 knees). Conclusion. Fixed MA targets in TKA lead to substantial changes from constitutional alignment, primarily a significant increase in JLO. These findings enhance our understanding of alignment alterations resulting from both unintended changes to knee phenotypes and surgical resection imprecision. Cite this article: Bone Jt Open 2024;5(2):109–116

Aims. The aims of this study were: 1) to describe extended restricted kinematic alignment (E-rKA), a novel alignment strategy during robotic-assisted total knee arthroplasty (RA-TKA); 2) to compare residual medial compartment tightness following virtual surgical planning during RA-TKA using mechanical alignment (MA) and E-rKA, in the same set of osteoarthritic varus knees; 3) to assess the requirement of soft-tissue releases during RA-TKA using E-rKA; and 4) to compare the accuracy of surgical plan execution between knees managed with adjustments in component positioning alone, and those which require additional soft-tissue releases. Methods. Patients who underwent RA-TKA between January and December 2022 for primary varus osteoarthritis were included. Safe boundaries for E-rKA were defined. Residual medial compartment tightness was compared following virtual surgical planning using E-rKA and MA, in the same set of knees. Soft-tissue releases were documented. Errors in postoperative alignment in relation to planned alignment were compared between patients who did (group A) and did not (group B) require soft-tissue releases. Results. The use of E-rKA helped restore all knees within the predefined boundaries, with appropriate soft-tissue balancing. E-rKA compared with MA resulted in reduced residual medial tightness following surgical planning, in full extension (2.71 mm (SD 1.66) vs 5.16 mm (SD 3.10), respectively; p < 0.001), and 90° of flexion (2.52 mm (SD 1.63) vs 6.27 mm (SD 3.11), respectively; p < 0.001). Among the study population, 156 patients (78%) were managed with minor adjustments in component positioning alone, while 44 (22%) required additional soft-tissue releases. The mean errors in postoperative alignment were 0.53 mm and 0.26 mm among patients in group A and group B, respectively (p = 0.328). Conclusion. E-rKA is an effective and reproducible alignment strategy during RA-TKA, permitting a large proportion of patients to be managed without soft-tissue releases. The execution of minor alterations in component positioning within predefined multiplanar boundaries is a better starting point for gap management than soft-tissue releases. Cite this article: Bone Jt Open 2024;5(8):628–636

Aims. Accurate identification of the ankle joint centre is critical for estimating tibial coronal alignment in total knee arthroplasty (TKA). The purpose of the current study was to leverage artificial intelligence (AI) to determine the accuracy and effect of using different radiological anatomical landmarks to quantify mechanical alignment in relation to a traditionally defined radiological ankle centre. Methods. Patients with full-limb radiographs from the Osteoarthritis Initiative were included. A sub-cohort of 250 radiographs were annotated for landmarks relevant to knee alignment and used to train a deep learning (U-Net) workflow for angle calculation on the entire database. The radiological ankle centre was defined as the midpoint of the superior talus edge/tibial plafond. Knee alignment (hip-knee-ankle angle) was compared against 1) midpoint of the most prominent malleoli points, 2) midpoint of the soft-tissue overlying malleoli, and 3) midpoint of the soft-tissue sulcus above the malleoli. Results. A total of 932 bilateral full-limb radiographs (1,864 knees) were measured at a rate of 20.63 seconds/image. The knee alignment using the radiological ankle centre was accurate against ground truth radiologist measurements (inter-class correlation coefficient (ICC) = 0.99 (0.98 to 0.99)). Compared to the radiological ankle centre, the mean midpoint of the malleoli was 2.3 mm (SD 1.3) lateral and 5.2 mm (SD 2.4) distal, shifting alignment by 0.34. o. (SD 2.4. o. ) valgus, whereas the midpoint of the soft-tissue sulcus was 4.69 mm (SD 3.55) lateral and 32.4 mm (SD 12.4) proximal, shifting alignment by 0.65. o. (SD 0.55. o. ) valgus. On the intermalleolar line, measuring a point at 46% (SD 2%) of the intermalleolar width from the medial malleoli (2.38 mm medial adjustment from midpoint) resulted in knee alignment identical to using the radiological ankle centre. Conclusion. The current study leveraged AI to create a consistent and objective model that can estimate patient-specific adjustments necessary for optimal landmark usage in extramedullary and computer-guided navigation for tibial coronal alignment to match radiological planning. Cite this article: Bone Jt Open 2022;3(10):767–776

INTRODUCTION. Mechanical alignment in TKA introduces significant anatomic modifications for many individuals, which may result in unequal medial-lateral or flexion-extension bone resections. The objective of this study was to calculate bone resection thicknesses and resulting gap sizes, simulating a measured resection mechanical alignment technique for TKA. METHODS. Measured resection mechanical alignment bone resections were simulated on 1000 consecutive lower limb CT-Scans from patients undergoing TKA. Bone resections were simulated to reproduce the following measured resection mechanical alignment surgical technique. The distal femoral and proximal tibial cuts were perpendicular to the mechanical axis, setting the resection depth at 8mm from the most distal femoral condyle and from the most proximal tibial plateau (Figure 1). If the resection of the contralateral side was <0mm, the resection level was increased such that the minimum resection was 0mm. An 8mm resection thickness was based on an implant size of 10mm (bone +2mm of cartilage). Femoral rotation was aligned with either the trans-epicondylar axis or with 3 degrees of external rotation to the posterior condyles. After simulation of the bone cuts, media-lateral gap difference and flexion-extension gaps difference were calculated. The gap sizes were calculated as the sum of the femoral and tibial bone resections, with a target bone resection of 16mm (+ cartilage corresponding to the implant thickness). RESULTS. For both the varus and valgus knees, the created gaps in the medial and lateral compartments were reduced in the vast majority of cases (<16mm). The insufficient lateral condyle resection distalises the lateral joint surface by a mean of 2.1mm for the varus and 4.4mm for the valgus knees. The insufficient medial tibial plateau resection proximalises the medial joint surface by 3.3mm for the varus and 1.2mm for the valgus knees. Medio-lateral gap imbalances in the extension space of more than 2mm) occurred in 25% of varus and 54% of valgus knees and significant imbalances of more than 5mm were present in up to 8% of varus and 19% of valgus knees. Higher medio-lateral gap imbalances in the flexion space were created with trans epicondylar axis versus 3 degrees to the posterior condyles (p<0.001). Using trans epicondylar axis, only 49% of varus and 18% of valgus knees had less than 3mm of imbalance in both media-lateral and flexion-extension gaps together. DISCUSSION AND CONCLUSION. A systematic use of the tested measured resection mechanical alignment technique for TKA leads to many cases with medio-lateral or flexion-extension gap asymmetries. Some medio-lateral imbalances may not be correctable surgically and may results in TKA instability. Other versions of the mechanical alignment technique or other alignment methods that better reproduce knee anatomies should be explored. For any figures or tables, please contact the authors directly

Aims. Sagittal plane imbalance (SPI), or asymmetry between extension and flexion gaps, is an important issue in total knee arthroplasty (TKA). The purpose of this study was to compare SPI between kinematic alignment (KA), mechanical alignment (MA), and functional alignment (FA) strategies. Methods. In 137 robotic-assisted TKAs, extension and flexion stressed gap laxities and bone resections were measured. The primary outcome was the proportion and magnitude of medial and lateral SPI (gap differential > 2.0 mm) for KA, MA, and FA. Secondary outcomes were the proportion of knees with severe (> 4.0 mm) SPI, and resection thicknesses for each technique, with KA as reference. Results. FA showed significantly lower rates of medial and lateral SPI (2.9% and 2.2%) compared to KA (45.3%; p < 0.001, and 25.5%; p < 0.001) and compared to MA (52.6%; p < 0.001 and 29.9%; p < 0.001). There was no difference in medial and lateral SPI between KA and MA (p = 0.228 and p = 0.417, respectively). FA showed significantly lower rates of severe medial and lateral SPI (0 and 0%) compared to KA (8.0%; p < 0.001 and 7.3%; p = 0.001) and compared to MA (10.2%; p < 0.001 and 4.4%; p = 0.013). There was no difference in severe medial and lateral SPI between KA and MA (p = 0.527 and p = 0.307, respectively). MA resulted in thinner resections than KA in medial extension (mean difference (MD) 1.4 mm, SD 1.9; p < 0.001), medial flexion (MD 1.5 mm, SD 1.8; p < 0.001), and lateral extension (MD 1.1 mm, SD 1.9; p < 0.001). FA resulted in thinner resections than KA in medial extension (MD 1.6 mm, SD 1.4; p < 0.001) and lateral extension (MD 2.0 mm, SD 1.6; p < 0.001), but in thicker medial flexion resections (MD 0.8 mm, SD 1.4; p < 0.001). Conclusion. Mechanical and kinematic alignment (measured resection techniques) result in high rates of SPI. Pre-resection angular and translational adjustments with functional alignment, with typically smaller distal than posterior femoral resection, address this issue. Cite this article: Bone Jt Open 2024;5(8):681–687

Mechanical alignment has been a fundamental tenet of total knee arthroplasty (TKA) since modern knee replacement surgery was developed in the 1970s. The objective of mechanical alignment was to infer the greatest biomechanical advantage to the implant to prevent early loosening and failure. Over the last 40 years a great deal of innovation in TKA technology has been focusing on how to more accurately achieve mechanical alignment. Recently the concept of mechanical alignment has been challenged, and other alignment philosophies are being explored with the intention of trying to improve patient outcomes following TKA. This article examines the evolution of the mechanical alignment concept and whether there are any viable alternatives

Introduction. Varus alignment in total knee replacement (TKR) results in a larger portion of the joint load carried by the medial compartment. [1]. Increased burden on the medial compartment could negatively impact the implant fixation, especially for cementless TKR that requires bone ingrowth. Our aim was to quantify the effect varus alignment on the bone-implant interaction of cementless tibial baseplates. To this end, we evaluated the bone-implant micromotion and the amount of bone at risk of failure. [2,3]. Methods. Finite element models (Fig.1) were developed from pre-operative CT scans of the tibiae of 11 female patients with osteoarthritis (age: 58–77 years). We sought to compare two loading conditions from Smith et al.;. [1]. these corresponded to a mechanically aligned knee and a knee with 4° of varus. Consequently, we virtually implanted each model with a two-peg cementless baseplate following two tibial alignment strategies: mechanical alignment (i.e., perpendicular to the tibial mechanical axis) and 2° tibial varus alignment (the femoral resection accounts for additional 2° varus). The baseplate was modeled as solid titanium (E=114.3 GPa; v=0.33). The pegs and a 1.2 mm layer on the bone-contact surface were modeled as 3D-printed porous titanium (E=1.1 GPa; v=0.3). Bone material properties were non-homogeneous, determined from the CT scans using relationships specific to the proximal tibia. [2,4]. The bone-implant interface was modelled as frictional with friction coefficients for solid and porous titanium of 0.6 and 1.1, respectively. The tibia was fixed 77 mm distal to the resection. For mechanical alignment, instrumented TKR loads previously measured in vivo. [5]. were applied to the top of the baseplate throughout level gait in 2% intervals (Fig.1a). For varus alignment, the varus/valgus moment was modified to match the ratio of medial-lateral force distribution from Smith et al. [1]. (Fig.1b). Results. For both alignments and all bones, the largest micromotion and amount of bone at risk of failure occurred during mid stance, at 16% of gait (Figs.2,3). Peak micromotion, located at the antero-lateral edge of the baseplate, was 153±32 µm and 273±48 µm for mechanical and varus alignment, respectively. The area of the baseplate with micromotion above 40 µm (the threshold for bone ingrowth. [3]. ) was 28±5% and 41±4% for mechanical and varus alignment, respectively. The amount of bone at risk of failure at the bone-implant interface was 0.5±0.3% and 0.8±0.3% for the mechanical and varus alignment, respectively. Discussion. The peak micromotion and the baseplate area with micromotion above 40 µm increased with varus alignment compared to mechanical alignment. Furthermore, the amount of bone at risk of failure, although small for both alignments, was greater for varus alignment. These results suggest that varus alignment, consisting of a combination of femoral and tibial alignment, may negatively impact bone ingrowth and increase the risk of bone failure for cementless tibial baseplates of this TKR design

Aims. Our objective was to conduct a systematic review and meta-analysis, to establish whether differences arise in clinical outcomes between autologous and synthetic bone grafts in the operative management of tibial plateau fractures. Methods. A structured search of MEDLINE, EMBASE, the online archives of Bone & Joint Publishing, and CENTRAL databases from inception until 28 July 2021 was performed. Randomized, controlled, clinical trials that compared autologous and synthetic bone grafts in tibial plateau fractures were included. Preclinical studies, clinical studies in paediatric patients, pathological fractures, fracture nonunion, or chondral defects were excluded. Outcome data were assessed using the Risk of Bias 2 (ROB2) framework and synthesized in random-effect meta-analysis. The Preferred Reported Items for Systematic Review and Meta-Analyses guidance was followed throughout. Results. Six studies involving 353 fractures were identified from 3,078 records. Following ROB2 assessment, five studies (representing 338 fractures) were appropriate for meta-analysis. Primary outcomes showed non-significant reductions in articular depression at immediate postoperative (mean difference -0.45 mm, p = 0.25, 95%confidence interval (CI) -1.21 to 0.31, I. 2. = 0%) and long-term (> six months, standard mean difference -0.56, p = 0.09, 95% CI -1.20 to 0.08, I. 2. = 73%) follow-up in synthetic bone grafts. Secondary outcomes included mechanical alignment, limb functionality, and defect site pain at long-term follow-up, perioperative blood loss, duration of surgery, occurrence of surgical site infections, and secondary surgery. Mean blood loss was lower (90.08 ml, p < 0.001, 95% CI 41.49 to 138.67) and surgery was shorter (16.17 minutes, p = 0.04, 95% CI 0.39 to 31.94) in synthetic treatment groups. All other secondary measures were statistically comparable. Conclusion. All studies reported similar methodologies and patient populations; however, imprecision may have arisen through performance variation. These findings supersede previous literature and indicate that, despite perceived biological advantages, autologous bone grafting does not demonstrate superiority to synthetic grafts. When selecting a void filler, surgeons should consider patient comorbidity, environmental and societal factors in provision, and perioperative and postoperative care provision. Cite this article: Bone Jt Open 2022;3(3):218–228

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal

Limb alignment in total knee arthroplasty (TKA) influences periarticular soft-tissue tension, biomechanics through knee flexion, and implant survival. Despite this, there is no uniform consensus on the optimal alignment technique for TKA. Neutral mechanical alignment facilitates knee flexion and symmetrical component wear but forces the limb into an unnatural position that alters native knee kinematics through the arc of knee flexion. Kinematic alignment aims to restore native limb alignment, but the safe ranges with this technique remain uncertain and the effects of this alignment technique on component survivorship remain unknown. Anatomical alignment aims to restore predisease limb alignment and knee geometry, but existing studies using this technique are based on cadaveric specimens or clinical trials with limited follow-up times. Functional alignment aims to restore the native plane and obliquity of the joint by manipulating implant positioning while limiting soft tissue releases, but the results of high-quality studies with long-term outcomes are still awaited. The drawbacks of existing studies on alignment include the use of surgical techniques with limited accuracy and reproducibility of achieving the planned alignment, poor correlation of intraoperative data to long-term functional outcomes and implant survivorship, and a paucity of studies on the safe ranges of limb alignment. Further studies on alignment in TKA should use surgical adjuncts (e.g. robotic technology) to help execute the planned alignment with improved accuracy, include intraoperative assessments of knee biomechanics and periarticular soft-tissue tension, and correlate alignment to long-term functional outcomes and survivorship

