Comparison of the ACL and ACL graft forces before and after ACL reconstruction: an in-vitro robotic investigation

BACKGROUND

Long-term follow-up studies have indicated that there is an increased incidence of arthrosis following anterior cruciate ligament (ACL) reconstruction, suggesting that the reconstruction may not reproduce intact ACL biomechanics. We studied not only the magnitude but also the orientation of the ACL and ACL graft forces.

METHODS

10 knee specimens were tested on a robotic testing system with the ACL intact, deficient, and reconstructed (using a bone-patella tendon-bone graft). The magnitude and orientation of the ACL and ACL graft forces were determined under an anterior tibial load of 130 N at full extension, and 15, 30, 60, and 90 degrees of flexion. Orientation was described using elevation angle (the angle formed with the tibial plateau in the sagittal plane) and deviation angle (the angle formed with respect to the anteroposterior direction in the transverse plane).

RESULTS

ACL reconstruction restored anterior tibial translation to within 2.6 mm of that of the intact knee under the 130-N anterior load. Average internal tibial rotation was reduced after ACL reconstruction at all flexion angles. The force vector of the ACL graft was significantly different from the ACL force vector. The average values of the elevation and deviation angles of the ACL graft forces were higher than that of the intact ACL at all flexion angles.

INTERPRETATION

Contemporary single bundle ACL reconstruction restores anterior tibial translation under anterior tibial load with different forces (both magnitude and orientation) in the graft compared to the intact ACL. Such graft function might alter knee kinematics in other degrees of freedom and could overly constrain the tibial rotation. An anatomic ACL reconstruction should reproduce the magnitude and orientation of the intact ACL force vector, so that the 6-degrees-of-freedom knee kinematics and joint reaction forces can be restored.

Erratum to "The change in length of the medial and lateral collateral ligaments during in vivo knee flexion"

The collateral ligaments of the knee are important in maintaining knee stability. However, little data has been reported on the in vivo function of the collateral ligaments. The objective of this study was to investigate the change in length of different fiber bundles of the medial collateral ligament (MCL), deep fibers of the MCL (DMCL) and the lateral collateral ligament (LCL) during in vivo knee flexion. The knees of five healthy subjects were scanned using magnetic resonance imaging. These images were used to create three-dimensional models of the tibia and femur, including the insertions of the collateral ligaments. The MCL, DMCL, and LCL were each divided into three equal portions: an anterior bundle, a middle bundle and a posterior bundle. Next, the subjects were imaged from two orthogonal directions using fluoroscopy while performing a quasi-static lunge from 0 degrees to 90 degrees of flexion. The models and fluoroscopic images were then used to reproduce the in vivo motion of the knee. From these models, the length of each bundle of each ligament was measured as a function of flexion. The length of the anterior bundle of the MCL did not change significantly with flexion. The length of the posterior bundle of the MCL consistently decreased with flexion (p < 0.05). The change in length of the DMCL with flexion was similar to the trend observed for the MCL. The length of the anterior bundle of the LCL increased with flexion and the length of the posterior bundle decreased with flexion. These data indicate that the collateral ligaments do not elongate uniformly as the knee is flexed, with different bundles becoming taut and slack. These data may help to provide a better understanding of the in vivo function of the collateral ligaments and be used to improve surgical reconstructions of the collateral ligaments. Furthermore, the data suggest that the different roles of various portions of the collateral ligaments along the flexion path should be considered before releasing the collateral ligaments during knee arthroplasty.

