Patellofemoral Contact Pressure Research Articles

Effects of patellar resurfacing on contact area and contact stress in total knee arthroplasty

The objective of this study was to examine the effects of patellar resurfacing on patellofemoral joint contact pressure and contact area in total knee arthroplasty. We tested seven fresh-frozen cadaveric knees using a custom knee jig which permits the simulation of physiologic quadriceps loading. Before patellar resurfacing, the mean peak contact pressure of medial and lateral patellofemoral joints was less than 10 MPa at knee flexion angles of 30°, 60° and 90°, that of medial and lateral patellofemoral joints were 11.63 MPa and 11.42 MPa at a knee flexion angle of 120° respectively, and the mean contact area of patellofemoral joint ranged from 70 to 150 mm 2. After patellar resurfacing, the mean peak contact pressure of medial and lateral patellofemoral joints ranged from 50 to 100 Mpa ( P < 0.05), which exceeds the yield strength of ultrahigh molecular weight polyethylene, and the mean contact area of patellofemoral joint reduced to 10–15 mm 2 ( P < 0.05). The contact pressure of patellofemoral joint was lower than the yield strength of articular cartilage before patellar resurfacing. Our results indicate that the yield stress of UHMWPE is exceeded after patellar resurfacing.

Dynamic measurement of patellofemoral kinematics and contact pressure after lateral retinacular release: an in vitro study

The purpose of this study was to investigate the influence of lateral retinacular release and medial and lateral retinacular deficiency on patellofemoral position and retropatellar contact pressure. Human knee specimens (n = 8, mean age = 65 SD 7 years, all male) were tested in a kinematic knee-simulating machine. During simulation of an isokinetic knee extension cycle from 120 degrees to full extension, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The position of the patella was measured using an ultrasound based motion analysis system (CMS 100, Zebris). The amount of patellofemoral contact pressure and its pressure distribution was measured using a pressure sensitive film (Tekscan, Boston). Patellar position and contact pressure were first investigated in intact knee conditions, after a lateral retinacular release and a release of the medial and lateral retinaculum. After lateral retinacular release the patella continuously moved from a significant medialised position at flexion (P = 0.01) to a lateralised position (P = 0.02) at full knee extension compared to intact conditions, the centre of patellofemoral contact pressure was significantly medialised (0.04) between 120 degrees and 60 degrees knee flexion. Patellofemoral contact pressure did not change significantly. In the deficient knee conditions the patella moved on a significant lateralised track (P = 0.04) through the entire extension cycle with a lateralised centre of patellofemoral pressure (P = 0.04) with a trend (P = 0.08) towards increased patellofemoral pressure. The results suggest that lateral retinacular release did not inevitably stabilise or medialise patellar tracking through the entire knee extension cycle, but could decrease pressure on the lateral patellar facet in knee flexion. Therefore lateral retinacular release should be considered carefully in cases of patellar instability.

Anteromedialization of the Tibial Tubercle

Anteromedialization of the tibial tubercle (Fulkerson operation) predictably leads to pain reduction and better function in initial and moderate patellofemoral arthritis. This result has been shown in the literature and is supported by our own worl. Indications are based on symptoms, clinical evaluation, s-rays, and magnetic resonance imaging. The Fulkerson operation combines recentering of the patella and reduction of patellofemoral contact pressure. Rehabilitation lasts for 6 to 8 months because anteromedialization leads to a temporary weakening of the proximal tibia . Proximal tibial fracture is a complication of Fulkerson’s osteotomy if the tibia is stressed to early.

Dynamic measurement of patellofemoral contact pressure following reconstruction of the medial patellofemoral ligament: An in vitro study