Introduction. Although total knee arthroplasty (TKA) is generally considered successful, 16–30% of patients are dissatisfied. There are multiple reasons for this, but some of the most frequent reasons for revision are instability and joint stiffness. A possible explanation for this is that the implant alignment is not optimized to ensure joint stability in the individual patient. In this work, we used an artificial neural network (ANN) to learn the relation between a given standard cruciate-retaining (CR) implant position and model-predicted post-operative knee kinematics. The final aim was to find a patient-specific implant alignment that will result in the estimated post-operative knee kinematics closest to the native knee. Methods. We developed subject-specific musculoskeletal models (MSM) based on magnetic resonance images (MRI) of four ex vivo left legs. The MSM allowed for the estimation of secondary knee kinematics (e.g. varus-valgus rotation) as a function of contact, ligament, and muscle forces in a native and post-TKA knee. We then used this model to train an ANN with 1800 simulations of knee flexion with random implant position variations in the ±3 mm and ±3° range from mechanical alignment. The trained ANN was used to find the implant alignment that resulted in the smallest mean-square-error (MSE) between native and post-TKA tibiofemoral kinematics, which we term the dynamic alignment. Results. Dynamic alignment average MSE kinematic differences to the native knees were 1.47 mm (± 0.89 mm) for translations and 2.89° (± 2.83°) for rotations. The implant variations required were in the range of ±3 mm and ±3° from the starting mechanical alignment. Discussion. In this study we showed that the developed tool has the potential to find an implant position that will restore native tibiofemoral kinematics in TKA. The proposed method might also be used with other alignment strategies, such as to optimize implant position towards native ligament strains. If native knee kinematics are restored, a more normal gait pattern can be achieved, which might result in improved patient satisfaction. The small changes required to achieve the dynamic alignment do not represent large modifications that might compromise implant survivorship. Conclusion. Patient-specific implant position predicted with MSM and ANN can restore native knee function in a post-TKA knee with a standard CR implant

The emergence of patient specific instrumentation has seen an expansion from simple radiographs to plan total knee arthroplasty (TKA) with modern systems using computed tomography (CT) or magnetic resonance imaging scans. Concerns have emerged regarding accuracy of these non-weight bearing modalities to assess true mechanical axis. The aim of our study was to compare coronal alignment on full length standing AP imaging generated by the EOS acquisition system with the CT coronal scout image. Eligible patients underwent unilateral or bilateral primary TKA for osteoarthritis under the care of investigating surgeon between 2017 and 2022, with both EOS X-Ray Imaging Acquisition System and CT scans performed preoperatively. Coronal mechanical alignment was measured on the supine coronal scout CT scan and the standing HKA EOS. Pre-operative lower limb coronal alignment was assessed on 96 knees prior to TKA on the supine coronal scout CT scan and the standing HKA EOS. There were 56 males (56%), and 44 right knees (44%). The mean age was 68 years (range 53-90). The mean coronal alignment was 4.7 degrees (SD 5.3) on CT scan and 4.6 degrees (SD 6.2) on EOS (p=0.70). There was a strong positive correlation of coronal alignment on CT scan and EOS (pearson. 0.927, p=0.001). The mean difference between EOS and CT scan was 0.9 degrees (SD 2.4). Less than 3 degrees variation between measures was observed in 87% of knees. On linear regression for every 1° varus increase in CT HKA alignment, the EOS HKA alignment increased by 0.93° in varus orientation. The model explained 86% of the variability. CT demonstrates excellent reliability for assessing coronal lower limb alignment compared to EOS in osteoarthritic knees. This supports the routine use of CT to plan TKA without further weight bearing imaging in routine cases

Our objective was to conduct a systematic review and meta-analysis, comparing differences in clinical outcomes between either autologous or synthetic bone grafts in the operative management of tibial plateau fractures: a traumatic pattern of injury, associated with poor long-term functional prognosis. A structured search of MEDLINE, EMBASE, The Bone & Joint and CENTRAL databases from inception until 07/28/2021 was performed. Randomised, controlled, clinical trials that compared autologous and synthetic bone grafts in tibial plateau fractures were included. Preclinical studies, clinical studies in paediatric patients, pathological fractures, fracture non-union or chondral defects were excluded. Outcome data was assessed using the Risk of Bias 2 (ROB2) framework and synthesised in random-effect meta-analysis. Preferred Reported Items for Systematic Review and Meta-Analysis guidance was followed throughout. Six comparable studies involving 352 patients were identified from 3,078 records. Following ROB2 assessment, five studies (337 patients) were eligible for meta-analysis. Within these studies, more complex tibia plateau fracture patterns (Schatzker IV-VI) were predominant. Primary outcomes showed non-significant reductions in articular depression at immediate postoperative (mean difference −0.45mm, p=0.25, 95% confidence interval (95%CI): −1.21-0.31mm, I. 2. =0%) and long-term (>6 months, standard mean difference −0.56, p=0.09, 95%CI: −1.20-0.08, I. 2. =73%) follow-up in synthetic bone grafts. Secondary outcomes included mechanical alignment, limb functionality, defect site pain, occurrence of surgical site infections, secondary surgery, perioperative blood loss, and duration of surgery. Blood loss was lower (90.08ml, p<0.001, 95%CI: 41.49-138.67ml, I. 2. =0%) and surgery was shorter (16.17minutes, p=0.04, 95%CI: 0.39-31.94minutes, I. 2. =63%) in synthetic treatment groups. All other secondary measures were statistically comparable. Our findings supersede previous literature, demonstrating that synthetic bone grafts are non-inferior to autologous bone grafts, despite their perceived disadvantages (e.g. being biologically inert). In conclusion, surgeons should consider synthetic bone grafts when optimising peri-operative patient morbidity, particularly in complex tibial plateau fractures, where this work is most applicable

Abstract. Introduction. OtisMed Shape Match ® patient specific implant cutting jigs were designed to place TKA in kinematic alignment (KA) rather than traditional mechanical alignment (MA). This product was withdrawn from the market in 2013. It has been hypothesised that KA might lead to early implant failure. Initial evidence has not supported this. We present 10 year outcome data for the largest single centre cohort to date. Methodology. Between 2010 and 2013, 127 Shape Match® TKAs were implanted in 119 individuals. Retrospective review of long leg post-operative radiographs assessed femoral mechanical anatomical angle (FMA), tibial mechanical angle (TMA), hip-knee-ankle angle (HKA), posterior tibial slope (PTS) and femoral component flexion. Oxford Knee Scores (OKS), revision and further surgery rates were reviewed. Results. 4 (3.1%) patients underwent revision for instability, recurrent haemarthrosis, stiffness and infection respectively. In this subgroup, PTS ranged from 9–25° (SD 7.5°). PTS range for non-revision subgroup was 1–23° (SD 4.6). 1 patient with a PTS of 21° had failure of quadriceps tendon, but was not revised. Mean OKS at 1year = 38.1 (SD 1.08), 2 years = 39.3 (SD 1.08), 5 years = 40.8 (SD 4.11). PTS had the largest impact on OKS, with <10° slope conferring a higher OKS. Conclusions. At 10 year follow up, this cohort did identify several cases where excessive PTS was evident. This may have led to revision surgery and contributed post-operative complications. PTS, unlike other alignment measures, impacted OKS results. Overall revision rate and OKS were consistent with registry and other published data

Aims. A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA). Methods. A radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type. Results. There was similar frequency distribution between healthy and arthritic groups across all CPAK types. The most common categories were Type II (39.2% healthy vs 32.2% OA), Type I (26.4% healthy vs 19.4% OA) and Type V (15.4% healthy vs 14.6% OA). CPAK Types VII, VIII, and IX were rare in both populations. Across all CPAK types, a greater proportion of KA TKAs achieved optimal balance compared to MA. This effect was largest, and statistically significant, in CPAK Types I (100% KA vs 15% MA; p < 0.001), Type II (78% KA vs 46% MA; p = 0.018). and Type IV (89% KA vs 0% MA; p < 0.001). Conclusion. CPAK is a pragmatic, comprehensive classification for coronal knee alignment, based on constitutional alignment and JLO, that can be used in healthy and arthritic knees. CPAK identifies which knee phenotypes may benefit most from KA when optimization of soft tissue balance is prioritized. Further, it will allow for consistency of reporting in future studies. Cite this article: Bone Joint J 2021;103-B(2):329–337

Dissatisfaction following total knee arthroplasty is a well-documented phenomenon. Although many factors have been implicated, including modifiable and nonmodifiable patient factors, emphasis over the past decade has been on implant alignment and stability as both a cause of, and a solution to, this problem. Several alignment targets have evolved with a proliferation of techniques following the introduction of computer and robotic-assisted surgery. Mechanical alignment targets may achieve mechanically-sound alignment while ignoring the soft tissue envelope; kinematic alignment respects the soft tissue envelope while ignoring the mechanical environment. Functional alignment is proposed as a hybrid technique to allow mechanically-sound, soft tissue-friendly alignment targets to be identified and achieved. Cite this article: Bone Joint J 2020;102-B(3):276–279

Introduction. Total knee arthroplasty (TKA) reliably improves pain and function in patients with knee osteoarthritis (OA), though a substantial percentage of patients remain unsatisfied. Reasons include the presence of complications, persistent pain, and unmet expectations. The aim of this study was to determine whether the sequential addition of accelerometer-based navigation of the distal femoral cut and sensor-assisted soft tissue balancing changed complication rates, radiographic alignment, or patient-reported outcomes (PROs) compared to TKA performed with conventional instrumentation. Methods. This retrospective cohort study included 371 TKAs in 319 patients. All surgeries were performed by a single surgeon in sequential fashion using a measured resection technique with a goal of mechanical alignment. The historical control group, utilizing intramedullary guides for distal femoral resection and surgeon-guided soft tissue balancing, was compared to group 1 (accelerometer-based navigation for distal femoral resection, surgeon-guided balancing) and group 2 (navigated femoral resection, sensor-guided balancing). Primary outcome measures were PROMIS scores including physical function computerized adaptive test (PF CAT), and the Global 10 health assessment (including physical, mental, and pain scores), and Knee Injury Osteoarthritis and Outcome Score (KOOS), measured preoperatively and at 6 weeks and 12 months postoperatively. Radiographic measurements included component position and overall mechanical alignment of the limb and were made at 6 weeks by a single examiner from hip to ankle standing films. Charts were reviewed for pre- and postoperative ROM at 6 weeks, polyethylene insert morphology, and postoperative hematocrit change. Complications were recorded, including manipulation under anesthesia and reoperation. Our study was powered to detect a difference of 1 standard deviation in PF CAT score with 100 patients. Statistical analysis was performed by a statistician including t-tests, multivariate regression, and time series plot analyses. Results. There were 194 patients in the control group, 103 in group 1, and 74 in group 2. There was no difference in baseline patient demographics. Patients in group 2 had higher baseline mental health subscores than control and group 1 patients (53.2 vs 50.2 vs 50.2, p=0.04). There were no differences in 6-week and one-year postop PF CAT, physical or mental subscores, pain scores, or KOOS scores (all p>0.05). There were 8 total complications in the control group (4.1%), 4 in group 1 (3.8%), and 1 in group 2 (1.4%) (p>0.4). The postoperative mechanical axis of the limb was within 3 degrees of neutral in 71.6% of control patients, 74.8% in group 1, and 85.1% in group 2 (p=0.1). There was no difference in femoral component coronal alignment between groups (p=0.91), though controls had a small but significantly higher degree of flexion in the sagittal plane (6.5 degrees) than groups 1 and 2 (5.4 degrees in both, p=0.003). There was no difference in postoperative ROM or blood loss. Conclusions. The sequential addition of imageless navigation of the distal femoral cut and sensor-guided ligament balancing did not confer any benefit to short term PROs, radiographic outcomes, or complication rates over conventional techniques. While overall mechanical alignment of the limb was improved in groups 1 and 2 compared to controls, this did not reach statistical significance. The additive costs of navigation and soft-tissue balancing technologies may not be justified. For figures, tables, or references, please contact authors directly

Aims. Our aim was to compare kinematic with mechanical alignment in total knee arthroplasty (TKA). Patients and Methods. We performed a prospective blinded randomised controlled trial to compare the functional outcome of patients undergoing TKA in mechanical alignment (MA) with those in kinematic alignment (KA). A total of 71 patients undergoing TKA were randomised to either kinematic (n = 36) or mechanical alignment (n = 35). Pre- and post-operative hip-knee-ankle radiographs were analysed. The knee injury and osteoarthritis outcome score (KOOS), American Knee Society Score, Short Form-36, Euro-Qol (EQ-5D), range of movement (ROM), two minute walk, and timed up and go tests were assessed pre-operatively and at six weeks, three and six months and one year post-operatively. Results. A total of 78% of the kinematically aligned group (28 patients) and 77% of the mechanically aligned group (27 patients) were within 3° of their pre-operative plan. There were no statistically significant differences in the mean KOOS (difference 1.3, 95% confidence interval (CI) -9.4 to 12.1, p = 0.80), EQ-5D (difference 0.8, 95% CI -7.9 to 9.6, p = 0.84), ROM (difference 0.1, 95% CI -6.0 to 6.1, p = 0.99), two minute distance tolerance (difference 20.0, 95% CI -52.8 to 92.8, p = 0.58), or timed up and go (difference 0.78, 95% CI -2.3 to 3.9, p = 0.62) between the groups at one year. Conclusion. Kinematically aligned TKAs appear to have comparable short-term results to mechanically aligned TKAs with no significant differences in function one year post-operatively. Further research is required to see if any theoretical long-term functional benefits of kinematic alignment are realised or if there are any potential effects on implant survival. Cite this article: Bone Joint J 2016;98-B:1360–8

Introduction. There are conflicting views when assessing the best imaging modality by which to assess long leg alignment pre and post operatively for patients’ receiving primary total hip replacements. It has been a long standing standard that long-leg radiographs are used for measuring and interpreting alignment of the lower limb, but recently it has been suggested that CT imaging may be a better option for this assessment. Methods. Patients awaiting total knee replacement surgeries were invited to participate in this clinical trial. 120 participants’ consented and completed both pre and post-operative long-leg radiographs, and lower limb CT scans. Long leg radiographs were analysed and measured by senior orthopaedic surgeons pre and post-operatively, while CT scans were analysed using the perth protocol method by trained radiologists. Mechanical alignment of the lower limb was calculated using both imaging modalities, the CT “scout” scan was used for the measurement of the mechanical alignment. Pre-operatively the patients had their imaging performed between 1 year and 1 week pre-operatively, and following surgery their imaging was standardised to 6 months post-operatively. For long leg radiographs, patients were asked to stand with their feet shoulder width apart and toes forward facing (on occasion deformities would not allow for this stance, and they were asked to adopt this stance to the best of their ability). Result. The results were analysed using pearsons correlation tests, correlation was shown to be good between the mechanical alignment measurements taken from long leg radiographs, and also from CT scout scans. Preliminary results have shown that correlation between the two modalities is 0.7, displaying a good level of correlation. Interobserver and intra observer analysis of the mechanical alignment taken from long leg radiographs is shown to be excellent with preliminary correlation being 0.9. Conclusion. The correlation results show that CT scans could be using in place of long leg radiographs, and this could assist in measuring the alignment of patients with deformities rendering them unable to stand. Radiation dose has been a main focus of many papers reviewing this correlation previously, but as the mechanical alignment does not require an investigational CT scan to be performed, but only a scout CT scan, the radiation dose is quite comparable to that of a long leg radiograph. CT scan have the additional ability of being able to place the whole image of the leg onto one screen, whereas x-ray of the entire leg required the merging of three different cassettes. This leads to additional human error with the aligning of these cassettes by the radiographer prior to taking the image, and following exposure. CT scans should be considered for measuring the alignment of the lower limb prior to and after total knee replacement