The change in length of the medial and lateral collateral ligaments during in vivo knee flexion

The collateral ligaments of the knee are important in maintaining knee stability. However, little data has been reported on the in vivo function of the collateral ligaments. The objective of this study was to investigate the change in length of different fiber bundles of the medial collateral ligament (MCL), deep fibers of the MCL (DMCL) and the lateral collateral ligament (LCL) during in vivo knee flexion. The knees of five healthy subjects were scanned using magnetic resonance imaging. These images were used to create three-dimensional models of the tibia and femur, including the insertions of the collateral ligaments. The MCL, DMCL, and LCL were each divided into three equal portions: an anterior bundle, a middle bundle and a posterior bundle. Next, the subjects were imaged from two orthogonal directions using fluoroscopy while performing a quasi-static lunge for 0 degree to 90 degrees of flexion. The models and fluoroscopic images were then used to reproduce the in vivo motion of the knee. From these models, the length of each bundle of each ligament was measured as a function of flexion. The length of the anterior bundle of the MCL did not change significantly with flexion. The length of the posterior bundle of the MCL consistently decreased with flexion (p less than 0.05). The changes in deformation of the DMCL and LCL as a function of flexion were similar to each other. The length of the anterior bundles increased with flexion and the length of the posterior bundles decreased with flexion. These data indicate that the collateral ligaments do not elongate uniformly as the knee is flexed, with different bundles becoming taut and slack. These data may help to provide a better understanding of the in vivo function of the collateral ligaments and be used to improve surgical reconstruction of the collateral ligaments. Furthermore, the data suggest that the different roles of various portions of the collateral ligaments along the flexion path should be considered before releasing the collateral ligaments during knee arthroplasty.

In vivo tibiofemoral contact analysis using 3D MRI-based knee models

This paper quantified the motion of the tibiofemoral contact points during in vivo weight bearing flexion using MRI- based 3D knee models and two orthogonal fluoroscopic images. The contact points on the medial and lateral tibial plateau were calculated by finding the centroid of the intersection of the tibial and femoral cartilage layers and by using the bony geometry alone. Our results indicate that the medial femoral condyle remains in the central portion of the tibial plateau and the lateral condyle translates posteriorly with increasing flexion. Using the bony contact model increased the total translation of the medial and lateral condyles by 250 and 55%, respectively, compared to the cartilage contact model. These results suggest that using the bony geometry alone may not accurately represent the articular surfaces of the knee. Articular cartilage geometry may have to be used to accurately quantify tibiofemoral contact.

The cartilage thickness distribution in the tibiofemoral joint and its correlation with cartilage-to-cartilage contact

OBJECTIVE

The objective of this study was to investigate whether regions of cartilage in the tibiofemoral joint where cartilage-to-cartilage contact occurred was thicker than other regions.

DESIGN

In vivo human subjects.

BACKGROUND

The thickness of the cartilage in the knee has been investigated in various studies. However, the factors that influence the thickness distribution within the joint remain unclear.

METHODS

Six healthy living knees (5 male, 1 female, average age = 27) were scanned using magnetic resonance imaging. Three-dimensional models of the tibial and femoral cartilage layers were created. The cartilage thickness distribution was compared between regions where cartilage-to-cartilage contact was observed during in vivo weightbearing flexion and regions with no contact.

RESULTS

The regions with cartilage-to-cartilage contact were significantly thicker than the regions without cartilage-to-cartilage contact (P < 0.05). On the medial condyle, the cartilage-to-cartilage contact regions were up to 40% thicker than regions with no contact. On the lateral femoral condyle, the maximum difference between these regions was 20%. On the tibial plateau, the maximal differences between regions with and without cartilage-to-cartilage contact were found to be 40% on the medial side and 50% on the lateral side.

CONCLUSIONS

The data suggested that in normal knees, the cartilage was thicker in regions where cartilage-to-cartilage contact was present. Future studies should investigate the effects of in vivo loading on cartilage maintenance and growth. Relevance Injuries that alter knee kinematics might load regions of the joint where the cartilage is thinner. This might alter the stress distributions within the cartilage.

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 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees 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 degrees 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 degrees-30 degrees) under muscle loads (P < .05). At 30 degrees of flexion, under muscle loads, the tibia of the reconstructed knee was 1.9 degrees 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.

In vivo articular cartilage contact kinematics of the knee: an investigation using dual-orthogonal fluoroscopy and magnetic resonance image-based computer models

BACKGROUND

Quantifying the in vivo cartilage contact mechanics of the knee may improve our understanding of the mechanisms of joint degeneration and may therefore improve the surgical repair of the joint after injury.

