Differences in patellofemoral kinematics between weight‐bearing and non‐weight‐bearing conditions in patients with patellofemoral pain

Patellar maltracking is thought to be one source of patellofemoral pain. Measurements of patellar tracking are frequently obtained during non‐weight‐bearing knee extension; however, pain typically arises during highly loaded activities, such as squatting, stair climbing, and running. It is unclear whether patellofemoral joint kinematics during lightly loaded tasks replicate patellofemoral joint motion during weight‐bearing activities. The purpose of this study was to: evaluate differences between upright, weight‐bearing and supine, non‐weight‐bearing joint kinematics in patients with patellofemoral pain; and evaluate whether the kinematics in subjects with maltracking respond differently to weight‐bearing than those in nonmaltrackers. We used real‐time magnetic resonance imaging to visualize the patellofemoral joint during dynamic knee extension from 30° to 0° of knee flexion during two conditions: upright, weight‐bearing and supine, non‐weight‐bearing. We compared patellofemoral kinematics measured from the images. The patella translated more laterally during the supine task compared to the weight‐bearing task for knee flexion angles between 0° and 5° (p = 0.001). The kinematics of the maltrackers responded differently to joint loading than those of the non‐maltrackers. In subjects with excessive lateral patellar translation, the patella translated more laterally during upright, weight‐bearing knee extension for knee flexion angles between 25° and 30° (p = 0.001). However, in subjects with normal patellar translation, the patella translated more laterally during supine, non‐weight‐bearing knee extension near full extension (p = 0.001). These results suggest that patellofemoral kinematics measured during supine, unloaded tasks do not accurately represent the joint motion during weight‐bearing activities. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:312–317, 2011     

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     

Patellofemoral contact pressures exceed the compressive yield strength of UHMWPE in total knee arthroplasties

To address mechanisms involved in wear and permanent deformation of patellofemoral components in total knee arthroplasties, a previously reported knee joint loading model and pressure-sensitive film were used to measure patellofemoral contact areas and pressures in human cadaver knee joints after implantation with six different total knee joint designs. The joints were tested at three different Q angles (physiologic, −10°, and +10°) and four different flexion angles (30°, 60°, 90°, and 120°). Patellofemoral contact areas at normal Q angles ranged from 0.13 to 0.68 cm² and increased with flexion angle up to 90°. These contact areas differed significantly with flexion angle but not with Q angle. Variations in contact area with type of knee system were only marginally significant (P < .04), and post hoc tests showed no significant differences between individual knee designs. Contact pressures at normal Q angle also increased with flexion angle and ranged from 10 MPa to more than 49 MPa. Contact pressures at flexion angles greater than 60° were, for all systems, well in excess of the compressive yield strength of ultrahigh-molecular-weight polyethylene and at least three to four times greater than the recommended maximum compressive stress level of 10 MPa.     

In‐vivo patellar tracking in individuals with patellofemoral pain and healthy individuals

Understanding of the exact cause of patellofemoral pain has been limited by methodological challenges to evaluate in‐vivo joint motion. This study compared six degree‐of‐freedom patellar motion during a dynamic lunge task between individuals with patellofemoral pain and healthy individuals. Knee joints of eight females with patellofemoral pain and ten healthy females were imaged using a CT scanner in supine lying position, then by a dual‐orthogonal fluoroscope while they performed a lunge. To quantify patellar motion, the three‐dimensional models of the knee bones, reconstructed from CT scans, were registered on the fluoroscopy images using the Fluomotion registration software. At full knee extension, the patella was in a significantly laterally tilted (PFP: 11.77° ± 7.58° vs. healthy: 0.86° ± 4.90°; p = 0.002) and superiorly shifted (PFP: 17.49 ± 8.44 mm vs. healthy: 9.47 ± 6.16 mm, p = 0. 033) position in the patellofemoral pain group compared with the healthy group. There were also significant differences between the groups for patellar tilt at 45°, 60°, and 75° of knee flexion, and for superior‐inferior shift of the patella at 30° flexion (p ≤ 0.031). In the non‐weight‐bearing knee extended position, the patella was in a significantly laterally tilted position in the patellofemoral pain group (7.44° ± 6.53°) compared with the healthy group (0.71° ± 4.99°). These findings suggest the critical role of passive and active patellar stabilizers as potential causative factors for patellar malalignment/maltracking. Future studies should investigate the associations between patellar kinematics with joint morphology, muscle activity, and tendon function in a same sample for a thorough understanding of the causes of patellofemoral pain. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2193–2201, 2018.

