Patella alta: association with patellofemoral alignment and changes in contact area during weight-bearing

BACKGROUND: Patella alta is a condition which may predispose individuals to patellofemoral joint dysfunction. We compared patellofemoral joint alignment and contact area in subjects who had patella alta with subjects who had normal patellar position, to determine the effect of high vertical patellar positions on knee extensor mechanics. METHODS: Twelve subjects with patella alta and thirteen control subjects participated in the study. Lateral patellar displacement (subluxation), lateral tilt, and patellofemoral joint contact area were quantified from axial magnetic resonance images of the patellofemoral joint acquired at 0 degrees , 20 degrees , 40 degrees , and 60 degrees of knee flexion with the quadriceps contracted. RESULTS: With the knee at 0 degrees of flexion, the subjects with patella alta demonstrated significant differences compared with the control group, with greater lateral displacement (mean [and standard error], 85.4% +/- 3.6% and 71.3% +/- 3.0%, respectively, of patellar width lateral to the deepest point in the trochlear groove; p = 0.007), greater lateral tilt (mean, 21.6 degrees +/- 1.9 degrees and 15.5 degrees +/- 1.8 degrees ; p = 0.028), and less contact area (157.6 +/- 13.7 mm(2) and 198.8 +/- 14.3 mm(2); p = 0.040). Differences in displacement and tilt were not observed at greater knee flexion angles; however, contact area differences were observed at all angles evaluated. When data from both groups were combined, the vertical position of the patella was positively associated with lateral displacement and lateral tilt at 0 degrees of flexion and was negatively associated with contact area at all knee flexion angles. CONCLUSIONS: These data indicate that the vertical position of the patella is an important structural variable that is associated with patellofemoral malalignment and reduced contact area in patients with patella alta.     

Effect of femoral and tibial component position on patellar tracking following total knee arthroplasty: 10-year follow-up of Miller-Galante I knees

Rotational alignment of the femoral and tibial components using computed tomography (CT) was evaluated to establish if errors of alignment have a significant effect on patellofemoral complications. From 1987-1990, 54 knees in 39 patients were replaced with the Miller-Galante I knee system. Of these, 10 patients (13 knees) comprised this study. All patients had osteoarthritis. Mean patient age at surgery was 70.3 years. Mean follow-up was 10.3 years. On CT, rotational position of the femoral component relative to the epicondylar axis and the position of the tibial component relative to the tibial tubercle were evaluated. Patellar displacement and patellar tilt angle also were evaluated when the knee was flexed at 30 degrees. Mean rotation of the femoral component was 6.1 degrees of internal rotation (2.7 degrees-11.2 degrees). Mean rotation of the tibial component was 16.7 degrees of internal rotation (2.4 degrees-27.7 degrees). Mean lateral patellar tilt angle was 2.9 degrees (-6.0 degrees-11.9 degrees), and mean lateral displacement was 2.7 mm (-3.2-8.9 mm). Rotational position of both the femoral and tibial components showed a statistically significant correlation with the patellar tilt angle. This study showed the internally rotated femoral and tibial component were related to the patellar maltracking. This malalignment of the components, as well as nonanatomical patellar groove and metal-backed patellar component, could be one of the causes of the patellofemoral complications with the Miller-Galante I knee.     

Effect of tibial component position on patellar strain following total knee arthroplasty

Patellar fracture following total knee arthroplasty has been related to component alignment and tibiofemoral joint-line position. The purpose of this study was to determine the effect of anteroposterior displacement of the tibial component and inferosuperior displacement of the tibiofemoral joint line on patellar strain following total knee arthroplasty with a cruciate-subsituting design. Patellar strain increased (decreased) with anterior and inferior (posterior and superior) displacement. When averaged across all flexion angles, the strain changed approximately 1.7%/mm of anteroposterior displacement and 1.0%/mm of inferosuperior displacement. For individual specimens, changes in strain as high as 3.2%/mm of inferosuperior displacement of the joint line were seen. These changes in strain may be associated with changes in the patellofemoral contact force seen for similar changes in tibiofemoral joint-line position. These changes in strain may be a biomechanical indicator of the efficacy of retaining the preoperative position of the tibiofemoral joint line.     

