Aim. Computer assisted total knee arthroplasty may have advantages over conventional surgery with respect to component positioning. Femoral component mal-rotation has been shown to be associated with poor outcomes, and may be related to posterior referencing jigs. We aimed to determine the variation between the transepicondylar axis (TEA) and posterior condylar axis (PCA) in a series of knees undergoing navigated total knee arthroplasty (TKA), and to determine the correlation between final intra-operative and post-operative coronal alignment. Method. A review of 184 consecutive patients undergoing primary TKA between June 2007 and August 2010, using Precision navigation and Triathlon implants (Stryker). The difference between the TEA and PCA was measured as was the initial and final coronal alignment. A standing four foot alignment radiograph was obtained 6 weeks after surgery to determine the weight-bearing mechanical axis. Results. The mean difference between the TEA and PCA was 3.94 degrees (−2.80 to 11.59) and median difference was 3.6 degrees. Females and valgus knees had a greater variation. The mean intra-operative alignment was 0.75 degrees (−3 to 6, SD 1.9) and the mean radiographic alignment was 1.24 degrees (−6.5 to 6.5, SD 1.6). The intra-operative and radiographic alignment showed correlation (coefficient 0.43). There was poor correlation between pre-operative deformity and degree of difference between intra-operative and radiographic alignment (coefficient −0.1). Conclusion. There is a wide variation in the difference between the TEA and PCA, and there is not a good relationship with coronal alignment. Although most valgus knees had a bigger difference, such a difference was also seen in many varus knees. This should alert the surgeon when using posterior referencing jigs when determining the femoral component size and rotation. There was reasonable correlation between the final intra-operative mechanical alignment and the weight-bearing alignment as determined by a standing radiograph

Computer assisted total knee arthroplasty may have advantages over conventional surgery with respect to component positioning. Femoral component mal-rotation has been shown to be associated with poor outcomes, and may be related to posterior referencing jigs. We aimed to determine the variation between the transepicondylar axis (TEA) and posterior condylar axis (PCA) in a series of knees undergoing navigated total knee arthroplasty, and to determine the correlation between final intra-operative coronal alignment and post-operative radiographic functional alignment. A review of 170 consecutive patients undergoing primary total knee arthroplasty between June 2007 and August 2010, using Precision navigation and Triathlon implants (Stryker). The difference between the TEA and PCA was measured as was the initial coronal alignment. Referencing of the TEA had been previously validated against computerised tomography in a previous study. During arthroplasty, neutral alignment was aimed for, and the final alignment after implant insertion was recorded. Pre- and 1 year post-operative flexion was measured. A standing four foot alignment radiograph was obtained 6 weeks after surgery to determine the weight-bearing mechanical axis. The mean difference between the TEA and PCA was 3.94 degrees (−2.80 to 11.59) and median difference was 3.6 degrees. (A positive value implies the PCA is internally rotated with respect to the TEA). The median pre-operative flexion was 120 degrees (80–130) and the median post-operative flexion was 125 (85–145). The mean change in flexion was −2.5 degrees (−40 to 40; p=0.001). The mean intra-operative alignment was 0.75 degrees (−3 to 6, SD 1.9) and the mean radiographic alignment was 1.24 degrees (−6.5 to 6.5, SD 1.6). Taking −3 to +3 to be neutral, the outlier rate intra-operatively was 6.5% and radiographically was 16.5%. The intra-operative and radiographic alignment showed correlation (coefficient 0.289). There was poor correlation between pre-operative deformity and degree of difference between intra-operative and radiographic alignment (coefficient −0.1). Conclusion: There is a wide variation in the difference between the TEA and PCA, and there is not a good relationship with coronal alignment. Although most valgus knees had a bigger difference, such a difference was also seen in many varus knees. This should alert the surgeon when using posterior referencing jigs when determining the femoral component size and rotation. Although these patients achieved good post-operative flexion, this was determined by the pre-operative range. There was reasonable correlation between the final intra-operative mechanical alignment and the weight-bearing alignment as determined by a standing radiograph