Surgical reconstruction of the medial patellofemoral ligament used to stabilize the patella against lateral dislocation may concomitantly produce alteration of the patellofemoral contact pressure distribution. Two different tendon transfer techniques of reconstructing the medial patellofemoral ligament, one dynamic and one static, as well as a proximal soft tissue realignment of the patella were investigated. Eight human knee specimens were mounted in a kinematic knee simulator and isokinetic extension motion was simulated. Patellofemoral pressure was measured using a pressure sensitive film while a 100 N laterally directed dislocation load was applied to the patella. The specimens were evaluated in a physiologic state, as well as after dynamic reconstruction of the medial patellofemoral ligament using a distal transfer of the semitendinosus tendon, following static reconstruction using a semitendinosus autograft, and following proximal soft tissue realignment of the patella. Following both reconstruction techniques of the medial patellofemoral ligament patellofemoral contact pressure was not significantly (P=0.49) altered. In contrast, after proximal realignment a trend (P=0.07) towards higher contact pressure near knee extension was observed. In the absence of a lateral dislocation load dynamic and static reconstruction resulted in a medialization (P=0.04) of the center of pressure, whereas under the application of a 100 N dislocation load the center of pressure showed no significant alteration. Following proximal realignment the center of pressure was significantly medialized without (P<0.01) and with a dislocation load (P=0.01) throughout the entire range of knee motion. Static and dynamic ligament reconstruction of the medial patellofemoral ligament did not alter patellofemoral pressure. Proximal realignment, on the other hand, resulted in a constant medialization of the patellofemoral pressure. The data suggest that the reconstruction techniques would be associated with a low risk of causing premature cartilage degeneration due to excessive patellofemoral contact pressure, whereas proximal realignment could cause medial overload of the patellofemoral joint.

The effect of rotational alignment of the femoral components on the patellofemoral biomechanics in total knee arthroplasty

To study the effect of rotational alignment of the femoral components on the patellofemoral biomechanics in total knee arthroplasty (TKA) demonstrated on autopsy specimens, as the guide for surgeons to choose the correct reference axis for rotational alignment of the femoral components and to reduce the patellofemoral joint complications. Select 9 frozen fresh human cadaver knees without gross deformities or instabilities and mount specimens on a patellofemoral joint testing jig connected to a Model 8501 Instron machine (Instron Corporation, Canton, MA). The study simulated the action of squatting from the standing position with the foot firmly planted. Standard TKA was performed in each specimen by the same senior surgeon using Nexgen LPS total knee system (Zimmer Corporation, Warsaw Indiana). Alter rotational alignment of the femoral components referenced to the transepicondylar axis and the Whiteside's line respectively. Measure biomechanics of the patellofemoral joints using Fuji prescale film at 30 degrees , 60 degrees , 90 degrees , 120 degrees of knee flexion respectively. The digital values were obtained by the handheld pressure measurement systems (FPD-305E, FPD-306E) and Autocad software. The rotational alignment of the femoral components paralleled to the transepicondylar axis had the best results of the peak value of the patellofemoral contact pressure (P < 0.05). There were no statistically significant differences in patellofemoral contact area (P > 0.05). But the patellofemoral contact area had the close correlations to the angles of the knee flexion and the specimens. Rotational alignment of the femoral components has a great influence on the patellofemoral contact pressure in total knee arthroplasty. It is reliable for surgeons to choose the transepicondylar axis as the reference axis to rotate femoral components.

Assessment of patellofemoral joint contact pressure in an uninjuried knee

Assessment of patellofemoral joint contact pressure in an uninjuried knee

The Effect of Anterior Cruciate Ligament Reconstruction on Knee Joint Kinematics under Simulated Muscle Loads

Background Numerous studies have investigated anterior stability of the knee during the anterior drawer test after anterior cruciate ligament reconstruction. Few studies have evaluated anterior cruciate ligament reconstruction under physiological loads. Purpose To determine whether anterior cruciate ligament reconstruction reproduced knee motion under simulated muscle loads. Study Design Controlled laboratory study. Methods Eight human cadaveric knees were tested with the anterior cruciate ligament intact, transected, and reconstructed (using a bone–patellar tendon–bone graft) on a robotic testing system. Tibial translation and rotation were measured at 0 °, 15 °, 30 °, 60 °, and 90 ° of flexion under anterior drawer loading (130 N), quadriceps muscle loading (400 N), and combined quadriceps and hamstring muscle loading (400 N and 200 N, respectively). Repeated-measures analysis of variance and the Student-Newman-Keuls test were used to detect statistically significant differences between knee states. Results Anterior cruciate ligament reconstruction resulted in a clinically satisfactory anterior tibial translation. The anterior tibial translation of the reconstructed knee was 1.93 mm larger than the intact knee at 30 ° of flexion under anterior load. Anterior cruciate ligament reconstruction overconstrained tibial rotation, causing significantly less internal tibial rotation in the reconstructed knee at low flexion angles (0 °-30 °) under muscle loads (P<. 05). At 30 ° of flexion, under muscle loads, the tibia of the reconstructed knee was 1.9 ° externally rotated compared to the intact knee. Conclusions Anterior cruciate ligament reconstruction may not restore the rotational kinematics of the intact knee under muscle loads, even though anterior tibial translation was restored to a clinically satisfactory level under anterior drawer loads. These data suggest that reproducing anterior stability under anterior tibial loads may not ensure that knee joint kinematics is restored under physiological loading conditions. Clinical Relevance Decreased internal rotation of the knee after anterior cruciate ligament reconstruction may lead to increased patellofemoral joint contact pressures. Future anterior cruciate ligament reconstruction techniques should aim at restoring 3-dimensional knee kinematics under physiological loads.