Patellar tendon orientation and patellar tracking in male and female knees

Knowledge of patellofemoral joint biomechanics is important for understanding sex‐related dimorphism in patellofemoral pathologies and advancement of related treatments. We evaluated the hypotheses that sex differences exist in patellar tendon (PT) orientation and patellar tracking during weight‐bearing knee flexion and that they relate to differences in tibiofemoral rotation. The PT orientation and patellar tracking were measured in healthy subjects (18 male, 13 female) during weight‐bearing knee flexion, using magnetic resonance and dual fluoroscopic imaging. These data were analyzed for sex differences and correlation with previously reported tibiofemoral rotation data. The results indicated a significant effect of sex on PT orientation, particularly at low flexion angles. In females, the PT was oriented more anteriorly in the sagittal plane, more medially in the coronal plane, and showed greater external tilt in the transverse plane of the tibia (p < 0.05). Significant correlations between tibiofemoral rotation and PT orientation (p < 0.01) indicated that sex differences in coronal and transverse plane orientation of the PT relate to differences in tibiofemoral rotation. Patellar tracking did not show significant sex differences or correlation to tibiofemoral rotation. Further studies are warranted to determine implications for patellofemoral pathologies and treatments like total knee arthroplasty. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:322–328, 2010     

Comparison of patellar mobility in female adults with and without patellofemoral pain

STUDY DESIGN: Case control study. OBJECTIVE: To compare the patellar mobility of female adult subjects with and without patellofemoral pain (PFP). BACKGROUND: Although abnormal patellar mobility is believed to be one of the causes of PFP, there is currently no published evidence to support this contention. In part, this lack of evidence is because a reliable clinical measurement method to measure patellar mobility and objective criteria to define abnormal patellar mobility have not been established. METHODS AND MEASURES: The study sample was comprised of 22 females with PFP (PFP group) and 22 females who had no knee pain (control group), matched by age, height, and body mass index to the subjects with PFP. Patellar mobility was measured objectively using a specially designed apparatus. Measurements of lateral and medial patellar displacement, patellar mobility balance (lateral minus medial patellar displacement), lateral patellar mobility index (lateral patellar displacement divided by patellar width), and medial patellar mobility index (medial patellar displacement divided by patellar width) were used. RESULTS: Lateral and medial patellar mobility values were not significantly different between the individuals in the PFP and control groups. When normal patellar mobility was arbitrarily defined as the average mobility +/- 2 SDs, based on the data from the control group, normal lateral patellar displacement was within a range of 7.2 to 17.6 mm and normal medial patellar displacement was within a range of 6.8 to 14.0 mm. The intraclass correlation coefficient for intratester and intertester reliability of lateral and medial patellar displacement measurements varied from 0.80 to 0.97. CONCLUSION: Although there were no significant differences in patellar mobility between females with and without PFP, these measurements give reference information about normal patellar mobility for this group. LEVEL OF EVIDENCE: Diagnosis, level 5.     

Radiographic measures in subjects who are asymptomatic and subjects with patellofemoral pain syndrome

Lateral tilt and displacement of the patella are considered characteristic features of patellofemoral pain syndrome. It has been suggested that abnormal patellar tilt and displacement are detected best with the knee near full extension, which requires computed tomography or magnetic resonance imaging. The objective of the current study was to determine whether alignment abnormalities could be detected in subjects with patellofemoral pain syndrome from axial radiographs obtained at 35 degrees knee flexion using a new, standardized radiographic technique. Thirty-three subjects with patellofemoral pain syndrome and 33 matched control subjects were recruited from a military population. Lateral and axial (unloaded and with quadriceps contraction) radiographs were taken using the Patellofemoral QUESTOR Precision Radiograph system. Measures of patellar tilt and displacement, and anatomic measures (sulcus angle, patellar facet angle, patella alta) were obtained from the radiographs. No significant differences in patellar tilt or displacement were detected between the groups (paired t tests) in either the unloaded or loaded (quadriceps contracted) condition, suggesting that these measures, obtained at this knee angle are not useful diagnostic or outcome measures in patellofemoral pain syndrome. Patellar angle, sulcus angle, and patellar height also did not differ between groups suggesting that these are not etiologic factors in patellofemoral pain syndrome.     