Background. Accurate implant positioning is of supreme importance in total knee replacement (TKR). The rotational profile of the femoral and tibial components can affect outcomes, and the aim is to achieve coronal conformity with parallelism between the medio-lateral axes of the femur and tibia. Aims. The aim of this study is to determine the accuracy of implant rotation in total knee replacement. Methods. Intra-operatively, the trans-epicondylar axis of the femur (TEA) and Whiteside's line were used as the reference points, aiming to externally rotate the femoral component by 1 degree. The medial third of the tibial tuberosity was used as the anatomical reference point, aiming to reproduce the rotation of the native tibia. Pre-and post-operative CT scans were reviewed. The difference in femoral rotation was calculated by determining the femoral posterior condylar axis (PCA) of the native femur pre-operatively and the implant post-operatively. Tibial rotational difference was calculated between the native tibial posterior condylar axis and tibial baseplate. Results. Pre and post-operative CT scans of 41 knees in 31 patients were analysed. All surgeries were carried out by a single surgeon using the same implant. The mean difference in rotation of the femur post-operatively was 1.2 degrees external rotation (ER), range −4.7 to 6.9 degrees ER. 83% of femoral components were within 3 degrees of the target rotation. Mean difference in tibial rotation was −3.8 degrees ER, range −11.1 to 12.4 ER. Only 39% of tibial components were within 3 degrees of the target rotation. A line perpendicular to the midpoint of the tibial PCA was actually medial to the tibial tubercle in 33 knees, and only corresponded to the medial 1/3 of the tibial tubercle in 8 of 41 knees. Conclusions. Femoral component rotation is seen to be more accurate than tibial in this group. It may be that the anatomical landmarks used intra-operatively to judge tibial rotation are more difficult to accurately identify. Posterior landmarks are difficult to locate in vivo. This study would suggest that using the anterior anatomical landmark of the medial 1/3 of the tibial tubercle does not allow accurate reproduction of tibial rotation in total knee replacement

Introduction. Three anatomic landmarks are typically used to estimate proper femoral component rotation in total knee arthroplasty: the transepicondylar axis (TEA), Whiteside's line, and the posterior condylar axis (PCA). Previous studies have shown that the presence of tibia vara may be accompanied by a hyperplastic posteromedial femoral condyle, which affects the relationship between the PCA and the TEA. The purpose of this study was to determine the relationship of tibia vara with the PCA. Methods. Two hundred and forty-eight knees underwent planning for total knee arthroplasty with MRI. The MRI was used to characterize the relationship between the transepicondylar axis and the posterior condylar axis. Long-leg standing films (LLSF) were obtained to evaluate the medial proximal tibial angle. The MPTA is defined as the medial angle formed between a line along the anatomic axis of the tibia and a line along the tibial plateau. Results. There were 168 knees in varus and 80 in valgus. The PCA in the patient group was 2.38 degrees ± 1.6 degrees. Regression analysis of tibial varus compared to the PCA showed a small association where for each degree of tibial varus, there was an additional 0.07 degrees of internal rotation of the PCA (p = 0.01). When defining tibia vara as a MPTA <84 degrees, there was no difference between patients with and without tibia vara (p=0.0661) although there was a trend toward a smaller PCA with increased tibia vara. When defining tibia vara as a MPTA <82 degrees there was again no difference in PCA between patients with and without tibia vara (p=0.825). Conclusion. Tibia vara did not influence the PCA to a clinically significant degree. This result is in contrast to previous studies which indicated that increased tibial varus correlated to increased internal rotation of the PCA with respect to the TEA

Introduction. Positioning of a femoral sizing guide has been cited as being a critical intraoperative step during measured-resection based TKA as it determines femoral component rotation. Consequently, modern femoral sizing guides permit surgeons to ‘dial in’ external rotation when placing the guide. Although this feature facilitates guide placement, its effect on posterior femoral condylar resection and flexion gap stability is unknown. This study examines the effect of rotation on posterior femoral condylar resection among different posterior-referencing TKA designs. Methods. Left-sided posterior-referencing femoral sizing guides and cutting blocks from nine posterior-referencing femoral sizing guides belonging to six TKA manufacturers were collected. Each guide underwent high-resolution photography at a setting of zero, three and greater than three degrees of external rotation. The axis of rotation for each guide was then identified and its location from the posterior condylar axis was recorded (figure). Cutting blocks from each system were then photographed and the amount of posterior condylar resection from the medial and lateral condyles was calculated for each setting of external rotation (figure). The posterior resection was then compared to the standard distal resections for each system. Results. Two sizing guides had axes of rotation that were eccentrically located and in proximity to the posterior condylar axis, six were centrally based and one was slightly eccentric. Axis of rotation location had substantial effects on posterior condylar resection. Guides with centrally-based axes tended to resect more medial posterior condyle and less lateral condyle as rotation increased. Guides with eccentric axes tended to resect either less lateral or more medial condyle only. Discussion. This study is the first to investigate femoral rotation and posterior condylar resection, and the first to compare different sizing guide designs. Our results indicate that guides with centrally-based axes of rotation increase medial condylar resection as external rotation increases. This increased resection may unintentionally create a larger flexion gap in the case of a valgus knee