OBJECTIVE

To measure tibiofemoral articular cartilage contact kinematics during in vivo knee flexion.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Orthogonal fluoroscopic images and magnetic resonance image-based computer models were used to measure the motion of the cartilage contact points during a quasi-static lunge in 5 human subjects.

RESULTS

On the tibial plateau, the contact point moved in both the anteroposterior and the mediolateral directions during knee flexion. On the medial tibial plateau, flexion angle did not have a statistically significant effect on the location of the contact points. The total translation of the contact point from full extension to 90 degrees of flexion was less than 1.5 mm in the anteroposterior direction, whereas the translation in the mediolateral direction was more than 5.0 mm. In the anteroposterior direction, the contact points were centered on the medial tibial plateau. On the lateral tibial plateau, there was a statistically significant difference between the location of the contact point at full extension and the locations of the contact points at other flexion angles in the anteroposterior direction. No significant difference was detected between the location of the contact points at other flexion angles. The overall range of contact point motion was about 9.0 mm in the anteroposterior direction and about 4.0 mm in the mediolateral direction. The contact points were primarily on the inner half of the medial and lateral tibial plateaus (the half closest to the tibial spine). The contact points on both femoral condyles were also on the inner half of the condyles (near the condylar notch).

CONCLUSIONS

The tibiofemoral contact points move in 3 dimensions during weightbearing knee flexion. The medial tibiofemoral contact points remained within the central portion of the tibial plateau in the anteroposterior direction. Both the medial and lateral tibiofemoral contact points were located on the inner portions of the tibial plateau and femoral condyles (close to the tibial spine), indicating that the tibial spine may play an important role in knee stability.

CLINICAL RELEVANCE

The results of this study may provide important insight as to the mechanisms contributing to the development of osteoarthritis after ligament injuries.

In vivo function of the posterior cruciate ligament during weightbearing knee flexion

BACKGROUND

Current knowledge of posterior cruciate ligament function is mainly based on in vitro cadaveric studies. There are few studies on the in vivo function of the posterior cruciate ligament. The objective of the study was to quantify the multidimensional deformation of the posterior cruciate ligament.

HYPOTHESIS

During in vivo weightbearing flexion, the posterior cruciate ligament undergoes complex 3-dimensional deformations, including elongation, twist, and changes in orientation.

STUDY DESIGN

In vivo biomechanical study.

METHODS

Magnetic resonance images of 5 human knees were used to create 3-dimensional computer models of each subject's knee, including the insertion areas of the posterior cruciate ligament. Orthogonal fluoroscopic images of each subject's knee were acquired as a quasi-static lunge was performed. The images and computer models were used to reproduce the in vivo motion of the knee. The relative motion of the femoral and tibial insertions was described in terms of elongation, twist, elevation (the angle between the tibial plateau and posterior cruciate ligament, measured in the sagittal plane), and deviation (mediolateral orientation, measured in plane of tibial plateau).

RESULTS

The length of the posterior cruciate ligament increased significantly with increasing flexion. It twisted almost 80 degrees as the knee flexed from 0 degrees to 90 degrees . The elevation angle remained relatively constant at 50 degrees . The deviation angle was medially oriented by 20 degrees at full extension, then decreased to approximately 10 degrees at 30 degrees through 90 degrees of flexion.

CONCLUSION

The posterior cruciate ligament undergoes a complex twisting motion as it elongates with flexion.

CLINICAL RELEVANCE

During reconstruction, the tunnels and graft may need to be placed such that the multidimensional deformation of the intact posterior cruciate ligament is reproduced.

The effect of posterior knee capsulotomy on posterior tibial translation during posterior cruciate ligament tibial inlay reconstruction

PURPOSE

To measure the biomechanical effect of the surgical capsulotomy made during a posterior cruciate ligament reconstruction using the tibial inlay technique.

HYPOTHESIS

The posterior capsule contributes to posterior tibial stability.

STUDY DESIGN

Controlled laboratory experiment.