Using real‐time MRI to quantify altered joint kinematics in subjects with patellofemoral pain and to evaluate the effects of a patellar brace or sleeve on joint motion

Abnormal patellofemoral joint motion is a possible cause of patellofemoral pain, and patellar braces are thought to alleviate pain by restoring normal joint kinematics. We evaluated whether females with patellofemoral pain exhibit abnormal patellofemoral joint kinematics during dynamic, weight‐bearing knee extension and assessed the effects of knee braces on patellofemoral motion. Real‐time magnetic resonance (MR) images of the patellofemoral joints of 36 female volunteers (13 pain‐free controls, 23 patellofemoral pain) were acquired during weight‐bearing knee extension. Pain subjects were also imaged while wearing a patellar‐stabilizing brace and a patellar sleeve. We measured axial‐plane kinematics from the images. Females with patellofemoral pain exhibited increased lateral translation of the patella for knee flexion angles between 0°and 50° (p = 0.03), and increased lateral tilt for knee flexion angles between 0° and 20° (p = 0.04). The brace and sleeve reduced the lateral translation of the patella; however, the brace reduced lateral displacement more than the sleeve (p = 0.006). The brace reduced patellar tilt near full extension (p = 0.001), while the sleeve had no effect on patellar tilt. Our results indicate that some subjects with patellofemoral pain exhibit abnormal weight‐bearing joint kinematics and that braces may be effective in reducing patellar maltracking in these subjects. Published by Wiley Periodicals, Inc. J Orthop Res 27: 571–577, 2009     

In vivo movement analysis of the patella using a three-dimensional computer model

We used three-dimensional movement analysis by computer modelling of knee flexion from 0 degrees to 50 degrees in 14 knees in 12 patients with recurrent patellar dislocation and in 15 knees in ten normal control subjects to compare the in vivo three-dimensional movement of the patella. Flexion, tilt and spin of the patella were described in terms of rotation angles from 0 degrees . The location of the patella and the tibial tubercle were evaluated using parameters expressed as percentage patellar shift and percentage tubercle shift. Patellar inclination to the femur was also measured and patellofemoral contact was qualitatively and quantitatively analysed. The patients had greater values of spin from 20 degrees to 50 degrees , while there were no statistically significant differences in flexion and tilt. The patients also had greater percentage patellar shift from 0 degrees to 50 degrees , percentage tubercle shift at 0 degrees and 10 degrees and patellar inclination from 0 degrees to 50 degrees with a smaller oval-shaped contact area from 20 degrees to 50 degrees moving downwards on the lateral facet. Patellar movement analysis using a three-dimensional computer model is useful to clearly demonstrate differences between patients with recurrent dislocation of the patella and normal control subjects.     

Magnetic resonance imaging of patellofemoral kinematics with weight-bearing

BACKGROUND: Previous studies of the patellofemoral joint have been limited by the use of invasive techniques, measurements under non-weight-bearing conditions, cadaveric specimens, or computerized models. It has been shown that soft tissue and bone can be accurately quantified with magnetic resonance imaging. The present study was designed to define the relationship between the patellofemoral contact area and patellofemoral kinematics in vivo. METHODS: Ten subjects with clinically normal knee joints were scanned with high-resolution magnetic resonance imaging while they pushed a constant weight (133 N) on the foot-plate of a custom-designed load-bearing apparatus. Images were obtained at five positions of flexion between -10 degrees and 60 degrees. Three-dimensional reconstructions were used to measure the patellofemoral cartilage contact area, patellar centroid, patellar medial and inferior translation, patellar medial and inferior tilt, and patellar varus-valgus rotation. All translation and area measurements were normalized on the basis of the interepicondylar distance. Random-effects models of quadratic regressions were used to evaluate the data. RESULTS: The mean contact area ranged from 126 mm(2) in extension to 560 mm(2) at 60 degrees of flexion. The patella translated inferiorly to a maximum distance of 34 mm at 60 degrees of flexion and translated medially to a maximum distance of 3.2 mm at 30 degrees of flexion before returning to nearly 0 mm at 60 degrees of flexion. The patella tilted inferiorly to a mean of nearly 35 degrees at 60 degrees of flexion and medially to a maximum of 4.2 degrees at 30 degrees of flexion. By 60 degrees of flexion, the centroid of the contact area had shifted to an inferior and posterior maximum of 20 and 10 mm, respectively. CONCLUSIONS: We found that lateral patellar subluxation and tilt occurred in these normal knees at full extension and the patella was reduced into the trochlear groove at 30 degrees of flexion. Therefore, we believe that lateral patellar tilt and subluxation observed during arthroscopy of the extended knee may not represent a pathological condition.     