Unicompartmental knee replacement (UKR) has good outcomes for the treatment of compartmental osteoarthritis of the knee. Mechanical alignment overcorrection is associated with early failure of the femoral and tibial components. Preoperative mechanical alignment is the most important predictor of postoperative alignment. However, most studies do not take into consideration the magnitude of preoperative deformity when reporting on mechanical alignment outcomes after UKR. We aimed to determine the magnitude of postoperative mechanical alignment achieved based on the magnitude of preoperative alignment; and to compare the number of cases of overcorrection into valgus to historical data. This was a radiographic review of patients who underwent robotic medial UKR by a single surgeon between 2007 and 2011. Two examiners measured pre- and postoperative mechanical alignment for all patients on long-leg radiographs. Patients were classified into three groups of preoperative mechanical alignment: mild varus (0–5®); moderate varus (5–10®); and severe varus (>10®). Patients with valgus alignment (<0®) were excluded. Linear regression was used to estimate the magnitude of postoperative alignment for each group, adjusting for age, BMI, gender, side, implant type, and polyethylene thickness. 89 patients were included. Mean preoperative alignment was 7.3® varus (95% CI = 6.6®–8®; range, 0.1–15® varus). Mean postoperative alignment was 2.8® varus (95% CI = 1.9®–3.8®; range, 1.4® valgus–9.7® varus). There was a significant difference in postoperative mechanical alignment between the three groups (Table 1) (P<0.05). Four overcorrections (4.5%) were detected, all under 1.5® valgus. This percentage of overcorrection was significantly better than previous conventional UKR reports (mean = 12.6%; P = 0.04). The magnitude of postoperative alignment in medial UKR depends on the severity of the preoperative deformity. Reports on radiographic outcomes of UKR should be stratified by the magnitude of preoperative alignment. The risk of overcorrection is reduced when using robotic assistance compared to using the conventional manual technique

Background. The JOURNEY™ II Cruciate-Retaining Total Knee System (JIICR) and the JOURNEY™ II Bi-Cruciate Stabilized Total Knee System (JIIBCS) (both, Smith & Nephew, Memphis, TN, USA) are used for the treatment of end-stage degenerative knee arthritis. Belonging to the JOURNEY family of knee implants, the relatively new devices are designed to provide guided motion. Studies suggest that long-term outcomes of robotic-assisted navigation in total knee arthroplasty (TKA) are superior to the classical approach. This is the first report describing early postoperative outcomes of the NAVIO® robotic-assisted surgical navigation using the JOURNEY™ II family of knee implants. Materials & Methods. In this ongoing study, six investigational sites in the US prospectively enrolled 122 patients (122 TKAs, 64 JIIBCS and 58 JIICR). Patients underwent TKA using the NAVIO system (Figure 1), a next-generation semi-autonomous tool that uses handheld miniaturized robotic-assisted instrumentation that the surgeon manipulates in 6 degrees of freedom, but restricts cutting to within the confines of the pre-designated resection area of the patient's bone. The primary outcome was postoperative mechanical alignment on long leg X-ray at one month postoperative compared to operative target alignment. Alignment within ±3 degrees of the target alignment was considered a success. Results. Average age was 65.7 years (range, 39–79); 60.7% were females. All patients underwent patella resurfacing. Two patients had revision prior to the one-month follow-up visit; two patients withdrew from the study. 95% (112/118) attended the one-month follow-up. Four patients were missing either baseline or follow-up long leg X-ray, resulting in 108 evaluated TKAs. Overall, 92.6% (100/108) of TKAs were within 3 degrees of the target alignment. Of these, 24.1%, 39.8-, 19.4%, and 9.3% were at 0, 1, 2, and 3 degrees of the target alignment, respectively. There were two revisions, one at 18 days postoperative and the second at 27 days postoperative. Discussion. At the one-month follow-up, the NAVIO™ Robotic Assisted TKA procedures resulted in a very high success rate of 92.6% in achieving planned mechanical alignment compared to standard instruments as historical control (73.4%) based on literature. 1. This demonstrates the improved accuracy and reliability of the NAVIO™ Robotic Assisted Surgical System for TKA procedures. For any figures or tables, please contact the authors directly

Aims. It is unknown whether kinematic alignment (KA) objectively improves knee balance in total knee arthroplasty (TKA), despite this being the biomechanical rationale for its use. This study aimed to determine whether restoring the constitutional alignment using a restrictive KA protocol resulted in better quantitative knee balance than mechanical alignment (MA). Methods. We conducted a randomized superiority trial comparing patients undergoing TKA assigned to KA within a restrictive safe zone or MA. Optimal knee balance was defined as an intercompartmental pressure difference (ICPD) of 15 psi or less using a pressure sensor. The primary endpoint was the mean intraoperative ICPD at 10° of flexion prior to knee balancing. Secondary outcomes included balance at 45° and 90°, requirements for balancing procedures, and presence of tibiofemoral lift-off. Results. A total of 63 patients (70 knees) were randomized to KA and 62 patients (68 knees) to MA. Mean ICPD at 10° flexion in the KA group was 11.7 psi (SD 13.1) compared with 32.0 psi in the MA group (SD 28.9), with a mean difference in ICPD between KA and MA of 20.3 psi (p < 0.001). Mean ICPD in the KA group was significantly lower than in the MA group at 45° and 90°, respectively (25.2 psi MA vs 14.8 psi KA, p = 0.004; 19.1 psi MA vs 11.7 psi KA, p < 0.002, respectively). Overall, participants in the KA group were more likely to achieve optimal knee balance (80% vs 35%; p < 0.001). Bone recuts to achieve knee balance were more likely to be required in the MA group (49% vs 9%; p < 0.001). More participants in the MA group had tibiofemoral lift-off (43% vs 13%; p < 0.001). Conclusion. This study provides persuasive evidence that restoring the constitutional alignment with KA in TKA results in a statistically significant improvement in quantitative knee balance, and further supports this technique as a viable alternative to MA. Cite this article: Bone Joint J. 2020;102-B(1):117–124

Introduction. Restoration of a neutral mechanical axis has been a widely held tenet of primary total knee arthroplasty (TKA), however new technologies are recently being marketed which claim correction of alignment deformity is unimportant. This study was undertaken to determine whether the outcome of aseptic loosening was associated with post-operative mal-alignment of the mechanical axis. Methods. A 1:9 matched case-control analysis was conducted within a cohort of 1,030 consecutive cemented posterior stabilized TKAs with 7 to 11.5 yrs follow-up (average 9 yrs). Aseptic loosening had occurred in 10 knees (1.0%). Nine controls were randomly selected for each case within matching criteria for age and minimum time in situ. Post-operative mechanical alignment was determined using retrieved long leg radiographs. Age-adjusted relative risk was estimated using conditional logistic regression. Results. Radiographs revealed 8 of the 10 loosened cases had been placed in 3 or more degrees varus mechanical alignment (range, 2? varus to 7? varus), compared to only 4 of the 90 age-matched controls (range, 4? valgus to 4? varus). A single degree change of mechanical alignment in the varus direction was associated with a more than 4-fold increase of risk of loosening (odds ratio 4.6, 95% confidence interval 1.7–12.7; p=0.0035). The relative risk for mechanical alignment >= 3? varus compared to <= 2? varus (dichotomous) was 69.2 (95% confidence interval 8.1–589; p=.0001). BMI, gender, and pre-op deformity were not significant. Discussion. These results suggest that avoidance of varus postoperative alignment is an extremely important determinant of TKA fixation durability

Inter- and intra-observer variation has been noted in the analysis of radiographic examinations with regard to experience of surgeons, and the monitors used for conducting the evaluations. The aim of this study is to evaluate inter/intra observer variation in the measurement of mechanical alignment from long-leg radiographs. 40 patients from the elective waiting list for TKA underwent long leg radiographs pre-operatively and 6 months post-operatively (total of 80 radiographs). The x-rays were analysed by 5 observers ranging in experience from medical student to head orthopaedic surgeon. Two observers re-analysed their results 6 months later to determine intraobserver correlation, and one observer re-measured the alignment on a different monitor. These measurements were all conducted blindly and none of the observers had access to the others’ results. 80 radiographs were analysed in total, 40 pre-op and 40 post-op. The mechanical alignment was analysed using Pearson's correlation (r = 0 no agreement, r = 1 perfect agreement) and revealed that experience as an orthopaedic surgeon has little effect on the measurement of mechanical alignment from long leg radiograph. The results for the different monitor analysis were also analysed using Pearson's correlation of long leg alignment. Monitor quality does seem to affect the correlation between alignment measurements when reviewing both intra and inter observer correlation on different computer monitors. Surgical experience has little impact on the measurement of alignment on long leg radiographs. Of greater concern is that monitors of different resolution can affect measurement of mechanical alignment. As there might be a range of monitors in use in different institutions, and also in outpatient clinics to surgical theatres, close attention should be paid to the implications of these results

Background. The current orthopaedic literature demonstrates a clear relationship between acetabular component positioning, polyethylene wear and risk of dislocation following Total Hip Arthroplasty (THA). Problems with edge loading, stripe wear and squeaking are also associated with higher acetabular inclination angles, particularly in hard-on-hard bearing implants. The important parameters of acetabular component positioning are depth, height, version and inclination. Acetabular component depth, height and version can be controlled with intra-operative reference to the transverse acetabular ligament. Control of acetabular component inclination, particularly in the lateral decubitus position, is more difficult and remains a challenge for the Orthopaedic Surgeon. Lewinnek et al described a ‘safe zone’ of acetabular component orientation: Radiological acetabular inclination of 40 ± 10° and radiological anteversion of 15 ± 10°. Accurate implantation of the acetabular component within the ‘safe zone’ of radiological inclination is dependent on operative inclination, operative version and pelvic position. Traditionally during surgery, the acetabular component has been inserted with an operative inclination of 45°. This assumes that patient positioning is correct and does not take into account the impact of operative anteversion or patient malpositioning. However, precise patient positioning in order to orientate acetabular components using this method cannot always be relied upon. Hill et al demonstrated a mean 6.9° difference between photographically simulated radiological inclination and the post-operative radiological inclination. The most likely explanation was felt to be adduction of the uppermost hemipelvis in the lateral decubitus position. The study changed the practice of the senior author, with target operative inclination now 35° rather than 40° as before, aiming to achieve a post-operative radiological inclination of 42° ± 5°. Aim. To determine which of the following three techniques of acetabular component implantation most accurately obtains a desired operative inclination of 35 degrees:. Freehand. Modified (35°) Mechanical Alignment Guide, or. Digital inclinometer assisted. Methods. 270 patients undergoing primary uncemented THA were randomised to one of the three methods of acetabular component implantation. Target operative inclination for all three techniques was 35°. Operative inclination was measured intra-operatively using both a digital inclinometer and stereophotogrammetric system. For both the freehand and Mechanical Alignment Guide implantation techniques, the surgeon was blinded to intra-operative digital inclinometer readings. Results. The freehand implantation technique had an operative inclination range of 25.2 – 43.2° (Mean 32.9°, SD 2.90°). The modified (35°) Mechanical Alignment Guide implantation technique had an operative inclination range of 29.3 – 39.3° (Mean 33.7°, SD 1.89°). The digital inclinometer assisted technique had an operative inclination range of 27.5 – 37.5° (Mean 34.0°, SD 1.57°). Mean unsigned deviation from target 35° operative inclination was 2.92° (SD 2.03) for the freehand implantation technique, 1.83° (SD 1.41) for the modified (35°) Mechanical Alignment Guide implantation technique and 1.28° (SD 1.33) for the digital inclinometer assisted technique. Conclusions. When aiming for 35° of operative inclination, the digital inclinometer technique appears more accurate than either the freehand or Mechanical Alignment Guide techniques. In order to improve accuracy of acetabular component orientation during Total Hip Arthroplasty, the surgeon should consider using such a technique

Introduction. Aseptic loosening is one of the highest causes for revision in total knee arthroplasty (TKA). With growing interest in anatomically aligned (AA) TKA, it is important to understand if this surgical technique affects cemented tibial fixation any differently than mechanical alignment (MA). Previous studies have shown that lipid/marrow infiltration (LMI) during implantation may significantly reduce fixation of tibial implants to bone analogs [1]. This study aims to investigate the effect of surgical alignment on fixation failure load after physiological loading. Methods. Alignment specific physiological loading was determined using telemetric tibial implant data from Orthoload [2] and applying it to a validated finite element lower limb model developed by the University of Denver [3]. Two high demand activities were selected for the loading section of this study: step down (SD) and deep knee bend (DKB). Using the lower limb model, hip and ankle external boundary conditions were applied to the ATTUNE. ®. knee system for both MA and AA techniques. The 6 degree of freedom kinetics and kinematics for each activity were then extracted from the model for each alignment type. Mechanical alignment (MA) was considered to be neutral alignment (0° Hip Knee Ankle Angle (HKA), 0° Joint Line (JL)) and AA was chosen to be 3° varus HKA, 5° JL. It is important not to exceed the limits of safety when using AA as such it is noted that DePuy Synthes recommends staying within 3º varus HKA and 3º JL. The use of 5º JL was used in this study to account for surgical variation [Depuy-Synthes surgical technique DSUS/JRC/0617/2179]. Following a similar method described by Maag et al [1] ATTUNE tibial implants were cemented into a bone analog with 2 mL of bone marrow in the distal cavity and an additional reservoir of lipid adjacent to the posterior edge of the implant. Tibial implant constructs were then subjected to intra-operative ROM/stability evaluation, followed by a hyperextension activity until 15 minutes of cement curing time, and finally 3 additional ROM/stability evaluations were performed using an AMTI VIVO simulator. The alignment specific loading parameters were then applied to the tibial implants using an AMTI VIVO simulator. Each sample was subjected to 50,000 DKB cycles and 120,000 SD cycles at 0.8 Hz in series; approximating 2 years of physiological activity. After physiological loading the samples were tested for fixation failure load by axial pull off. Results. Following alignment specific physiological loading the average fixation pull-off load for MA was 3289 ± 400 N and for AA was 3378 ± 133 N (Figure 1). There was no statistically significant difference fixation failure load by axial pull-off between the two alignment types (p=0.740). Conclusion. This study indicated that anatomic alignment, as defined with the alignment limits of this study, does not adversely affect the fixation failure load of ATTUNE tibial implants. For any figures or tables, please contact the authors directly

Purpose of the study: It has been demonstrated that navigation systems improve the quality of implantation of total knee arthroplasty (TKA). The definitions of the reference alignment for the femur are not however consensual. We wanted to define the different alignments of the femur on the lateral view, including the femoral head and comparing the alignments with those defined by the measured axes during navigated implantation. Material and methods: We analysed 30 navigated TKA or unicompartmental prosthesis implantations. The following lines were drawn on the pre and postoperative lateral telemetric views: anatomic axis aligned on the anterior cortical of the femur, mechanical alignment n°1 (centre of the femoral head to the most distal point of the Blumensaat line), mechanical alignment n°2 (centre of the femoral head to the junction between the anterior two-thirds and the posterior third of the femoral condyles). The anatomic diaphyseal alignment was taken as the reference and the angles between this reference line and the other lines was measure. In addition, the sagittal orientation of the femoral component measured during the operation by the navigation system in relation to the n°2 mechanical alignment was noted; this orientation was also measured on the postoperative lateral telemetric views in relation to this same mechanical alignment. Results: The mean difference between the anatomic cortical alignment and the reference was 0.3 (−1 to +). The mean difference between the n°1 mechanical alignment and the reference was −1.1 (−5 to +3). The mean difference between the mechanical alignment n°2 and the reference was 0.8 (−4 to 4). The mean intraoperative sagittal orientation of the femoral component was 0.0 (−2 to 2). The mean postoperative sagittal orientation of the femoral component was 1.1 (−4 to 6). Discussion: The differences between the orientations of the different sagittal alignments of the femur were minimal. The cortical axis has a smaller variance and could be considered as the most reliable reference, but this alignment does not include the femoral anteversion. The difference between the sagittal orientation of the femoral component as measured by the navigation system and as measured on the postoperative x-rays was also minimal, and probably of no significance clinically. Conclusion: The choice of the sagittal alignment of the femur is of little importance. The intraoperative navigated measurement of the sagittal orientation of the femoral component is reliable