Contact Pressure at Osteochondral Donor Sites in the Patellofemoral Joint

Background The lowest contact pressure point is presumed to be the best site to harvest an osteochondral plug and minimize morbidity. Hypothesis Patellofemoral contact pressures are not uniform and are lowest along the medial patellofemoral articulation. Study Design Controlled laboratory study. Methods Seven cadaveric knees were tested with an electroresistive, dynamic pressure sensor placed onto the femoral side of the patellofemoral joint. The extensor mechanism was loaded with 89.1 N and 178.2 N, and the knee was manually cycled 3 times (0°-105°) per load. Mean trochlear pressures were calculated. Results Mean contact pressures were greatest in the central trochlea (5.80 kgf/cm2), followed by the lateral (2.56 kgf/cm2) and medial trochlea (1.60 kgf/cm2) at 89.1 N (P < .05). At 178.2 N, pressures increased to 9.47, 5.81, and 2.75 kgf/cm2, respectively (P < .05). Lateral trochlear pressures decreased moving distally from 1.25 to 0.50 kgf/cm2 at 89.1 N and 4.57 to 1.29 kgf/cm2 at 178.2 N. Conclusions Contact pressures are lowest along the medial trochlea and decrease distally along the lateral trochlea. Clinical Relevance Osteochondral plugs from the medial femoral trochlea may be desirable if trochlear size permits. If harvesting from the lateral femoral trochlea, consider harvesting distally near the sulcus terminalis.

Patellofemoral Contact Characteristics in Total Knee Prostheses with and Without Anterior Patellar Flange

A new design of total knee prosthesis without anterior patellar flange was developed to preserve the anatomical shape of the patellofemoral joint. The aim of the current study was to experimentally compare patellofemoral contact area and pressure in a nonreplaced knee, in a knee after implantation of a conventionally designed total knee arthroplasty, and in a knee after implantation of the newly designed total knee arthroplasty without patellar flange. Six cadaveric legs were examined before and after implantation of either a conventional or a newly developed total knee arthroplasty, both without patellar replacement. The essential change in design is the absence of an anterior patellar flange. Contact area and pressure were measured using pressure sensitive films in 45°, 60°, 90°, and 120° of flexion and the results were compared between the different prosthesis designs and with the nonreplaced knee. The prosthesis without patellar flange showed less average and maximum pressure than the conventional prosthesis. Compared with the nonreplaced knee, the conventional prosthesis led to increased average and maximum pressure and decreased contact area. In an experimental test setup, the newly developed total knee arthroplasty without patellar flange showed reduced patello-femoral contact pressure in comparison with a total knee prosthesis with conventional patellofemoral design. This could possibly lead to a lower incidence of anterior knee complaints in patients.

The effect of tibiofemoral joint kinematics on patellofemoral contact pressures under simulated muscle loads

Altered patellofemoral joint contact pressures are thought to contribute to patellofemoral joint symptoms. However, little is known about the relationship between tibiofemoral joint kinematics and patellofemoral joint contact pressures. The objective of this paper was to investigate the effect of tibiofemoral joint kinematics on patellofemoral joint pressures using an established in vitro robotic testing experimental setup. Eight cadaveric knee specimens were tested at 0°, 30°, 60°, 90°, and 120° of flexion under an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Tibiofemoral joint kinematics were measured by the robot and contact pressures by a TekScan pressure sensor. The isolated quadriceps loading caused anterior translation and internal rotation of the tibia up to 60° of flexion and posterior translation and external rotation of the tibia beyond 60°. The co-contraction of the hamstring muscles caused a posterior translation and external rotation of the tibia relative to the motion of the tibia under the quadriceps load. Correspondingly, the contact pressures were elevated significantly at all flexion angles. For example, at 60° of flexion, the hamstrings co-contraction increased the posterior tibial translation by approximately 2.8 mm and external tibial rotation by approximately 3.6°. The peak contact pressure increased from 1.4 ± 0.8 to 1.7 ± 1.0 MPa, a 15% increase. The elevated contact pressures after hamstrings co-contraction indicates an intrinsic relation between the tibiofemoral joint kinematics and the patellofemoral joint biomechanics. An increase in posterior tibial translation and external rotation is accompanied by an increase in contact pressure in the patellofemoral joint. These results imply that excessive strength conditioning with the hamstring muscles might not be beneficial to the patellofemoral joint. Knee pathology that causes an increase in tibial posterior translation and external rotation might contribute to degeneration of the patellofemoral joint. These results suggest that conservative treatment of posterior cruciate ligament injury should be reconsidered.