The effect of component placement on knee kinetics after arthroplasty with an unconstrained prosthesis.

The mechanical success of a total knee replacement demands stable patellar tracking without subluxation and, stable tracking, in turn, can depend largely on the medial-lateral forces restraining the patella. Patellar button medialization has been advocated as a means of reducing subluxation, and experimental evidence has shown femoral component rotation also affects medial-lateral forces. Surgeons have choices in femoral component rotation and patellar button medialization and must frequently make intra-operative decisions concerning component placement because of anatomical variations among patients. Thus, in seeking to minimize medial-lateral patellar force, we examined the effects of patellar button medialization and external femoral component rotation. The study used an unconstrained total knee system implanted in nine cadaveric specimens tested on a knee simulator operating through flexion angles up to 100 degrees. Tests included all combinations of external femoral component rotation of 0 degree, 2.5 degrees, and 5 degrees and patellar placement at the geometric center and at 3.75 mm medial to the geometric center. A video-based motion analysis system tracked patellar and tibial kinematics while a six-component load cell measured patellofemoral loads. Repeated measures analysis of variance revealed a statistically significant decrease in the average medial-lateral force with button medialization but no significant change with femoral component rotation. Neither femoral component rotation nor patellar button medialization had an effect on the normal component of the patellar reaction force. External femoral component rotation did cause significant increases in lateral patellar tilt, in tibial varus angle, and in external tibial rotation. Button medialization caused significant increases in lateral patellar tracking, lateral patellar tilt and external tibial rotation. The results in medial-lateral patellar forces quantify the benefit of patellar button medialization and discount any benefit of femoral rotation. The change in tibial kinematics with patellar button medialization and femoral component rotation cannot be measured in vivo with current technology, and the precise clinical implications are unknown.     

Q-angle influences tibiofemoral and patellofemoral kinematics.

Numerous surgical procedures have been developed to correct patellar tracking and improve patellofemoral symptoms by altering the Q-angle (the angle between the quadriceps load vector and the patellar tendon load vector). The influence of the Q-angle on knee kinematics has yet to be specifically quantified, however. In vitro knee simulation was performed to relate the Q-angle to tibiofemoral and patellofemoral kinematics. Six cadaver knees were tested by applying simulated hamstrings, quadriceps and hip loads to induce knee flexion. The knees were tested with a normal alignment, after increasing the Q-angle and after decreasing the Q-angle. Increasing the Q-angle significantly shifted the patella laterally from 20 degrees to 60 degrees of knee flexion, tilted the patella medially from 20 degrees to 80 degrees of flexion, and rotated the patella medially from 20 degrees to 50 degrees of flexion. Decreasing the Q-angle significantly tilted the patella laterally at 20 degrees and from 50 degrees to 80 degrees of flexion, rotated the tibia externally from 30 degrees to 60 degrees of flexion, and increased the tibiofemoral varus orientation from 40 degrees to 90 degrees of flexion. The results show that an increase in the Q-angle could lead to lateral patellar dislocation or increased lateral patellofemoral contact pressures. A Q-angle decrease may not shift the patella medially, but could increase the medial tibiofemoral contact pressure by increasing the varus orientation.     

Influence of prosthetic joint line position on knee kinematics and patellar position

Prosthetic joint line position after total knee arthroplasty (TKA) was investigated using sagittal roentgenograms obtained from six fresh frozen cadaver knees. A specially designed knee testing device was developed that allowed for a controlled flexion angle while maintaining a constant quadriceps force. Pre- and postoperative roentgenograms were obtained from 30 degrees to 120 degrees in 15 degrees intervals. Steinman pins inserted into the medial femoral condyle and patella were used as reference points in the roentgenograms. A displacement vector between the medial femoral condyle and tibial plateau was used to analyze the tibiofemoral joint relationship. The functional patellar length (Insall-Salvati ratio), was used to determine correct patellar height. Another displacement vector was used to measure the patellofemoral joint relationship, and the angle between the patellar cut surface and femoral long axis was also calculated. Bone resection thickness from the femoral, tibial, and patellar surfaces was equal to the prosthetic thickness. This reconstructive scheme produced correct ligament balance and flexibility of the knee without the aid of tensioning devices or special measurements. Patellar tracking appeared to be identical before and after surgery. This accurate but simple surgical technique also reproduced normal knee extensor mechanisms that may influence longevity and long-term results of TKA.     