The relationships between the transepicondylar axis (TEA), Whiteside's line(WL), and posterior condylar axis (PCA) are commonly used to determine the rotational alignment of the femur in total knee arthroplasty (TKA). It has been previously reported that may be gender differences in the rotational and mechanical anatomy of the distal femur1. The aim of our study was to examine the distal femur in a large number of patients to report on any gender differences within the group. The MRIs of a large cohort of prospectively chosen patients (n= 217) were examined retrospectively in order to determine the rotational femoral alignment. Varus/valgus relationship of their knees prior to prosthesis insertion was also examined. Measurements pertained to femoral rotation (relationships between WL, TEA and PCA) and varus/valgus alignment were calculated directly from MRI studies by a single observer. Gender differences were examined using an unpaired students t-test. Averages and standard deviations are reported to within two significant figures. The posterior condylar axis was 2.6 ± 1.5 degrees relative to the transepicondylar axis and 91.8 ± 1.7 degrees relative to Whiteside's line. The varus to valgus ratio was 4.6 ± 5.9. Males in the group had a PCA of 2.4 ± 1.6 degrees relative to TEA compared to females in the group (2.8 ± 1.4 degrees). There was no significant difference between both groups (p=0.06). The PCA relative to WL was 92.1 ± 1.6 degrees for males compared to 91.6 ± 1.9 degrees for females with no significant difference between both groups (p=0.06). Finally, the varus to valgus ratio was 5 ± 5.7 for males compared to females (4.3 ± 6.2) with no statistical significance achieved between both groups (p=0.39). Our results show that there is no significant difference in the rotational anatomy and varus/valgus alignment between men and women in a large cohort. Interestingly, the large standard deviation for values pertaining to femoral rotational anatomy (>3 degrees) suggest a significant degree of variability between patients. Thus, operative planning embracing our findings may prove to be of great clinical benefit by advocating individualising operative treatment in TKA surgery

The “correct” rotational alignment and “normal” rotational alignment may not be the same position. Because of natural tibial plateau has average 3° varus but classical TKA method make tibial cut perpendicularly to tibial mechanical axis. Consequently femoral rotational compensation to 3° becomes necessary. While anatomical TKA method performed tibial cut in 3° varus. Then posterior femoral cut will be parallel to posterior condylar axis and component rotation theoretically should be aligned in natural anatomy. This study compares the rotational alignment between two methods. Study conducted on 80 navigated TKAs with modified gap technique. Intraoperative femoral rotation retrieved from navigation. Rotational alignment was calculated using the Berger protocol with postoperative computerised tomography scanning. The alignment parameters measured were tibial and femoral component rotations and the combined component rotations. 57 knees with PS design can be classified into 35 knees as anatomical group and 22 knees as classical group. 23 knees with CR design had 12 knees as anatomical group and 11 knees as classical group. The intraoperative femoral rotation in anatomical group had less external rotation than classical group significantly in PS design (0.77°±1.03° vs 2.86°±1.49°, p = 0.00) and also had the same results in CR design (1.33°±1.37°vs 2.64°±0.81°, p = 0.012). However, the postoperative excessive femoral and tibial component rotation compared with native value and combined rotation had no significant differences between classical and anatomical method in both implant design. Using CAS TKA with gap technique showed no difference in postoperative rotational alignment between classical and anatomical method

Introduction. The posterior condylar axis of the knee is the most common reference for femoral anteversion. However, the posterior condyles, nor the transepicondylar axis, provide a functional description of femoral anteversion, and their appropriateness as the ideal reference has been questioned. In a natural standing positon, the femur can be internally or externally rotated, altering the functional anteversion of the native femoral neck or prosthetic stem. Uemura et al. found that the femur internally rotates by 0.4° as femoral anteversion increases every 1°. The aim of this study was to assess the relationship between femoral anteversion and the axial rotation of the femur before and after total hip replacement (THR). Method. Fifty-nine patients had a pre-operative CT scan as part of their routine planning for THR. The patients were asked to lie in a comfortable position in the CT scanner. The internal/external rotation of the femur, described as the angle between the posterior condyles and the CT coronal plane, was measured. The native femoral neck anteversion, relative to the posterior condyles, was also determined. Identical measurements were performed at one-week post-op using the same CT methodology. The relationship between femoral IR/ER and femoral anteversion was studied pre- and post-op. Additionally, the effect of changing anteversion on the axial rotation of the femur was investigated. Results. There was a strong correlation between axial rotation of the femur and femoral anteversion, both pre-and post-operatively. Pearson correlation coefficients of 0.64 and 0.66 respectively. This supported Uemura et al.'s findings that internal rotation of the femur increases with increasing anteversion. Additionally, there was a moderate correlation, r = 0.56, between the change in axial rotation of the femur and change in anteversion. This trend suggested that external rotation of the leg would increase, if stem anteversion was decreased from the native. Conclusions. Patients with high femoral anteversion may have a natural mechanism of “correction” with femoral internal rotation. Equally, patients with femoral retroversion tend to naturally externally rotate their leg. Decreasing stem anteversion from native, trended toward an increase in external rotation of the femur. This finding is supported by the clinical observation of patients with high anteversion and compensatory in-toe, who have normal foot progression angle post-operatively after having their anteversion decreased. These findings have implications when planning implant alignment in THR

