The August 2024 Knee Roundup³⁶⁰ looks at: Calcification’s role in knee osteoarthritis: implications for surgical decision-making; Lower complication rates and shorter lengths of hospital stay with technology-assisted total knee arthroplasty; Revision surgery: the hidden burden on surgeons; Are preoperative weight loss interventions worthwhile?; Total knee arthroplasty with or without prior bariatric surgery: a systematic review and meta-analysis; Aspirin triumphs in knee arthroplasty: a decade of evidence; Efficacy of DAIR in unicompartmental knee arthroplasty: a glimpse from Oxford.

The April 2024 Knee Roundup. 360. looks at: Challenging the status quo: re-evaluating the impact of obesity on unicompartmental knee arthroplasty outcomes; Timing matters: the link between ACL reconstruction delays and cartilage damage; Custom fit or off the shelf: evaluating patient outcomes in tailored versus standard knee replacements; Revolutionizing knee replacement: a comparative study on robotic-assisted and computer-navigated techniques; Pre-existing knee osteoarthritis and severe joint depression are associated with the need for total knee arthroplasty after tibial plateau fracture in patients aged over 60 years; Modern digital therapies?; A matched study on fracture rates following knee replacement surgeries;

Aims

Periprosthetic femoral fracture (PPF) is a major complication following total hip arthroplasty (THA). Uncemented femoral components are widely preferred in primary THA, but are associated with higher PPF risk than cemented components. Collared components have reduced PPF rates following uncemented primary THA compared to collarless components, while maintaining similar prosthetic designs. The purpose of this study was to analyze PPF rate between collarless and collared component designs in a consecutive cohort of posterior approach THAs performed by two high-volume surgeons.

Aims

The aim of this study was to compare the clinical outcomes of robotic arm-assisted bi-unicompartmental knee arthroplasty (bi-UKA) with conventional mechanically aligned total knee arthroplasty (TKA) during the first six weeks and at one year postoperatively.

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. Computer-assisted hip navigation offers the potential for more accurate placement of hip components, which is important in avoiding dislocation, impingement, and edge-loading. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA. Methods and Materials. We retrospectively reviewed 72 patients who underwent computer-navigated revision THA [Fig. 1] between January 2015 and December 2016. Demographic variables, indication for revision, type of procedure, and postoperative complications were collected for all patients. Clinical follow-up was performed at 3 months, 1 year, and 2 years. Dislocations were defined as any episode that required closed or open reduction or a revision arthroplasty. Data are presented as percentages and was analyzed using appropriate comparative statistical tests (z-tests and independent samples t- tests). Results. All 72 patients (48% female; 52% male) were included in the final analysis [Fig. 2]. Mean age of patients undergoing revision THA was 70.4 ± 11.2 years. Mean BMI was 26.4 ± 5.2 kg/m. 2. The most common indications for revision THA were instability (31%), aseptic loosening (29%), osteolysis/eccentric wear (18%), infection (11%), and miscellaneous (11%). During revision procedure, polyethylene component was most commonly changed (46%), followed by femoral head (39%), and acetabular component (15%). At 3 months, 1 year, and final follow-up, there were no dislocations among all study patients (0%). Compared to preoperative dislocation values, there was a significant reduction in the rate of dislocation with the use of computer-assisted hip navigation (31% vs. 0%; p<0.05). Discussion. Our study demonstrates a significant reduction in the rate of dislocation following revision THA with the use of computer navigation. Although the cause of postoperative dislocation is often multifactorial, the use of computer-assisted surgery may help to curtail femoral and acetabular malalignment in revision THA

Background

Stress fractures at tracker after computer navigated total knee replacement are rare. Periprosthetic fracture after Minimally Invasive Plate Osteosynthesis (MIPO) of stress fracture through femoral tracker is unique in orthopaedic literature. We are reporting this unique presentation of periprosthetic fractures after MIPO for stress fracture involving femoral pin site track in computer assisted total knee arthroplasty, treated by reconstruction nail (PFNA).

Aims

The aim of this study was to investigate the local recurrence rate at an extended follow-up in patients following navigated resection of primary pelvic and sacral tumours.

