Purpose. The complication of patellofemoral compartment was quite often in total knee arthroplasty. One of the impotant factors in these complications would be the femoral component rotation in TKA. To determine the rotation of the femoral component, the reference of the surgical epicondylar axis (SEA), posterior condylar axis (PCA), AP axis with three dimensional model achieved from computed tomography data were considered. There are some limitations with pre-oprerative CT-based planning such as radio exposure, cost, time and detection of the depth of cartilage. We evaluate the determination of the femoral component rotation with image-free registration method to compare with three-dimensional template system. Material and Methods. Thirty six knees were evaluated to determine the femoral component rotation. The reference points were marked to measure the PCA (posterior condylar axis), SEA (surgical transepicondylar axis), and APA (anteroposterior axis, Whiteside line) intra-operatively and calculated the angle from PCA to SEA and PCA to APA with Image free navigation system (BrainLAB). Those knees were preoperatively evaluated the angle deviation from SEA to PCA with three dimensional template system. These angle deviations, which suggested the femoral component rotation obtained from preoperative template system, were statistically compared with the femoral rotation angle in clinical situation. Results. The mean angle from PCA to SEA was external rotated 2.7 degrees (SD=1.8 degrees) with the template system. During image- free system in TKA, the mean angle from PCA to SEA was external rotated 2.2 degrees (SD=4.5 degrees), and the mean angle from APA to SEA was 0.5 degrees (SD=4.4 degrees). Discussion. The preoperative 3 dimensional template system showed the small ranges and standard deviations in PCA and SEA even when the residual cartilage of the surface at the femur was not considered to evaluate. Meanwhile, the three reference axes obtained from image free navigation system showed the large amount of deviations and thus the variability in these references was difficult to decide the rotation of the femoral component. Now navigation system provided the appropriate gap balance during knee motion. This gap-navigation technique would be one of the keys to obtain the proper rotation of the component

Purpose. To validate accuracy of transepicondylar axis as a reference for femoral component rotation in primary total knee arthroplasty. Methods. A prospective study done from dec 2010 to dec 2011 at tertiary centre. 80 knees were included (43 females and 21 males). All surgeries were carried out by one senior arthroplasty surgeon. All patients undergoing primary total knee replacement were included and all revision cases were excluded. Intraoperative assessment of TEA was done by palpating most prominent point on lateral epicondyle and sulcus on medial epicondyle and passing a k wire through it. Confirmation is done under image intensifier C arm with epicondylar view. Postoperative TEA was assessed by taking CT scan, measuring condylar twist angle and posterior condylar angle. Also correlation of femoral component rotation with postoperative anterior knee pain was assessed. Results. The mean PCA was around 4° with TEA as reference and only 10% patients required an additional lateral release of which 2% patient had preop patellar maltracking. No postoperative patellar maltracking was seen. Anterior knee pain was present in 8% patients. No postop infection is noted. Alignment ranging from 3° to 9° external rotation. Conclusion. TEA is most accurate reference for femoral component rotation even in severely deformed arthritic knees. Key words – Transepicondylar axis, total knee arthroplasty, femoral component rotation,

