Patellofemoral Joint Contact Pressures Research Articles

Lateral Retinacular Release During Medial Unicompartmental Knee Arthroplasty in the Presence of Patello-Femoral Joint Arthritis Relieves Patello-Femoral Joint Pressure and Improves Associated Symptoms

BackgroundThis study evaluated the effects of concomitant lateral patellar retinacular release (LPRR) during medial unicompartmental knee arthroplasty (UKA). MethodsWe retrospectively analyzed 100 patients who had patello-femoral joint (PFJ) arthritis who underwent medial UKA with (n = 50) and without (n = 50) LPRR who had ≥2 years follow-up. Radiological parameters associated with lateral retinacular tightness, including patellar tilt angle (PTA), lateral patello-femoral angle (LPFA), and congruence angle, were measured. Functional evaluation was performed using the Knee Society Pain Score, Knee Society Function Score (KSFS), Kujala Score, and the Western Ontario McMaster Universities Osteoarthritis Index score. Intraoperative patello-femoral pressure evaluation was performed on 10 knees to evaluate the pressure changes before and after LPRR. Mann–Whitney U-tests were used for statistical analyses. ResultsDemographic data did not differ between the LPRR(+) and LPRR(−) groups. A decrease in PTA and an increase in LPFA were observed in the LPRR(+) group compared to those in the LPRR(−) group (PTA; −0.54 versus −1.74, P = .002, LPFA; 0.51 versus 2.01, P = .010). The LPRR(+) group showed significantly better KSFS and Kujala scores than the LPRR(−) group (KSFS: 90 versus 80, P = .017; Kujala score: 86 versus 79, P = .009). Intraoperative patello-femoral pressure analysis showed a 22.6% reduction in the PFJ contact pressure and an 18.7% reduction in PFJ peak pressure after LPRR. (P = .0015, P < .0001, respectively) ConclusionA LPRR during UKA may be a simple and useful adjunct procedure to relieve PFJ symptoms with concomitant PFJOA.

Persistent underloading of patellofemoral joint following hamstring autograft ACL reconstruction is associated with cartilage health

To determine the longitudinal changes of patellofemoral joint (PFJ) contact pressure following anterior cruciate ligament reconstruction (ACLR). To identify the associations between PFJ contact pressure and cartilage health. Forty-nine subjects with hamstring autograft ACLR (27 males; age 28.8 [standard deviation, 8.3] years) and 19 controls (12 males; 30.7 [4.6] years) participated. A sagittal plane musculoskeletal model was used to estimate PFJ contact pressure. A combined T1ρ/T2 magnetic resonance sequence was obtained. Assessments were performed preoperatively, at 6 months, 1, 2, and 3 years postoperatively in ACLR subjects and once for controls. Repeated Analysis of Variance (ANOVA) was used to compare peak PFJ contact pressure between ACLR and contralateral knees, and t-tests to compare with control knees. Statistical parametric mapping was used to evaluate the associations between PFJ contact pressure and cartilage relaxation concurrently and longitudinally. No changes in peak PFJ contact pressure were found within ACLR knees over 3 years (preoperative to 3 years, 0.36 [CI, -0.08, 0.81] MPa), but decreased over time in the contralateral knees (0.75 [0.32, 1.18] MPa). When compared to the controls, ACLR knees exhibited lower PFJ contact pressure at all time points (at baseline, -0.64 [-1.25, -0.03] MPa). Within ACLR knees, lower PFJ contact pressure at 6 months was associated with elevated T2 times (r=-0.47 to -0.49, p=0.021-0.025). Underloading of the PFJ following ACLR persists for up to 3 years and has concurrent and future consequences in cartilage health. The non-surgical knees exhibited normal contact pressure initially but decreased over time achieving limb symmetry.

Simultaneous Measurement of Patellofemoral Joint Kinematics and Contact Mechanics in Intact Knees: A Cadaveric Study.