Introduction. High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee by shifting the center of force towards the lateral compartment. The amount of alignment correction to be performed is usually calculated prior to surgery and it's based on the patient's lower limb alignment using long-leg radiographs. While the procedure is generally effective at relieving symptoms, an accurate estimation of change in intraarticular contact pressures and contact surface area has not been developed. Using electromyography (EMG), Meyer et al. attempted to predict intraarticular contact pressures during gait patterns in a patient who had received a cruciate retaining force-measuring tibial prosthesis. Lundberg et al. used data from the Third Grand Challenge Competition to improve contact force predictions in total knee replacement. Mina et al. performed high tibial osteotomy on eight human cadaveric knees with osteochondral defects in the medial compartment. They determined that complete unloading of the medial compartment occurred at between 6° and 10° of valgus, and that contact pressure was similarly distributed between the medial and lateral compartments at alignments of 0° to 4° of valgus. In the current study, we hypothesised that it would be possible to predict the change in intra-articular pressures based on extra-articular data acquisition. Methods. Seven cadavers underwent an HTO procedure with sequential 5º valgus realignment of the leg up to 15º of correction. A previously developed stainless-steel device with integrated load cell was used to axially load the leg. Pressure-sensitive sensors were used to measure intra-articular contact pressures. Intraoperative changes in alignment were monitored in real time using computer navigation. An axial loading force was applied to the leg in the caudal-craneal direction and gradually ramped up from 0 to 550 N. Intra-articular contact pressure (kg) and contact area (mm2) data were collected. Generalised linear models were constructed to estimate the change in contact pressure based on extra-articular force and alignment data. Results. The application of an axial load results in axial angle changes and load distribution changes inside the knee joint. Preliminary analysis has shown that it is possible to predict lateral and medial compartment pressures using externally acquired data. For lateral compartment pressure estimation, the following equation had an R of 0.86: Lateral compartment pressure = −1.26*axial_force + 37.08*horizontal_force − 2.40*vertical_force − 271.66*axial_torque − 32.64*horizontal_torque + 18.98*vertical_torque − 24.97*varusvalgus_angle_change + 86.68*anterecurvature_angle_change − 17.33*axial_angle_change − 26.14. For medial compartment pressure estimation, the following equation had an R2 of 0.86: Medial compartment pressure = −2.95*axial_force −22.93*horizontal_force − 9.48*vertical_force − 34.53*axial_torque + 6.18*horizontal_torque − 127.00*vertical_torque − 110.10*varusvalgus_angle_change − 15.10*anterecurvature_angle_change + 55.00*axial_angle_change + 193.91. Discussion. The most important finding of this study was that intra-articular pressure changes in the knee could be accurately estimated given a set of extra-articular parameters. The results from this study could be helpful in developing more accurate lower limb realignment procedures. This work complements and expands on previous research by other groups aimed at predicting intra-articular pressures and identifying optimal alignment for unloading arthritic defects. A possible clinical application of these findings may involve the application of a predetermined axial force to the leg intra-operatively. Given the estimated output from the predictive equation, one could then perform the opening wedge until the desired estimated intra-articular pressure is achieved. With this method, an arthrotomy and placement of intra-articular pressure sensors would not be needed. This work is not without its limitations. This experiment was performed on cadaveric specimens. Therefore, we cannot directly predict what the pressures would be in a de-ambulating patient. However, these sort of experiments do help us understand the complex biomechanics of the knee in response to alterations in multi-planar alignment. Further in vivo research would be warranted to validate these results. Additionally, given our current experimental setup, only axial loading could be performed for testing. Further experiments involving dynamic motion of the lower limb under load would further help us understand the changes in pressure at difference flexion angles. Continued experiments would help us gather additional data to better understand the relationship between these variables and to construct a more accurate predictive model. In summary, we have established a framework for estimating the change in intra-articular contact pressures based on extra-articular, computer-navigated measurements. Quantifying the resulting changes in load distribution, alignment changes, torque generation and deflection will be essential for generating appropriate algorithms able to estimate joint alignment changes based on applied loads

