Louis E. DeFrate

The 6 Degrees of Freedom Kinematics of the Knee After Anterior Cruciate Ligament Deficiency An In Vivo Imaging Analysis

Background Previous studies of knee joint function after anterior cruciate ligament deficiency have focused on measuring anterior-posterior translation and internal-external rotation. Few studies have measured the effects of anterior cruciate ligament deficiency on 6 degrees of freedom knee kinematics in vivo. Objective To measure the 6 degrees of freedom knee kinematics of patients with anterior cruciate ligament deficiency. Study Design Controlled laboratory study. Methods The knee joint kinematics of 8 patients with unilateral anterior cruciate ligament rupture was measured during a quasi-static lunge. Kinematics was measured from full extension to 90° of flexion using imaging and 3-dimensional modeling techniques. The healthy, contralateral knee of each patient served as a control. Results Anterior cruciate ligament deficiency caused a statistically significant anterior shift (approximately 3 mm) and internal rotation of the tibia (approximately 2°) at low flexion angles. However, ligament deficiency also caused a medial translation of the tibia (approximately 1 mm) between 15° and 90° of flexion. Conclusion The medial shift of the tibia after anterior cruciate ligament deficiency might alter contact stress distributions in the tibiofemoral cartilage near the medial tibial spine. These findings correlate with the observation that osteoarthritis in patients with anterior cruciate ligament injuries is likely to occur in this region. Clinical Relevance The data from this study suggest that future anterior cruciate ligament reconstruction techniques should reproduce not only anterior stability but also medial-lateral stability.

In Vivo Kinematics of the Knee After Anterior Cruciate Ligament Reconstruction A Clinical and Functional Evaluation

Background Recent follow-up studies have reported a high incidence of joint degeneration in patients with anterior cruciate ligament reconstruction. Abnormal kinematics after anterior cruciate ligament reconstruction have been thought to contribute to the degeneration. Hypothesis Anterior cruciate ligament reconstruction, which was designed to restore anterior knee laxity under anterior tibial loads, does not reproduce knee kinematics under in vivo physiological loading conditions. Study Design Controlled laboratory study. Methods Both knees of 7 patients with complete unilateral rupture of the anterior cruciate ligament were magnetic resonance imaged, and 3D models were constructed from these images. The anterior cruciate ligament of the injured knee was arthroscopically reconstructed using a bone–patellar tendon–bone autograft. Three months after surgery, the kinematics of the intact contralateral and reconstructed knees were measured using a dual-orthogonal fluoroscopic system while the subjects performed a single-legged weightbearing lunge. The anterior laxity of both knees was measured using a KT-1000 arthrometer. Results The anterior laxity of the reconstructed knee as measured with the arthrometer was similar to that of the intact contralateral knee. However, under weightbearing conditions, there was a statistically significant increase in anterior translation of the reconstructed knee compared with the intact knee at full extension (approximately 2.9 mm) and 15° (approximately 2.2 mm) of flexion. In addition, there was a mean increase in external tibial rotation of the anterior cruciate ligament–reconstructed knee beyond 30° of flexion (approximately 2° at 30° of flexion), although no statistical significance was detected. Conclusion The data demonstrate that although anterior laxity was restored during KT-1000 arthrometer testing, anterior cruciate ligament reconstruction did not restore normal knee kinematics under weightbearing loading conditions. Clinical Relevance Future reconstruction techniques should aim to restore function of the knee under physiological loading conditions.

Anterior Cruciate Ligament Deficiency Alters the In Vivo Motion of the Tibiofemoral Cartilage Contact Points in Both the Anteroposterior and Mediolateral Directions