The Effect of Posterior Cruciate Ligament Reconstruction on Patellofemoral Contact Pressures in the Knee Joint under Simulated Muscle Loads

Background The mechanism of cartilage degeneration in the patellofemoral joint (PFJ) and medial compartment of the knee following posterior cruciate ligament (PCL) injury remains unclear. PCL reconstruction has been recommended to restore kinematics and prevent long-term degeneration. The effect of current reconstruction techniques on PFJ contact pressures is unknown. Purpose To measure PFJ contact pressures after PCL deficiency and reconstruction. Method Eight cadaveric knees were tested with the PCL intact, deficient, and reconstructed. Contact pressures were measured at 30 °, 60 °, 90 °, and 120 ° of flexion under simulated muscle loads. Knee kinematics were measured by a robotic testing system, and the PFJ contact pressures were measured using a thin film transducer. A single bundle achilles tendon allograft was used in the reconstruction. Results PCL deficiency significantly increased the peak contact pressures measured in the PFJ relative to the intact knee under both an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Reconstruction did not significantly reduce the increased contact pressures observed in the PCL-deficient knee. Conclusion The elevated contact pressures observed in the PCL-deficient knee and reconstructed knee might contribute to the long-term degeneration observed in both the non-operatively treated and PCL-reconstructed knees.

The influence of tibial and femoral rotation on patellofemoral contact area and pressure.

Fixed rotation of either the femur or tibia has a significant influence on the patellofemoral joint contact areas and pressures. This is due to the anatomic asymmetry in the knee with respect to all planes, as well as the laterally directed force vector that naturally exists in bipedal lower-limb biomechanics. Specifically, femoral rotation results in an increase in patellofemoral contact pressures on the contralateral facets of the patella, and tibial rotation results in an increase in patellofemoral contact pressures on the ipsilateral facets of the patella. This difference can be elucidated when one considers that rotation of the femur is biomechanically different than rotation of the tibia. For both tibial and femoral rotations, the patella's distal attachment to the tibial tubercle influences the direction of patellar movement. The biomechanical evidence reviewed in this manuscript suggests that the determining factor in patellofemoral pathology is the derangement of normal joint mechanics. However, despite considerable experimental data supporting this position, there also are theories that suggest otherwise. This illustrates a very important point in patellofemoral joint pathology, where no one factor may be the sole defining etiology. Instead, the patellofemoral joint is one of the most complex diarthrodial joints in the body and there are a number of etiologic factors that can lead to pathology. This should be considered for developing repair and rehabilitation strategies.

The role of foot orthoses as an intervention for patellofemoral pain.

Foot orthoses often are prescribed for patients with patellofemoral pain. The purpose of this clinical commentary is to review the theoretical and research basis that might support this intervention and to provide our own clinical experience in providing foot orthoses for these patients. Literature is reviewed regarding (1) the effects of foot orthoses on pain and function, (2) the relationship between foot and lower-extremity/patellofemoral joint mechanics, (3) the effects of foot orthoses on lower-extremity mechanics, and (4) the effects of foot orthoses on patellofemoral joint position. The literature and our own clinical experience suggest that patients with patellofemoral pain may benefit from foot orthoses if they also demonstrate signs of excessive foot pronation and/or a lower-extremity alignment profile that includes excessive lower-extremity internal rotation during weight bearing and increased Q angle. The mechanism for foot orthoses having a positive effect on pain and function for these patients may include (1) a reduction in internal rotation of the lower extremity; (2) a reduction in Q angle; (3) reduced laterally-directed soft tissue forces from the patellar tendon, the quadriceps tendon, and the iliotibial band; and (4) reduced patellofemoral contact pressures and altered patellofemoral contact pressure mapping. Foot orthoses may be a valuable adjunct to other intervention strategies for patients who present with the previously stated structural alignment profile.