INTRODUCTION. There is a growing interest in surgical variables that are controlled by the orthopaedic surgeon, including lower leg alignment and soft tissue balancing. Since more tight control over these factors is associated with improved outcomes of total knee arthroplasty (TKA), several computer navigation systems have been developed. Many meta-analyses showed that mechanical axis accuracy and component positioning are improved using computer navigation and one may therefore expect better outcomes with computer navigation but studies showing this are lacking. Therefore, a systematic review with meta-analysis was performed on studies comparing functional outcomes of computer-navigated and conventional TKA. Goals of this study were to (I) assess outcomes of computer-navigated versus conventional TKA and (II) to stratify these results by the surgical variables the systems aim to control. METHODS. A systematic search in PubMed, Embase and Cochrane Library was performed for comparative studies reporting functional outcomes of computer-navigated versus conventional TKA. Knee Society Scores (KSS) Total were most often reported and studies reporting this outcome score were included. Outcomes of computer-navigated and conventional TKA were compared (I) in all studies and (II) stratified by navigation systems that only controlled for lower leg alignment or systems that controlled for lower leg alignment and soft tissue balancing. Level of evidence was determined using the adjusted Oxford Centre for Evidence-Based Medicine tool and methodological quality was assessed using Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) tool. Outcomes were reported in mean difference (MD) with 95% confidence intervals [Lower Bound 95%, Upper Bound 95%]. RESULTS. Twenty-eight studies reported KSS Total outcomes in 3,504 patients undergoing computer-navigated or conventional TKA. Fifteen studies were evidence level I, five studies level II and eight studies level III. Study quality varied between low and high with most studies having high methodological quality. Patients reported better outcomes following computer navigated TKA than conventional TKA (MD 2.86 [0.96, 4.76], p=0.003), which was both seen at short-term follow-up of six months and one year (MD 5.20 [3.41, 7.00] and MD 8.46 [0.65, 16.28], respectively) and at mid-term follow-up (≥4 years) (MD 2.65 [0.96, 4.76]) (Figure 1). In studies that used computer navigation for controlling lower leg alignment, no difference in functional outcomes was seen between computer-navigated and conventional TKA (MD 0.66 [−2.06, 3.38], p=0.63, Figure 2). However, in studies that used computer navigation for controlling lower leg alignment and soft tissue balancing, patients reported superior functional outcomes following computer-navigate over conventional TKA (MD 4.84 [1.61, 8.07], p=0.003, Figure 3). CONCLUSION. This is the first meta-analysis showing superior functional outcomes following computer-navigated over conventional TKA. Stratifying results by variables the systems control, superiority in functional outcomes following computer-navigated over conventional TKA were only seen in systems that controlled soft tissue balancing. This suggests that soft tissue balancing plays an important role in short-term outcomes of TKA. Manually controlling all these surgical variables can be difficult for the orthopaedic surgeon and findings in this study suggest that computer navigation may help managing these multiple variables and improve outcomes. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Navigation in total hip arthroplasty (THA) has the goal to improve accuracy of cup orientation. Measurement of cup orientation on conventional pelvic radiographs is susceptible to error due to pelvic malpositioning during acquisition. A recently developed and validated software using a postoperative radiograph in combination with statistical shape modelling allows calculation of exact 3-dimensional cup orientation independent of pelvic malpositioning. Objectives. We asked (1) what is the accuracy of computer-navigated cup orientation (inclination and anteversion) and (2) what is the percentage of outliers (>10° difference to aimed inclination and anteversion) using postoperative measurement of 3-dimensional cup orientation. Methods. We performed a retrospective comparative study including a single surgeon series with 114 THAs (109 patients). Surgery was performed through the anterolateral approach with the patient in supine position. An image-free navigation system (PiGalileo, Smith & Nephew) with a passive digital reference base for the pelvic wing and one for the distal femur was used. The anterior pelvic plane (APP) was registered manually using a pointer and used as anatomical reference. After implantation of the press-fit cup (EP-Fit plus, Smith & Nephew) the final cup orientation (inclination and anteversion) was registered with the navigation system. Postoperative orientation was calculated using validated software to calculate 3-dimensional cup orientation. The postoperative anteroposterior pelvic radiograph in combination with a statistical model of the pelvis allowed calculation of inclination and anteversion referenced to the APP. The software was previously validated using CT measurements and revealed a mean accuracy of 0.4° for inclination 0.6° for anteversion with a maximum error of 3.3° and 3.6°, respectively. The mean postoperative inclination in the current series was 46° ± 4° (range, 35° – 60°) and the mean anteversion was 23° ± 6° (range, 11° – 37°). Accuracy was calculated as the absolute difference of the intraoperative registered cup orientation and the postoperative calculated orientation. An outlier was defined if cup orientation was outside a range of ±10° of inclination and/or anteversion. Results. (1) The mean accuracy for inclination was 3 ± 3° (0 – 17°) and 6 ± 5° (0 – 22°) for anteversion. (2) Three out of 114 cups (3%) were outliers for inclination. An increased percentage of outliers was found for anteversion with 23 out of 114 cups (20%; p<0.001). In total, 25 cups (22%) were outliers (See Figure 1). Conclusions. Previous studies evaluating accuracy of cup orientation were limited in numbers of hips due to the use of CT or used measurements on conventional postoperative radiographs which are prone to error due to pelvic malpositioning. Novel and validated software allows accurate and anatomically referenced measurement of postoperative cup orientation. This study is the single largest case series with 3-dimensional measurement of cup orientation for validation of navigated THA. Computer-assisted image-free navigation of cup orientation showed a high accuracy of cup orientation with 78% within a narrow range of ±10° of inclination and anteversion. Accuracy of cup inclination was increased compared to cup anteversion. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