减少髌骨厚度对膝关节置换术后髌股关节功能的影响

目的探讨减少髌骨厚度对膝关节置换术后髌股关节功能的影响。 方法收集2014年7月至2016年7月间在作者本院行单侧初次全膝关节置换术的122病例资料,分为常规髌骨打磨组与减少髌骨厚度组,术后随访2年。观察比较两组患者的一般情况、术前术后膝关节功能评分（HSS评分）、髌骨评分（Feller评分）、疼痛视觉模拟评分（VAS评分）,复查X线观察髌骨倾斜角、合适角。 结果术前两组一般资料无差异性,术前的HSS评分及Feller评分比较,差异无统计学意义。两组患者术后3个月、术后半年、术后1年及术后2年HSS评分、Feller评分、疼痛评分（VAS）及膝关节活动度经过重复测量设计的方差分析,显示两组的组间差异有统计学意义（P<0.05）,组别与时间点间存在交互作用,减少髌骨厚度组及常规髌骨打磨组在除术后1月外的其余术后各时间点间差异均有统计学意义。术后随访X线的髌骨倾斜角及合适角的对比无差异性。 结论全膝关节置换术可明显改善膝关节功能,如适当减少髌骨厚度,减轻髌股关节压力,较常规髌骨打磨更有利于改善髌股关节功能。但减少髌骨厚度的远期疗效及可能出现的并发症有待进一步随访、观察。     

Patellaposition und Patellofemoralarthrose nach unikompartimentellem Kniegelenkersatz

Background

Changes of patellar position (height, tilt, and shift) and arthritis of the patellofemoral joint might potentially influence outcome after unicompartmental knee replacement.

Objectives

The purpose of this work is to evaluate the influence of the aforementioned parameters on postoperative outcome.

Methods

Literature analysis via PubMed.

Results

A total of 12 relevant studies (three about Patellar height, two about patellar tilt and shift, seven about patellofemoral osteoarthritis) could be identified. Regarding Patellar height, two out of three studies demonstrated a postoperative decrease. With regard to patellar tilt and shift, only one study identified postoperative lateralization of the patella to be a predictor for poor outcome. The radiological appearance of arthritis of the patellofemoral joint does not significantly influence postoperative knee function except for cases where only the lateral patellar facet is affected. Anterior knee pain has no influence on clinical outcome.

Conclusion

Literature data do not allow for a precise statement about the possible influence of patellar position on the outcome after unicompartmental knee replacement. With proper patient selection, good results can be achieved despite patellofemoral osteoarthritis.     

Patellar component positioning in total knee arthroplasty

Five human anatomic specimen knees were used to determine the effect of patellar component position on patellofemoral kinematics, contact pressures, and contact areas after total knee arthroplasty using a polyethylene, domed patellar component. Each patellar component was positioned at the anatomic center of the resected patellar surface and then repositioned 5 mm proximally, distally, medially, and laterally. Patellar tilt was greatest with medial positioning of the patellar component and least with central and lateral positioning. At higher knee flexion angles, patellofemoral joint contact pressures increased at the medial facet with the medialized component and at the lateral facet for the lateralized component. The centralized component had the most evenly balanced patellar facet contact pressures. Distally positioned patellar components resulted in decreased patellar component loading at higher knee flexion angles. Central positioning of the patellar component results in optimal patellofemoral mechanics when maximal coverage of the resected patella is desired.     

Axial computed tomography of the patellofemoral joint with and without quadriceps contraction

Computed tomography was used to analyze the patellofemoral relationship during the first 60° of knee flexion in patients with chronic patellofemoral pain syndrome (49 knees) and a healthy control group (15 knees). The patellofemoral joints were imaged axially through the center of the patella articular cartilage with the knee flexed 0°, 0° with maximal quadriceps muscle contraction, 30°, and 60°. In 0° of knee flexion, the sulcus angle was greater in the symptomatic group than in normal controls. The patella displaced further laterally, and the lateral patellar tilt was greater. The patellar lateral index was found to be greater at 0° and indicated severe abnormality with full quadriceps muscle contraction. The Laurin angle was pathologic with increased medial opening, especially with muscle contraction. At 30° of knee flexion, these differences were less marked than at 0°. No relevant differences were found with 60° of knee flexion. This study showed that the sulcus angle, lateral patellar displacement, lateral patellar tilt, patella lateral condyle index, and Laurin angle are relevant diagnostic features in 0° of knee flexion, indicating a pathological femoral patellar gliding mechanism. Our evaluation also demonstrated the influence of full quadriceps muscle contraction, especially regarding lateral patellar displacement and the Laurin angle, and it was most prominent on the patella lateral condyle index. Thus, quadriceps muscle contraction often creates a more pathological displacement of the patella, which can be depicted using axial computed tomography.     