BACKGROUND Quantifying the effects of anterior cruciate ligament deficiency on joint biomechanics is critical in order to better understand the mechanisms of joint degeneration in anterior cruciate ligament-deficient knees and to improve the surgical treatment of anterior cruciate ligament injuries. We investigated the changes in position of the in vivo tibiofemoral articular cartilage contact points in anterior cruciate ligament-deficient and intact contralateral knees with use of a newly developed dual orthogonal fluoroscopic and magnetic resonance imaging technique. METHODS Nine patients with an anterior cruciate ligament rupture in one knee and a normal contralateral knee were recruited. Magnetic resonance images were acquired for both the intact and anterior cruciate ligament-deficient knees to construct computer knee models of the surfaces of the bone and cartilage. Each patient performed a single-leg weight-bearing lunge as images were recorded with use of a dual fluoroscopic system at full extension and at 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. The in vivo knee position at each flexion angle was then reproduced with use of the knee models and fluoroscopic images. The contact points were defined as the centroids of the areas of intersection of the tibial and femoral articular cartilage surfaces. RESULTS The contact points moved not only in the anteroposterior direction but also in the mediolateral direction in both the anterior cruciate ligament-deficient and intact knees. In the anteroposterior direction, the contact points in the medial compartment of the tibia were more posterior in the anterior cruciate ligament-deficient knees than in the intact knees at full extension and 15 degrees of flexion (p < 0.05). No significant differences were observed with regard to the anteroposterior motion of the contact points in the lateral compartment of the tibia. In the mediolateral direction, there was a significant lateral shift of the contact points in the medial compartment of the tibia toward the medial tibial spine between full extension and 60 degrees of flexion (p < 0.05). The contact points in the lateral compartment of the tibia shifted laterally, away from the lateral tibial spine, at 15 degrees and 30 degrees of flexion (p < 0.05). CONCLUSIONS In the presence of anterior cruciate ligament injury, the contact points shift both posteriorly and laterally on the surface of the tibial plateau. In the medial compartment, the contact points shift toward the medial tibial spine, a region where degeneration is observed in patients with chronic anterior cruciate ligament injuries.

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.

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° 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.

Femoral Tunnel Placement During Anterior Cruciate Ligament Reconstruction: An In Vivo Imaging Analysis Comparing Transtibial and 2-Incision Tibial Tunnel–Independent Techniques

Background Recent studies have questioned the ability of the transtibial technique to place the anterior cruciate ligament graft within the footprint of the anterior cruciate ligament on the femur. There are limited data directly comparing the abilities of transtibial and tibial tunnel—independent techniques to place the graft anatomically at the femoral attachment site of the anterior cruciate ligament in patients. Hypothesis Because placement with the tibial tunnel–independent technique is unconstrained by the tibial tunnel, it would allow for more anatomic tunnel placement compared with the transtibial technique. Study Design Cross-sectional study; Level of evidence, 3. Methods High-resolution, multiplanar magnetic resonance imaging and advanced 3-dimensional modeling techniques were used to measure in vivo femoral tunnel placement in 8 patients with the transtibial technique and 8 patients with a tibial tunnel–independent technique. Femoral tunnel placement in 3 dimensions was measured relative to the center of the native anterior cruciate ligament attachment on the intact contralateral knee. Results The tibial tunnel–independent technique placed the graft closer to the center of the native anterior cruciate ligament attachment compared with the transtibial technique. The transtibial technique placed the tunnel center an average of 9 mm from the center of the anterior cruciate ligament attachment, compared with 3 mm for the tibial tunnel–independent technique. The transtibial technique resulted in a more anterior and superior placement of the tunnel compared with the tibial tunnel– independent technique. Conclusion The tibial tunnel–independent technique allowed for more anatomic femoral tunnel placement compared with the transtibial technique.

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° 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.

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 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.

Increased tibiofemoral cartilage contact deformation in patients with anterior cruciate ligament deficiency

OBJECTIVE To investigate the in vivo cartilage contact biomechanics of the tibiofemoral joint following anterior cruciate ligament (ACL) injury. METHODS Eight patients with an isolated ACL injury in 1 knee, with the contralateral side intact, participated in the study. Both knees were imaged using a specific magnetic resonance sequence to create 3-dimensional models of knee bone and cartilage. Next, each patient performed a lunge motion from 0 degrees to 90 degrees of flexion as images were recorded with a dual fluoroscopic system. The three-dimensional knee models and fluoroscopic images were used to reproduce the in vivo knee position at each flexion angle. With this series of knee models, the location of the tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation were compared between intact and ACL-deficient knees. RESULTS Rupture of the ACL changed the cartilage contact biomechanics between 0 degrees and 60 degrees of flexion in the medial compartment of the knee. Compared with the contralateral knee, the location of peak cartilage contact deformation on the tibial plateaus was more posterior and lateral, the contact area was smaller, the average cartilage thickness at the tibial cartilage contact area was thinner, and the resultant magnitude of cartilage contact deformation was increased. Similar changes were observed in the lateral compartment, with increased cartilage contact deformation from 0 degrees to 30 degrees of knee flexion in the presence of ACL deficiency. CONCLUSION ACL deficiency alters the in vivo cartilage contact biomechanics by shifting the contact location to smaller regions of thinner cartilage and by increasing the magnitude of the cartilage contact deformation.

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° 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°). Eighteen fresh‐frozen human knee specimens were tested on a robotic testing system from full extension to 150° 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° 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°, 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° (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° in response to each of the loads.