Introduction. Patient matched instrumentation (PMI) have been proposed the accuracy of bone cuts through custom cutting blocks and provide the proper alignment of total knee arthroplasty (TKA). On the other hand, there are some reports that the introduction of PMI for guiding bone cuts could increase the incidence of malalignment in primary TKA. Recent comparisons between patient-specific cutting guides and quantitative assessments of postoperative alignment have revealed the presence of outliers with respect to coronal alignment. The purpose of this study was to assess the implanted component alignment post-operatively between one type of MRI based PMI (Visionaire; Smith & Nephew, Inc, Memphis, Tenn) and conventional surgical instrumentation (CI) using radiographs and CT scan. Methods. 32 knees in 32 patients (25 women) with medial type knee osteoarthritis were underwent cruciate retaining TKA between September 2013 and May 2015, and were included in this study. Preoperative MRI scanning of the hip, knee, and ankle was performed for PMI group (n=12) and CT scanning was performed for CI group (n=20) 6 weeks before surgery according to a standard scanning protocol to determine the surgical epicondylar axis (SEA). Postoperatively, we compared operation time, blood loss, and mechanical alignment of two groups. Post-surgical mechanical alignments such as hip-knee-ankle angle (HKA), frontal femoral component angle (FFC), and frontal tibial component angle (FTC) were determined using long leg radiographs (Fig. 1). CT scans were used to assess the condylar twist angle (CTA) made by SEA and posterior condylar axis (Fig. 2). Each measurement was performed by two, blinded independent observers, and interclass correlation for each measurement was calculated. A student's two-tailed t test was used to compare the two cohorts, with statistical significance set at a p-value of <0.05. Results. There was no significant difference between the two groups regarding preoperative age, body mass index, degree of mechanical deformity, mean operation time or mean blood loss. Mean pre / postoperative HKA in the PMI group was 166.8 ± 6.4°/ 176.7 ±1.9° and 168.3 ±8.3° / 178.8 ±2.1°in the CI group. There was no significant difference between two groups, but there were fewer ± 3° HKA outliers with CI group (20%) than with PMI group (50%). Postoperative FFC was 89.1 ± 0.6° in PMI group and 88.1 ± 1.2° in CI group. FTC was 87.8 ± 1.4° in PMI group and 89.3 ± 1.6° in CI group. CTA was −0.8 ± 0.6 ° in PMI group and −1.2 ± 1.1° in CI group. There was no significant difference between PMI and CI group in postoperative mechanical alignment, but there were higher ± 3° FTC outliers in PMI group (50%) compared to CI group (10%)(p=0.01). (Fig.3). Discussion and Conclusion. Although the overall mean mechanical alignment for PMI group was similar to CI group, these results suggest that PMI did not significantly improve alignment. It should be recommended to use only for the femoral component. To view tables/figures, please contact authors directly

Introduction. In total knee arthroplasty (TKA), component realignment with bone-based surgical correction (BBSC) can provide soft tissue balance and avoid the unpredictability of soft tissue releases (STR) and potential for more post-operative pain. Robotic-assisted TKA enhances the ability to accurately control bone resection and implant position. The purpose of this study was to identify preoperative and intraoperative predictors for soft tissue release where maximum use of component realignment was desired. Methods. This was a retrospective, single center study comparing 125 robotic-assisted TKAs quantitatively balanced using load-sensing tibial trial components with BBSC and/or STR. A surgical algorithm favoring BBSC with a desired final mechanical alignment of between 3° varus and 2° valgus was utilized. Component realignment adjustments were made during preoperative planning, after varus/valgus stress gaps were assessed after removal of medial and lateral osteophytes (pose capture), and after trialing. STR was performed when a BBSC would not result in knee balance within acceptable alignment parameters. The predictability for STR was assessed at four steps of the procedure: Preoperatively with radiographic analysis, and after assessing static alignment after medial and lateral osteophyte removal, pose capture, and trialing. Cutoff values predictive of release were obtained using receiver operative curve analysis. Results. STR was necessary in 43.5% of cases with medial collateral ligament (MCL) release being the most common. On preoperative radiographs, a medial tibiofemoral angle (mTFA) ≤177° predicted MCL release (AUC = 0.76. p< 0.01) while an mTFA ≥188° predicted ITB release (AUC = 0.79, p <0.01). Intraoperatively after removal of osteophytes, a robotically assessed mechanical alignment (MA) ≥8° varus predicted MCL release (AUC = 0.84. p< 0.01) while a MA ≥2° valgus (AUC = 0.89, p< 0.01) predicted ITB release. During pose-capture, in medially tight knees, an extension gap imbalance ≥2.5mm (AUC = 0.82, p <0.01) and a flexion gap imbalance ≥2.0mm (AUC = 0.78, p <0.01) predicted MCL release while in laterally tight knees, any extension or flexion gap imbalance >0 mm predicted ITB release (AUC = 0.84, p <0.01 and AUC = 0.82, p <0.01 respectively). During trialing, in medially tight knees, a medial>lateral extension load imbalance ≥18 PSI (AUC = 0.84. p< 0.01) and a flexion load imbalance ≥ 35 PSI (AUC = 0.83, p< 0.01) predicted MCL release while, in laterally tight knees, a lateral>medial extension load imbalance ≥3 PSI (AUC = 0.97, p< 0.01) or flexion load imbalance ≥ 9.5 PSI (AUC = 0.86, p< 0.01) predicted ITB release. Of all identified predictors, load imbalance at trialing had the greatest positive predictive value for STR. Conclusion. There are limitations to the extent that TKA imbalance that can be corrected with BBSC alone if one has a range of acceptable alignment parameters. The ability to predict STR improves from pose-capture to trialing stages during detection of load imbalance. Perhaps this may be due to posterior osteophytes that are still present at pose capture. Further investigation of the relationship between the presence, location and size of posterior osteophytes and need for STR during TKA is necessary

Aims. The goal of the current systematic review was to assess the impact of implant placement accuracy on outcomes following total knee arthroplasty (TKA). Methods. A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using the Ovid Medline, Embase, Cochrane Central, and Web of Science databases in order to assess the impact of the patient-reported outcomes measures (PROMs) and implant placement accuracy on outcomes following TKA. Studies assessing the impact of implant alignment, rotation, size, overhang, or condylar offset were included. Study quality was assessed, evidence was graded (one-star: no evidence, two-star: limited evidence, three-star: moderate evidence, four-star: strong evidence), and recommendations were made based on the available evidence. Results. A total of 49 studies were identified for inclusion. With respect to PROMs, there was two-star evidence in support of mechanical axis alignment (MAA), femorotibial angle (FTA), femoral coronal angle (FCA), tibial coronal angle (TCA), femoral sagittal angle (FSA), femoral rotation, tibial and combined rotation/mismatch, and implant size/overhang or offset on PROMs, and one-star evidence in support of tibial sagittal angle (TSA), impacting PROMs. With respect to survival, there was three- to four-star evidence in support FTA, FCA, TCA, and TSA, moderate evidence in support of femoral rotation, tibial and combined rotation/mismatch, and limited evidence in support of MAA, FSA, and implant size/overhang or offset impacting survival. Conclusion. Overall, there is limited evidence to suggest that PROMs are impacted by the accuracy of implant placement, and malalignment does not appear to be a significant driver of the observed high rates of patient dissatisfaction following TKA. However, FTA, FCA, TCA, TSA, and implant rotation demonstrate a moderate-strong relationship with implant survival. Efforts should be made to improve the accuracy of these parameters in order to improve TKA survival. Cite this article: Bone Joint J 2021;103-B(9):1449–1456

Long-term implant survivorship in total knee arthroplasty (TKA) depends on the alignment of the tibial and femoral components, as well as on the mechanical alignment of the leg. Computer navigation improves component and limb alignment in TKA compared to the manual technique. However, its use is often associated with an increase in surgical time. We aimed to evaluate the use of adjustable cutting blocks (ACB) in navigated TKA. We hypothesised that the use of ACB would (1) improve tibial and femoral component positioning; (2) improve postoperative mechanical leg alignment; and (3) decrease tourniquet time, when compared to conventional cutting blocks (CCB). This was a retrospective cohort study of 94 navigated primary TKA. Patients were classified into two groups according to whether the surgery had been performed using ACB or CCB. There were sixty-four patients in the CCB group and 30 patients in the ACB group. Charts were reviewed to obtain the following data: age, gender, body mass index (BMI), tourniquet time and operated side. Pre- and postoperative standing full-leg radiographs and lateral radiographs were reviewed. Mean coronal femoral alignment for the CCB group was 0.8® varus (SD = 1.95®) and for the ACB group it was 1.1® varus (SD = 1.5®) (P = 0.12). Mean coronal tibial alignment for the CCB group was 0.1® valgus (SD = 1.3®) and for the ACB group it was 0.5® varus (SD = 1.01) (P = 0.15). Sagittal tibial alignment was a mean 0.5® of anterior slope (SD = 2.9®) for the CCB group and 0.7® anterior slope (SD = 2.5®) for the ACB group (P = 0.38). Preoperatively, the CCB group had a mean mechanical alignment of 1.8® varus (SD = 9.6®), while the ACB group had a mean 1.8® varus (SD = 9.37®) (P = 0.88). After surgery, mechanical leg alignment for the CCB group improved to a mean 0.7® varus (SD = 2.7®) (P = 0.0001), while the ACB group improved to 1.8® varus (SD = 1.7®) (P<0.0001). There was significantly less variability in postoperative mechanical alignment in the ACB group (P = 0.0091). Mean tourniquet time for the CCB group was 91 minutes (SD = 17.7 minutes). The ACB group a mean tourniquet time of 76 minutes (SD = 16.7 minutes) (P = 0.01). In the multiple linear regression model, the use of an ACB reduced tourniquet time by 16.8 minutes (P = 0.001). Adjustable cutting blocks for TKA significantly reduced postoperative mechanical alignment variability and tourniquet time compared to conventional navigated instrumentation, while providing equal or better component alignment

Introduction. Deformity influences the weight bearing stresses on the knee joint. Correction of mechanical alignment is performed to offload the knee and slow the rate of degenerative change. Fixator assisted deformity correction facilitates accurate correction prior to internal fixation. We present our results with standard Ilizarov and UNYCO system assisted deformity correction of the lower limb. Materials and Methods. Retrospective analysis of adult surgical cases of mechanical re-alignment performed between 2010 and 2019 in a tertiary referral centre. We recorded standard demographics and operative time from the electronic patient record. We analysed digitalised radiographs to record pre- and post-operative measurements of: Mechanical axis deviation (MAD), femoral tibial angle (FTA), Medial Proximal tibial angle (MPTA) and Mechanical lateral distal femoral angle (mLDFA). The accuracy of the correction was analysed. Time to healing, secondary interventions and complications were also recorded. Results. 7 patients underwent fixator assisted deformity correction with the UNYCO system and 11 with a standard Ilizarov frame. Mean pre-op MAD was 45.8mm in the UNYCO group and 43.4mm in Ilazrov; Mean post-op MAD was 9.5mm in the UNYCO group (5–15) and 12.3 in the Ilizarov group (1–25) p=0.07. The average surgical time in the UNYCO group was 200 minutes (128–325) and 252 minutes (203–301) in the Ilizarov group p=0.07. The mean post op MPTA was 90.2 (87–96) in the UNYCO group and 87.4 (81–94) in the Ilizarov group. The mean mLDFA was 90.0(81–93.5) in the UNYCO group and 87.3(82.2–93.9) in the Ilizarov group. All the corrections involved a plate or nail fixation and mean time to union was 76.3 days in the UNYCO and 117.3 in the Ilizarov group. Conclusions. Both systems allowed accurate correction of deformity and limb alignment. In this small series we were unable to show a difference in theatre time. The application of the principles of deformity correction are as important as the surgical methods

Posterior stabilized (PS) total knee arthroplasty (TKA), wherein mechanical engagement of the femoral cam and tibial post prevents abnormal anterior sliding of the knee, is a proven surgical technique. However, many patients complain about abnormal clicking sensation, and several reports of severe wear and catastrophic failure of the tibial post have been published. In addition to posterior cam-post engagement during flexion, anterior engagement with femoral intercondylar notch can also occur during extension. The goal of this study was to use dynamic simulations to explore sensitivity of tibial post loading to implant design and alignment, across different activities. LifeModeler KneeSIM software was used to calculate tibial post contact forces for four contemporary PS implants (Triathlon PS, Stryker; Journey BCS and Legion PS, Smith & Nephew; LPS Flex, Zimmer Biomet). An average model of the knee, including cartilage and soft tissue insertion locations, created from MRI data of 40 knees was used to mount and align the component. The Triathlon femoral component was mounted with posterior and distal condylar tangency at: a) both medial and lateral condylar cartilage (anatomic alignment), b) at the medial condylar cartilage and perpendicular to mechanical axis (mechanical alignment with medial tangency), and c) at lateral condylar cartilage and perpendicular to mechanical axis (mechanical alignment with lateral tangency). The influence of implant design was assessed via simulations for the other implant systems with the femoral components aligned perpendicular to mechanical axis with lateral tangency. Five different activities were simulated. The anterior contact force was significantly smaller than the posterior contact force, but it varied noticeably with tibial insert slope and implant design. For Triathlon PS, during most activities anatomic alignment of the femoral component resulted in greater anterior contact force compared to mechanical alignment, but absolute magnitude of forces remained small (<100N). Mechanical alignment with medial tangency resulted in greater posterior contact force for deep knee bend and greater anterior force for chair sit activity. For all implants, peak posterior contact forces were greater for activities with greater peak knee flexion. The magnitude of posterior contact forces for the various implants was comparable to other reports in literature. Overall activity type, implant design and slope had greater impact on post loading than alignment method. Tibial insert slope was shown to be important for anterior post loading, but not for posterior post loading. Anatomic alignment could increase post loading with contemporary TKA systems. In the case of the specific design for which effect of alignment was evaluated, the changes in force magnitude with alignment were modest (<200N). Nonetheless, results of this study highlight the importance of evaluating the effect of different alignment approaches on tibial post loading

Introduction:. One of the primary goals in total knee arthroplasty (TKA) is restoration of the mechanical alignment. The accuracy of conventional mechanical alignment guides and computer-assisted navigation systems has been extensively studied. The purpose of this study is to assess the accuracy of a hand-held accelerometer-based navigation system for TKA. Methods:. Fifty three patients undergoing TKA utilizing the KneeAlign system (OrthAlign Inc, Aliso Viejo, CA) (Figure 1) were performed by two surgeons. Intraoperative data including tourniquet time, device assembly time, and resection times were recorded. Target alignment goals were 0° femoral, tibial, and overall mechanical coronal alignment and 3° femoral flexion and posterior tibial slope. Coronal/sagittal alignment of the implant and the mechanical axis were measured by two independent observers on full length (54 inch) postoperative hip to ankle radiographs. Results:. Average femoral coronal alignment was 0.29° varus ± 2.2° with 13% of patients exceeding 3° of varus/valgus. Average tibial coronal alignment was 0.25° valgus ± 1.4° with 4% of patients exceeding 3° of varus/valgus. Average femoral flexion angle was 87.2° and the average tibial posterior slope was 2.8° ± 1.8 °. Average postoperative mechanical axis was 0.2° varus ± 2.1°with 13% of patients exceeding 3° of varus/valgus (Figure 2). The average time to completion of femoral and tibial resection was 4.8 and 4.6 minutes, respectively, with an overall tourniquet time of 62 minutes. Conclusion:. The KneeAlign system was accurate for reestablishing the mechanical axis and the femoral and tibial component alignment in TKA without increasing surgical time. Accuracy was better for tibial than femoral resection, but overall superior to mechanical alignment guides and comparable to computer-assisted navigation