Evaluation of a computational model used to predict the patellofemoral contact pressure distribution

One possible cause of patellofemoral pain syndrome is excessive lateral force acting on the patella. Although several treatment methods focus on decreasing the lateral force acting on the patella, the relationship between the lateral force and the patellofemoral contact pressure distribution is unclear. A computational model has been developed to determine how loading variations alter the patellofemoral force and pressure distributions for individual knees. The model allows variation in the quadriceps and patella tendon forces, and calculates the predicted contact pressure distribution using the discrete element analysis technique. To characterize the accuracy of the model, four cadaver knees were flexed on a knee simulator with three initial Q-angles, while recording the force and pressure distributions with a pressure sensor. A model of each knee was created from CT data. Using the external force applied to the knee, the geometry of the knee, and the quadriceps origin as input, the pressure distribution was calculated during flexion. Similar trends were noted for the computational and experimental results. The percentage of the total force applied to the lateral cartilage increased with the Q-angle. The maximum contact pressure increased during flexion. The maximum lateral contact pressure increased with the Q-angle for three knees. For the other knee, increasing the Q-angle decreased the maximum lateral pressure. The maximum medial contact pressure decreased as the Q-angle increased. By characterizing the influence of patellofemoral loading on the force and pressure distributions, the computational model could be used to evaluate treatment methods prescribed for patellofemoral pain.

Accuracy and repeatability of a pressure measurement system in the patellofemoral joint

The objective of this study was to assess how accurately and repeatably the Iscan system measures force and pressure in the natural patellofemoral joint. These measurements must be made to test widely held assumptions about the relationships between mechanics, pain and cartilage degeneration. We assessed the system's accuracy by using test rigs in a materials testing machine to apply known forces and force distributions across the sensor. The root mean squared error in measuring resultant force (for five trials at each of seven load levels) was 6.5±4.4% (mean±standard deviation over all trials at all load levels), while the absolute error was −5.5±5.6%. For force distribution, the root mean squared error (for five trials at each of five force distributions) was 0.86±0.58%, while the absolute error was −0.22±1.03%. We assessed the repeatability of the system's measurements of patellofemoral contact force, pressure and force distribution in four cadaver specimens loaded in continuous and static flexion. Variability in measurement (standard deviation expressed as a percentage of the mean) was 9.1% for resultant force measurements and 3.0% for force distribution measurements for static loads, and 7.3% for resultant force and 2.2% for force distribution measurements for continuous flexion. Cementing the sensor to the cartilage lowered readings of resultant force by 31±32% (mean±standard deviation), area by 24±13% and mean pressure by 9±34% (relative to the uncemented sensor). Maximum pressure measurement, however, was 24±43% higher in the cemented sensor than in the uncemented sensor. The results suggest that the sensor measures force distribution more accurately and repeatably than absolute force. A limitation of our work, however, is that the sensor must be cemented to the patellar articular surface to make the force distribution measurements, and our results suggest that this process reduces the accuracy of force, pressure and area measurements. Our results suggest that the Iscan system's pressure measurement accuracy and repeatability are comparable to that of Fuji Prescale film, but its advantages are that it is thinner than most Fuji Prescale film, it measures contact area more accurately and that it makes continuous measurements of force, pressure and area.

Gender Differences in Patellofemoral Joint Biomechanics

Patellofemoral pain is associated with patellar malalignment and quadriceps weakness which are seen more commonly in women. The objective of the current study was to determine the effects of gender, vastus medialis strength, and tibial rotation on patellofemoral joint biomechanics. Twelve fresh-frozen knees from cadavers were tested using a custom knee jig. Anatomic multiplane loading of the extensor mechanism was used with varying vastus medialis loads. Patellofemoral contact area and pressure were measured using pressure sensitive film at knee flexion angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees with the tibia in neutral and 15 degrees internal and external tibial rotation. Patellofemoral joint contact areas in specimens from men were larger at knee flexion angles greater than 30 degrees. A significant increase in mean patellofemoral contact pressures was seen for specimens from women when compared with specimens from men at 0 degrees and 30 degrees knee flexion. The knees from women also showed a greater change in contact pressures to varying vastus medialis load at knee flexion angles of 0 degrees, 30 degrees, and 60 degrees. The results of the current study indicate that there are gender differences in patellofemoral contact areas and pressures. These differences may help explain the increased incidence of patellofemoral disorders in women.