Introduction. Proper femoral component rotation is a crucial factor in successful total knee arthroplasty (TKA). Femoral component rotation using anatomic landmarks has traditionally been established by referencing the transepicondylar axis (TEA), Whiteside's Line (WSL), or the posterior condylar axis (PCA). TEA is thought to best approximate the flexion-axis of the knee, however WSL or PCA are commonly used as surrogates of the TEA in the operating room due to their accessibility. The relationship of these anatomic landmarks has been previously investigated in anatomic and computed tomography based studies. The relatively few knees evaluated have limited the power of these studies. Patient Specific Instrumentation (PSI) utilizing magnetic resonance imaging (MRI) is an emerging technology in total knee replacement. The purpose of this study was to use magnetic resonance imaging based planning software to assess the relationship of WSL and PCA to the TEA and to determine if the relationships were influenced by the magnitude of the pre-operative coronal deformity. Methods. Five hundred sixty total knee replacements were performed in 510 patients utilizing PSI. The Materialize preoperative planning software was utilized to determine the rotational relationships of TEA, WSL, and PCA (Fig 1). The coronal plane deformity of each patient was also evaluated utilizing the MRI-based imaging and planning software. Results. The WSL is externally rotated by 90.36 degrees (SD ±2.3 degrees) compared to the TEA and the PCA is 2.38 degrees (SD ±1.6 degrees) internally rotated compared to the TEA in the overall population (p<0.001). The relationship of WSL to TEA has more variability than the relationship of PCA to TEA. In the overall population only 77% of WSL and 74% of PCA based resection will be within 2 degrees of the TEA. The PCA is more internally rotated in females and in valgus knees (P<0.001) however is not affected by the degree of valgus deformity (p = 0.211). Discussion. Femoral component rotation is determined based on one of three axis options. Classic studies have shown that the TEA is perpendicular to the WSL and the PCA is 3 degrees internally rotated to the TEA. However, there is wide variation in the relationships. Our MRI based evaluation shows that both WSL and PCA approximate the TEA in valgus knees regardless of the degree of deformity. Our study also shows that on average the PCA is 2.38 degrees internally rotated compared to the TEA, not the previously assumed 3 degrees. Our study indicates that the PCA is more internally rotated compared to the TEA in female patients and patients with valgus deformity. Males with varus knees may only require a 2 degree internal rotation correction rather than the historically established 3 degrees. WSL also shows more variability in its relationship to the TEA compared to the PCA. Advanced imaging can assist surgeons in assessing their options for femoral component rotation in TKA. Our data indicates that the relationships of axis options and historical assumptions may need to be reassessed as imaging technology advances

Purpose. To assesment of geometric center of knee as a reference for femoral component rotation in primary total knee arthroplasty. Methods. A prospective study done from dec 2009 to dec 2011 at tertiary centre. 180 knees were included (124 females and 56 males). All cases were randomly allocated into 2 groups: navigated and non navigated. All surgeries were carried out by two senior arthroplasty surgeons. All patients undergoing primary total knee replacement were included and all revision cases were excluded. Postoperative geometric center of knee was assessed by taking CT scan. Results. The mean PCA was around 5° with geometric knee centre axis and 9° in TEA. No postoperative patellar maltracking was seen. Anterior knee pain was present in 7% patients. No postop infection is noted. Alignment ranging from 3° to 12° external rotation. Conclusion. Geometric centre of knee is most accurate measure for referencing of femoral component rotation, as compared TEA, which can lead to excessive external rotation. Key words – Geometric centre of knee, total knee arthroplasty, femoral component rotation

Introduction. Most surgeons utilize one of three axis options in conventional total knee arthroplasty (TKA), the transepicondylar axis (TEA), Whiteside's line (WSL) or the posterior condylar axis (PCA) with an external rotation correction factor. Each option has limitations and no clear algorithm has been determined for which option to use and when. Many surgeons believe the TEA to be the gold standard for determining rotation however it can be difficult to access intraoperatively. WSL and PCA have been used as surrogates for determining axial rotation in conventional TKA but may also be prone to error. MRI based preoperative planning systems overcome intraoperative limitations while accounting for the individual anatomy of each patient, thus helping optimize femoral component rotation. The goal of this study was to examine if coronal plane deformity had any effect on the relationship of conventional referencing options such as WSL and PCA to the TEA. Methods. Utilizing a preoperative planning software based on MRI, we compared the preoperative posterior femoral condyle resections for three different axis options in 176 TKA. The difference in bone resection amount was used to determine the rotational differences between the axis options in all knees. Assuming that the TEA was the ideal rotational axis, we compared the TEA to both WSL and PCA. A 1-sample t-test and paired t-test were then used to determine if there was a significant rotational difference between the various axis options when accounting for degree and direction of preoperative deformity in the coronal plane. Results. In the overall population of 176 knees (42 valgus, 134 varus), neither WSL or PCA approximated the TEA accurately (p=0.016 and 0.001). In valgus deformity, WSL was found to approximate the TEA (p=0.68) better than the PCA (p=0.21). Minor varus deformity (< 3 degrees) favored the use of PCA (0.53) while moderate varus deformity (3–6 degrees) favored use of WSL (p=0.76). Severe varus (>6 degrees) deformity favored use of PCA due to lower variability. For complete results see Figure 2. Conclusion. Based on MRI data, our study indicates that preoperative coronal plane deformity should help determine the specific referencing option utilized for femoral component rotation in TKA. Broad application of either WSL or the PCA to all patients regardless of preoperative deformity did not accurately approximate TEA in femoral component rotation. Rather, analysis of the degree and direction of preoperative coronal plane deformity indicates that WSL and PCA should be used in specific scenarios to approximate the TEA. When WSL or PCA either both approximate or do not approximate the TEA, we recommend using the option with a lower standard deviation, and thus less variability. Although this MRI based technology is not in widespread use, we believe our findings (Figure 1) can assist the majority of surgeons determine when to use WSL or the PCA based on preoperative coronal plane deformity