ObjectivePatellofemoral kinematics and contact mechanics are important measurements for the assessment of patellofemoral joint (PFJ) problems. Simultaneously measuring PFJ contact pressures and kinematics is a challenging task. The purpose of this study was to simultaneously measure the kinematics and mean/peak contact pressures in the PFJs of cadaveric knees.MethodsThis was a comparative study performed on fresh cadaveric knees. The kinematic data was acquired for nine cadaveric knees using an optical tracking system. Data about the contact pressure and contact area in the PFJ was obtained at knee flexion angles of 0°, 30°, 60°, 90°, and 120° using a pressure sensor. Intraclass correlation coefficients (ICCs) and minimal detectable differences (MDDs) of six degrees of freedom (6 DOF) in the PFJs were calculated. ICCs and the MDDs of contact pressure, peak pressure, and contact area in the PFJs were also analyzed. We also compared the kinematics of the cadaveric knees before and after the insertion of the pressure sensor.ResultsAll ICC values of 6 DOF in the PFJs were found to be greater than or equal to 0.924. Regarding medial–lateral rotation, the patellar showed a simplified movement pattern that demonstrated progressive lateral rotation of 4.8° ± 3.4° at 120° of knee flexion. While for patellar tilting, the patella showed medial tilting that peaked at 7.2 ± 2.5° at 30° of knee flexion. Whereas no significant differences in PFJ kinematics were found between with and without the placement of the pressure sensor at all knee flexions (P > 0.05). Most of the ICC values for contact pressure, peak contact pressure, and contact area ranged from 0.8 to 0.9. The MDDs for rotational displacement were 0.9° and 0.6 mm for translational displacement. No statistical differences in patellar kinematics were found before and after the insertion of the pressure sensor.ConclusionsThe setup in the present study enables researchers to simultaneously and synchronously collect real‐time PFJ kinematics and tibiofemoral joint (TFJ) biomechanical kinematic data with high reliability. The low MDDs enabled the researchers to obtain an accurate interpretation of the kinematic and contact mechanics measurement using the experimental setting used in the present study.

Posterior Tibial Loading Results in Significant Increase of Peak Contact Pressure in the Patellofemoral Joint During Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

Background: Inappropriate posterior tibial loading and initial graft tension during anterior cruciate ligament (ACL) reconstruction may cause altered patellofemoral joint (PFJ) contact mechanics, potentially resulting in pain and joint degeneration. Hypothesis: PFJ contact pressure would increase with the increases in posterior tibial loading and graft tension during ACL reconstruction. Study Design: Controlled laboratory study. Methods: Nine fresh-frozen, nonpaired human cadaveric knees were tested in a customized jig from 0° to 120° of knee flexion. First, the knee was tested in the ACL-intact state. Second, reconstruction of the ACLs using different posterior tibial loadings and graft tensions were performed. The posterior tibial loading was evaluated at 2 levels: 33.5 and 67 N. Graft tension was assessed at 3 levels: low tension (20 N), medium tension (60 N), and high tension (80 N). Maximum values of peak contact pressure in the medial and lateral patellar facets were compared between ACL-intact and ACL-reconstructed knees. The PFJ kinematics between ACL-intact knees and ACL-reconstructed knees were compared during knee flexion at 30°, 60°, 90°, and 120°. Results: Reconstruction of ACLs with both low and high posterior tibial loading resulted in significant increases of peak contact pressure in the medial (range of differences, 0.46-0.92 MPa; P < .05) and lateral (range of differences, 0.51-0.83 MPa; P < .05) PFJ compared with the ACL-intact condition. However, no significant differences in PFJ kinematics were identified between ACL-reconstructed knees and ACL-intact knees. In ACL-reconstructed knees, it was found that a high posterior tibial loading resulted in high peak contact pressure on the medial patellar side (range of differences, 0.37-0.46 MPa; P < .05). No significant difference in peak contact pressure was observed among the differing graft tensions. Conclusion: In this cadaveric model, ACL reconstruction resulted in significant increases of peak contact pressure in the PFJ facet when compared with the ACL-intact condition. A high posterior tibial loading can lead to high medial PFJ peak contact pressure. Graft tension was found to not significantly affect PFJ contact pressure during ACL reconstruction. Clinical Relevance: An excessive posterior tibial loading during ACL reconstruction resulted in increased PFJ contact pressures at time of surgery. These data suggest that a low posterior tibial loading might be preferred during ACL reconstruction surgery to reduce the PFJ contact pressure close to that of the ACL-intact condition.

Effect of Vastus Medialis Loss on Rabbit Patellofemoral Joint Contact Pressure Distribution.