Background. Authors sought to determine the degree of lateral condylar hypoplasia of distal femur was related to degree of valgus malalignment of lower extremity in patients who underwent TKA. Authors also examined the relationships between degree of valgus malalignment and degree of femoral anteversion or tibial torsion. Methods. This retrospective study included 211 patients (422 lower extremities). Alignment of lower extremity was determined using mechanical tibiofemoral angle (mTFA) measured from standing full-limb AP radiography. mTFA was described positive value when it was valgus. Patients were divided into three groups by mTFA; more than 3 degrees of valgus (valgus group, n = 31), between 3 degrees of valgus to 3 degrees of varus (neutral group, n = 78), and more than 3 degrees of varus (varus group, n = 313). Condylar twisting angle (CTA) was used to measure degree of the lateral femoral condylar hypoplasia. CTA was defined as the angle between clinical transepicondylar axis (TEA) and posterior condylar axis (PCA). Femoral anteversion was measured by two methods. One was the angle formed between the line intersecting femoral neck and the PCA (pFeAV). The other was the angle formed between the line intersecting femoral neck and clinical TEA (tFeAV). Tibial torsion was defined as a degree of torsion of distal tibia relative to proximal tibia. It was determined by the angle formed between the line connecting posterior cortices of proximal tibial condyles and the line connecting the most prominent points of lateral and medial malleolus. Positive values represented relative external rotation. Negative values represented relative internal rotation. Results. Greater lateral femoral condylar hypoplasia was related to increased valgus alignment of lower extremity. Correlation coefficient between mTFA and CTA was 0.253 (p < 0.001). Valgus group showed increased CTA, which was 10.2° ± 1.9°. CTA was 7.4° ± 2.5° in neutral group and 6.6° ± 4.8° in varus group. There was significant positive correlation between the degree of valgus alignment and the degree of femoral anteversion (r = 0.145, p = 0.003). pFeAV was 16.7° ± 5.8° in valgus group, 12.1° ± 6.0° in neutral group and 10.9° ± 7.0° in varus group. There was no correlation between degree of valgus alignment and degree of femoral anteversion (r = 0.060, p = 0.218). In terms of tibial torsion, increased valgus malalignment was associated with increased tibial torsion (r = 0.374, p < 0.001). Valgus group showed increased tibial torsion than other groups. Tibial torsion was 32.6° ± 6.2° in valgus group, 26.3° ± 6.9° in neutral group and 22.6° ± 7.2° in varus group. Conclusions. Increased valgus alignment of lower extremity was related to greater lateral femoral condylar hypoplasia. However, increased valgus alignment was not related to degree of femoral anteversion whereas it was related to increased external tibial torsion. Our findings should be considered when determining proper rotational alignment in TKA

Background. A careful consideration of change of the rotational profiles of total limb after unilateral total knee arthroplasty is necessary. The aim of the present study was to evaluate the discrepancies of rotational profiles of total limb between operated and non-operated limb following unilateral total knee arthroplasty. Methods. We conducted a retrospective analysis the CT data from 32 patients undergoing primary unilateral total knee arthroplasty using measured resection technique, which femur implant was applied at an external rotation of 3° relative to the posterior condylar axis from July 2009 to April 2013 in our hospital. Using these CT studies, rotational profiles of total limb such as femoral torsion angle (femoral neck anteversion angle; FTA), tibial torsion angle (TTA), neck-malleolar angle (NMA), knee joint rotation angle (rotational mismatch; KJRA) and total limb rotation (TLR) were measured. Results. There were significant discrepancies of FTA and KJRA between operated and non-operated limb following unilateral total knee arthroplasty. The mean difference of operated and non-operated side for FTA and KJRA were −6.5 ± 11.9° (p=0.004) and −6.8 ± 5.0° (p < 0.001) respectively. However, there were no significant discrepancies of TLR, TTA and NMA. Conclusion. With comparison with non-operated side, although FTA is significantly decreased in operated limb than non-operated limb following total knee arthroplasty, there were no significant discrepancies of NMA and TLR, because of the compensatory effect of KJRA. However, excessive external rotation of femur implant can affect adversely on rotational profiles of total limb. Further long term studies will be required to evaluate the change of the rotational profiles following unilateral total knee arthroplasty

