Patellofemoral Contact Area Research Articles

Changes of contact pressure and area in patellofemoral joint after different meniscectomies

We investigated the contact pressure and area of the patellofemoral joint both before and after different meniscectomies to provide a biomechanical basis for selecting meniscectomy and its clinical application for meniscus injuries. Six fresh cadaveric knees were used in the study. Using Staubli robots and an ultra-low-min-type pressure-sensitive tablet, changes in contact area and stress in the patellofemoral joint were measured at various flexion angles following different parts and degrees of meniscectomy. The patellofemoral contact area enlarged with the increase of knee flexion angle. From the values obtained from contact areas and average contact pressure of the patellofemoral joint, we found no significant difference between partial meniscectomy and intact knees, but a significant difference was found between total meniscectomy and intact knees. The contact area after lateral meniscectomy was statistically less than that of intact knees. The mean patellofemoral contact pressure after lateral meniscectomy was larger than in intact knees at each angle of flexion. No significant difference in contact area was observed between intact knees and medial meniscectomy. The average patellofemoral contact pressure after medial meniscectomy was larger than in intact knees from 0° ~ 30° of knee flexion, and no significant differences were found between intact knees and medial meniscectomy while knee bending from 60° to 90°. Different meniscectomies result in high contact pressure or disordered distribution of contact pressure, which may be the cause of postoperative patellofemoral degenerative arthrosis.

Patellofemoral joint stress during running in females with and without patellofemoral pain

Patellofemoral pain (PFP) is a common complaint among female runners. The etiology for PFP is frequently associated with increased patellofemoral joint stress (PFJS) and altered hip and knee joint kinematics during running. However, whether PFJS during running is increased among runners with PFP is unknown. The primary aim of this study was to compare PFJS during running among females with and without PFP. We also compared hip and knee transverse plane kinematics during running due to their potential influence on patellofemoral contact area and PFJS. Three dimensional hip and knee running kinematics and kinetics were obtained from 20 females with PFP and 20 females with no pain. Patellofemoral joint stress during running was estimated using patellofemoral contact area and a sagittal plane patellofemoral joint model previously described. Patellofemoral joint stress, PFJS-time integral, and hip and knee transverse plane kinematics at the time of impact peak and peak ground reaction force were compared between groups using a multivariate analysis of variance. The results show that peak PFJS and PFJS-time integral were similar between groups. Peak knee flexion angle and net knee extension moment were not different between groups. However, females with PFP demonstrated hip internal rotation that was 6° greater (P=0.04) when ground reaction forces were greatest. The extent these results are influenced by compensations for pain is unclear. However, if increased PFJS contributes to the etiology or exacerbation of PFP, interventions to minimize altered transverse plane hip kinematics may be indicated among runners who demonstrate this characteristic.

The effect of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral contact pressure during simulated partial weight-bearing knee flexion

The purpose of this in vitro study was to investigate the influence of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral pressure. A dynamic muscle-loaded knee squat was simulated on eight knee specimens with an upright knee simulator while measuring tibiofemoral joint kinematics and patellofemoral pressure distribution. The quadriceps muscle was attached to three actuators simulating the three main extensor muscles, and five different quadriceps loading patterns were tested. Tibial axial and varus-valgus-rotation are affected most while changing quadriceps loading patterns from lateral to medial. Higher internal tibial rotation is associated with higher medial muscle load compared to the symmetrical loading condition. Contact force, contact area and maximum peak pressure rise with increasing flexion angles. Accentuating the vastus lateralis muscle induces a significant reduction in patellofemoral contact force and a 30% diminished contact area at 90° of flexion. Strengthening the vastus medialis muscle leads to increased internal tibial rotation, thus optimizing patella tracking by lowering the Q-angle. In contrast, weakness of the vastus medialis muscle causes decreased tibial internal rotation and is associated with lower patellofemoral contact pressure and contact area. Vastus medialis exercise is advisable to improve patella tracking but may not be recommended in patients with disorders due to increased patellofemoral contact pressure.