METHODS

Six knee specimens were tested on a robotic testing system from 0 degrees to 120 degrees of flexion with the posterior cruciate ligament intact and resected and with a posterior capsulotomy identical to that performed during tibial inlay reconstruction (sham surgery). A longitudinal incision with medial and lateral soft tissue stripping sufficient to mount an inlay bone block and pass an Achilles tendon graft into the knee was made in the oblique popliteal ligament, muscle belly of the popliteus, and posterior capsule. The posterior tibial translation was measured under a posterior tibial load of 130 N at multiple flexion angles.

RESULTS

Capsulotomy increased the posterior laxity compared with the posterior cruciate ligament-resected knee at every flexion angle. An additional 0.97 +/- 0.48 mm, 0.65 +/- 0.47 mm, 0.56 +/- 0.33 mm, 0.48 +/- 0.38 mm, and 0.94 +/- 0.60 mm of posterior laxity was recorded at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion, respectively. These values were all statistically significant (P < .001).

CONCLUSIONS

A posterior capsulotomy alone, without associated posteromedial or posterolateral disruption, produces additional posterior tibial translation in vitro compared with posterior cruciate ligament-deficient knee with intact capsule.

CLINICAL RELEVANCE

Damage to the posterior capsule may contribute to the residual posterior laxity noted clinically after posterior cruciate ligament reconstruction.

In vivo elongation of the anterior cruciate ligament and posterior cruciate ligament during knee flexion

BACKGROUND

Most knowledge regarding cruciate ligament function is based on in vitro experiments.

PURPOSE

To investigate the in vivo elongation of the functional bundles of the anterior cruciate ligament and posterior cruciate ligament during weightbearing flexion.

HYPOTHESIS

The biomechanical role of functional bundles of the anterior cruciate ligament and posterior cruciate ligament under in vivo loading is different from that measured in cadavers.

STUDY DESIGN

In vivo biomechanical study.

METHODS

Elongation of the anterior cruciate ligament and posterior cruciate ligament was measured during a quasi-static lunge using imaging and 3-dimensional computer-modeling techniques.

RESULTS

The anterior-medial bundle of the anterior cruciate ligament had a relatively constant length from full extension to 90 degrees of flexion. The posterior-lateral bundle of the anterior cruciate ligament decreased in length with flexion. Both bundles of the posterior cruciate ligament had increased lengths with flexion.

CONCLUSION

The data did not demonstrate the reciprocal function of the 2 bundles of the anterior cruciate ligament or the posterior cruciate ligament with flexion observed in previous studies. Instead, the data suggest that there is a reciprocal function between the anterior cruciate ligament and posterior cruciate ligament with flexion. The anterior cruciate ligament plays a more important role in low-flexion angles, whereas the posterior cruciate ligament plays a more important role in high flexion.

CLINICAL RELEVANCE

Understanding the biomechanical role of the knee ligaments in vivo is essential to reproduce the structural behavior of the ligament after injury (especially for 2-bundle reconstructions) and thus improve surgical outcomes.

Feasibility of using orthogonal fluoroscopic images to measure in vivo joint kinematics

Accurately determining in vivo knee kinematics is still a challenge in biomedical engineering. This paper presents an imaging technique using two orthogonal images to measure 6 degree-of-freedom (DOF) knee kinematics during weight-bearing flexion. Using this technique, orthogonal images of the knee were captured using a 3-D fluoroscope at different flexion angles during weight-bearing flexion. The two orthogonal images uniquely characterized the knee position at the specific flexion angle. A virtual fluoroscope was then created in solid modeling software and was used to reproduce the relative positions of the orthogonal images and X-ray sources of the 3-D fluoroscope during the actual imaging procedure. Two virtual cameras in the software were used to represent the X-ray sources. The 3-D computer model of the knee was then introduced into the virtual fluoroscope and was projected onto the orthogonal images by the two virtual cameras. By matching the projections of the knee model to the orthogonal images of the knee obtained during weight-bearing flexion, the knee kinematics in 6 DOF were determined. Using regularly shaped objects with known positions and orientations, this technique was shown to have an accuracy of 0.1 mm and 0.1 deg in determining the positions and orientations of the objects, respectively.