     

Effect of fatigue on joint position sense of the knee

This study was designed to test position sense of the knee joint before and after fatigue in order to determine whether muscle or capsular receptors are the primary sensors for joint position sense. Reproduction of passive positioning and detection of the onset of motion (kinesthesia) were employed to measure joint position sense. Eleven subjects underwent joint position sense measurement before and after a fatigue protocol. A significant worsening of reproduction of knee joint angle after fatigue was noted (p < 0.05). Threshold (kinesthesia) showed no statistically significant change after fatigue. A significant correlation of reproduction measurements and threshold measurements prior to fatigue (p < 0.01) demonstrated that the same neural mechanism is applicable in the rested state, but these variables did not correlate significantly after fatigue. There was a significant correlation between reproduction measurements before and after fatigue (p = 0.018), while no correlation was seen for the pre- and postfatigue threshold measurements, suggesting a change in the neural path after fatigue. Since both tests of joint position sense are affected by fatigue, we conclude that muscle receptors are a prominent, if not primary, determinant of joint position sense, and capsular receptors may have a secondary role. Reproduction ability is decreased, presumably through the loss of efficiency of muscle receptors. The threshold data suggest a change in the mechanism of appreciation after fatigue, possibly due to increased sensitivity of capsular receptors from muscle-fatigue-induced laxity.     

Diagnosis and treatment of excessive lateral pressure syndrome of the patellofemoral joint caused by military training

Objective: To investigate the diagnosis and surgical treatment of excessive lateral pressure syndrome of the patellofemoral joint caused by military training. Methods: Fifteen patients (patient group) and 18 healthy volunteers (control group) were involved in this retrospective study. Radiographs of the knee joints of all patients and volunteers were taken. The bone architecture was assessed, the trochlear angle, coincidence angle and patellofemoral joint index measured in both groups, and the resulting data compared. All 15 patients (17 knees) were treated by lateral collateral retinaculum release. Pre‐ and post‐operative pain was evaluated with a visual analog scale (VAS). Results: The differences between the two groups in coincidence angle (patient group: 7.67°± 5.81°; control group: ?2.2°±?2.71°) and patellofemoral joint index (patient group: 2.49 ± 1.40; control group: 1.25 ± 0.15) were statistically significant. Subchondral bone sclerosis and osteophytosis in the patellofemoral joint were more pronounced in the patient group than in the control group. The VAS was higher preoperatively (7.06 ± 0.85) than postoperatively (6 months postoperatively: 3.87 ± 0.24; 1 year postoperatively: 3.01 ± 0.17), and the differences between preoperative and postoperative were statistically significant. Conclusions: Apart from the case history, typical symptoms and physical signs, X‐ray examination is the most basic way to diagnose excessive lateral pressure syndrome of the patellofemoral joint, and the patellofemoral joint index is the most reliable for diagnosis. Lateral collateral retinaculum release with a small‐incision is an effective treatment for this disease.     

Unconstrained shoulder joint position sense does not change with body orientation

Our knowledge of the role of muscle activation on proprioception is incomplete. Previous work has either focused on comparing active and passive motions or manipulated both muscle activation and joint angles simultaneously. We conducted an experiment at the shoulder in which subjects' trunks were tilted backwards to decouple joint angle from joint torque. Twenty three healthy subjects underwent testing in an unconstrained joint position sense task. Kinematics were measured with a magnetic tracking device. The joint position sense task consisted of subjects moving their arms to a predetermined orientation in space with the help of visual feedback from the magnetic tracking device presented to the subjects through a head‐mounted display. Subjects were then asked to reproduce the presented joint position in the absence of visual feedback. The protocol was performed under two tilts: upright and trunk tilted back 45°. This allowed for a comparison of joint position sense at different joint angles (at the same resistive torque) and at different resistive torques (at the same joint angles). When comparing these two tilts, we found that matching based on elevation angle demonstrated no significant difference, while matching based on torques did find differences. These results implicate elevation angle at the shoulder as playing a more important role in modulating joint position sense than joint torque. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 885–890, 2009     