Patellofemoral contact during squat simulation on cadaveric knees

The Ghent Knee Rig was built in 2006 for studying the biomechanical behavior of postmortem human knees. To validate this test rig the patellofemoral contact pressures and areas were investigated in 3 post-mortem knees tested under the same circumstances and compared to results in literature. To load the quadriceps, the vastus intermedius and rectus femoris were separated and clamped together. The pulling cable was aligned according to the shaft of the femur to keep the Qangle at physiological values. A pressure film was inserted in the patellofemoral joint to measure the patellofemoral contact area and pressure. The results follow the general accepted trends of patellofemoral contact during knee flexion and extension; when the patella enters the trochlear groove at approximately 20 degrees of knee flexion, the intra articular contact pressure and area start to build up and the contact area on the patella shifts from distal to proximal. Though working with cadaveric specimens remains a simulation of in vivo situations with well known limitations, the test rig shows a good repeatability and reliability. The next stage of this research project is a comparison of normal with pathological knees

Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction Restores Patellofemoral Contact Areas and Pressures More Closely Than Nonanatomic Single-Bundle Reconstruction

To investigate the effects of anterior cruciate ligament (ACL) deficiency and nonanatomic single-bundle (SB) and anatomic double-bundle (DB) ACL reconstruction on the contact characteristics of the patellofemoral (PF) joint. By use of a materials testing system, 7 fresh-frozen human cadaveric knees were tested. The following states were tested: ACL-intact knee, nonanatomic SB ACL reconstruction, anatomic DB ACL reconstruction, and ACL-deficient knee. Hamstring autografts were used. PF contact pressures and areas were measured with pressure-sensitive film at 30°, 60°, and 90° of knee flexion with a constant 100-N load on the quadriceps tendon. The total contact area of ACL-deficient and nonanatomic SB ACL-reconstructed knees (123.8 ± 63.9 and 149.6 ± 79.3 mm(2), respectively) significantly decreased when compared with those of the intact knee (206.1 ± 83.6 mm(2)) at 30° of knee flexion. The lateral-facet peak pressure of ACL-deficient and nonanatomic SB ACL-reconstructed knees (1.12 ± 0.52 and 1.22 ± 0.54 MPa, respectively) significantly decreased when compared with those of the intact knee (0.68 ± 0.38 MPa) at 90° of knee flexion. Anatomic DB ACL reconstruction restored the contact pressures and areas to values similar to those of the intact knee (no significant difference). ACL deficiency resulted in a significant decrease in the total and medial PF contact areas and in an increase in the lateral PF contact pressure. Anatomic DB ACL reconstruction more closely restored normal PF contact area and pressure than did nonanatomic SB ACL reconstruction. Our findings suggest that the changes in the PF contact area and pressures in ACL deficiency and after nonanatomic SB ACL reconstruction may be one of the causes of PF osteoarthritis or other related PF problems found at long-term follow-up. Anatomic DB ACL reconstruction may reduce the incidence of PF problems by closely restoring the contact area and pressure.

Regulation of the patellofemoral contact area: An essential mechanism in patellofemoral joint mechanics?

Although the relationship between contact area and pressure under physiological loading has been described in the feline patellofemoral joint, this interaction has only been examined under simplified loading conditions and/or considerably lower forces than those occurring during demanding activities in humans. We hypothesized that patellofemoral contact area increases non-linearly under an increasing joint reaction force to regulate patellofemoral pressure. Eight human cadaveric knees were ramp loaded with muscle forces representative of the stance phase of stair climbing at 30° knee flexion. Continuous pressure data were acquired with a pressure sensitive film that was positioned within the patellofemoral joint. While pressure was linearly dependent upon the resulting joint reaction force, contact area asymptotically approached a maximum value and reached 95% of this maximum at patellofemoral forces of 349–723 N (95% CI). Our findings indicate that the regulatory influence of increasing contact area to protect against high patellofemoral pressure is exhausted at relatively low loads.