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. In total knee arthroplasty (TKA), the setting position of component and the angle influence surgical results. 3D matching evaluation method using the CT before and after operation was a useful method as a rating system after operation. The anterior femoral cortical line (AFCL) is an anatomical landmark for determining intraoperative femoral component rotation in total knee arthroplasty (Fig.1). Our aim in this study is to evaluate the effectiveness of the JIGEN (Jig Engaged 3D Pre-Operative Planning System for TKA) (LEXI, Japan) operation support system using AFCL. Patients and methods. We performed TKA used GENUS MB (Adler, Italy) by January, 2015 from October, 2013. As for 5 male knees, 37 woman knees, the operation average age were 68 years old. The operation was based on each insertion parameter of the rod in marrow provided by a preoperative plan by the JIGEN system and at first installed a target device in the femoral front and manufactured a insertion point and inserted a rod in the marrow to plan insertion depth (Figure 1). We performed CT photography of the whole lower limbs after operation like preoperation and femoral component setting was located after operation using evaluation software (LEXI, Japan) and evaluated it. Result. In the 3D evaluation, femoral components implanted less than 3 degrees were 98% in the coronal plane, 67% in the sagittal plane, and 79% in the axial plane (Figure 2). The rotational malposition of femoral component was found in the case that the distal femoral front was round. Conclusion. The JIGEN system is useful for operation support in TKA. AFCL has the advantages of easy access and because of its extra-articular position is not affected by articular cartilage or processes that destroy the joint (such as degeneration or osteolysis). We considered that the JIGEN system using AFCL can be effective for determining intraoperative femoral component rotation in TKA

The anterior femoral cortical line (AFCL) is an anatomical landmark which has been used by the senior author for 20 years to assess femoral rotation in over 4000 TKR's. The AFCL describes the alignment of the anterior cortex of the distal femur proximal to the trochlear articular cartilage. The AFCL was compared with the surgical epicondylar (SEA), anteroposterior (Whiteside's line) and posterior condylar (PC) axes using 50 dry-bone cadaveric femora, 16 wet cadaveric specimens, 50 axial MRI's and 58 TKR patients intra-operatively. In the dry-bone/cadaveric femora (measuring relative to the SEA the AFCL and Whiteside's AP axis were 1° externally rotated and the PC axis was 1° internally rotated. By MRI (relative to the SEA) the AFCL was 8° internally rotated, Whiteside's was 2° externally rotated and the PC axis was 3° internally rotated. In the clinical study (measuring relative to a perpendicular to Whiteside's line alone) the AFCL was 4° degrees internally rotated, which equates to 2-3° of internal rotation relative to the SEA. The AFCL is another axis, completing the ‘compass points’ around the knee. It may prove particularly useful when one or all of the other reference axes are disturbed such as in revision TKR, lateral condylar hypoplasia or where there has been previous epicondylar trauma. We suggest building in 5° external rotation with respect to the anterior femoral cortical line for femoral component rotation

Purpose:. To compare accuracy of transepicondylar axis as a reference for femoral component rotation in primary navigated versus non navigated total knee arthroplasty in severely deformed knees. Methods:. A prospective study done from dec 2009 to dec 2011 at tertiary centre. 180 knees were included (124 females and 56 males). All cases were randomly allocated into 2 groups: navigated and non navigated. All surgeries were carried out by two senior arthroplasty surgeons. All patients undergoing primary total knee replacement were included and all revision cases were excluded. Intraoperative assessment of TEA was done by palpating most prominent point on lateral epicondyle and sulcus on medial epicondyle and passing a k wire through it. Confirmation is done under image intensifier C arm with epicondylar view in Non navigated knees. Postoperative TEA was assessed by taking CT scan, measuring condylar twist angle and posterior condylar angle (PCA). Results:. The mean PCA was around 4° with TEA as reference in Navigated and 6° in Non navigated knees and only 7% patients required an additional lateral release of which 2% patient had preop patellar maltracking. No postoperative patellar maltracking was seen. Anterior knee pain was present in 10% patients. No postop infection is noted. Alignment ranging from 4° to 8° external rotation. Conclusion:. Navigation is most accurate measure for TEA as reference, as compared to non navigated TKA, which can lead to excessive external rotation especially in severely deformed knees