Vastus medialis (VM) weakness is thought to alter patellar tracking, thereby changing the loading of the patellofemoral joint (PFJ), resulting in patellofemoral pain. However, it is challenging to measure VM force and weakness in human studies, nor is it possible to measure the associated mechanical changes in the PFJ. To obtain fundamental insight into VM weakness and its effects on PFJ mechanics, the authors determined PFJ loading in the presence of experimentally simulated VM weakness. Skeletally mature New Zealand White rabbits were used (n = 6), and the vastus lateralis, VM, and rectus femoris were stimulated individually through 3 custom-built nerve cuff electrodes. Muscle torque and PFJ pressure distribution were measured while activating all muscles simultaneously, or when the vastus lateralis and rectus femoris were activated, while VM was not, to simulate a quadriceps muscle strength imbalance. For a given muscular joint torque, peak pressures were greater and joint contact areas were smaller when simulating VM weakness compared with the condition where all muscles were activated simultaneously. The results in the rabbit model support that VM weakness results in altered PFJ loading, which may cause patellofemoral pain, often associated with a strength imbalance of the knee extensor muscle group.

Patellofemoral Joint Contact Pressures: Current Concepts and Use in Patellar Instability Studies.

The patellofemoral joint is thought to be a common source for knee pain. Improper alignment and function of the patellofemoral joint can lead to abnormal contact pressures, which may explain patients' symptoms. In this review, the authors examine techniques for measuring patellofemoral joint contact pressures and summarize the relevant patellofemoral joint anatomy and contact pressures in normal knee kinematics. Finally, they discuss the results of studies investigating contact pressure changes in cases of patellar instability. This includes both reconstruction of the medial patellofemoral ligament and tibial tubercle osteotomy. [Orthopedics. 2019; 42(2):e172-e179.].

Effect of Anterolateral Complex Sectioning and Tenodesis on Patellar Kinematics and Patellofemoral Joint Contact Pressures

Background: Anterolateral complex injuries are becoming more recognized. While these are known to affect tibiofemoral mechanics, it is not known how they affect patellofemoral joint behavior. Purpose: To determine the effect of (1) sectioning the anterolateral complex and (2) performing a MacIntosh tenodesis under various conditions on patellofemoral contact mechanics and kinematics. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric knees were tested in a customized rig, with the femur fixed and tibia free to move, with optical tracking to record patellar kinematics and with thin pressure sensors to record patellofemoral contact pressures at 0°, 30°, 60°, and 90° of knee flexion. The quadriceps and iliotibial tract were loaded with 205 N throughout testing. Intact and anterolateral complex–sectioned states were tested, followed by 4 randomized tenodeses applying 20- and 80-N graft tension, each with the tibia in its neutral intact alignment or left free to rotate. Statistical analyses were undertaken with repeated measures analysis of variance, Bonferroni post hoc analysis, and paired samples t tests. Results: Patellar kinematics and contact pressures were not significantly altered after sectioning of the anterolateral complex (all: P > .05). Similarly, they were not significantly different from the intact knee in tenodeses performed when fixed tibial rotation was combined with 20- or 80-N graft tension (all: P > .05). However, grafts tensioned with 20 N and 80 N while the tibia was free hanging resulted in significant increases in lateral patellar tilt (P < .05), and significantly elevated lateral peak patellofemoral pressures (P < .05) were observed for 80 N. Conclusion: This work did not find that an anterolateral injury altered patellofemoral mechanics or kinematics, but adding a lateral tenodesis can elevate lateral contact pressures and induce lateral patellar tilting if the tibia is pulled into external rotation by the tenodesis. Although these in vitro changes were small and might not be relevant in a fully loaded knee, controlling the position of the tibia at graft fixation is effective in avoiding overconstraint at time zero in a lateral tenodesis. Clinical Relevance: Small changes in lateral patellar tilt and patellofemoral contact pressures were found at time zero with a MacIntosh tenodesis. These changes were eliminated when the tibia was held in neutral rotation at the time of graft fixation. The risk of overconstraint after a lateral tenodesis therefore seems low and in accordance with recent published reports.