Management of Chondral Injuries Associated With Patellar Instability

The treatment of cartilage injuries secondary to patellar instability is multifactorial. These factors include the time frame of patellar instability, the pathoanatomic factors, the extent of symptoms, and the size and location of the cartilage injury. The chondral or osteochondral injury which occurs with acute patellar instability is managed with either reduction and internal fixation or removal. The treatment of the patellar instability component is controversial in the acute setting, especially when there is no need for an osteochondral surgery. In such cases, patellar dislocations are treated nonoperatively. However, if the patient is indicated for surgery for treatment of osteochondral fracture and intra-operatively the medial patellofemoral ligament (MPFL) remains pathologically lax and presents with a discrete MPFL injury site, there is the option of acute repair. Chondral injury associated with recurrent patellar instability may be subdivided into 2 overlapping groups: (1) chondral damage resulting from the instability episodes (distal medial region of the patellar and/or lateral proximal region of the lateral femoral condyle) and (2) chondrosis secondary to the chronic lateral tracking of the patella (chronic patellar subluxation) from patholaxity of the MPFL (lateral chondrosis to patella and trochlea in addition to the injuries sustained from the actual instability episodes). The treatment is based on the patient's chief complaints and the unique underlying pathoanatomy. Many of these patients will have one or more predisposing factors, such as patella alta, trochlear dysplasia, patholaxity of the MPFL and an excessively lateral position of the tibial tuberosity. Therefore, the key to managing this patient population is to address each patient's specific pathoanatomy, which by definition will include addressing the MPFL patholaxity. The goals are to stabilize the patella, normalize patellofemoral contact area and/or forces, and then restore the articular cartilage based on relevant symptoms. As of this writing, treatment options in the United States include debridement, marrow stimulation, osteochondral auto and allograft, autologous chondrocyte implantation, and the use of particulate articular cartilage.

Effect of bracing on dynamic patellofemoral contact mechanics

Decreases in patellofemoral pain have been demonstrated with bracing; however, the mechanisms of pain reduction remain unclear. Our purpose was to evaluate the hypothesis that patellofemoral bracing decreases peak pressure on the retropatellar surface through an increase in patellofemoral contact area. Nine cadaveric knees were tested during simulated free-speed walking with no brace, a knee sleeve, two different patellar stabilization sleeves, and a wrap-style patellar stabilization brace. Contact area and pressure were measured using a dynamic pressure sensor located in the patellofemoral joint. For the unbraced knee, contact area and peak pressure varied with knee flexion angle, ranging from 0.30 ± 0.3 cm(2) and 1.80 ± 1.7 MPa at full extension to 2.28 ± 0.5 cm(2) and 4.19 ± 1.7 MPa at peak knee flexion. All braces increased contact area, while the wrap-style brace decreased peak pressure (p < 0.001). Sleeve braces compress the quadriceps tendon causing the patella to engage the trochlear groove earlier during knee flexion. The wrap-style brace reduced peak pressure by shifting the location of highest pressure to a region with increased articular cartilage thickness. Sleeve braces may be useful for treatment of patellar subluxation disorders, while wrap-style braces may be effective for treatment of disorders associated with degenerative cartilage changes.

CSM 2010 Orthopaedic Section Platform Presentations (Abstracts OPL1-OPL67)

CSM 2010 Orthopaedic Section Platform Presentations (Abstracts OPL1-OPL67)

Three-Dimensional In Vivo Patellofemoral Kinematics and Contact Area of Anterior Cruciate Ligament–Deficient and –Reconstructed Subjects Using Magnetic Resonance Imaging