Purpose

Femoral component malrotation is a common cause for persisting symptoms and revision following total knee arthroplasty (TKA). There is ongoing debate about the most appropriate use of femoral landmarks to determine rotation. The Sulcus Line (SL, See Figure 1) is a three-dimensional curve produced from multiple points along the trochlear groove. Whiteside's Line, also known as the anteroposterior axis (APA), is derived from single anterior and posterior points. The purposes of the three studies presented are to i) assess the SL in a large clinical series, ii) demonstrate the effect of parallax error on rotational landmarks, and iii) assess the accuracy of a device which transfers a geometrically corrected SL onto the distal cut surface of the femur.

There are basically 4 ways advocated to determine the proper femoral component rotation during TKA: (1) The Trans-epicondylar Axis, (2) Perpendicular to the “Whiteside Line,” (3) Three to five degrees of external rotation off the posterior condyles, and (4) Rotation of the component to a point where there is a balanced symmetric flexion gap. This last method is the most logical and functionally, the most appropriate. Of interest is the fact that the other 3 methods often yield flexion gap symmetry, but the surgeon should not be wed to any one of these individual methods at the expense of an unbalanced knee in flexion. In correcting a varus knee, the knee is balanced first in extension by the appropriate medial release and then balanced in flexion by the appropriate rotation of the femoral component. In correcting a valgus knee, the knee can be balanced first in flexion by the femoral component rotation since balancing in extension almost never involves release of the lateral collateral ligament (LCL) but rather release of the lateral retinaculum. If a rare LCL release is anticipated for extension balancing, then it would be performed prior to determining the femoral rotation since the release may open up the lateral flexion gap to a point where even more femoral component rotation is needed to close down that lateral gap. It is important to know and accept the fact that some knees will require internal rotation of the femoral component to yield flexion gap symmetry. The classic example of this is a knee that has previously undergone a valgus tibial osteotomy that has led to a valgus tibial joint line. In such a case, if any of the first 3 methods described above is utilised for femoral component rotation, it will lead to a knee that is very unbalanced in flexion being much tighter laterally than medially. A LCL release to open the lateral gap will be needed, increasing the complexity of the case. My experience has shown that intentional internal rotation of the femoral component when required is well-tolerated and rarely causes problems with patellar tracking. It is also of interest to note that mathematical calculations reveal that internally rotating a femoral component as much as 4 degrees will displace the trochlear groove no more that 2–3 mm (depending on the FC size), an amount easily compensated for by undersizing the patellar component and shifting it medially those few mm. There are basically 3 ways to determine the proper tibial component rotation during TKA: (1) Anatomically cap the tibial cut surface with an asymmetric tibial component, (2) Align the tibial rotation relative to a fixed anatomic tibial landmark (most surgeons use this method and align relative to the medial aspect of the tibial tubercle), (3) Rotate the tibial component to a point where there is rotational congruency in extension between the femoral and tibial articulating surfaces. This third method must be used with fixed bearing arthroplasties (especially with conforming articulations) to avoid rotational incongruency between the components during weight-bearing that can create abnormal and deleterious torsional forces on posterior stabilised posts, insert tray interfaces and bone-cement interfaces. Rotating platform articulations can tolerate rotational mismatch unless it is to a point where the polyethylene insert rotates excessively and causes symptomatic soft tissue impingement

Introduction

Total knee arthroplasty is traditionally performed using bone anatomy to dictate femoral implant rotation and soft tissue release to balance any resulting deficiencies. A force sensing device has been developed that reverses this conventional order. It measures the forces in the medial and lateral compartments and dictates the femoral rotation cuts when these are equal. The purpose of this study was to compare the traditional methods of femoral rotation (TEA, AP axis, and posterior referenced) to this novel approach using computer navigation with the force sensor to determine a balanced flexion gap.