Purpose. The purpose of this study is to investigate the relationship between the angles made by the reference axes on the computerized tomography (CT) images and comparison of the knee alignment between healthy young adults and patients who is scheduled to have total knee arthroplasty. Materials and Methods. This study was conducted in 102 patients with osteoarthritis of knee joint who underwent preoperative computerized tomography (CT). The control group included 50 patients having no arthritis who underwent CT of knee. Axial CT image of the distal femur were used to measure the angles among the the anteroposterior (AP) axis, the posterior condylar axis (PCA), clinical transepicondylar axis (cTEA) and the surgical transepicondylar axis (sTEA). Then, the differences in amounts of rotation between normal and osteoarthritic knee was evaluated. Results. The mean angle between cTEA and PCA in the osteoarthritis group was 5.0°±2.2, whereas that in the control group was 5.5°±2.0. The mean angle between cTEA and sTEA in the osteoarthritis group was 3.7°±0.8, whereas that in the control group was 4.3°±0.6. The mean angle between AP axis and PCA in the osteoarthritic group was 93.25°±2.0, whereas in the control group was 96.3°±1.9. There was significant differences in angles between AP axis and PCA. But, no significant difference was seen in angles between cTEA and PCA, cTEA and sTEA in two groups. Conclusion. In result of this study, the angle between cTEA and PCA showed an average external rotation of 5.0° in osteoarthritic group. More external rotation was needed for the femoral component alignment than 3° recommended in usual total knee arthroplasty. The angle between AP axis and PCA is decreased in osteoarthritic knee compared with normal knee. But, osteoarthritic change of knee joint had no significant effect on the relationships of other axes

In TKA, prosthetic femoral and tibial implants must be symmetrically placed and matched in the mechanical axis and the ligament gaps must be correctly balanced. The collateral ligaments are the key guide, as they arise from the epicondyles of the distal femur, are perpendicular to the AP axis of Whiteside, and are coincident with the transtibial axis of the proximal tibial surface. A perpendicular bisection of the transtibial axis creates the AP axis of the tibia which is coincident in space with the AP axis of Whiteside (Berger). Measured distal femoral resection targets including TEA, AP axis of Whiteside, and 3 degrees external to the posterior condylar axis works because the stout posterior cruciate ligament limits laxity in flexion, allowing for the anatomical variation of these landmarks to be accommodated. The Insall, Ranawat gap balancing methods work to balance the knee in flexion, often matching the results of a measured resection, but guaranteeing a symmetrically balanced flexion gap. Distal femoral internal rotation can result if the medial collateral is over-released, but experience has shown this not to be a problem if the gaps are well balanced. Tibial tray position must be placed coincident with the AP axis of the tibia, which also is coincident with Akagi's line (line from medial margin of patellar tendon to center of the posterior cruciate ligament). The surgeon can make a line from the AP axis of Whiteside to the anterior tibial which matches the AP tibial axis