The purpose of this study was to test whether (1) the 3-dimensional in vivo patellofemoral kinematics and patellofemoral contact area of anterior cruciate ligament (ACL)-deficient knees are different from those of normal, contralateral knees and (2) ACL reconstruction restores in vivo patellofemoral kinematics and contact area. Ten ACL-deficient knees and twelve ACL-reconstructed knees, as well as the contralateral uninjured knees, were tested. Magnetic resonance imaging was performed at full extension and 40 degrees of flexion under simulated partial weight-bearing conditions. Six-degrees of freedom patellofemoral kinematics, patellofemoral contact area, and contact location were analyzed by use of magnetic resonance image-based 3-dimensional patellofemoral knee models. The patella in the ACL-deficient knees underwent significantly more lateral tilt during flexion (P < .05) and tended to translate more laterally (P = .083) than the patella in contralateral knees. After ACL reconstruction, no kinematic parameters were significantly different from those in contralateral knees. The patellofemoral contact areas of ACL-deficient knees at both the extended and flexed positions (37 +/- 22 mm(2) and 357 +/- 53 mm(2), respectively) were significantly smaller than those of contralateral knees (78 +/- 45 mm(2) and 437 +/- 119 mm(2), respectively) (P < .05). After reconstruction, the patellofemoral contact area of ACL-reconstructed knees in the extended position (86 +/- 41 mm(2)) was significantly larger (P < .05) than that of contralateral knees (50 +/- 34 mm(2)), but no difference was detected in the flexed position. Reproducibility of all patellofemoral kinematic parameters, contact centroid translation, and contact area showed coefficients of variation of less than 6.8%. ACL injuries alter patellofemoral kinematics including patellar tilt and patellar lateral translation, but ACL reconstruction with hamstring or allograft restores altered patellar tilt. ACL injuries reduce the patellofemoral contact area at both the extended and flexed positions, but ACL reconstruction enlarges the patellofemoral contact area at extension and restores the normal contact area at low angles of flexion. Level III, case-control study.

Is there a biomechanical explanation for anterior knee pain in patients with patella alta?

The purpose of this study was to test the hypothesis that patella alta leads to a less favourable situation in terms of patellofemoral contact force, contact area and contact pressure than the normal patellar position, and thereby gives rise to anterior knee pain. A dynamic knee simulator system based on the Oxford rig and allowing six degrees of freedom was adapted in order to simulate and record the dynamic loads during a knee squat from 30 degrees to 120 degrees flexion under physiological conditions. Five different configurations were studied, with variable predetermined patellar heights. The patellofemoral contact force increased with increasing knee flexion until contact occurred between the quadriceps tendon and the femoral trochlea, inducing load sharing. Patella alta caused a delay of this contact until deeper flexion. As a consequence, the maximal patellofemoral contact force and contact pressure increased significantly with increasing patellar height (p < 0.01). Patella alta was associated with the highest maximal patellofemoral contact force and contact pressure. When averaged across all flexion angles, a normal patellar position was associated with the lowest contact pressures. Our results indicate that there is a biomechanical reason for anterior knee pain in patients with patella alta.

Magnetic resonance imaging of in vivo patellofemoral kinematics after total knee arthroplasty

Simulated partial weight bearing during magnetic resonance imaging of the knee was used to measure patellar tilt, medial–lateral patellar shift, and patellofemoral contact area in three groups of subjects; patients with posterior cruciate retaining (PCR) TKA, patients with bicruciate substituting (BCS) TKA, and healthy controls. Contact stress was also calculated based on the contact area and body weight-based estimates of contact force. Contact stress was significantly (p<0.05) higher in PCR knees (2.5±3.0 MPa) than in BCS knees (0.2±0.1 MPa) when knees were fully extended, but this difference was not significant (3.7±3.5 MPa for PCR knees vs. 1.4±1.9 MPa for BCS knees; p>0.05) in early flexion. The results also indicate that patellar tilt (normal=2.4°±4.8°, BCS=5.5°±5.5°, PCR=−3.0°±6.9° change in lateral tilt when moving from full extension to early flexion) and contact area (full extension: normal=267±111 mm2, BCS=344±201 mm2, PCR=83±80 mm2; early flexion: normal=723±306 mm2, BCS=417±290 mm2, PCR=246±108 mm2) in BCS TKA mimic those in the normal knees more closely than PCR knees do. These results suggest that the patellar component in BCS TKA may be expected to experience less wear than the patellar component in PCR TKA over time.

Patellofemoral Kinematics After Limited Resurfacing of the Trochlea

Patellofemoral kinematics after a limited resurfacing of the trochlea was investigated. Patellofemoral contact pressure, area, and force were measured for intact state; after creation of a 20-mm full-thickness trochlear defect; and after trochlear resurfacing implant (Arthrosurface) in serial flexion positions (45 degrees, 60 degrees, 75 degrees). In the defect state, edge loading and peak contact forces were highest at the periphery. The chondral defect increased peak contact force (13 to 18 N, P < .01) and peak contact pressure (23 to 31 kg/cm2, P < .02) compared with the intact state. Peak contact pressure and force were restored to 90% (P < .01) and 88% (P < .01). Implantation of the device restored contact area to 85% of the intact state. Limited resurfacing of the trochlea restores contact area, peak pressure, and peak force to the intact state. These findings highlight the potential clinical use of limited patellofemoral resurfacing in trochlear chondral defects.