安装大腿近侧气囊止血带对髌股关节运动的影响

目的探讨膝关节屈曲和伸直状态下安装大腿近侧气囊止血带对髌股关节运动的影响。方法收集住院的非髌股关节疾病患者,选择膝关节20侧,在腰麻或连续硬膜外状态下屈膝30°时测量膝关节髌骨高度和股骨滑车角,然后分伸膝位安装止血带和屈膝位安装止血带两组自身先后对比,测量膝关节不同屈曲角度下Laurin髌股关节外侧角和Merchant吻合角。比较气囊止血带在膝关节不同屈伸状态下对髌股关节运动学的影响。结果在膝关节屈曲30°时,髌骨高度的Caton指数为(1.02±0.19),股骨滑车角(138.9±7.4)°。在膝关节屈曲过程中,髌股关节呈现Merchant吻合角增大的趋势,尤其在膝关节屈曲30~45°的时候变化明显,当屈曲角度继续增大时吻合角基本稳定;Lauren髌股关节外侧角保持相对稳定。伸直位和屈曲位安装止血带引起髌股关节Merchant吻合角和Lauren髌股关节外侧角间的差异没有统计学意义。结论在正常膝关节,大腿近侧气囊止血带对髌股轨迹的影响主要表现为最初屈曲的45°内Merchant髌股吻合角的的增大,而Laurin髌股关节外侧较保持相对稳定。伸直位和屈曲位安装大腿近侧气囊止血带对正常膝关节髌股关节运动的改变没有统计学意义。     

Measurement of rotational alignment of the distal femur in total knee arthroplasty

Objectives: To measure and compare the included angle between the surgical transepicondylar axis (STEA) and the posterior condylar line (PCL) and the included angle between the femoral anteroposterior line (APL) and PCL, and to discuss the value of STEA, APL, and PCL as rotational alignment landmarks of the distal femur in total knee arthroplasty (TKA). Methods: Seventy‐five normal femoral specimens from Chinese adult cadavers were randomly selected. An axial photograph of every femoral specimen was taken with a digital camera and put into a personal computer. Using Photoshop 7.0.1 software, the included angle between the perpendicular line of APL and the PCL, noted as APA, together with the posterior condylar angle (PCA) between STEA and PCL were measured and compared using a paired‐samples t‐test. Results: The value for PCA was 3.67°± 1.62° (range, 0.75°–5.90°) and for APA 3.50°± 1.40° (range, 1.34°–5.65°). There was no significant difference between these two angles (t= 0.949, P= 0.359). Considering their relatively small means, these two angles showed wide variations. Conclusions: The rotational alignment of the femoral component can not accurately be determined by using PCL as a landmark. In order to get a proper rotational alignment of the femoral component in most cases of TKA, APL and STEA should be used as a double check.     

Patellar motion analyzed by kinematic and dynamic axial magnetic resonance imaging in patients with anterior knee pain syndrome

Ten consecutive patients (12 knees), all women, with anterior knee pain syndrome participated in the study. The patellofemoral joints were examined with the knee in 0°, 10°, 20°, and 30° of flexion. At each knee position, kinematic and dynamic, an axial magnetic resonance (MR) image was used to focus on the sagittal plane, followed by an axial image focused through the middle of the patella. Ten healthy volunteers (20 knees) with no history of previous or current knee problems or anterior knee pain also underwent MRI scanning following the same procedure. Three angles were measured: patellar tilt angle (PTA), sulcus angle (SA), and congruence angle (CA). For statistical analyses, we used the Mann-Whitney U-test. Compared with the control knees, five patterns of malalignment were identified. The most frequently observed was tilt and lateralisation, with elevated CA and decreased PTA. In extension, the average CA for this group was 22° and PTA –4.8° vs –8.1° and 14.3° for control knees respectively. Contraction of the muscles caused tilt of the patella in symptomatic knees. This decrease of the PTA was statistically significant in extension (P < 0.05) and in 10° of flexion (P < 0.05). Contraction of the thigh muscle increased CA in 30° of flexion. This lateral pull was statistically significant (P < 0.05). There were no statistically significant differences of SA between the groups, regardless of muscle contraction or flexion angle. At 30° of flexion, muscle contraction increased CA and decreased PTA. In our opinion, imaging in the first 30° of flexion with thigh muscle contraction is necessary for a correct diagnosis. Received: 17 February 1998     