Purpose. Implant positioning is one of the critical factors influencing the postoperative outcome in total hip arthroplasty (THA). Conventional (manual) intraoperative stem adjustment may result in variability and inaccuracy of stem antetorsion (AT). Since March 2013, we have measured stem antetorsion with CT free Navigation system (OrthoPilot Navigation System THA Pro Ver4.2, B/Braun Aesculap Germany: Navi). We have developed a simple instrument, the Gravity-guide (G-guide), for intraoperative assessment and adjustment of stem AT. We evaluated the accuracy and effectiveness of G-guide and navigation software as referenced to postoperative CT evaluation with 3D template system (Zed hip, LEXI, Japan). Method. Between March 2013 and December 2014, 50 patients underwent primary THA were evaluated. Surgeries were performed with routine techniques with a modified Hardinge approach with the patient at a lateral decubitus position in all cases. The G-guide consists of two parts: one attached to the lower leg and the other attached to the handle of the rasp. During surgery, AT value was determined with navigation at the time of final rasping of the femur. Additionally, the G-guide was utilised at the time of final rasp insertion. In intraoperative AT assessment using this instrument, a correction was required considering the discrepancy between the perpendicular to the posterior condylar axis and the longitudinal axis of the lower leg. The angle of discrepancy between posterior condylar line and femoral trans-epicondyler axis needs to be taken into consideration. Therefore, correction by the angle between the trans-epicondylar and posterior condylar lines (correction angle) was required for each patient when the intraoperative AT as measured by the G-guide. Therefore, the correction angle should be added to the AT value obtained from the G-guide for comparison with postoperative value measured with Zed Hip. Result. The discrepancy between the intraoperative G-guide with correction angle and postoperative Zed Hip measurements was 4.7° ± 3.9°. The discrepancy between Navi AT and postoperative Zed HIP measurements was 5.9° ± 4.1°. A discrepancy was 10° or more were 7 cases in Navi and 4 cases in G-guide. Conclusion. Navi and G-guide measured intraoperative stem antetorsion was comparable utility

Introduction. The posterior condylar axis of the distal femur is the common reference used to describe femoral anteversion. In the context of Total Hip Arthroplasty (THA), this reference can be used to define the native femoral anteversion, as well as the anteversion of the stem. However, these measurements are fixed to a femoral reference. The authors propose that the functional position of the proximal femur must be considered, as well as the functional relationship between stem and cup (combined anteversion) when considering the clinical implications of stem anteversion. This study investigates the post-operative differences between anatomically-referenced and functionally-referenced stem and combined anteversion in the supine and standing positions. Method. 18 patients undergoing pre-operative analysis with the Trinity OPS® planning (Optimized Ortho, Sydney Australia, a division of Corin, UK) were recruited for post-operative assessment. Anatomic and functional stem anteversion in both the supine and standing positions were determined. The anatomic anteversion was measured from CT and referenced to the posterior condyles. The supine functional anteversion was measured from CT and referenced to the coronal plane. The standing functional anteversion was measured to the coronal plane when standing by performing a 3D/2D registration of the implants to a weight-bearing AP X-ray. Further, functional acetabular anteversion was captured to determine combined functional anteversion in the supine and standing positions. Results. The average anatomical stem anteversion was 9.9° (6.7° to 13.0°). In all cases, the anatomical stem anteversion was different than the measured functional stem anteversion in both the supine and standing positions. The functional femoral anteversion decreased from supine to stand by an average of 7.1° (4.9°−9.2°), suggesting more internal rotation of the femurs when weight-bearing. In all patients, the pelvis rotated posteriorly in the sagittal plane from supine to standing, increasing the functional acetabular anteversion by a mean of 5.1°. Conclusions. Anatomic stem anteversion differs significantly from functional stem anteversion in both the supine and standing positions, as a consequence of the patient specific differences in internal/external rotation of the femur in the functional postures. In the same way that the Anterior Pelvic Plane is now widely recognized as an inappropriate reference for cup orientation due to variation in sagittal pelvic tilt, referencing the femoral stem anteversion to the native anatomy (distal femur) maybe also be misleading and not provide a suitable description of the functional anteversion of the stem. This has implications for determining optimal combined alignment in THA

Introduction. A femoral rotational alignment is one of the essential factors, affecting the postoperative knee balance and patellofemoral tracking in total knee arthroplasty (TKA). To obtain an adequate alignment, the femoral component must be implanted parallel to the surgical epicondylar axis (SEA). We have developed “a superimposable Computed Tomography (CT) scan-based template”, in which the SEA is drawn on a distal femoral cross section of the CT image at the assumed bone resection level, to determine the precise SEA. Therefore, the objective of this study was to evaluate the accuracy of the rotational alignment of the femoral component positioned with the superimposed template in TKA. Patients and methods. Twenty-six consecutive TKA patients, including 4 females with bilateral TKAs were enrolled. To prepare a template, all knees received CT scans with a 2.5 mm slice thickness preoperatively. Serial three slices of the CT images, in which the medial epicondyle and/or lateral epicondyle were visible, were selected. Then, these images were merged into a single image onto which the SEA was drawn. Thereafter, another serial two CT images, which were taken at approximately 9 mm proximal from the femoral condyles, were also selected, and the earlier drawn SEA was traced onto each of these pictures. These pictures with the SEA were then printed out onto transparent sheets to be used as potential “templates” (Fig. 1-a). In the TKA, the distal femur was resected with the modified measured resection technique. Then, one template, whichever of the two potential templates, was closer to the actual shape, was selected and its SEA was duplicated onto the distal femoral surface (Fig. 1-b). Following that, the distal femur was resected parallel to this SEA. The rotational alignment of the femoral component was evaluated with CT scan postoperatively. For convention, an external rotation of the femoral component from the SEA was given a positive numerical value, and an internal rotation was given a negative numerical value. Results. The subjects were 4 knees in 4 males and 26 knees in 22 females. A mean age (for 30 knees) at the operation was 76.7 ± 6.1 years (range from 66.4 to 88.3). The posterior condylar angle was −0.27 ± 1.43, and the outlier, more than 3 degrees, was 1 case. Discussion. Conventionally, the SEA is palpated intraoperatively, however, the sulcus of the medial condyle sometimes cannot be identified precisely in osteoarthritic degeneration at the medial condyle. Also, the SEA is determined from the posterior condylar axis (PCA) by calculating the posterior condylar angle, which is between the SEA and the PCA, with the measurements from the preoperative CT scan. However, the residual cartilage thickness is not considered in this method, and thus, the SEA is possible to be inaccurate. The simple technology of our template allowed us to determine the SEA directly on the femoral surface, without any influence from bone degeneration. The femoral components could be implanted accurately, and therefore, the superimposed template was considered to improve TKA outcomes with the accurate SEA