Determination of contact surfaces of the femoropatellar joint with reference to the localization of chondromalacia

At 13 post-mortem-knees we investigated the patello-femoral contact area in different degrees of function, referring to the localization of chondromalacia. We found that the localization of chondromalacia didn't accord to the contact area in 50% of all cases. Possible other causes are discussed.

Patellofemoral Contact Area and Pressure after Medial Patellofemoral Ligament Reconstruction

Background It is not known whether nonisometric femoral graft attachment diminishes the effectiveness of medial patellofemoral ligament reconstruction. Purpose To determine whether a nonisometric femoral attachment point is associated with differences in contact area and pressure in the patellofemoral joint as compared with an isometric attachment point. Study Design Controlled laboratory study. Methods Eleven cadaveric knees were amputated and secured in a loading fixture. The quadriceps tendon was clamped 5 cm above the proximal pole of the patella and fixed to a plate. Colinear compressive forces were applied. Forces were set to achieve isometric quadriceps moments at 30°, 45°, 60°, and 90° of knee flexion. Contact areas and pressures were measured using a sensor system. Initially, isometric reconstruction was done using the known isometric femoral attachment point of the posterior medial epicondyle. The attachment was then revised in each specimen to the known nonisometric femoral attachment of the adductor tubercle. Results Before medial patellofemoral ligament reconstruction, average facet patellofemoral contact area and pressure generally increased with angle of knee flexion. With few exceptions, initial versus postprocedure data and isometric versus nonisometric contact area and pressure data did not differ significantly at any angle tested. Percentage contact area and contact pressure in the medial facet did not differ significantly from the initial percentage for either attachment, and no difference was found in the percentage medial contact area or pressure for isometric versus nonisometric attachment at the angles tested. Conclusion Use of the nonisometric attachment point of the adductor tubercle in medial patellofemoral ligament reconstruction did not appear to alter knee contact area or contact pressures as compared with isometric femoral attachment at the posterior medial epicondyle. Clinical Relevance In medial patellofemoral ligament reconstruction, patellofemoral contact area and pressure may not be adversely affected by use of the nonisometric femoral attachment point used in this study.

Biomechanical Effects of Kneeling After Total Knee Arthroplasty

Kneeling following total knee arthroplasty can be a difficult task, impairing the activities of patients to varying degrees. Little is known about the biomechanical effects of kneeling following total knee replacement. The objective of this study was to quantify the effects of kneeling on patellofemoral joint contact areas and pressures, knee joint reaction force, and patellar kinematics. Total knee arthroplasties were performed on eight fresh-frozen cadaveric knees, and they were tested with use of a custom knee jig, which permits the simulation of physiologic quadriceps loading as well as the application of an anterior force to simulate kneeling. The knees were tested at flexion angles of 90 degrees , 105 degrees , 120 degrees , and 135 degrees with no anterior force (mimicking a squatting position) and with an anterior force application simulating double-stance kneeling and single-stance kneeling. Patellofemoral joint contact areas and pressures were measured with pressure-sensitive film, and the knee joint reaction force was measured with use of a six-degree-of-freedom load cell. Patellar kinematics were assessed with use of digital photographs tracking fixed markers on the patella. Compared with the condition without kneeling, both single-stance and double-stance kneeling demonstrated significant increases in patellofemoral contact area (p < 0.05) and pressure at all flexion angles (p < 0.05), with the exception of double-stance kneeling at 135 degrees of flexion. The resultant knee joint -reaction force increased with kneeling at all flexion angles. The compressive component of this force increased with kneeling for most conditions, while the lateral component of this force decreased significantly (p < 0.05) with kneeling only at 90 degrees , and the anterior component of this force increased significantly at all knee flexion angles (p < 0.05). Overall, kneeling had minimal changes on patellar tilt, with significant changes in patellar tilt seen only with kneeling at 120 degrees (p = 0.02 for double stance, and p = 0.03 for single stance). The findings of this study suggest that kneeling at a higher flexion angle (135 degrees ) after total knee arthroplasty has a smaller effect on patellofemoral joint contact area and pressure than kneeling at lower flexion angles (<or=120 degrees ).