The goals of total knee arthroplasty are to restore the mechanical axis of the knee and create equal and symmetric tension on the ligaments throughout an arc of motion. What surgical technique best achieves this goal remains controversial. In gap balancing, the extension space is created (distal femur and proximal tibia) and balanced. The flexion space and femoral component rotation are then set by placing tension on the collateral ligaments. This allows the femoral component to be rotated to create an equal and symmetric flexion gap based on the tension of collateral ligaments rather than arbitrary bony landmarks. In the measured resection technique, fixed bony landmarks are utilised to set femoral component rotation. Bony landmarks are subject to variations in patient's anatomy and inconsistency of the surgeon to reliably and reproducibly locate them during surgery. Fehring et al. demonstrated that 49% of knees using bony landmarks had rotational errors of greater than 3 degrees. A recent study determined that the amount of femoral component rotation necessary to create a balanced flexion gap varied based on the amount of ligament release required, calling into question the validity of using this technique to set femoral component rotation. Additionally, a study by Dennis et al. showed that setting femoral component rotation based solely on bony landmarks leads to asymmetry in the flexion gap and excessive condylar lift-off in flexion in over 60% of knees performed with a measured resection technique

The goals of total knee arthroplasty are to restore the mechanical axis of the knee and create equal and symmetric tension on the ligaments throughout an arc of motion. What surgical technique best achieves this goal remains controversial. In gap balancing, the extension space is created (distal femur and proximal tibia) and balanced. The flexion space and femoral component rotation are then set by placing tension on the collateral ligaments. This allows the femoral component to be rotated to create an equal and symmetric flexion gap based on the tension of collateral ligaments rather than arbitrary bony landmarks. In the measured resection technique, fixed bony landmarks are utilised to set femoral component rotation. Bony landmarks are subject to variations in patient's anatomy and inconsistency of the surgeon to reliably and reproducibly locate them during surgery. Fehring et al demonstrated that 49% of knees using bony landmarks had rotational errors of greater than 3 degrees. A recent study determined that the amount of femoral component rotation necessary to create a balanced flexion gap varied based on the amount of ligament release required, calling into question the validity of using this technique to set femoral component rotation. Additionally, a study by Dennis et al, showed that setting femoral component rotation based solely on bony landmarks leads to asymmetry in the flexion gap and excessive condylar lift off in flexion in over 60% of knees performed with a measured resection technique

Introduction. Malrotation of a femoral component is a cause of patellofemoral maltracking after total knee arthroplasty (TKA). We have developed a balanced gap technique in posterior stabilized total knee arthroplasty (PS-TKA) using an original tensor instrument. One of characteristics of this instrument is the ability to measure gaps even if there is a bone defect, because it has two paddles, and we can attach block augmentations. In addition it can measure the gap after a reduction of the patella with an offset mechanism. In the balanced gap technique, the femoral component rotation is decided by a tibial cut surface and ligaments balance using the tensor device. This study investigated retrospectively whether rotational alignment of femoral component rotation influenced patellofemoral joint congruency in PS- TKA. Material and Methods. We evaluated the radiographs of 52 knees of 42 patients, who underwent TKA (NexGen LPS-Flex, fixed surface, Zimmer) by one surgeon (S.A.) for osteoarthritis or rheumatoid arthritis. All procedures were performed through a medial parapatellar approach and a balanced gap technique using a developed versatile tensor device. We measured lateral patella tilt and lateral patella shift at post-op. 6 months. To assess the rotational alignment of femoral component rotation, condylar twist angle (CTA) was measured, and to assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was measured using the epicondylar view radiographs. Results. We performed the lateral release on 4 knees (7.6%). The average lateral patella tilt and CTA, and LOA were 3.00 ± 3.2°, 0.95 ± 2.5°, 1.50 ± 1°, respectively. There were two cases which had more than 10°tilt. We did not find any case of lateral patella shift. There was no statistical correlation with lateral patella tilt and CTA (r=0.17, p=0.2) (figure 1). There was no statistical correlation with the patella tilt and LOA (r=-0.1, p=0.9) (figure2). The case with 13.4°patella tilt was post-traumatic osteoarthritis (ACL and MCL injury). There were two cases which were cut patella obliquely, and each patella tilt was 13.0°and 3.3°. Discussion. Previously we reported that the rate of a lateral release decreased by a balanced gap technique compared with a conventional measured resection technique. Although the balanced gap technique resulted in a patient's specific wide variability for femoral component rotation, this variable rotation was not found to be associated with abnormal patella tilt and patella shift