Posture Influence on the Pendulum Test of Spasticity in Patients with Spinal Cord Injury

The study aims to investigate the influence of different postures on spasticity results by pendulum test in patients with spinal cord injury (SCI). The setting was at the University of Campinas (UNICAMP), Campinas, SP, Brazil. Five individuals with SCI and five individuals in the control group were included. All individuals went through the pendulum test in three different positions: supine, semi‐supine at an angle of 30°, and sitting up at an angle of 60°. An electrogoniometer was attached to the right leg for measurement of knee joint angles. All situations were performed five times. Blood pressure was monitored during tests. Relaxation index (RI), normalized relaxation index (RIn), test duration in seconds, initial flexion angle, and resting angle were analyzed at three different positions. Results were compared between different positions, and statistically no differences were found. In individuals with SCI, RI (1.83 ± 0.2), RIn (1.14 ± 0.13), and test duration values (13.95 ± 4.14), in sitting up position, were similar to the control group results. In sitting up position, patients showed spasticity reduction. However, the other two postures produce pain and increase blood pressure in patients with tetraplegia. Therefore, these postures should be avoided in patients with lesions above T6, due to possible autonomic dysreflexia symptoms.     

Knee – spine syndrome: correlation between sacral inclination and patellofemoral joint pain

 Low back pain is an enormous clinical and public health problem. When we use spinal instrumentation, measurements of spinal and leg alignment in the standing position are thought to be important. Knee joint pain has also become an enormous clinical problem in the increasing elderly population. However, the correlation between spinal alignment, particularly sacral inclination, and knee joint pain is not clear. We examined the correlation between lumbar lordosis, sacral inclination, and patellofemoral joint pain in elderly subjects. Three hundred and ninety-nine people aged 50–85 years were examined. Clinical findings and physical status were determined. Measurements and determination of total lordosis from L1 to S1 and sacral inclination were made from standing radiographs. The knee joints were evaluated by using the standing knee flexion angle, radiographs, and the patellofemoral (PF) joint grinding test. Thirty-nine percent of subjects were excluded because they had definite osteo-arthritis at the femorotibial joints. Fifty-eight percent of the subjects had felt low back pain within the previous 3 months, and 16% of the subjects complained of PF joint grinding pain. Sixteen percent of the subjects showed knee flexion when standing. There was a significant difference in sacral inclination between the groups with and without PF joint grinding pain (P < 0.01). Sacral inclination was approximately 5° less in the knee flexion group. A correlation between sacral inclination and PF joint pain is defined, and its prevalence in the elderly is reported. We speculate that this phenomenon is caused by changing of lumbar alignment. In addition, we think this is a new pathological concept that we call the knee – spine syndrome. Received: July 23, 2001 / Accepted: May 2, 2002     

Patellofemoral evaluation after total knee arthroplasty. Validation of a new weight-bearing axial radiographic view

BACKGROUND: Radiographic assessment of the patella after total knee arthroplasty is typically performed with use of static, unloaded views that may not reproduce the in vivo patellofemoral kinematics. The purpose of the present study was to evaluate and validate the reliability and reproducibility of a weight-bearing radiographic assessment of the patellofemoral joint in patients who have undergone total knee arthroplasty. METHODS: Radiographs were made for 100 knees in sixty-nine patients who had undergone total knee arthroplasty. Radiographic assessment of the patellofemoral joint was performed with use of both the standard Merchant axial view and a modification of that view. The Merchant axial view was modified by positioning the standing patient in the semi-squatted position with the knees in 45 degrees of flexion. The relationship between the x-ray source, the angle of incidence on the joint, and the cassette position was kept unchanged from the original view. The standing position and consequent muscle involvement were the only differences. RESULTS: Compared with the standard Merchant axial view, the weight-bearing axial view showed a number of patellofemoral tracking changes. Specifically, lateral tilt and subluxation of the patella were significantly reduced; the rate of exposed, uncovered patellar bone contact with the femoral trochlea was significantly increased; and radiographic evidence of maltracking was more closely correlated with clinical symptoms. CONCLUSIONS: An axial weight-bearing radiographic view with the patient in the semi-squatting position was developed to reproduce patellofemoral joint loading. This view demonstrates that the position of the patella, as seen on the standard unloaded Merchant view, changes during squatting. Utilization of this axial weight-bearing view to evaluate total knee arthroplasty may provide additional information over standard radiographic views.     