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?

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

Background. Surgical planning of long bone surgery often takes place using outdated 2D axes on 2D images such as long leg standing X-rays. This leads to errors and great variation between intra- and inter- observers due to differing frames of reference. With the advent of 3D planning software, researchers developed 3D axes of the knee such as the Flexion Facet Axis (FFAx) and Trochlear Axis (TrAx), and these proved easy to derive and reliable. Unlike 2D axes, clinicians and scientists can use a single 3D axis to obtain measurements relative to other 3D axes, in all three planes Deriving a 3D axis also does not require an initial frame of reference, such as in trying to derive the 2D Posterior Condylar Axis (PCAx), whereby a slight change in slice orientation will affect its position. However, there is no 3D axis derived for the tibial plateau yet. Measurements of tibial joint line obliquity are with a 2D axis drawn on AP long leg standing X-rays. The same applies to tibial plateau rotation, as measured by 2D axes drawn on axial CT/MRI slices. this study aimed to to develop a novel new 3D axis for the tibial plateau to quantify both tibial plateau joint line obliquity and axial rotation. Methods. Materialise software version 8.0 (Materialise Inc., Belgium) handled segmentation of CT data and for analysis of bony morphology. A line joining the centroids of the medial and lateral tibial plateaus formed the TCAx (Fig1). A line joining the middle coordinate of the TCAx, to the centre of the best-fit sphere between the medial and lateral malleolus formed the Tibial Mechanical Axis (TMAx). A standard frame of reference aligned 72 tibias with the TCAx horizontal in the axial view, and the TMAx aligned parallel to the global reference coordinate system vertical axis. Tibial joint line obliquity was the angle between the TCAx and TMAx on the medial side, also known as the Medial Tibial Plateau Angle (MPTA)(Fig2). The authors compared reliability and accuracy of the TCAx against three other rotational axes of the tibia as described in the literature. Results. Our methods showed excellent reproducibility using Bland-Altman analysis between intra- and inter-observers. The tibial joint line as defined by the TCAx is oblique (varus) in the majority of knees (MPTA = 85 ± 2°), and becomes perpendicular (MPTA = 90 ± 2°) in constitutional valgus. The TCAx is also parallel to the Anatomical Tibial Axis (ATAx), (SD = 2°), which is currently the gold standard and most reliable axis in defining tibial axial rotation. Conclusions. The TCAx is a reliable axis for referencing both coronal and rotational alignment of the tibial plateau. it can be used for planning and postoperative analysis of knee replacement. (Fig 3). The variable obliqueness of the joint line suggests that neutral alignment in knee arthroplasty may not be suitable for all knees