The influence of patellar bracing on patellar and knee load-distribution and kinematics: an experimental cadaver study

The aim of this study was to analyze the biomechanical consequences of patella bracing in order to evaluate possible mechanisms supporting its clinical application. The hypothesis is that the patellar bracing reduces patellofemoral pressure by influencing patellar and knee kinematics, and load distribution. Physiologic isokinetic knee extension motions were simulated on ten human knee cadaver specimens using a knee kinematic simulator. Joint kinematics were evaluated using an ultrasound-based motion analysis system and patellofemoral contact pressure was measured using a thin-film piezoresistive pressure measuring system. Infrapatellar tissue pressure was analyzed using a closed sensor-cell. Three different patella braces were fitted to the knee cadavers and their influence on the kinematic and kinetic biomechanical parameters were evaluated and compared to the physiologic situation. Patellar bracing resulted in a significant (p = 0.05) proximalization of the patella up to 3 mm. Depending on the type of brace used, a decrease in the infrapatellar fat pad pressure was found and the patellofemoral contact area was decreased significantly (p = 0.05) between 60 degrees of knee flexion and full extension (maximum 22%). Patella bracing significantly (p = 0.05) reduced the patellofemoral contact pressure an average of 10%, as well as the peak contact pressure which occurred. Patellar bracing significantly influences patella biomechanics in a reduction of the patellofemoral contact area and contact pressure as well as a decrease in the infrapatellar tissue pressure. The application of infrapatellar straps is suggested for the treatment and prevention of anterior knee pain, especially in high level sports.

Patellofemoral Joint Contact Area Is Influenced by Tibiofemoral Rotation Alignment in Individuals Who Have Patellofemoral Pain

Observational, cohort study. To test the hypothesis that patellar alignment and tibiofemoral rotation alignment explain unique portions of variance in patellofemoral joint contact area in individuals with patellofemoral pain (PFP) and in pain-free control subjects. PFP has been proposed to result from increased patellofemoral joint stress due to decreased contact area. Patellar malalignment (lateral displacement and tilt) is believed to be the main contributor to decreased contact area. Recent studies suggest that transverse plane rotation of the femur and/or tibia may also contribute to decreased contact area. Twenty-one subjects with PFP (16 female, 5 male) and 21 pain-free subjects (14 female, 7 male) participated. Subjects underwent magnetic resonance imaging with the knee in full extension and the quadriceps contracted. Measures of patellofemoral joint contact area, lateral patellar displacement, patellar tilt angle, tibiofemoral rotation angle, and patellar width were obtained. Hierarchical multiple regression analyses were performed for each group using contact area as the dependent variable. The order of independent variables was patellar width, patellar tilt angle, and tibiofemoral rotation angle. To avoid multicolinearity, lateral patellar displacement was not included. In the PFP group, patellar width and tibiofemoral rotation angle explained 46% of the variance in contact area. In pain-free subjects, patellar width was the only predictor of contact area, explaining 31% of its variance. Patellar tilt angle did not predict contact area in either group. Addressing factors that control tibiofemoral rotation may be indicated to increase contact area and reduce pain in individuals with PFP. Future studies should investigate the contributions of patellar alignment and tibiofemoral rotation to patellofemoral joint contact area at a variety of knee flexion angles.

Patellofemoral Joint Contact Area Is Influenced by Tibiofemoral Rotation Alignment in Individuals Who Have Patellofemoral Pain

Patellofemoral Joint Contact Area Is Influenced by Tibiofemoral Rotation Alignment in Individuals Who Have Patellofemoral Pain

Patella Alta

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°, 20°, 40°, and 60° of knee flexion with the quadriceps contracted. Results: With the knee at 0° 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° ± 1.9° and 15.5° ± 1.8°; p = 0.028), and less contact area (157.6 ± 13.7 mm2 and 198.8 ± 14.3 mm2; 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° 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.