Biomechanische Aspekte in der Rehabilitation des Patellofemoralgelenks

Specific knowledge of the biomechanics of the patellofemoral joint is crucial for successful nonoperative or postsurgical rehabilitation. The biomechanical aspects of different situations should be considered when designing an exercise program. Joint reaction forces, contact area, and contact stress are dependent on flexion angle and exercise situations. In weight-bearing activities, the amount of knee flexion directly influences the magnitude of quadriceps muscle force, which affects the magnitude of patellofemoral joint reaction forces. Open and closed chain exercises should be performed within a safe range of motion to allow quadriceps activation while minimizing patellofemoral joint reaction forces. The isolated knee extension (90°–40°), the squat (0°–30°–60°), and the leg press (0°–30°–60°) are the three main exercise situations in the acute rehabilitation phase. Controlled body positions and low levels of pain and symptoms should also be emphasized to achieve a functional progression, focusing on neuromuscular control.     

Joint Gap in Mid-Flexion Is Not a Predictor of Postoperative Flexion Angle After Total Knee Arthroplasty

Background

Postoperative knee flexion angle is one of the most important outcomes of total knee arthroplasty (TKA). Intraoperative ligament balancing may affect the postoperative range of motion of the knee. However, the relationship between intraoperative ligament balancing and postoperative flexion angle was still controversial. The purpose of this study was to determine whether intraoperative joint gap affects postoperative knee flexion angle or not.

Patellofemoral joint kinetics while squatting with and without an external load

STUDY DESIGN: Single-group repeated measures design. OBJECTIVE: To quantify patellofemoral joint reaction forces and stress while squatting with and without an external load. BACKGROUND: Although squatting exercises in the rehabilitation setting are often executed to a relatively shallow depth in order to avoid the higher joint forces associated with increased knee flexion, objective criteria for ranges of motion have not been established. Methods and Measures: Fifteen healthy adults performed single-repetition squats to 90 degrees of knee flexion without an external load and with an external load (35% of the subject's body weight [BW]). Anthropometric data, three-dimensional kinematics, and ground reaction forces were used to calculate knee extensor moments (inverse dynamics approach), while a biomechanical model of the patellofemoral joint was used to quantify the patellofemoral joint reaction forces and patellofemoral joint stress. Data were analyzed during the eccentric (0-90 degrees) and concentric (90-0 degrees phases of the squat maneuver. RESULTS: In both conditions, knee extensor moments, patellofemoral joint reaction forces, and patellofemoral joint stress increased significantly with greater knee flexion angles (P < 0.05). Peak patellofemoral joint force and stress was observed at 90 degrees of knee flexion. Patellofemoral joint stress at 45 degrees, 60 degrees, 75 degrees, and 90 degrees of knee flexion during the eccentric phase, and at 75 degrees and 90 degrees during the concentric phase, was significantly greater in the loaded trials versus the unloaded trials. CONCLUSION: The data indicate that during squatting, patellofemoral joint stress increases as the knee flexion angle increases, and that the addition of external resistance further increases patellofemoral joint stress. These findings suggest that in order to limit patellofemoral joint stress during squatting activities, clinicians should consider limiting terminal joint flexion angles and resistance loads.     