Background. Posterior referencing (PR) total knee arthroplasty (TKA) aims to restore posterior condylar offset. When a symmetric femoral implant is externally rotated (ER) to the posterior condylar axis, it is impossible to anatomically restore the offset of both condyles. PR jigs variously reference medially, laterally, or centrally. The distal femoral cutting jigs typically reference off the more distal medial condyle, causing distal and posterior resection discrepancies. We used sawbones to elucidate differences between commonly used PR cutting jigs with regards to posterior offset restoration. Materials/Methods. Using 32 identical sawbones, we performed distal and posterior femoral resections using cutting guides from 8 widely available TKA systems. 6 systems used a central-referencing strategy, 1 system used a lateral-referencing strategy, and 1 system used a medial-referencing strategy with implants of asymmetric thickness. Distal femoral valgus resection was set at 5 degrees for all specimens. Rotation was set at 3 degrees for 2 sawbones and 5 degrees for 2 sawbones with each system. We measured the thickness of all bone resections, and compared those values to known implant thickness. Results. Central- and lateral-referenced systems with symmetric implants showed distal lateral under-resection. The medial-referenced system with asymmetric implants restored the anatomic joint line medially and laterally. Central-referenced systems showed close to 1mm (SD ±0.2) postero-lateral offset over-restoration and postero-medial offset under-restoration at 3 degrees of ER, and a 1.6mm change in each offset at 5 degrees of ER. The lateral-referenced system demonstrated a 1.7mm mismatch between the distal-medial and the postero-medial resections at 3 degrees of rotation. There was a 3.9mm mismatch at 5 degrees of ER. Medial-referenced systems demonstrated a mismatch between the distal-lateral and postero-lateral resections, present only with 5 degrees of ER. Conclusion. Our data offers insight for arthroplasty surgeons into the bony resections taken by widely used TKA instrumentation systems. The lateral-referenced jigs reduced the postero-medial offset by 4 degrees at 5 degrees, a difference on the order of 1 to 2 femoral sizes depending on the implant system. The medial-referenced system, with the use of asymmetric condylar thicknesses, restored condylar anatomy within 1mm in the majority of circumstances. When set at 5 degrees of external rotation, over-restoration of the postero-lateral femoral offset occurred. Center-referenced systems resulted in minor changes in offset at 3 degrees of rotation, but a decrease in the postero-medial offset by 2mm at 5 degrees of external rotation. The distal femoral cutting jig typically restores the medial joint line in extension when there is minimal medial wear. Referencing laterally in flexion may introduce a discrepancy between the extension and flexion gaps. Available medial- and lateral-referenced jigs provide the option of shifting the bony resections anteriorly or posteriorly and adjusting the sizing as needed

Aim. The aim of this study is to evaluate the effect of three-dimensional (3D) simulation with 3D planning software ZedKnee® (ZK) in total knee arthroplasty (TKA). Materials and methods. The participants in this study were all TKA patients whose operations were simulated by using ZK. The alignment of all components was evaluated with the ZK valuation software in postoperative computer tomography. Thirty patients (43 knees) met the inclusion criteria. 6 patients were male and 24 patients were female. The mean age of the 30 patients was 72 years old. Diagnoses for surgery were: osteoarthritis- 40 knees, rheumatoid arthritis- 2 knees and osteonecrosis- 1 knee. TKA was performed using the measured resection technique. The distal femur axis where the intramedullary rod would be inserted was drawn manually on the 3D image. Then, the angle between the distal femoral axis and the mechanical axis was measured. The rotational angles of the femoral components were determined from the automatically calculated angle between the posterior condylar axis and the surgical epicondylar axis (SEA) by using ZK. The ZK data used during the operation was the posterior condylar angle, the angle between the distal femoral axis and the mechanical axis and implant size. Results. The angle in coronal plane between the 3D mechanical axis and the distal femoral axis in preoperative planning ranged between 3 degrees and 11 degrees, mean 6.7 (SD 2.2) degrees. The postoperative femoral component alignment was on average 0.7 (SD 1.3) degrees in varus. Outlier of more than 3 degrees in coronal alignment was recognized in 3 cases (7%). The mean posterior condylar angle in preoperative planning was 3.8 (SD 1) degrees. The postoperative femoral component alignment was on average 1.5 (SD 1.6) degrees in external rotation to surgical epicondylar axis. Outlier of more than 3 degrees in rotational alignment was recognized in 6 cases (14%). The concordance rate between the preoperative planning size and the intraoperative selective size was 91%. Discussion. Some errors may be observed in the preoperative TKA X-ray planning, because of the rotational position of the femur while having the X-ray taken or angle of the X-ray beam. Kanekasu et al reported the measurement of the condylar twist angle during the X-ray and it was relatively correct compared with the measurement during CT. Max 1.9 degrees error occurred in the measurements using X-rays. It appeared that preoperative planning using CTs was more accurate than using X-rays. Conclusion. Femoral components with 3D simulation using ZK were fixed perpendicularly against the mechanical axis and parallel to the surgical epicondylar axis with high accuracy. We considered that the ZK 3D simulation in TKA is useful for the accurate alignment of femoral components