Purpose. Various alignment philosophies for total knee arthroplasty (TKA) have been described, all striving to achieve excellent long-term implant survival and good functional outcomes. In recent years, in search of higher functionality and patient satisfaction, a shift towards more patient-specific alignment is seen. Robotics is the perfect technology to tailor alignment. The purpose of this study was to describe ‘inverse kinematic alignment’ (iKA) technique, and to compare clinical outcomes of patients that underwent robotic-assisted TKA performed by iKA versus adjusted mechanical alignment (aMA). Methods. The authors analysed the records of a consecutive series of patients that received robotic assisted TKA with iKA (n=40) and with aMA (n=40). Oxford Knee Score (OKS) and satisfaction on a visual analogue scale (VAS) were collected at a follow-up of 12 months. Clinical outcomes were assessed according to patient acceptable symptom state (PASS) thresholds, and uni- and multivariable linear regression analyses were performed to determine associations of OKS and satisfaction with 6 variables (age, sex, body mass index (BMI), preoperative hip knee ankle (HKA) angle, preoperative OKS, alignment technique). Results. The iKA and aMA techniques yielded comparable outcome scores (p=0.069), with OKS respectively 44.6±3.5 and 42.2±6.3. VAS Satisfaction was better (p=0.012) with iKA (9.2±0.8) compared to aMA (8.5±1.3). The number of patients that achieved OKS and satisfaction PASS thresholds was significantly higher (p=0.049 and p=0.003, respectively) using iKA (98% and 80%) compared to aMA (85% and 48%). Knees with preoperative varus deformity, achieved significantly (p=0.025) better OKS using iKA (45.4±2.0) compared to aMA (41.4±6.8). Multivariable analyses confirmed better OKS (β=3.1; p=0.007) and satisfaction (β=0.73; p=0.005) with iKA. Conclusions. The results of this study suggest that iKA and aMA grant comparable clinical outcomes at 12-months follow-up, though a greater proportion of knees operated by iKA achieved the PASS thresholds for OKS and satisfaction. Notably. in knees with preoperative varus deformity, iKA yielded significantly better OKS and satisfaction than aMA

Aims. The aims of this retrospective study were to determine the incidence of extra-articular deformities (EADs), and determine their effect on postoperative alignment in knees undergoing mobile-bearing, medial unicompartmental knee arthroplasty (UKA). Patients and Methods. Limb mechanical alignment (hip-knee-ankle angle), coronal bowing of the femoral shaft and proximal tibia vara or medial proximal tibial angle (MPTA) were measured on standing, full-length hip-to-ankle radiographs of 162 patients who underwent 200 mobile-bearing, medial UKAs. Results. Incidence of EAD was 7.5% for coronal femoral bowing of >5°, 67% for proximal tibia vara of >3° (MPTA<87°) and 24.5% for proximal tibia vara of >6° (MPTA<84°). Mean postoperative HKA angle achieved in knees with femoral bowing ≤5° was significantly greater when compared to knees with femoral bowing >5° (p=0.04); in knees with proximal tibia vara ≤3° was significantly greater when compared to knees with proximal tibia vara >3° (p=0.0001) and when compared to knees with proximal tibia vara >6° (p=0.0001). Conclusion. Extra-articular deformities are frequently seen in patients undergoing mobile-bearing medial UKAs, especially in knees with varus deformity>10°. Presence of an EAD significantly affects postoperative mechanical limb alignment achieved when compared to limbs without EAD and may increase the risk of limbs being placed in varus>3° postoperatively. Clinical Relevance. Since the presence of an EAD, especially in knees with varus deformity>10°, may increase the risk of limbs being placed in varus>3° postoperatively and may affect long-term clinical and implant survival outcomes, UKR in such knees should be performed with caution

Today controversy exists whether restoration of neutral mechanical alignment should be attempted in all patients undergoing TKA. The restoration of constitutional rather than neutral mechanical alignment may in theory lead to a more physiological strain pattern in the collateral ligaments, and could therefore potentially be beneficial to patients. It was therefore our purpose to measure collateral ligament strains during three motor tasks in the native knee and compare them with the strains noted after TKA in different postoperative alignment conditions. Six cadaver specimens were examined using a validated knee kinematics rig under physiological loading conditions. The effect of coronal malalignment was evaluated by using custom made tibial implant inserts in order to induce different alignment conditions. The results indicated that after TKA insertion the strains in the collateral ligaments resembled best the preoperative pattern of the native knee specimens when constitutional alignment was restored. Restoration to neutral mechanical alignment was associated with greater collateral strain deviations from the native knee. Based upon this study, we conclude that restoration of constitutional alignment during TKA leads to more physiological periarticular soft tissue strains during loaded as well as unloaded motor tasks

Introduction. The purpose of this study was to determine if better outcomes occur with use of robotic-arm assistance by comparing consecutive series of non-robotic assisted (NR-TKA) and robotic-arm assisted (NR-TKA) total knee arthroplasties with the same implant. Methods. 80 NR-TKAs and then 101 RA-TKAs were performed consecutively. 70 knees in each group that had a minimum two-year follow-up were retrospectively reviewed. Range of motion, Knee Society (KS) scores, and forgotten joint scores (FJS) were compared using Mann-Whitney U tests. Tourniquets, used for all cases, had their inflation time recorded. Component realignment to minimize soft tissue releases was used in both groups with the goal to stay within a mechanical alignment of 3° of varus to 2° of valgus. The use of soft tissue releases for balance were compared. Results. There were no statistical differences in baseline characteristics including pre-operative Knee Society scores between cohorts. The two-year NR-TKA and RA-TKA median KS knee and functional scores were 99.0 and 90.0 and 100.0 and 100.0 respectively. Mann-Whitney U test indicated a statistically significant difference in KS-KS (p<.00001) and near statistically significant difference in KS-FS (p=0.075). The 10-point higher KS-FS is considered a minimal clinically important difference. The median FJS at two years for the NR-TKA was 61.5 and the RA-TKA was 75.0. Although not statistically significant (p=0.1556), the 13.5-point increase in the RA-TKA cohort also represents a minimal clinically important difference. RA-TKA patients had statistically significant 5° higher knee flexion (p<.00001). Desired post-operative coronal alignment was present in 92.9% of NR-TKAs and 94.3% of RA-TKAs. 28.6% more of the RA-TKA cases were able to be balanced without a soft tissue release. Median tourniquet time was only 3.9 minutes longer for the robotic-arm assisted cohort. Conclusion. This comparison study demonstrates potential benefits in use of robotic-arm assistance over manual instrumentation in TKA

Introduction. Instability is a common reason for revision after total knee arthroplasty. A balanced flexion gap is likely to enhance stability throughout the arc of motion. This is achieved differently by the gap balancing and measured resection techniques. Given similar clinical results with the two techniques, one would expect similar rotation of the femoral component in the axial plane. We assessed posterior-stabilized femoral component axial rotation placed with computer navigation and a modified gap balancing technique. We hypothesized that there would be little variation in rotation. Methods. 90 surgeons from 8 countries used a modified gap-balancing technique and the same posterior-stabilized implant for this retrospective study. Axial rotation of the femoral component was collected from a navigation system and reported relative to the posterior condylar line. Patients were stratified by their preoperative coronal mechanical alignment (≥ 3° varus, < 3° varus to < 3° valgus, and ≥ 3° valgus). Results. 2442 consecutive patients were included in the analysis; 835 with ≥ 3° varus, 1343 with < 3° varus to < 3° valgus, and 264 with ≥ 3° valgus. Mean rotation was external 2.4. 0. +/− 3.4. 0. (range, 10. 0. internal − 21. 0. external). In 16.4% of the cohort, axial rotation was set in a position of internal rotation. In 15.6% of the cohort, axial rotation was set at > 5. 0. of external rotation. Compared to both the neutral and varus groups, valgus knees required a different mean rotation to achieve a balanced flexion gap (p < .0001). Conclusion. These data show a wide range of femoral rotation was needed to achieve a rectangular flexion gap. This suggests that choosing a pre-determined femoral implant axial rotation (measured resection) may lead to flexion gap asymmetry more frequently compared to adjusting the axial rotation intraoperatively (gap-balancing). Correlation to clinical outcome scores is needed

Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) may introduce significant anatomic modifications, as it is known that few patients have neutral femoral, tibial or overall lower limb mechanical axes. A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. MA tibial and femoral bone resections were simulated. Femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Medial-lateral (DML) and flexion-extension (DFE) gap differences were calculated. Extension space ML imbalances (3mm) occurred in 25% of varus and 54% of valgus knees and significant imbalances (5mm) were present in up to 8% of varus and 19% of valgus knees. For the flexion space DML, higher imbalance rates were created by the TEA technique (p < 0 .001). In valgus knees, TEA resulted in a DML in flexion of 5 mm in 42%, compared to 7% for PC. In varus knees both techniques performed better. When all the differences between DML and DFE are considered together, using TEA there were 18% of valgus knees and 49% of varus knees with < 3 mm imbalances throughout, and using PC 32% of valgus knees and 64% of varus knees. Significant anatomic modifications with related ML or FE gap imbalances are created using MA for TKA. Using MA techniques, PC creates less imbalances than TEA. Some of these imbalances may not be correctable by the surgeon and may explain post-operative TKA instability. Current imaging technology could predict preoperatively these intrinsic imitations of MA. Other alignment techniques that better reproduce knee anatomies should be explored

Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) introduces significant anatomic modifications and secondary ligament imbalances. A restricted kinematic alignment (rKA) protocol was proposed to minimise these issues and improve TKA clinical results. A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. rKA tibial and femoral bone resections were simulated. rKA is defined by the following criteria: Independent tibial and femoral cuts within ± 5° of the bone neutral mechanical axis and, a resulting HKA within ± 3° of neutral. Medial-lateral (ΔML) and flexion-extension (ΔFE) gap differences were calculated and compared with MA results. With the MA technique, femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Extension space ML imbalances (>/=3mm) occurred in 33% of TKA with MA technique versus 8% of the knees with rKA (p /=5mm) were present in up to 11% of MA knees versus 1% rKA (p < 0 .001). Using the MA technique, for the flexion space ΔML, higher imbalance rates were created by the TEA technique (p < 0 .001). rKA again performed better than both MA techniques using TEA of 3 degrees PC techniques (p < 0 .001). When all the differences between ΔML and ΔFE are considered together: using TEA there were 40.8% of the knees with < 3 mm imbalances throughout, using PC this was 55.3% and using rKA it was 91.5% of the knees (p < 0 .001). Significantly less anatomic modifications with related ML or FE gap imbalances are created using rKA versus MA for TKA. Using rKA may help the surgeon to balance a TKA, whilst keeping the alignment within a safe range

Many aspects of total knee arthroplasty have changed since its inception. Modern prosthetic design, better fixation techniques, improved polyethylene wear characteristics and rehabilitation, have all contributed to a large change in revision rates. Arthroplasty patients now expect longevity of their prostheses and demand functional improvement to match. This has led to a re-examination of the long-held belief that mechanical alignment is instrumental to a successful outcome and a focus on restoring healthy joint kinematics. A combination of kinematic restoration and uncemented, adaptable fixation may hold the key to future advances. Cite this article: Bone Joint J 2015;97-B(10 Suppl A):16–19

Introduction. Acetabular component orientation is an important determinant of outcome following total hip arthroplasty (THA). Although surgeons aim to achieve optimal cup orientation, many studies demonstrate their inability to consistently achieve this. Factors that contribute are pelvic orientation and the surgeon's ability to correctly orient the cup at implantation. The goal of this study was to determine the accuracy with which surgeons can achieve cup orientation angles. Methods. In this in vitro study using a calibrated left and right sawbone hemipelvis model, participants (n=10) were asked to place a cup mounted on its introducer giving different targets. Measurements of cup orientation were made using a stereophotogrammetry protocol to measure radiographic inclination and operative anteversion (OA). A digital inclinometer was used to measure the intra-operative inclination (IOI) which is the angle of the cup introducer relative to the floor. First, the participant stated his or her preferred IOI and OA and positioned the cup accordingly. Second, the participant had to position the cup parallel to the anteversion of the transverse acetabular ligament (TAL). Third, the participant had to position the cup at IOI angles of 35°, 40° and 45°. Fourth, the participant used the mechanical alignment guide (45° of IOI and 30° of OA) to orient the cup. Each task was analysed separately and subgroup analysis included left versus right side and hip surgeons versus non-hip surgeons. Results. For the first task, hip surgeons preferred smaller IOI and larger OA than non-hip surgeons, but there was no significant difference in accuracy between both groups. When aiming for TAL, both surgeon groups performed similar, but accuracy on the non-dominant side was significantly better compared with the dominant side (mean deviation 0.6° SD 2.4 versus −2.6° SD 2.3) (p=0.004). When aiming for a specific IOI target of 35°, 40° or 45°, non-hip surgeons outperformed hip surgeons (mean deviation form target IOI 1.9° SD 2.7 versus −3.1° SD 3.8) (p<0.0001) with less variance (p=0.03). Contrary to version, accuracy on the dominant side was significantly better compared with the non-dominant side (mean deviation −0.4° SD 3.4 versus −2.1° SD 4.8). When using a mechanical guide, surgeons performed similar (0.6° SD 1.2 versus −0.4° SD 2.1 for inclination p=0.11 and −0.5° SD 2.6 versus −1.8° SD 3.3 for version p=0.22) and these values did not differ significantly from the actual IOI and OA of the mechanical guide. When using a mechanical guide, there was no difference in accuracy between the dominant and non-dominant side. Conclusion. There was no difference in accuracy between hip surgeons and non-hip surgeons when they aimed for their preferred IOI and OA or used a mechanical guide. When aiming for a specific IOI target, non-hip surgeons outperformed hip surgeons. Hip surgeons overestimate IOI and underestimate OA, presumably because this helps to achieve the desired radiographic cup orientation. Regarding accuracy, the non-dominant side was better for version and the dominant side for inclination. When aiming for a specific IOI and OA target, using a mechanical guide is significantly better than freehand cup orientation

Background. Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) introduce significant anatomic modifications and secondary ligament imbalances. A restricted kinematic alignment (rKA) protocol was proposed to minimize these issues and improve TKA clinical results. Method. rKA tibial and femoral bone resections were simulated on 1000 knee CT-Scans from a database of patients undergoing TKA. rKA is defined by the following criteria: Independent tibial and femoral cuts within ± 5° of the bone neutral mechanical axis and; a resulting HKA within ±3° of neutral. Medial-lateral (ΔML) and flexion-extension (ΔFE) gap differences were calculated and compared with measured resection MA results. Results. Extension space ML imbalances ≥3mm occurred in 33% of TKA with MA technique versus 8% with rKA, and ≥5mm were present in up to 11% of MA knees versus 1% rKA (p<0.001). Using the MA technique, for the flexion space, higher ML imbalance rates were created by both MA techniques (using TEA or 3°PC) versus rKA (p<0.001). When all the differences between ΔML and ΔFE are considered together: using MA with TEA there were 41% of the knees with <3mm imbalances throughout; using PC this was 55% and using rKA it was 92% (p<0.001). Conclusion. Significantly less ML or FE gap imbalances are created using rKA versus MA for TKA. Using rKA may help the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range