Gender differences in trochlear groove orientation and rotational kinematics of human knees

Knowledge of the morphology and kinematics of the male and female knees is important for understanding gender‐related dimorphism in knee pathology and improvement of related surgical treatments. Twelve male and 12 female subjects with healthy knees were recruited, and each subject performed a single leg lunge while images of the knee were recorded by two fluoroscopes. Tibiofemoral joint motion was then reproduced using bony models matched to the fluoroscopic images. Femoral trochlear groove orientation was also measured in each knee. While many of the measured parameters were found to be similar between the genders, a few interesting differences were also noted. Females showed greater external tibial rotation at 0° flexion (?5.4° vs. ?1.3 °, p = 0.03), smaller internal rotation at 30° flexion (1.7° vs. 6.4°, p = 0.04) and greater range of tibial rotation (18.2° vs. 12.4°, p = 0.01) compared to males. Female knees also had a more medially oriented proximal trochlear groove (10.0° vs. 4.5°, p = 0.04). These gender differences in rotational kinematics and trochlear groove orientation may warrant further studies to determine implications for surgical treatments such as total knee arthroplasty, and gender‐related dimorphism in certain knee injuries and pathologies, like anterior cruciate ligament injury and patellofemoral problems. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 871–878, 2009     

Measurement of change on medial and lateral joint gaps by navigation system in multi-radius PS TKA

Background

The purpose of this study was to evaluate the joint gap kinematics in posterior-stabilized total knee arthroplasty (PS TKA).

In vivo comparisons of patellofemoral kinematics before and after ADVANCE? Medial-Pivot total knee arthroplasty

Purpose

ADVANCE? Medial-Pivot (MP) (Wright Medical Technology, Arlington, TN, USA) total knee arthroplasty (TKA) was developed to replicate normal tibiofemoral knee joint kinematics, allowing medial-pivot knee motion. The design concept of the prosthesis is unique; therefore, the influence on the patellofemoral knee joint remains unclear at present. The purpose of this study was to determine the in vivo patellofemoral kinematics with ADVANCE? MP TKA and compare them with the pre-operative conditions.

Methods

ADVANCE? MP TKA was performed in ten subjects with osteoarthritis (OA). At before and one?month after surgery, lateral radiographs with weight-bearing at maximum extension, 30, 60 and 90° were taken, and patella flexion angle (PF), tibiopatellar angle (TP) and estimated patellofemoral contact point (PC) were evaluated, according to a previously reported method.

Results

In PF and TP, there was no statistically significant change between pre-operative and postoperative values. Pre-operative PC reached its peak at 90°; however, its peak was at 60° at one?month after surgery. Postoperative PC at maximum extension was significantly higher compared to before surgery.

Conclusions

The results in this study indicated that ADVANCE? MP TKA changed patellofemoral joint kinematics compared to before surgery. Early postoperative evaluation is the limitation of this study; however, we consider that the results in this study might be one of the keys to resolving the kinematic features of this prosthesis, helping clinicians to comprehend this prosthesis.     

In vivo comparison of medialized dome and anatomic patellofemoral geometries using subject‐specific computational modeling

Successful outcome following total knee arthroplasty (TKA) with patella resurfacing is partly determined by the restoration of patellofemoral (PF) function and recovery of the quadriceps mechanism. The current study compared two patellar TKA geometries (medialized dome and anatomic) to determine their impact on PF mechanics and quadriceps function. In‐vivo, subject‐specific patellar mechanics were evaluated using a sequential experimental and modeling approach. First, stereo radiography, marker‐based motion capture, and force plate data were collected for TKA patients (10 dome, 10 anatomic) performing a knee extension and lunge. Second, subject‐specific, whole‐body, musculoskeletal models, including 6 degrees‐of‐freedom (DOF) knee joint kinematics, were created for each subject and activity to predict quadriceps forces. Last, finite element models of each subject and activity were created to predict PF kinematics, patellar loading, moment arm, and patellar tendon angle. Differences in mechanics between dome and anatomic patients were highlighted during load‐bearing (lunge) activity. Anatomic subjects demonstrated greater PF flexion angles (avg. 11 ± 3°) compared to dome subjects during lunge. Similar to the natural knee, contact locations on the patella migrated inferior to superior as the knee flexed in anatomic subjects, but remained relatively superior in dome subjects. Differences in kinematics and contact location likely contributed to altered mechanics with anatomic subjects presenting greater load transfer from the quadriceps to the patellar tendon in deep flexion (>75°), and dome subjects demonstrating larger contact forces during lunge. Although there was substantial patient variability, evaluations of PF mechanics suggested improved quadriceps function and more natural kinematics in the anatomic design. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1910–1918, 2018.