Introduction. Component position and overall limb alignment following total knee arthroplasty (TKA) have been shown to influence prosthetic survivorship and clinical outcomes. Robotic-assisted (RA) total knee arthroplasty has demonstrated improved accuracy to plan in cadaver studies compared to conventionally instrumented (manual) TKA, but less clinical evidence has been reported. The objective of this study was to compare the three-dimensional accuracy to plan of RATKA with manual TKA for overall limb alignment and component position. Methods. A non-randomized, prospective multi-center clinical study was conducted to compare RATKA and manual TKA at 4 U.S. centers between July 2016 and August 2018. Computed tomography (CT) scans obtained approximately 6 weeks post-operatively were analyzed using anatomical landmarks. Absolute deviation from surgical plans were defined as the absolute value of the difference between the CT measurements and surgeons’ operative plan for overall limb, femoral and tibial component mechanical varus/valgus alignment, tibial component posterior slope, and femoral component internal/external rotation. We tested the differences of absolute deviation from plan between manual and RATKA groups using stratified Wilcoxon tests, which controlled for study center and accounted for skewed distributions of the absolute values. Alpha was 0.05 two-sided. At the time of this abstract, data collections were completed for two centers (52 manual and 58 RATKA). Results. Comparing absolute deviation from plan between groups, RATKA demonstrated clear benefits for tibial component alignment (median absolute deviation from plan: 1.5° vs. 0.8°, manual vs RATKA, p<.001), tibial slope (2.7° vs. 1.1°, manual vs RATKA, p<.001), and femoral component rotation (1.4° vs. 0.9°, manual vs RATKA, p<0.02). Femoral component and overall limb alignment accuracy were comparable (p>0.10). Discussion and Conclusions. In this study, compared to manual TKA, RATKA cases were 47% more accurate for tibial component alignment, 59% more accurate for tibial slope, and 36% more accurate for femoral component rotation (percent differences of median absolute deviations from plan). Further clinical data is needed to study the longer-term benefits of robotic technologies. Nevertheless, this study supports improved accuracy to plan utilizing RATKA compared to manual TKA. For any figures or tables, please contact authors directly

Introduction. In order to achieve good clinical results in TKA, soft tissue balance is important. Soft tissue balance is closely related to knee kinematics which affects clinical results. Modified gap balancing technique is one of the standard techniques for posterior stabilized (PS) TKA. On the other hand, appropriate load for the measurement of gap balance has not been established. The purpose of the present study is to measure the mechanical properties of soft tissue structure of knee sleeve in flexion and extension during PS TKA using newly developed balancer. The understanding of the mechanical properties is crucial. In particular if these properties are used as input for surgical procedures, standard technique for many surgeons will be established. Materials and Methods. Medial compartmental osteoarthrosis (OA) patients (13 female and 7 male) were evaluated. Average age, BMI, and Varus deformity were 72.1 years, 26.9, and 12 degrees, respectively. The newly developed center paddle balancer consists of a built-in spring (Fig. 1). Figure 2 shows the sequence of surgery and measurements. In the surgery, we measured the balance (degrees in Figure 1, A) and distance (mm in Figure 1, B) in extension with a load (Figure 1,C) at transition zone of toe region to linear region. Then, applying the load until flexion gap was the same as that in extension with a patella reduction, we measured the femoral component rotation from the balancer (degrees in Figure 1, A). The anterior and posterior femoral cuts were performed according to measured femoral component rotation which angle is parallel to tibial cut surface. Results. Load deformation curves of a knee sleeve structures showed toe and linear regions. The average stability range (transition zone of toe region to linear region) is 150 to 160N in extension and 130 to 140N in flexion. The distance of stability range between tibia and femur in extension is almost the same as the thickness of tibial component and femoral component (21mm). The distance of stability range between the tibia and femur in flexion is the same as the thickness of tibial component (10mm). Discussion. In the present study, load deformation curves of knee sleeve structures showed bimodal patterns that is the same as ligaments and tendons. It has been reported that a load on ligament is below the transition zone during 80% of normal daily activity. The results indicated that the so called “palpable endpoint” is stability range. According to the present data, we propose a standard modified gap balance technique in PS TKA for medial compartmental OA. The ligament balance is confirmed in extension with 160N of distracting force after soft tissue release and distal femur and proximal tibial cut. The femoral component rotation is then decided with the load that will open the distance to the thickness of the tibial component in flexion

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?