Purpose of the study: Conventional techniques for implantation of a TKA allow a neutral mechanical axis (HKA 180±3) in 70 to 86% of patients. The purpose of this work was to evaluate the contribution of intraoperative radiologic assistance for this objective. Material and methods: We conducted a prospective randomised study in a single-operator consecutive series of cemented TKA, model TC-SB, excluding revisions and frontal deviations > 25. The series included 65 women and 39 men, mean age 73 years. All operations were performed on a radiolucent table. An extramedullary guide was used for the tibial cut and an intramedullary guide for the femoral cup. Patient randomisation was done after the cuts. According to the randomisation, the orientation of the cuts in the frontal plane was measured radiographically using a fluoroscope and an aiming plate situated on the hip, then the ankle. Secondary cuts were made if the angular deviation was greater than 1°. The position of the TKA assisted by the fluoroscope (group R+, n=52) and that of the non-assisted TKA (group R-, n=52) was assessed on the digitalised goniometry. Results: Mean operative time was 70 minutes in group R+ and 59 minutes in group R-. In group R+, the mean mechanical alignment was 3.9 varus preoperatively and 0.13 valgus postoperatively (5 valgus to 3 varus) with 91% in the ±3 range. In group R-, the mean mechanical alignment was 6.7 varus preoperatively and 0.06 varus postoperatively (6 varus to 5 valgus) with 80% of the cases in the ±3 range. The standard deviation was 2 in group R+ and 2.7 in group R-, with no significant difference. Discussion: The accuracy of the implantation obtained with the conventional instrumentation for the TC-SB prosthesis is among the best reported in the literature. Intraoperative radiological assistance enabled a tighter spread of the results around the mechanical alignment. The technique was simple to use and precise. The mean duration of exposure to the fluoroscope was 3 s (PDS 3 – 35 gray cm. 2. ). Conclusion: We reserve this assistance in priority for patients with major bone deformities or medullary obstacles

Introduction. The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs with a loose extension gap in TKA. In the setting of a loose extension gap, we hypothesized that although full extension is achieved, a loose extension gap will ultimately lead to increased varus and/or valgus laxity throughout mid flexion. Methods. After obtaining IRB approval, six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, and the flexion and extension gaps were balanced using navigation, a 4 mm distal recut was made in the distal femur to create a loose extension gap (using the same thickness of polyethylene as the well-balanced case). Real implants were used in the study to eliminate error in any laxity inherent to the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line. (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm recut in the distal femur creating a loose extension gap. Results. In the setting of a loose extension gap (4 mm distal recut), overall coronal-plane laxity was increased by a mean of 3.6° at 30° of flexion, 3.4° at 45° of flexion, and 2.8° at 60° of flexion (p < 0.05 for each flexion angle). (Figure 2) However, there was no difference in coronal plane laxity between the well-balanced TKA and the TKA with a loose extension gap at 0° and 90° of flexion, when applying a standardized varus and valgus load. Conclusions. Using a reliable, accurate, and reproducible method of measuring coronal plane laxity, we have shown that in the setting of a loose extension gap during total knee arthroplasty, coronal plane laxity will be significantly higher in mid-flexion compared to the well balanced state

Introduction. The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs in a well-balanced knee with an elevated joint line of 4 mm. In the setting an elevated joint line, we hypothesized that we would observe an increased varus and/or valgus laxity throughout mid flexion. Methods. After obtaining IRB approval, nine fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS, OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, the flexion and extension gaps were balanced using navigation, and a 4 mm recut was made in the distal femur. The remaining femoral cuts were made, the femoral component was downsized by resecting an additional 4 mm of bone off the posterior condyles, and the polyethylene was increased by 4 mm to create a situation of a well-balanced knee with an elevated joint line. Real implants were used in the study to eliminate any inherent error or laxity in the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm joint line elevation with an otherwise well balanced knee. Results. In the setting of a 4 mm elevated joint line, overall coronal-plane laxity was increased by a mean of 1.5° at 45° of flexion, and 1.3° at 60° of flexion (p < 0.05 for each flexion angle). (Figure 2) However, there was no difference at 0° and 90° in the coronal plane laxity between the well-balanced TKA and the TKA that was well balanced but had a 4 mm elevated joint line. Conclusions. Using a reliable, accurate, and reproducible method of measuring coronal plane laxity, we have shown that in the setting of a an elevated joint during total knee arthroplasty, regardless if the knee is well balanced in full extension and 90° of flexion, coronal plane laxity will be significantly higher in mid-flexion compared to the well balanced state

Arthrofibrosis remains a dominant post-operative complication and reason for returning to the OR following total knee arthroplasty. Trauma induced by ligament releases during TKA soft tissue balancing and soft tissue imbalance are thought to be contributing factors to arthrofibrosis, which is commonly treated by manipulation under anesthesia (MUA). We hypothesized that a robotic-assisted ligament balancing technique where the femoral component position is planned in 3D based on ligament gap data would result in lower MUA rates than a measured resection technique where the implants are planned based solely on boney alignment data and ligaments are released afterwards to achieve balance. We also aimed to determine the degree of mechanical axis deviation from neutral that resulted from the ligament balancing technique. Methods. We retrospectively reviewed 301 consecutive primary TKA cases performed by a single surgeon. The first 102 consecutive cases were performed with a femur-first measured resection technique using computer navigation. The femoral component was positioned in neutral mechanical alignment and at 3° of external rotation relative to the posterior condylar axis. The tibia was resected perpendicular to the mechanical axis and ligaments were released as required until the soft tissues were sufficiently balanced. The subsequent 199 consecutive cases were performed with a tibia-first ligament balancing technique using a robotic-assisted TKA system. The tibia was resected perpendicular to the mechanical axis, and the relative positions of the femur and tibia were recorded in extension and flexion by inserting a spacer block of appropriate height in the medial and lateral compartments. The position, rotation, and size of the femoral component was then planned in all planes such that the ligament gaps were symmetric and balanced to within 1mm (Figure 1). Bone resection values were used to define acceptable limits of implant rotation: Femoral component alignment was adjusted to within 2° of varus or valgus, and within 0–3° of external rotation relative to the posterior condyles. Component flexion, anteroposterior and proximal-distal positioning were also adjusted to achieve balance in the sagittal plane. A robotic-assisted femoral cutting guide was then used to resect the femur according to the plan (Figure 2). CPT billing codes were reviewed to determine how many patients in each group underwent post-operative MUA. Post-operative mechanical alignment was measured in a subset of 50 consecutive patients in the ligament balancing group on standing long-leg radiographs by an independent observer. Results. Post-operative MUA rates were significantly lower in the ligament balancing group (0.5%; 1/199) than in the measured resection group (3.9%; 4/102), p=0.051. 91.3% (42/46) of knees were within 3° and 100% (46/46) were within 4° of neutral alignment to the mechanical axis post-operatively in the ligament balancing group. Conclusions. Gap driven femoral based planning in TKA resulted in a significantly lower post-operative manipulation rate than in the measured resection approach, while maintaining acceptable overall alignment to the mechanical axis

The final alignment of Patient Specific Instrumentation (PSI) TKA relies on the accuracy and the correct placement of the 3-D moulds, precision of saw cuts, soft tissue balancing and cementing technique. We aimed to compare the predicted alignment between PSI and Articulated Surface Mounted (ASM) computer navigation. Eight consecutive patients underwent knee replacement using MRI based PSI (Zimmer) with planning of 0º femoral and tibial mechanical alignment. After placing the conventional cutting blocks over the pins (placed according to PSI), the predicted alignment of cuts was verified with ASM navigation. PSI technique was used regardless of navigation values and alignment was compared. Good correlation was found for tibial cuts (maximum variation: coronal plane – 1º, sagittal plane – 2º) and femoral cuts in the sagittal plane (maximum variation 2º). However, in two patients the coronal plane variation in femur was > 2º (3º and 4º respectively). Navigation predicted combined final alignment of 5º valgus and 4º valgus in these patients. However, long leg standing x-rays revealed neutral and 1º valgus alignment in those two patients respectively, matching closely with PSI prediction. Final alignment in long-leg standing x-rays were independently reported by a musculoskeletal radiologist. Six knees were in neutral mechanical alignment (including the 2 navigation predicted outliers). The remaining 2 knees had a maximum deviation of 2 degrees from neutral. We conclude that there was overall good correlation between PSI and navigation. Even in cases where navigation predicted more than 3º combined varus/valgus alignment, PSI prediction was more accurate on long leg views

For patients suffering from osteoarthritis confined to one compartment of the knee joint, a successful unicondylar knee arthroplasty (UKA) has demonstrated an ability to provide pain relief and restore function while preserving bone and cruciate ligaments that a total knee arthroplasty (TKA) would sacrifice. Long-term survival of UKA has traditionally been inconsistent, leading to decreased utilisation in favour of alternative surgical treatment. Robot-assisted UKA has demonstrated an ability to provide more consistent implantation of UKA prosthesis, with the potential to increase long-term survivorship. This study reports on 65 patients undergoing UKA using an image-free, handheld robotic assistive navigation system. The condylar surface was mapped by the surgeon intra-operatively using a probe to capture a 3-dimensional representation of the area of the knee joint to be replaced. The intra operative planning phase allows the surgeon to determine the size and orientation of the femoral and tibial implant to suit the patients’ anatomy. The plan sets the boundaries of the bone to be removed by the robotic hand piece. The system dynamically adjusts the depth of bone being cut by the bur to achieve the desired result. The planned mechanical axis alignment was compared with the system's post-surgical alignment and to post-operative mechanical axis alignment using long leg, double stance, weight bearing radiographs. All 65 knees had knee osteoarthritis confined to the medial compartment and UKA procedures were completed using the handheld robotic assistive navigation system. The average age and BMI of the patient group was 63 years (range 45–82 years) and 29 kg/m. 2. (range 21–37 kg/m. 2. ) respectively. The average pre-operative deformity was 4.5° (SD 2.9°, Range 0–12° varus). The average post-operative mechanical axis deformity was corrected to 2.1° (range 0–7° varus). The post-operative mechanical axis alignment in the coronal plane measured by the system was within 1° of intra-operative plan in 91% of the cases. 3 out of 6 of the cases where the post-operative alignment was greater than 1° resulted due to an increase in the thickness of the tibia prosthesis implanted. The average difference between the ‘planned’ mechanical axis alignment and the post-operative long leg, weight bearing mechanical axis alignment was 1.8°. The average Oxford Knee Score (old version) pre and post operation was 38 and 24 respectively, showing a clinical and functional improvement in the patient group at 6 weeks post-surgery. The surgical system allowed the surgeons to precisely plan a UKA and then accurately execute their intra operative plan using a hand held robotically assisted tool. It is accepted that navigation and robotic systems have a system error of about 1° and 1mm. Therefore, this novel device recorded accurate post-operative alignment compared to the ‘planned’ post-operative alignment. The patients in this group have shown clinical and functional improvement in the short term follow up. The importance of precision of component alignments while balancing existing soft-tissue structures in UKA has been documented. Utilisation of robotic-assisted devices may improve the accuracy and long-term survivorship UKA procedure

Introduction. Operative inclination (OI) is defined as the angle between the acetabular axis and the sagittal plane. With the patient in the true lateral decubitus position, this corresponds to the angle formed between the handle of the acetabular component inserter and the theatre floor intra-operatively. Patients/Materials & Methods. The primary study aim was to determine which method of acetabular component insertion most accurately allows the surgeon to obtain a target OI of 35o. 270 consecutive patients undergoing cementless THA were randomised to one of three possible methods for acetabular component implantation:. 1. Freehand,. 2. 35o mechanical alignment guide (MAG), or. 3. Digital inclinometer assisted. Two surgeons participated. Target OI was 35o in all cases. OI was measured using a digital inclinometer. For the freehand and MAG cases, the surgeon was blinded to inclinometer readings intra-operatively. Results. Freehand: OI 25.2 – 43.2o. Mean deviation from target 2.92o. 35o MAG: OI 29.3 – 39.3o. Mean deviation from target 1.83o. Inclinometer assisted: OI 27.5 – 37.5o. Mean deviation from target 1.28o. Overall, when comparing mean deviation from target OI, a statistically significant difference between both the Freehand/Inclinometer group and Freehand/MAG group was demonstrated (p<0.001). A statistically significant difference between the Inclinometer/MAG groups was also demonstrated (p<0.023). Discussion. Both the 35o MAG and digital inclinometer assisted methods provided a considerably narrower OI range when compared to the freehand method. Though the range was similar for both the 35o MAG and digital inclinometer assisted methods, the SD was smaller in the inclinometer assisted group. Conclusion. The novel method of using a digital inclinometer to control operative inclination appears to be more accurate than both the freehand and mechanical alignment guide methods and may help further optimise acetabular component orientation

Background. Patient specific instrumentation (PSI) for total knee replacement (TKR) has demonstrated mixed success in simplifying the operation, reducing its costs, and improving limb alignment. Evaluation of PSI with tools such as radiostereometric analysis (RSA) has been limited, especially for cut-through style guides providing mechanical alignment. The primary goal of the present study was to compare implant migration following TKR using conventional and PSI surgical techniques, with secondary goals to examine whether the use of PSI reduces operative time, instrumentation, and surgical waste. Methods. The study was designed as a prospective, randomized controlled trial of 50 patients, with 25 patients each in the PSI and conventional groups, powered for the RSA analysis. Patients in the PSI group received an MRI and standing 3-foot x-rays to construct patient-specific cut-through surgical guides for the femur and tibia with a mechanical alignment. All patients received the same posterior-stabilized implant, with marker beads inserted in the bone around the implants to enable RSA imaging. Intraoperative variables such as time, number of instrumentation trays used, and mass of surgical waste were recorded. Patients underwent supine RSA exams at multiple time points (2&6 weeks, 3&6 months and yearly) with 6 months data currently available. Migration of the tibial and femoral components was calculated using model-based RSA software. WOMAC, SF-12, EQ5D, and UCLA outcome measures were recorded pre-operatively and post-operatively. Results. There were no demographic differences between groups. One patient in the PSI group was revised for infection, and three patients required manipulation, with no revisions or manipulations in the conventional group. There was no difference in maximum total point motion between groups for the tibia (mean 0.50 vs. 0.50 mm, p = 0.98) or femur (mean 0.46 vs. 0.48 mm, p = 0.87). The PSI group displayed greater tibial posterior tilt (p = 0.048, Fig. 1) and greater femoral anterior tilt (p = 0.01) and valgus rotation (p = 0.04, Fig. 2) than the conventional group, but there were no other differences in migrations. The PSI group required less instrument trays than the conventional group (mean 4.8 vs. 8.1 trays, p < 0.0001), but procedure time was equivalent (mean 79 vs. 74 min, p = 0.06). The PSI group produced less recyclable waste (mean 0.3 vs. 1.4 kg, p < 0.001), but total waste (Fig. 3) was equivalent between groups (mean 10.1 vs. 10.6 kg, p = 0.32). At 6 months there was no difference between groups for SF-12, WOMAC, EQ5D, or UCLA scores. Discussion. At early RSA follow-up, the two groups were broadly similar in implant fixation except for small rotational changes in the tibial and femoral components. The PSI group provided minimal or no advantage over the conventional group for operative time, instrumentation used, or surgical waste produced. The observed increase in manipulations in the PSI group is concerning, and requires additional investigation. Further radiographic and economic analysis is underway to determine if there is any benefit to the use of PSI for TKR during the perioperative and early follow-up period. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction and Objective. TKA have shown both excellent long-term survival rate and symptoms and knee function improvement. Despite the good results, the literature reports dissatisfaction rates around 20%. This rate of dissatisfaction could be due to the overstuff that mechanically aligned prostheses could produce during the range of motion. Either size discrepancy between bone resection and prosthetic component and constitutional mechanical tibiofemoral alignment (MTFA) alteration might increase soft tissue tension within the joint, inducing pain and functional limitation. Materials and Methods. Total knee arthroplasties performed between July 2019 and September 2020 were examined and then divided into two groups based on the presence (Group A) or absence (Group B) of patellofemoral overstuff, defined as a thickness difference of more than 2 mm between chosen component and bone resection performed, taking into account at least one of the following: femoral medial and lateral condyle, medial or lateral trochlea and patella. Based on pre and post-operative MTFA measurements, Group A was further divided into two subgroups whether the considered alignment was modified or not. Patients were assessed pre-operatively and at 6 months post-op using the Knee Society Score (KSS), Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Visual Analogue Scale (VAS) and Range of Motion (ROM). Results. One hundred total knee arthroplasties were included in the present study, 69 in Group A and 31 in group B. Mean age and BMI of patients was respectively 71 and 29.2. The greatest percentage of Patellofemoral Overstuff was found at the distal lateral femoral condyle. OKS, KSS functional score, and FJS were statistically significant higher in patients without Patellofemoral Overstuff. Therefore, Group A patients with a non-modified MTFA demonstrated statistically significant better KSS, ROM and FJS. Conclusions. Patellofemoral Overstuff decrease post-operative clinical scores in patients treated with TKA. The conventional mechanically aligned positioning of TKA components might be the primary cause of prosthetic overstuffing leading to worsened clinical results. Level of evidence: III; Prospective Cohort Observational study;