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 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees 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 degrees of flexion and posterior translation and external rotation of the tibia beyond 60 degrees. 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 degrees of flexion, the hamstrings co-contraction increased the posterior tibial translation by approximately 2.8 mm and external tibial rotation by approximately 3.6 degrees. 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 length on the structural properties of an Achilles tendon graft as used in posterior cruciate ligament reconstruction

BACKGROUND

The clinical outcomes of posterior cruciate ligament reconstruction are varied. No previous studies have investigated the effect of graft length on the structural properties of the graft.

HYPOTHESIS

Graft length significantly affects the structural properties of posterior cruciate ligament grafts.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight Achilles tendon grafts were tested under tensile loads up to 400 N at 3 different lengths: long (75 mm), medium (48 mm), and short (34 mm). These 3 lengths represent midtunnel fixation, inlay fixation, and fixation near the ligament insertions.

RESULTS

Shortening the graft from both long to medium and from medium to short increased the stiffness by approximately 25%. Long and medium grafts displaced significantly more than medium and short grafts, respectively.

CONCLUSION

The effective length of a graft, which is determined by where it is fixed, should be considered an important variable in posterior cruciate ligament reconstruction.

Effect of the posterior cruciate ligament on posterior stability of the knee in high flexion

Most biomechanical studies of the knee have focused on knee flexion angles between 0 degrees and 120 degrees. The posterior cruciate ligament (PCL) has been shown to constrain posterior laxity of the knee in this range of flexion. However, little is known about PCL function in higher flexion angles (greater than 120 degrees ). This in vitro study examined knee kinematics before and after cutting the PCL at high flexion under a posterior tibial load and various muscle loads. The results demonstrated that although the PCL plays an important role in constraining posterior tibial translation at low flexion angles, the PCL had little effect in constraining tibial translation at 150 degrees of flexion under the applied loads.

In situ forces of the anterior and posterior cruciate ligaments in high knee flexion: an in vitro investigation

The function of the anterior and posterior cruciate ligaments (ACL and PCL) in the first 120 degrees of flexion has been reported extensively, but little is known of their behavior at higher flexion angles. The aim of this investigation was to study the effects of muscle loads on the in situ forces in both ligaments at high knee flexion (>120 degrees). Eighteen fresh-frozen human knee specimens were tested on a robotic testing system from full extension to 150 degrees of flexion in response to quadriceps (400 N), hamstrings (200 N), and combined quadriceps and hamstrings (400 N/200 N) loads. The in situ forces in the ACL and PCL were measured using the principle of superposition. The force in the ACL peaked at 30 degrees of flexion (71.7 +/- 27.9 N in response to the quadriceps load, 52.3 +/- 24.4 N in response to the combined muscle load, 32.3 +/- 20.9 N in response to the hamstrings load). At 150 degrees, the ACL force was approximately 30 N in response to the quadriceps load and 20 N in response to the combined muscle load and isolated hamstring load. The PCL force peaked at 90 degrees (34.0 +/- 15.3 N in response to the quadriceps load, 88.6 +/- 23.7 N in response to the combined muscle load, 99.8 +/- 24.0 N in response to the hamstrings load) and decreased to around 35 N at 150 degrees in response to each of the loads. These results demonstrate that the ACL and PCL carried significantly less load at high flexion in response to the simulated muscle loads compared to the peak loads they carried in response to the same muscle loads at other flexion angles. The data could provide a reference point for the investigation of non-weight bearing flexion and extension knee exercises in high flexion. Furthermore, these data could be useful in designing total knee implants to achieve high flexion.