Surgical Technique: Anatomic Medial Patellofemoral Ligament Retensioning Repair

The medial patellofemoral ligament (MPFL) and the MPFL/vastus medialis obliquus complex are essential for patellar stability. Insufficiency of the MPFL can lead to altered biomechanics and patellofemoral joint contact pressure, high recurrence rate, osteochondral lesions, compromised knee function, and patellofemoral osteoarthritis. Most frequently surgical reconstruction of the MPFL is performed to address patellar instability; however, open physis and donor site morbidity can be a concern. This Technical Note presents a surgical technique to identify the insufficient MPFL and describes in detail an anatomical retensioning repair of the MPFL to restore patellar stability.

The Effect of Anterolateral Complex Sectioning and a Macintosh Tenodesis on Patellofemoral Joint Contact Pressures and Kinematics

The Effect of Anterolateral Complex Sectioning and a Macintosh Tenodesis on Patellofemoral Joint Contact Pressures and Kinematics

Biomechanical Consequences of Excessive Patellar Distalization

Iatrogenic patellar baja can be a result of excessive tibial tubercle distalization or overtightented patellar tendon repair. Tubercle distalization is increasing in popularity for the treatment of recurrent patella instability. Clinically, patellar baja can present as a debilitating problem with motion loss, increased pain, and arthrosis progression. However, previous biomechanical studies have not shown an increase in patellofemoral joint contact pressures. The purpose of this study is to examine the patellofemoral contact pressure after a tibial tubercle distalization osteotomy. Ten matched pair fresh-frozen cadaveric knees were studied. Average Blackburne-Peel ratio of the native knees was 0.91. The knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. A straight tubercle distalization osteotomy of 1 cm was performed and fixed with screws, with and without a lateral release. Patellofemoral contact pressures were measured at 0°, 10°, 20°, 30°, 45°, 60°, and 90° of flexion using pressure-sensitive films on the medial and lateral trochlea. The contact force, area and pressure were measured at the following states: (1) native knee, (2) with distalization and (3) distalization with lateral release. Average Blackburne-Peel ratio after distalization was 0.64. Tibial tubercle distalization resulted in a six fold increase in mean contact pressures at 0° (0.15 versus 0.90 MPa, p<0.001), and a 55% increase at 10° of flexion (0.70 versus 1.09 MPa, p=0.02). After distalization, total contact area was significantly higher at 0° of flexion (17.7 mm2 versus 58.4 mm2, p=0.02). Lateral release after distalization did not significantly change contact pressure (p>0.21). Our results suggest that patellar baja, as a result of excessive patellar distalization, can cause increased patellofemoral contact pressures during early flexion.

The Effect of Tibial Tuberosity Medialization and Lateralization on Patellofemoral Joint Kinematics, Contact Mechanics, and Stability

Background: Tibial tuberosity (TT) transfer is a common procedure to treat patellofemoral instability in patients with elevated TT–trochlear groove (TG) distances. However, the effects of TT lateralization or medialization on patellar stability, kinematics, and contact mechanics remain unclear. Hypothesis: Progressive medialization and lateralization will have increasingly adverse effects on patellofemoral joint kinematics, contact mechanics, and stability. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film behind the patella and an optical tracking system. The intact knee was measured with and without a 10-N patellar lateral displacement load, and recordings were repeated after TT transfer of 5, 10, and 15 mm medially and laterally. Statistical analysis used repeated-measures analysis of variance, Bonferroni post hoc analysis, and Pearson correlations. Results: Tibial tuberosity lateralization significantly elevated lateral joint contact pressures, increased lateral patellar tracking, and reduced patellar stability (P < .048). There was a significant correlation between mean lateral contact pressure and the TT position (r = 0.810, P < .001) at 10°. Tibial tuberosity medialization reduced lateral contact pressures (P < .002) and did not elevate peak medial contact pressures (P > .11). Conclusion: Progressive TT lateralization elevated lateral contact pressures, increased lateral patellar tracking, and reduced patellar stability. Medial contact pressure and tracking did alter with progressive TT medialization, but the changes were smaller. Clinical Relevance: Lateral patellofemoral joint contact pressures increased with progressive lateralization of the TT; medialization of the TT reduced these effects, restoring patellar stability, and did not cause excessive peak pressures. These data provide a rationale for medial TT transfer surgery in patients with elevated TT-TG distances.