Model predictions of increased knee joint loading in regions of thinner articular cartilage after patellar tendon adhesion

Patellar tendon adhesion is a complication from anterior cruciate ligament (ACL) reconstruction that may affect patellofemoral and tibiofemoral biomechanics. A computational model was used to investigate the changes in knee joint mechanics due to patellar tendon adhesion under normal physiological loading during gait. The calculations showed that patellar tendon adhesion up to the level of the anterior tibial plateau led to patellar infera, increased patellar flexion, and increased anterior tibial translation. These kinematic changes were associated with increased patellar contact force, a distal shift in peak patellar contact pressure, a posterior shift in peak tibial contact pressure, and increased peak tangential contact sliding distance over one gait cycle (i.e., contact slip). Postadhesion, patellar and tibial contact locations corresponded to regions of thinner cartilage. The predicted distal shift in patellar contact was in contrast to other patellar infera studies. Average patellar and tibial cartilage pressure did not change significantly following patellar tendon adhesion; however, peak medial tibial pressure increased. These results suggest that changes in peak tibial cartilage pressure, contact slip, and the migration of contact to regions of thinner cartilage are associated with patellar tendon adhesion and may be responsible for initiating patellofemoral pain and knee joint structural damage observed following ACL reconstruction. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1168–1177, 2011     

Mobile-Bearing Total Knee Arthroplasty Improves Patellar Tracking and Patellofemoral Contact Stress : In Vivo Measurements in the Same Patients

Controversies exist in clinical study concerning the effect of rotating platform on patellar tracking. The aim of this in vivo study was to compare tibial rotation, patellar tracking, and patellofemoral contact stress in mobile and fixed-bearing platform intraoperatively in the same knee. Sixty-six knees of posterior-stabilized total knee prostheses were evaluated using a computed tomography–guided navigation system. Medial shift and lateral tilt of patella were significantly smaller in mobile knee. Averaged maximum contact stress was significantly smaller in mobile knee than fixed knee. However, tibial rotation during flexion has no significant difference. This study showed that mobile platform total knee arthroplasty significantly improved patellar tracking and decreased patellofemoral contact stress.     

Radiographic evaluation of patellofemoral alignment in kinematically aligned total knee arthroplasty: A comparative study with mechanically aligned total knee arthroplasty

BackgroundKinematically aligned total knee arthroplasty (KA-TKA), in which femoral component is placed 3–5° of internal rotation relative to mechanically aligned (MA)-TKA, may have a potential risk of patellofemoral malalignment. This study aimed to assess patellofemoral alignment and compare the data between KA-TKA and MA-TKA, and the relationship with patellofemoral radiographic parameters and patient reported outcomes.MethodsAmong patients who underwent TKA in 2015 and 2016 in our institute, 28 KA-TKAs with a metal-backed patellar component were retrospectively assessed for patellofemoral alignment, and 28 MA-TKAs with a metal-backed patellar component served as controls. A year postoperatively, patellar tilt and shift at 30°, 60°, and 90° knee flexion were measured on Merchant views and compared between the two TKAs. Implant positioning in each patient was assessed based on preoperative CT images and correlations of femoral component positioning with patellar tilt/shift were assessed.ResultsPatellar shift at 30° flexion was significantly greater in KA-TKA than in MA-TKA (p = 0.04), whereas patellar tilt angle was comparable between the two TKAs. No statistical correlation was evident between femoral component positioning and patellar shift/tilt, regardless of knee flexion angle in the two TKAs. Knee Society Score 2011 at 1 year follow-up was comparable in all subcategories between the two TKAs.ConclusionRadiographic analysis of KA-TKA revealed lateral shift of the patella at 30° knee flexion at 1 year postoperatively, however patients with patellar shift were asymptomatic. Further long-term observation is required to examine the impact of KA-TKA on the patellofemoral complication.