INTRODUCTION

As computer navigated surgery continues to progress to the forefront of orthopedic care, the application of a navigated total shoulder arthroplasty has yet to appear. However, the accuracy of these systems is debated, as well as the dilemma of placing an accurate tool in an inaccurate hand. Often times a system's accuracy is claimed or validated based on postoperative imaging, but the true positioning is difficult to verify. In this study, a navigation system was used to preoperatively plan, guide, and implant surrogate shoulder glenoid implants and fiducials in nine cadaveric shoulders. A novel method to validate the position of these implants and accuracy of the system was performed using pre and post operative high resolution CT scans, in conjunction with barium sulfate impregnated PEEK surrogate implants.

Aim. Computer-navigated total knee arthroplasty has been shown to improve the outcome in outliers with consistent results. The aim of this study is to evaluate the clinical and radiographic outcomes of computer-navigated knee arthroplasty with respect to deformity and body mass index (BMI). Materials and Methods. Data was prospectively collected for 117 consecutive patients undergoing primary computer-navigated total knee arthroplasty using Ci Brainlab system with J&J PFC PS implants by a single surgeon utilising a tibia cut first, gap-balancing technique. Pre-operative and post-operative long-leg films, weight-bearing, films were taken and the long-axis was measured by a single observer. Intra-operative computer navigation long-axis values were stored as screenshots intra-operatively after registration and after implant was cemented. BMI, range of motion (ROM), SF 36 and Oxford knee scores were recorded both before surgery and on follow-up. Minimum 2-year follow-up. Eight patients were lost to follow-up and 8 had incomplete 2 year data. Data was analysed using the Chi-squared test for categorical variables and the t-test for continuous variables. Results. Eighty-four (83.2%) female, 17 (16.8%) male patients age 65.3±6.9 years with a pre-operative BMI of 27.2±4.1 (18.6 to 40.0). Eighty-eight (87.1%) met the Singapore definition of overweight with BMI>23 kg/m2. Forty-two (41.6%) had a BMI>27.5 kg/m2 indicative of obesity in Singapore. Pre-operative radiographic axis was 9.3±10.6° varus. Thirty (29.7%) patients had a pre-operative coronal plane deformity of more than 15°. Meanoperative duration 96.0±10.7 mins. Post-operative radiographic axis was 0.05±3.0° valgus. Significant improvement was seen in knee extension, knee flexion, SF 36 and Oxford knee scores at 2 years. No significant improvement in extensor lag and straight leg-raising at 2 years. Pre-operative axis >15° was not significantly related to operative duration. BMI>23 kg/m2 was significantly related to longer operative time (88.8±10.8 vs. 97.1±10.3 min, p<0.021). BMI >27.5 kg/m2 not significantly related to operative duration, pre-operative SF36 or Oxford knee scores. Post-operative axis deviation of more than 3° not significantly related to BMI > 23 or 27.5 kg/m2, similar to post-implant navigation axis. BMI >23 kg/m2 not significantly related to 2 year SF36, Oxford knee score and range of motion at 2 years. BMI >27.5 kg/m2 not significantly related to 2 year SF36 or Oxford knee scores. Conclusion. Although restoration of coronal alignment even in deformity >15° is possible with computer navigation, post-operative extensor lag and weakness is still a problem determined by pre-operative extensor lag and weakness in straight leg raising. Computer navigation is useful when exposure and landmarks to assess alignment are difficult such as in obesity where the standard external tibia jig doesn't sit well with the thick subcutaneous layer and for determining the epicondylar axis of the femur in a deep wound. Despite the technical challenges of performing a total knee arthroplasty with obesity, BMI is not a determinant of functional scores when computer navigation is used