Biomechanics of hyperflexion and kneeling before and after total knee arthroplasty.

The capacity to perform certain activities is frequently compromised after total knee arthroplasty (TKA) due to a functional decline resulting from decreased range of motion and a diminished ability to kneel. In this manuscript, the current biomechanical understanding of hyperflexion and kneeling before and after TKA will be discussed. Patellofemoral and tibiofemoral joint contact area, contact pressure, and kinematics were evaluated in cadaveric studies using a Tekscan pressure measuring system and Microscribe. Testing was performed on intact knees and following cruciate retaining and posterior stabilized TKA at knee flexion angles of 90°, 105°, 120°, and 135°. Three loading conditions were used to simulate squatting, double stance kneeling, and single stance kneeling. Following TKA with double stance kneeling, patellofemoral contact areas did not increase significantly at high knee flexion angle (135°). Kneeling resulted in tibial posterior translation and external rotation at all flexion angles. Moving from double to single stance kneeling tended to increase pressures in the cruciate retaining group, but decreased pressures in the posterior stabilized group. The cruciate retaining group had significantly larger contact areas than the posterior stabilized group, although no significant differences in pressures were observed comparing the two TKA designs (p < 0.05). If greater than 120° of postoperative knee range of motion can be achieved following TKA, then kneeling may be performed with less risk in the patellofemoral joint than was previously believed to be the case. However, kneeling may increase the likelihood of damage to cartilage and menisci in intact knees and after TKA increases in tibiofemoral contact area and pressures may lead to polyethyelene wear if performed on a chronic, repetitive basis.

Sectioning the medial patellofemoral ligament alters patellofemoral joint kinematics and contact mechanics

Medial patellofemoral ligament (MPFL) disruption may alter patellofemoral joint (PFJ) kinematics and contact mechanics, potentially causing pain and joint degeneration. In this controlled laboratory study, we investigated the hypothesis that MPFL transection would change patellar tracking and PFJ contact pressures and increase the distance between the attachment points of the MPFL. Eight fresh frozen dissected cadaveric knees were mounted in a rig with the quadriceps and ITB loaded to 205 N. An optical tracking system measured joint kinematics, and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Length patterns of the distance between the femoral and patellar attachments of the MPFL were measured using a suture led to a linear displacement transducer. Measurements were repeated with the MPFL intact and following MPFL transection. A significant increase in the distance between the patellar and femoral MPFL attachment points was noted following transection (p < 0.05). MPFL transection resulted in significantly increased lateral translation and lateral tilt of the patella in early flexion (p < 0.05). Peak and mean medial PFJ contact pressures were significantly reduced and peak lateral contact pressures significantly elevated in early knee flexion following MPFL transection (p < 0.05). MPFL transection resulted in significant alterations to PFJ tracking and contact pressures, which may affect articular cartilage health.

Changes in patellofemoral joint contact pressures caused by vastus medialis muscle weakness

BackgroundPatellofemoral joint pain is a common knee disorder, but its underlying causes remain unknown. One proposed mechanism is an imbalance in force in the knee extensor muscles. Specifically, the vastus medialis and vastus lateralis are thought to play a crucial role in proper patellar tracking, and weakness in vastus medialis is thought to lead to a lateral shift in the patella causing increased contact pressures and pain. The purpose of this study was to create an animal model of vastus medialis weakness and to test the effect of this weakness on patellofemoral contact pressures. MethodsExperiments were performed using New Zealand white rabbits (mass 4.9–7.7kg, n=12). Loading of the patellofemoral joint was produced by femoral nerve stimulation of the knee extensor muscles. Knee extensor imbalance was produced by vastus medialis ablation. Fuji pressure sensitive film was used to record contact area, shape and pressures for maximal and sub-maximal, matched-force contractions at knee angles of 30°, 60°, and 90°. FindingsPatellofemoral peak pressures, average pressures, contact areas and contact shapes were the same across all loading conditions for matched-force contractions before and after elimination of vastus medialis. InterpretationWe conclude that vastus medialis weakness does not cause changes in patellofemoral contact pressures. Since the muscular and knee joint geometry in rabbits and humans is similar, we question the idea of vastus medialis weakness as a cause of patellar mal-tracking and patellofemoral joint pain.

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 ).

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.

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.

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.