Biomechanical consequences of PCL deficiency in the knee under simulated muscle loads—an in vitro experimental study

The mechanism of chronic degeneration of the knee after posterior cruciate ligament (PCL) injury is still not clearly understood. While numerous biomechanical studies have been conducted to investigate the function of the PCL with regard to antero-posterior stability of the knee, little has been reported on its effect on the rotational stability of the knee. In this study, eight cadaveric human knee specimens were tested on a robotic testing system from full extension to 120° of flexion with the PCL intact and with the PCL resected. The antero-posterior tibial translation and the internal–external tibial rotation were measured when the knee was subjected to various simulated muscle loads. Under a quadriceps load (400 N) and a combined quadriceps/hamstring load (400/200 N), the tibia moved anteriorly at low flexion angles (below 60°). Resection of the PCL did not significantly alter anterior tibial translation. At high flexion angles (beyond 60°), the tibia moved posteriorly and rotated externally under the muscle loads. PCL deficiency significantly increased the posterior tibial translation and external tibial rotation. The results of this study indicate that PCL deficiency not only changed tibial translation, but also tibial rotation. Therefore, only evaluating the tibial translation in the antero-posterior direction may not completely describe the effect of PCL deficiency on knee joint function. Furthermore, the increased external tibial rotations were further hypothesized to cause elevated patello-femoral joint contact pressures. These data may help explain the biomechanical factors causing long-term degenerative changes of the knee after PCL injury. By fully understanding the etiology of these changes, it may be possible to develop an optimal surgical treatment for PCL injury that is aimed at minimizing the long-term arthritic changes in the knee joint.

The effects of removal and reconstruction of the anterior cruciate ligament on the contact characteristics of the patellofemoral joint.

Seven cadaveric knees were used to investigate the effects of removal and reconstruction of the anterior cruciate ligament with a bone-patellar tendon-bone graft on contact characteristics of the patellofemoral joint during physiologic levels of quadriceps muscle loads at 30 degrees, 60 degrees, and 90 degrees of knee flexion. Loads were applied to the quadriceps tendon to equilibrate externally applied flexion moments equivalent to one-third of values for maximum isometric extension moments. Patellofemoral contact areas and pressures were measured using pressure-sensitive film. Excision of the anterior cruciate ligament resulted in significant decreases in the total patellofemoral contact area by as much as 94 mm2 (68%), the medial facet contact area by as much as 55 mm2 (93%), the combined average contact pressure by 0.7 MPa (21%), the medial facet average contact pressure by 2.3 MPa (70%), the combined peak contact pressure by 3.0 MPa (38%), and the medial facet peak contact pressure by 5.4 MPa (76%), all at 30 degrees of knee flexion. Excision of the anterior cruciate ligament also resulted in significant decreases in total, medial facet, and lateral facet patellofemoral contact areas at 60 degrees and 90 degrees of knee flexion. Intraarticular reconstruction returned these to levels not significantly different from those of the intact knee.

Contact area and pressure distribution in the feline patellofemoral joint under physiologically meaningful loading conditions

The purpose of this study was to determine contact area and mean and peak pressures in the healthy feline patellofemoral joint over the complete range of possible applied force. Furthermore, we wanted to improve upon the repeatability of previous measurements while maximizing the physiological relevance of the results obtained. The patellae and femora were secured in a loading frame approximating an in situ loading configuration. Low- and medium-grade Fuji film was used to assess patellofemoral contact area and pressure distribution, respectively. Constant force was applied to the patellofemoral joints for 2 s (short duration trials) or 5 min (long duration trials). For the short duration trials, contact area was shown to increase logarithmically with the force applied. In contrast, mean and peak pressures increased linearly with force. Furthermore, the rate of increase of peak pressure with force was approximately three times greater than that of mean pressure. For the long duration trials, contact area increased up to 33% compared to the short duration trials. This effect could no longer be detected with our approach after an unloading period of 5–10 s. Increasing contact area is one mechanism that the feline patellofemoral joint may use to regulate the pressures experienced by the cartilage as the force applied to the joint increases. The attenuation of external forces inside a joint is achieved by the specific geometry of the articulating surfaces and the viscoelastic properties of the articular cartilage. It likely represents a natural protection of joints to high external load magnitudes.

Distribution of patellofemoral joint pressures after femoral trochlear osteotomy.

Anterior osteotomy of the lateral femoral condyle was designed for the treatment of recurrent patellar dislocations. This study examined whether anterior femoral trochlear osteotomy significantly elevates contact pressures in the patellofemoral joint. Static intrajoint loads and contact area determination were recorded using prescale Fuji pressure-sensitive film under static loading. Peak pressures, average pressures and contact areas of the patellofemoral joint were calculated on intact specimens and after anterior osteotomy of the lateral condyle. Our results indicate that a 6-mm or 10-mm anterior osteotomy of the lateral condyle significantly elevates patellofemoral contact pressures.