Introduction. 11%–19% of patients are unsatisfied with outcomes from Total Knee Arthroplasty (TKA). This may be due to problems of alignment or soft-tissue balancing. In TKA, often a neutral mechanical axis is established followed by soft tissue releases to balance and match the flexion/extension gaps with the distal femoral and proximal tibial resections at right angles to the mechanical axis. Potential issues with establishment of soft tissue balance are due to associated structures such as bone tissue of the knee, the static (or passive) stabilizers of the joint (medial and lateral collateral ligaments, capsule, and anterior and posterior cruciate ligaments), and the dynamic (or active) stabilizers around the knee. An optimized balance among these systems is crucial to the successful outcome of a TKA. Additionally, the importance of correct femoral rotation has been well documented due to its effect on patella alignment and flexion instability, range of motion, and polyethylene wear. There are several methods used in TKA procedures to establish femoral component rotation. The more prominent ones are a conventional method of referencing to the posterior condylar axis with a standard external rotation of 3° (PCR), anterior-posterior line or “Whiteside's line” (AP axis), transepicondylar axis (TEA) (Figure 1), and the gap balancing technique, however, it is not yet clear, which method is superior for femoral rotational component alignment. In the current study, we sought to investigate an alternative method based on soft-tissue, dynamic knee balancing (DKB) while using an alternative analysis approach. DKB dictates femoral component rotation on the basis of ligament balance and force measures. DKB has become more prominent in TKA surgeries. While retaining ligament balance in TKA, it is possible that this technique also leads to higher precision of rotational alignment to the anatomical axis. The primary objective of this study was to compare efficiency of DKB versus other methods for rotational implant alignment based on post-surgery computed tomography (CT). Methods. 31 patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a flexion gap balance device (Synvasive eLibra). Alternative, hypothetical alignments were assessed based on anatomical landmarks during the surgery. Postoperative computed tomography (CT) scans were analyzed to investigate post-surgery rotational alignment. Repeated measures ANOVA and Cochran's Q test were utilized to test differences between the DKB method and the other techniques. Results. Significant differences were observed between the DKB method and TEA method (p=0.02), between DKB and AP method (p=0.04), and DKB and PCR method (p=0.02): The DKB method showed the lowest rotational deviation from CT-determined true anatomical TEA (aTEA)(Figure 2). The DKB method established femoral rotation within ±3 more often than the other techniques (Figure 3), further analysis revealed a significant proportional difference between DKB and PCR method (p=0.01), between DKB and TEA (p=0.02) and DKB and AP (p=0.04). Conclusions. DKB showed promising results in our study regarding femoral rotation accuracy in comparison to other methods. DKB may be a valuable tool due to its ability to establish soft-tissue balance in addition to high accuracy of femoral rotation

Introduction. Hip and knee joint replacement is nowadays one of the most common surgeries in Germany. The frequency of peri- and post-operative complications varies depending on the study. Since 2001, every hospital in Germany is required to report any peri- and post-operative complication to an external institute for quality control. The purpose of this study was to evaluate the published data of these institutes and to differentiate between the rate of peri- and early postoperative complications of conventional and computer navigated surgical procedures. The hypothesis of the study was that there is no increase in the rate of peri- and early post-operative complications as a result of the navigated surgical procedure. Materials and Methods. A retrospective analysis of the data on primary total knee and hip replacements between 2004 and 2012 were conducted. The share of navigated procedures, additional operating time due to navigation, the peri- and early post-operative surgical and general rates of complications and the comparison of patient population (age, sex and ASA-classification) were subject of the analysis. Results. Overall, the number of implanted knee endoprostheses rose from 110.000 in 2004 to 133.000 in 2012, including a doubling in the share of the navigated knee endoprostheses from 6.8% to 11.2%. Additional operative time for the implantation of knee prostheses decreased from initially 20 min. to 11.3 min. The rate of patients with at least one surgical intra and post-operative surgical complication decreased nearly 50.0% both, conventional and computer-navigated total knee arthroplasty. Focusing solely on the rate of general post-operative complications, a decrease from 5.9 % (conventional) or 4.7% (navigated) to 2.9%, respectively, was observed. In the area of hip prostheses, the total number increased from 138.000 (2004) to 152.500 (2012), with a relatively stable share of navigated prostheses from 1.63% to 1.4%. Additional operative time in case of the navigation decreased from 14.8 min. to 5.3 min. The rate of patients with at least one surgical intra or post-operative complication showed a decrease from 5.0% to 3.0% for both. The rate of post-operative general complications with navigated prostheses showed a higher drop in percentage points from 4.5% to 1.85% than with non-navigated prostheses, which decreased from 5.0% to 3.0%. Discussion. Despite high expertise and having used navigation for years, still very few endoprostheses are navigated. However, through a regular application of the navigation, a significant reduction of the operational time was accomplished in knee and hip replacement. The analysis did not show an increase in either peri- or early post-operative appearance of complications

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

Objectives

Acetabular component orientation in total hip arthroplasty (THA) influences results. Intra-operatively, the natural arthritic acetabulum is often used as a reference to position the acetabular component. Detailed information regarding its orientation is therefore essential. The aim of this study was to identify the acetabular inclination and anteversion in arthritic hips.