Kinematics of the knee at high flexion angles: an in vitro investigation

Restoration of knee function after total knee, meniscus, or cruciate ligament surgery requires an understanding of knee behavior throughout the entire range of knee motion. However, little data are available regarding knee kinematics and kinetics at flexion angles greater than 120 degrees (high flexion). In this study, 13 cadaveric human knee specimens were tested using an in vitro robotic experimental setup. Tibial anteroposterior translation and internal-external rotation were measured along the passive path and under simulated muscle loading from full extension to 150 degrees of flexion. Anterior tibial translation was observed in the unloaded passive path throughout, with a peak of 31.2+/-13.2 mm at 150 degrees. Internal tibial rotation increased with flexion to 150 degrees on the passive path to a maximum of 11.1+/-6.7 degrees. The simulated muscle loads affected tibial translation and rotation between full extension and 120 degrees of knee flexion. Interestingly, at high flexion, the application of muscle loads had little effect on tibial translation and rotation when compared to values at 120 degrees. The kinematic behavior of the knee at 150 degrees was markedly different from that measured at other flexion angles. Muscle loads appear to play a minimal role in influencing tibial translation and rotation at maximal flexion. The results imply that the knee is highly constrained at high flexion, which could be due in part to compression of the posterior soft tissues (posterior capsule, menisci, muscle, fat, and skin) between the tibia and the femur.

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 degrees, 60 degrees, 90 degrees, and 120 degrees 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 biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads

BACKGROUND

The effectiveness of posterior cruciate ligament reconstruction in restoring normal kinematics under physiologic loading is unknown.

HYPOTHESIS

Posterior cruciate ligament reconstruction does not restore normal knee kinematics under muscle loading.

STUDY DESIGN

In vitro biomechanical study.

METHODS

Kinematics of knees with an intact, resected, and reconstructed posterior cruciate ligament were measured by a robotic testing system under simulated muscle loads. Anteroposterior tibial translation and internal-external tibial rotation were measured at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under posterior drawer loading, quadriceps muscle loading, and combined quadriceps and hamstring muscle loading.

RESULTS

Reconstruction reduced the additional posterior tibial translation caused by ligament deficiency at all flexion angles tested under posterior drawer loading. Ligament deficiency increased external rotation and posterior translation at angles higher than 60 degrees of flexion when simulated muscle loading was applied. Posterior cruciate ligament reconstruction reduced the posterior translation and external rotation observed in posterior cruciate ligament-deficient knees at higher flexion angles, but differences were not significant.

CONCLUSION

Under physiologic loading conditions, posterior cruciate ligament reconstruction does not restore six degree of freedom knee kinematics.

CLINICAL RELEVANCE

Abnormal knee kinematics may lead to development of long-term knee arthrosis.

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 degrees 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 degrees). Resection of the PCL did not significantly alter anterior tibial translation. At high flexion angles (beyond 60 degrees), 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 anteroposterior 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.

A minimally invasive method for the determination of force in the interosseous ligament

OBJECTIVE

The objective was to develop and utilize a minimally invasive testing system to determine the force in the interosseous ligament under axial compressive loads across the range of motion of the human forearm.

DESIGN

Eleven fresh frozen human cadaveric forearms were used (51-72 years).

BACKGROUND

Current studies investigating interosseous ligament forces altered the structure of the forearm by implanting load cells into the radius and ulna. This may affect load transfer through the forearm. Little information was available on interosseous ligament function over the entire flexion range of the elbow.

METHODS

A robotic joint testing system was used to apply a 100 N compressive load to the forearm and measure the resulting displacement. Each forearm was tested with no disruption of the bones and soft tissues of the forearm. The principle of superposition was used to calculate the forces in the interosseous ligament and was indirectly validated using fluoroscopy.

RESULTS

The force in the interosseous ligament ranged from a minimum of 8 N in neutral forearm rotation at full extension to a maximum of 43 N in supination at 30 degrees of flexion. The largest force was found in supination at all flexion angles.

CONCLUSIONS

The interosseous ligament is an important structure in the stability of the forearm. The force in the interosseous ligament depends on the elbow flexion angle and forearm rotation.

RELEVANCE

This study suggests that radial head fractures are best treated with the forearm in supination, since the interosseous ligament takes the largest load in this position. Complex injuries which have a poor prognosis, may require interosseous ligament reconstruction to improve clinical outcomes.