Introduction: I always aim for neutral mechanical axis alignment. My principles of a successful TKA are proper alignment in all 3 planes, soft tissue balance in extension first, flexion gap balancing by parallel to tibial cut technique, maintenance of joint line, correct sizing of femoral component, and proper cement fixation. Long-term Survivorship: There is long-term data that supports the efficacy and durability of the neutral position of proximal tibial cut. Over a 20-year follow-up there was a 92.6% success rate in my study. Other authors have found similarly successful survivorship for mechanical failure. Balance Technique in TKR: My technique to balance the knee is a balance extension gap first, which requires medial soft tissue balancing. Next, I balance the flexion gap parallel to the tibial cut. Our Results: In one study, I examined the clinical and radiographic data of 68 varus knees. Average post-operative mechanical alignment was 0 ± 3 degrees. There were no outliers which displays the reproducibility of the technique. This is the method of choice in the hands of most surgeons

INTRODUCTION. Cemented total knee arthroplasty (TKA) is a widely accepted treatment for end-stage knee osteoarthritis. During this procedure, the surgeon targets proper alignment of the leg and balanced flexion/extension gaps. However, the cement layer may impact the placement of the component, leading to changes in the mechanical alignment and gap size. The goal of the study was to assess the impact of cement layer on the tibial mechanical alignment and joint gap during cemented TKA. MATERIAL. Computer-assisted TKAs (ExactechGPS®, Blue-Ortho, Grenoble, FR) were performed by two fellowship trained orthorpaedic surgeons on five fresh-frozen non-arthritic pelvis-to-ankle cadaver legs. All the surgeries used a cemented cruciate retaining system (Optetrak Logic CR, Exactech, Gainesville, FL). After the bony resection, the proximal tibial resection plane was acquired by manually pressing an instrumented checker onto the resected tibial surface (resection plane). Once the prosthesis was implanted through standard cementing techniques, the top surface of the implanted tibial component was probed and recorded using an instrumented probe. A best fit plane was then calculated from the probed points and offset by the thickness of the prosthesis, representing the bottom plane of the component (component plane). The deviation of component alignment caused by the cement layer was calculated as the coronal and sagittal projection of the three-dimensional angle between the resection plane and the component plane. The deviation of the component height, reflecting a change in the joint gap, was assessed as the distance between the two planes calculated at the lowest points on the medial and lateral compartments of the proximal tibial surface. Statistical significance was defined as p≤0.05. RESULTS. The differences in alignment and component height between the tibial component placement and the ideal placement based on the bony resection are presented in Table 1. The magnitude of deviation in alignment was 1.2±0.9° for varus/valgus and 1.7±0.7° for posterior slope, with a tendency towards valgus (−0.2±1.6°) and reduced posterior slope (0.6±1.9°). The lateral compartment (2.4±0.9mm) had a generally higher increase in the height of the component compared to the medial compartment (1.0±0.9mm), the difference was close to being statistically significant (p=0.055). DISCUSSION. The finding of this study demonstrated that standard cement fixation during TKA may potentially influence the alignment and position of the tibial component. The formed cement layer generally results in elevated height, slightly more varus tibial alignment (overall limb valgus alignment) and less posterior slope in the implanted component. The results on the alignment are comparable to a previous study by Catani et al. [1]. More than 2°/2mm of deviation was found in the sagittal alignment (2 out of 5 knees), and medial (1 out of 5 knees) and lateral (3 out of 5 knees) component height, which may clinically impact the joint gap [2]. The varus/valgus alignment deviation found was clinically acceptable (≤3°). However when combined with other surgical variables, the accumulated impact on the alignment may warrant more investigation

Computer assisted total knee arthroplasty has been demonstrated to provide reproducible limb mechanical alignment within three degrees from the neutral mechanical axis. However, restoring proper implant and extremity alignment remains a significant challenge with proximal tibial deficiencies. In this prospective study, we describe the use of computer navigation to quantify the amount of bone loss on the medial or lateral tibial plateau and the use of this data to assess the need for augmentation with metallic tibial wedges. In this study, we demonstrate that CAS TKR in patients with significant tibial deformities can accurately measure severe tibial deformities, predict tibial augment thickness, and provide excellent mechanical alignment and restore the joint line without excessive bony resection, repeated osteotomies, and repeated augment trialing

Introduction. Studies have shown that dissatisfaction following TKA may stem from poor component placement and iatrogenic factors related to variability in surgical execution. A CT-based robotic assisted system (RA) allows surgeons to dynamically balance the joint prior to bone resection. This study aimed to determine if this system could improve TKA planning, reduce soft tissue releases, minimize bone resection, and accurately predict component size in varus knee. Method. Four hundred and seventy four cases with varus deformity undergoing primary RATKA were enrolled in this prospective, single center and surgeon study. Patient demographics and intraoperative surgical details were collected. Initial and final 3-dimensional alignment, component position, bone resection depths, use of soft tissue releases, knee balancing gaps, and component size were collected intraoperatively. WOMAC and KOOS Jr. scores were collected 6 months, and 1 year postoperatively. Descriptive statistics were applied to determine the changes in these parameters between initial and final values. Results. Native deformity ranged from 1 to 19 degrees of varus. 86% of patients in this study did not require a soft tissue release regardless of their level of coronal or sagittal deformity. Complex deformities who required a soft tissue release were corrected on average to 3 degrees varus while cases without releases were corrected to 2 degrees varus on average with the overall goal as traditional mechanical alignment. All surgeons achieved their planned sizes on the tibia and femur more than 98% of the time within one size, and 100% of the time within two sizes. Flexion and extension gaps during knee balancing were within 2mm (mean 1mm) for all knees. At latest follow-up, radiographic evidence suggested well-seated and well-fixed components. Radiographs also indicated the patella components were tracking well within the trochlear groove. No revision and re-operation were reported. Mean WOMAC total score was improved from 23.8±8.0 pre-op to 8.9±7.9 1-year post-op (p<0.01). Mean KOOS Jr. score was improved from 46.8±11.6 pre-op to 77.9±14.8 1-year post-op (p<0.01). Discussion and Conclusions. New tools may allow for enhanced execution and predictable balance for TKA, which may improve patient outcomes. In this study, preoperative planning via CT scan allowed surgeons to assess bony deformities and subtly adjust component position to reduce soft tissue trauma. While this study has several limitations, RATKA for varus knees should continue to be investigated. For any figures or tables, please contact authors directly

Conventional total knee arthroplasty aims to place the joint line perpendicular to the mechanical axis, despite the fact that the normal knee is inclined approximately 3 degrees, resulting in a medial proximal tibial angle of 87 degrees. The goal of a neutral mechanical axis is based largely on historical biomedical studies and the fact that it is easier to make a neutral tibial cut with conventional jigs and the eye. In order to balance the flexion and extension gap to accommodate a neutral tibial cut, in most patients, asymmetrical distal and posterior femoral cuts are required. The resulting position of the femoral component could be considered to be “mal-rotated” with respect to the patient's soft tissue envelope. Soft tissue releases are often required. The target of neutral mechanical axis, or “straight and narrow,” represents a compromise position with respect to the kinematics of the knee. Neutral mechanical alignment may not confer any befits with respect to survivorship but dissatisfaction rates are high globally, with approximately 20% of patients being dissatisfied after total knee arthroplasty in multiple studies. Computer assisted surgery and shape matching allow for consideration of placing total knee components to match an individual's anatomy, as opposed to forcing the knee into an unnatural neutral mechanical alignment

Abstract Detail. Interim results on a prospective, randomised, single-blinded pilot study to compare implant alignment using a patient-matched cutting guide versus a computer-assisted navigation system following total knee arthroplasty. Purpose of Study. To compare implant alignment using a patient-matched cutting guide (Visionaire) versus a computer-assisted navigation system (CAS) following total knee arthroplasty (TKA). Description of methods. Ethics approval was sought and granted by the South African Medical Association Research Ethics Committee. Patient consent for participation was obtained. Patients were randomized to TKA using Visionaire or CAS. Mechanical alignment was evaluated pre-operatively and at 3 months with a full leg X-Ray. Operative and post-operative parameters relating to resource utilization were captured. Clinical status according to the Knee Society Clinical Rating System (KSCRS) was assessed pre-operatively and at 3 months. Adverse events were noted. An independent Contract Research Organisation was used to monitor the site. Summary of results. Ten unique patients were enrolled, of whom 5 were randomized to Visionaire and 5 to CAS. Two patients in the Visionaire group have not yet reached their 3-month assessment. No significant difference in mechanical alignment between the 2 groups at 3 months was observed. The median duration of surgery was significantly shorter for the patient-matched cutting guide group across all assessed parameters (theatre time: 117 versus 150 minutes, p=0.009; operative time: 85 versus 108 minutes, p=0.0088; tourniquet time: 73 versus 99 minutes, p=0.009; and anaesthetist time: 117 versus 150 minutes, p=0.009). No other significant differences in operative or post-operative cost-drivers were noted between the 2 groups. No significant difference in KSCRS scores between the 2 groups at 3 months was observed. Two adverse were reported, one in each group, both unrelated to the medical devices, and both of which have resolved. Conclusion. While implant alignment appears consistent and comparable in both groups at 3 months, the median duration of surgery was significantly shorter for the Visionaire group. DISCLOSURE: Assistance and funding was received from Smith & Nephew

Introduction. Long term data on the survivorship of cemented total knee arthroplasty (TKA) has demonstrated excellent outcomes; however, with younger, more active patients, surgeons have a renewed interest in improved biologic fixation obtained from highly porous, cementless implants. Early designs of cementless total knees systems were fraught with high rates of failure for aseptic loosening, particularly on the tibial component. Prior studies have assessed the bone ingrowth extent for tibial tray designs reporting near 30% extent of bone ingrowth . (1,2). While these analyses were performed on implants that demonstrated unacceptably high rates of clinical failure, a paucity of data exists on the extent on bone ingrowth in contemporary implant designs with newer methods for manufacturing the porous surfaces. We sought to evaluate the extent of attached bone on retrieved cementless tibial trays to determine if patient demographics, device factors, or radiographic results correlate to the extent of bone ingrowth in these contemporary designs. Methods. Using our IRB approved retrieval database, 17 porous tibial trays were identified and separated into groups based on manufacturer: Zimmer Natural Knee (1), Zimmer NexGen (10), Stryker Triathlon (4) and Biomet Vanguard Regenerex (2). Differences in manufacturing methods for porous material designs were recorded. Patient demographics and reason for revision are described in Table 1. Radiographs were used to measure tibiofemoral alignment and the tibial mechanical axis alignment. Components were assessed using visual light microscopy and Photoshop to map bone ingrowth extent across the porous surface. ImageJ was used to threshold and calculate values for bone, scratched metal, and available surface for bone ingrowth (Fig. 1). Percent extent was determined as the bone ingrowth compared to the surface area excluding any scratched regions from explantation. Statistics were performed among tray designs as well as between the lateral and medial pegs, if designs had pegs available for bony ingrowth. Results. Mean bone ingrowth extent was 51.4% for the tibial tray for the entire cohort. Bone ingrowth extent was statistically greater in the Zimmer NexGen design (63.8%; p=.027) compared to the other three designs (Table 2). Four sets of pegs were excluded from analysis due to lack of porous coatings or pegs having been removed at revision surgery. Across all designs, the medial peg had 45.2% ingrowth and the lateral peg had 66.1% ingrowth. The medial peg for the NexGen design had significantly less bone ingrowth compared to the lateral peg (58.7% vs. 75.4%; p=0.044). No significant differences were found in tibiofemoral alignment or tibial mechanical axis alignment between the implant groups. No significant differences were found among implants revised for aseptic loosening versus any other reason for revision (54% vs 30%; p=.18). Discussion. Our results demonstrate high rates of bone ingrowth extent in contemporary designs, further supporting porous design rationales and a role for additive manufacturing to form enhanced porosity. We plan on exploring staining techniques to confirm our visual inspection. Contemporary designs have shown successful rates for improved longevity for cementless total knee systems. For any figures or tables, please contact the authors directly

Computer-assisted orthopaedic surgery (CAOS) improves mechanical alignment and the accuracy of surgical cuts in the context of total knee arthroplasty. A simplified, CAOS enhanced instrumentation system was assessed to determine if the same effects could be achieved through the use of a less intrusive system. Two cohorts of surgeons (experienced and trainees) performed a series of total knee arthroplasty resections in knee models with and without navigation-enhanced instrumentation. The percentage of resections that deviated from the planned cut by more than 2°or 2mm (outliers) was determined by post-resection advanced imaging for six unique outcome metrics. Within each experience level, the use of the CAOS enhanced system significantly reduced the total percentage of outliers as compared to conventional instrumentation (Figure 1). The experienced users improved from 35% to 4% outliers overall (p < .001) and the trainees from 34% to 10% outliers (p < .001). Comparing across experience levels, the experienced surgeons performed significantly better in only a single resection metric with conventional instrumentation (Figure 2A), varus/valgus tibial alignment, with 8.3% outliers compared to the trainee's 63% outliers (p = .004). The use of CAOS enhanced instrumentation eliminated any differences between the two user groups for all measured resections (Figure 2B). Comparing CAOS enhanced to conventional instrumentation specifically between anatomical deformity types revealed that there is significant improvement (p < .05) with the use of enhanced instrumentation for all three deformity types (Figure 3). These results suggest that non-intrusive CAOS enhanced instrumentation is a viable alternative to conventional instrumentation with possible benefits. This trial also demonstrates that additional experience may not correlate to improved surgical accuracy, and outliers may be less a result of individual surgeon ability or specific anatomic deformities, and more so related to limitations of the instrumentation used or other yet unidentified factors

Aims

The aim of this study was to investigate the distribution of phenotypes in Asian patients with end-stage osteoarthritis (OA) and assess whether the phenotype affected the clinical outcome and survival of mechanically aligned total knee arthroplasty (TKA). We also compared the survival of the group in which the phenotype unintentionally remained unchanged with those in which it was corrected to neutral.

Orthopaedic surgeons are currently faced with an overwhelming number of choices surrounding total knee arthroplasty (TKA), not only with the latest technologies and prostheses, but also fundamental decisions on alignment philosophies. From ‘mechanical’ to ‘adjusted mechanical’ to ‘restricted kinematic’ to ‘unrestricted kinematic’ — and how constitutional alignment relates to these — there is potential for ambiguity when thinking about and discussing such concepts. This annotation summarizes the various alignment strategies currently employed in TKA. It provides a clear framework and consistent language that will assist surgeons to compare confidently and contrast the concepts, while also discussing the latest opinions about alignment in TKA. Finally, it provides suggestions for applying consistent nomenclature to future research, especially as we explore the implications of 3D alignment patterns on patient outcomes.

Cite this article: Bone Joint J 2023;105-B(2):102–108.