Purpose. The purpose of this study was to elucidate kinematic change according to the implant's specific femoral rotation by using orthosensor (Verasense) implant with three degrees external rotation of femoral rotation rebuilt (Genesis-II) and traditional TKA implant without rebuilt of the femoral rotation (Anthem). Methods. Twenty-eight patients (34 knees) underwent TKA using Anthem (Smith & Nephew, Memphis, TN, USA) and 16 patients (22 knees) underwent TKA using Genesis-II (Smith & Nephew, Memphis, TN, USA). Patients were followed up for at least 1 year. Mean age of patients was 71.1 years (range, 60 to 80 years) at the time of surgery. After implantation of femur and tibial components, we applied Verasense, the orthosensor system, to evaluate femoral rollback of the new artificial joint. Femoral rollback was analyzed using digitized screenshot function of Verasense. Results. Overall femoral tracking proportion regardless of implants was significantly higher on the medial compartment compared to that on the lateral compartment (13.3 ± 8.4% vs. 6.3 ± 5.0%, p < 0.001). Regarding femoral tracking according to each compartment, Genesis-II and Anthem showed 12.1 ± 8.2% and 14.2 ± 8.6% (p = 0.371) on the medial compartment and 8.0 ± 5.8% and 5.2 ± 4.2% (p = 0.059) on the lateral compartment, respectively. Conclusion. Our study showed reverse femoral roll-back movement with higher tracking distance on the lateral compartment during TKA. Genesis-II TKA system with femoral component 3-degree rebuilt showed less roll-back difference between medial and lateral compartments compared to traditional TKA system. Fortunately, both TKA systems had excellent short-term clinical outcomes without having significant difference between the two. With longer follow-up and larger cohort, the advantage and effectiveness of femoral component rotation can be elucidated in the future

Custom instrumentation in TKA utilises pre-operative imaging to generate a customised guide for cutting block placement. The surgeon is able to modify the plan using three-dimensional software. Although this technology is increasingly gaining acceptance, there is a paucity of clinical data supporting it. One hundred and eleven patients underwent primary TKA using the Zimmer Patient-Specific Instrumentation (PSI) system, in 28 of the cases surgical navigation was used to validate the PSI-generated cuts. Alignment measurements included long-leg alignment and biplanar distal femoral and proximal tibial cuts. Further measurements evaluated femoral implant placement in the AP plane, femoral component rotation, measured bone resection and implant sizing accuracy. The mean final limb alignment as recorded by computer-assisted surgical (CAS) tools was 0.3° of varus. Only two limbs were malaligned by greater than 3°. The femoral component had a mean alignment of 0.3° of valgus and 4.5° of flexion (PSI plan 3° flexion). The predicted femoral size was accurate in 89% of cases and the anterior femoral cut was congruent with the anterior cortex in 92% of cases. The PSI-directed femoral component rotation was consistent with the surgeon's perceived rotation in 95% of cases. The posterior condylar bone resection had a mean difference of < 1mm from the predicted resection. The tibial component had a mean alignment of 0.5° of varus and 8.5° of posterior slope (PSI plan 7° posterior slope). The only statistically significant deviation in alignment was the increased tibial slope (p = 0.046). The tibial component size was accurately predicted in 66% of cases. Custom instrumentation in total knee arthroplasty accurately achieved implant and limb alignment in our study. The plan was more reproducible on the femoral slide. The overestimation of tibial slope and tibial sizing incongruity were related to some of the reference points for the software. A potential benefit of this technology is improved mid-flexion stability by accurately determining femoral component size, placement, and rotation. Further studies will need to be conducted to determine the efficiency and cost-effectiveness of this technology