Minimally invasive total hip replacement surgery not only decreases the number of visual cues necessary for proper acetabular component position, the small incision makes it technically more difficult to use traditional mechanical alignment guides. Furthermore, traditional mechanical guides have been shown to be unable to accurately predict component position as determined by intraoperative computer measurements.[ 1,2 ] Computer assisted intraoperative navigation can enable minimally invasive surgery by giving the surgeon immediate intra-operative feedback of actual component position. We wished to compare the intraoperative computer determined measurement of acetabular inclination with the postoperative radiographic measurement of inclination in order to validate the results of the computer assisted measurements in the clinical setting. To determine whether computer assisted navigation of the acetabular component allows the surgeon to accurately place the prosthesis in minimally invasive hip replacement and to compare the results of intraoperative navigation with the postoperative radiograph. 42 consecutive patients underwent a minimally invasive posterior approach for total hip arthroplasty with the assistance of CT based intraoperative navigation with the BrainLAB VectorVision software. Preoperative surgical planning was performed after acquisition of a CT scan. All components were templated to be placed in 45 degrees of inclination and 25 degrees of anteversion. Intraoperatively, cementless acetabular components were aligned with the computer navigation at these values prior to implant impaction. Because of the press fit nature and limited soft tissue exposure, many components would shift during impaction. Final component position was then verified and values recorded by detecting points on the acetabular surface. If the prosthesis was felt to be in an acceptable position, no attempt was made to modify component position to the predetermined values in order to avoid potentially compromising component fixation. Postoperative supine AP pelvis radiography was then used to determine final inclination. Measurements were made by drawing a line perpendicular to the acetabular teardrop and parallel to the acetabular component and measured with a standard goniometer. These data were then placed in an SPSS database and analyzed by an independent statistician. Assessing acetabular component position in routine total hip arthroplasty has been shown to be unreliable even with experienced surgeons with mechanical alignment guides. [1,3] In minimally invasive total hip arthroplasty, routine visual cues are limited and mechanical instruments are difficult to place in the small operative wounds making an already difficult task even more difficult. CT based image guided surgery can has been shown to improve the acetabular component position intraoperatively 2. However, postoperative validation studies comparing the intraoperative computer assessment with the postoperative radiographic measurement are scarce. [ 2 ] In this consecutive series, which represents the author’s first experience with this technology, several conclusions can be made. First, the act of impacting a solid, porous coated, hemispherical cementless acetabular component in minimally invasive hip surgery often leads to a final component position different from the intended position. Second, computer generated determination of implant position is reliable but care must be taken to make sure the reference arrays do not lose fixation during the procedure or spurious results can occur. Third, routine AP pelvis radiographic measurements are not accurate enough to determine whether the computer determined values are accurate. In spite of these measurement inaccuracies, the computer determined results and the radiographic results were within 10 degress 95 % of the time which is far more accurate than results obtained with mechanical alignment tools 3. Finally, further validation studies need to be done with postoperative CT scanning to determine the accuracy of the intraoperative computerized measurements and determine the measurement errors inherent in the clinical setting. Given these limitations, computer assisted navigation improves the accuracy and reliability of acetabular component position over traditional mechanical instruments and can be utilized in minimally invasive hip surgery to assist in the appropriate placement of the acetabular prosthesis

Computer Assisted Total Knee Arthroplasty (CAS TKR) has been shown to provide excellent and reproducible limb mechanical alignment. CAS TKR has also been demonstrated to reduce limb alignment variance and outliers. Previous studies have shown improved mechanical alignment both radiographically and clinically. Specifically, CAS TKR has been shown to result in alignment deviations less than 3 degrees from neutral mechanical femoral and tibial axes. Furthermore, CAS TKR also permits any significant pre-operative tibial deformity to be quantified prior to performing tibial osteotomies. In this study, we describe the use of computer navigation to quantify the amount of bone loss on the medial or lateral tibial plateau and the subsequent use of this data to assess the need for augmentation with tibial wedges. Two hundred and thirty consecutive primary computer assisted total knee arthroplasties were performed by one senior surgeon (L.P.) at Northwestern Memorial Hospital. In all cases, the tibial deformity was quantified and recorded intraoperatively using computer navigation software. The deformity was recorded in the navigation software by inputting the lowest point on the deformed tibial plateau and the mid point on the non-deformed tibial plateau using navigation markers. After Institutional Review Board approval was obtained, a retrospective review of the patient operative reports and patient charts was performed. Operative reports were reviewed to identify cases with the difference between the values of medial and lateral tibial plateaus exceeded thirteen millimeters and cases when tibial augmentation was performed. In cases utilising medial or lateral tibial augmentation, pre operative and post operative anterior posterior and lateral knee radiographs and long leg standing anterior posterior radiographs were reviewed to measure the joint line restoration and final mechanical limb alignment. All two hundred and thirty operative dictations and patient charts were reviewed. In seven cases, the difference between the values of the medial and lateral tibial plateaus was greater than thirteen millimeters. In all seven cases, tibial augmentation was utilized in order to prevent resection of tibial bone in excess of fourteen millimeters. In cases with a difference of medial and lateral tibial plateau values of less than thirteen millimeters, no tibial augmentation was utilised. For the seven cases using tibial augmentation, preoperative and post-operative knee and long standing radiographs were reviewed to examine joint line restoration and final limb alignment. In all seven patients, joint line restoration was successful within 4 millimeters and long standing radiographs revealed excellent limb alignment. Computer Assisted Total Knee Arthroplasty has already been shown to provide excellent limb alignment and reduce variance and outliers. We demonstrate that Computer Assisted Total Knee Arthroplasty in patients with significant tibial deformities can help assess and the amount of bone loss on the medial or lateral tibial plateaus. Excessive tibial resection to restore the mechanical axis and joint line can be avoided by quantifying the amount of tibial bone loss prior to osteotomy. Thus, Computer Assisted Total Knee Arthroplasty can successfully restore the joint line and overall limb alignment with conservative bone resection in patients with significant pre-operative tibial deformities

Introduction. Coronal plane alignment is one of the contributing factors to polyethylene wear in total knee arthroplasty (TKA). The goal of this study was to evaluate the wear and damage patterns of retrieved tibial polyethylene inserts in relationship to the overall mechanical alignment and to the position of the tibial component. Materials and methods. Based on full-length radiographs, ninety-five polyethylene inserts retrieved from primary TKA's with a minimum time in-vivo of five years were analysed for wear and damage. Four alignment groups were compared: valgus, neutral, mild varus and moderate varus. Varus and valgus positioning of the tibial component was analysed for damage score for the neutral and varus aligned groups. Results. A progression in the angle of wear was observed with progressively mechanical varus alignment. The valgus group was thinner laterally and the neutral, mild varus, and moderate varus groups were progressively thinner medially. The lateral compartment had greater damage in the mild and moderate varus group compared to the valgus group. There was a progression of increased lateral damage with increasingly varus HKA. No difference in damage was seen between groups for tibial component positioning. Conclusion. While greater wear of the lateral compartment in valgus aligned implants and progressively greater medial compartment wear in varus aligned implants was observed, greater damage scores were observed in the lateral compartment in the mild and moderate varus aligned TKAs compared to the valgus group. This observation is unique and might by explained by lateral condylar lift-off inducing impact and shear loading in the varus group

Aim. To assess the efficacy of combined medical and surgical management in obtaining normal lower limb mechanical alignment in a patient cohort with genotypically similar hypophosphataemic rickets. Methods. A notes and radiograph audit was performed of all patients attending our institution with hypophosphataemic rickets: a subset with PHEX gene anomalies was studied further. Lower limb radiographs were assessed at two points during childhood and note made of treatment start, compliance; indication, timing and result of surgery. Standing leg alignment radiographs were measured at skeletal maturity or at latest review. Results. 35 patients (16 females, 18 skeletally mature) were identified. 10 commenced treatment at <12m. 11 patients (5 female) underwent 24 surgical procedures (13 for varus deformities). Surgery was bilateral in 10/11 patients. 5/14 osteotomies were performed after skeletal maturity. Malalignment was common: with NSA (neck-shaft angle) abnormalities in 20%, abnormal angles at distal femur and proximal tibia in 58% and 60% respectively and ankle abnormalities in 24%, prior to surgery. Surgical management led to normal mechanical alignment at skeletal maturity. At latest review, no patient had a leg length difference. 40% of non-operated, skeletally immature limbs have significant malalignment despite medical therapy. There was no statistical relationship between treatment onset and need for surgical correction. The relationship between non-compliance with medical treatment and surgical intervention was confounded by the changing emphasis on preferred method of surgical correction from osteotomy to guided growth. Conclusion. Even when medical treatment is commenced promptly and adhered to, significant lower limb malalignment can occur requiring surgical correction. Guided growth principles allow early deformity correction. Significance. Lower limb malalignment should not be considered a failure of medical treatment but more a consequence of the disease process. Earlier surgical intervention may encourage a more normal pattern of growth

Summary. Study showed a simple acetabular placement plane formed by pelvic landmarks. The plane was adjusted by changing one of the landmarks to a fixed value for best representing the native acetabular orientation based on CT generated 3D pelvi. Introduction. Correct acetabular cup placement is a critical step to prevent dislocation in the total hip arthroplasty. There are many mechanical alignment devices available but they are usually only referencing to the body long axis and the table therefore are lack of accuracy. Recently more accurate guide was achieved by image or imageless hip navigation system. But they add more cost, steps and time. The purpose of this study was to find a simple acetabular cup placement plane by selcting bonny land marks. The plane was adjusted with a fixed value by comparing it to native acetabular orientation in CT constructed 3D pelvi. Methods. 274 anonymous CT pelvic scans from skeletally mature, normal Caucasian population with age range of 20–93 years old (mean age=64). The population included 164 males and 110 females (mean age for male=63 and female=65, P=0.40). CT data was converted to virtual bones using custom CT analytical software (SOMA™ V4.0). The acetabular anteversion angle was measured against coronal plane as AA defined by Murray. The inclination angle was measured from transverse plane. The native acetabular rim plane was constructed by three rim points of Ilium, ischium and pubis. The pelvic plane was based on and modified from previously reported alignment pelvic land marks. Anterior Inferior Iliac Spine (AIIS) was added to two local landmarks of Anterior Superior Iliac Spine (ASIS) and a point direct Lateral to Greater Sciatic Notch (LGSN). AIIS, ASIS and LGSN formed the local placement plane. The distance from three LGSN's to greater sciatic notch were 70mm, 75mm and 80mm. Three planes from three LGSN points were analyzed for anteversion and inclination angles. Results were compared with the same angles from native acetabulum. Student T test was performed with confidence level at P=0.05. Results. The mean anteversion angle/standard deviation for native acetabulum:25.7°/6.4° (male=24.6°/5.7°; female=27.3°/7.0°); plane LGSN+70mm: 21.9° /6.3°, (male= 20.3° /5.7°; female= 24.3° /6.4°); LGSN+75mm: 24.9°/6.3° (male= 23.3°/5.8°, female= 27.3°/6.2°); LGSN+80mm: 27.7°/6.1° (male= 26.1°/5.6°, female= 30.1°/6.0°). The mean inclination angle/standard deviation for native acetabulum were 51.5°/4.4° (male= 51.5°/4.2°, female= 51.5°/4.4°), plane LGSN+70mm: 51.8°/7.9° (male=53.3°/7.9°, female= 49.5°/7.4°), LGSN+75mm: 50.7°/7.8° (male= 52.3°/7.8°, female= 48.3°/7.3°); LGSN+80mm: 49.6°/7.8° (male= 51.2°/7.7°, female= 47.2°/7.2°). Student T test showed both anteversion and inclination angles of plane LGSN+75mm were not significantlydifferent from that of native acetabulum (P=0.12 and 0.11). (Table 1) The anteversion angle and inclination angle distribution are shown in Figure 1 and 2. Discussion/Conclusion. Unlike previously reported landmark methods, landmarks in this study were verified in large bone data base with exactly same measurements. The direct lateral point from GSN can be projected intraoperatively by calibrated hand along with other fixed landmarks to form an imaginative acetabular cup placement plane. This method also can be used for the imageless computer navigation as well as the mechanical alignment device

The exact alignment of the femoral component is crucial for the success of hip resurfacing arthroplasty. This prospective study was performed to find whether the imageless computer-assisted navigation surgery can improve the accuracy during hip resurfacing arthroplasty by comparing the alignment of the femoral component implanted with navigation system and conventional-mechanical guided system. Forty patients were randomly allocated into 2 groups for resurfacing hip arthroplasty using Birmingham hip resurfacing system. In the conventional group, femoral component positioning was assisted by mechanical alignment guides. In the navigation group, it was assisted by an imageless computer-assisted surgical system of Vectorvision. ®. (BrainLAB, Germany). We measured the difference between the preoperative plan of femoral component’s position and postoperative results on radiographs in the 2 groups. In the conventional group, a median difference of the stem alignment was 5.4° (range, 0.2°–10.9°) and a median difference of the stem anteversion was 2.6° (range, 0°–6.5°). In the navigated group, a median difference of the stem alignment was 2.3° (range, 0.2°–4.9°) and a median difference of the stem anteversion was 1° (range, 0°–3.6°). These differences between the 2 groups were statistically significant (P< 0.05). In resurfacing arthroplasty with a hip navigation, the procedure showed a good performance and reliability. It is achieved with greater precision with a navigation system than a mechanical alignment system

Introduction:. The number of medial unicompartmental knee arthroplasties (UKA) performed over the last decade has increased by 30%, as studies have demonstrated improved knee kinematics, range of motion, and decreased perioperative morbidity versus total knee arthroplasty. However, concerns remain regarding the future risk of revision due to lateral compartment degeneration. In patients with a varus mechanical alignment and tibiofemoral subluxation secondary to medial compartment osteoarthritis, the femoral and tibial articular surfaces of the lateral compartment subsequently become incongruous, potentially increasing the focal contact stresses seen with loading. The purpose of this study is to evaluate whether the tibiofemoral congruence of the lateral compartment of the knee is improved following a medial UKA. Methods:. This study is a retrospective review of 192 consecutive medial UKAs included in an IRB-approved, single-surgeon database. All UKAs were performed using a robot-assisted surgical technique. Preoperative and postoperative standing, anteroposterior hip-to-ankle radiographs controlling for lower extremity rotation were performed from which the congruence of the lateral compartment was measured. The preoperative and postoperative degree of articular congruence (congruence index, CI) was calculated using an iterative closest point (ICP)-based software code (Matlab, MathWorks Inc., Natick, MA), specially developed to evaluate congruence of knee compartments. Following digitization of the articular surfaces of the femur and tibia, the code performs a rigid transformation that best aligns the articular surfaces and evaluates the current degree of articular congruence. A congruence index (CI) is then calculated, with a value of 1 indicating complete congruence, and a value of 0 indicating a 100% dislocation of the articular surfaces. A student's t-test was used to compare the preoperative and postoperative values of lateral compartment congruence. Results:. The mean, preoperative congruence index of the lateral compartment was 0.88 (± 0.1), which was improved to 0.93 (± 0.07), following implantation of a medial UKA (p < 0.001). Congruence of the lateral compartment was improved in 158 of the UKAs (83%), while 34 (17%) demonstrated a decrease in the congruence index postoperatively. Conclusion:. Implantation of a medial unicompartmental knee arthroplasty improves the articular surface congruence of the lateral compartment in the majority of patients with isolated, medial compartment osteoarthritis (Figure 1). We hypothesize that this factor, combined with a controlled undercorrection of the overall mechanical alignment, will improved load distribution across the lateral compartment, reduce the risk of focal contact stress points, and decrease the risk of subsequent osteoarthritic degeneration of the lateral compartment. Medial UKA not only resurfaces the medial compartment, but also may treat potential lateral compartment degeneration by improving congruence and load distribution

Aims

The mid-term results of kinematic alignment (KA) for total knee arthroplasty (TKA) using image derived instrumentation (IDI) have not been reported in detail, and questions remain regarding ligamentous stability and revisions. This paper aims to address the following: 1) what is the distribution of alignment of KA TKAs using IDI; 2) is a TKA alignment category associated with increased risk of failure or poor patient outcomes; 3) does extending limb alignment lead to changes in soft-tissue laxity; and 4) what is the five-year survivorship and outcomes of KA TKA using IDI?

Aims

Patient dissatisfaction is not uncommon following primary total knee arthroplasty. One proposed method to alleviate this is by improving knee kinematics. Therefore, we aimed to answer the following research question: are there significant differences in knee kinematics based on the design of the tibial insert (cruciate-retaining (CR), ultra-congruent (UC), or medial congruent (MC))?