The 6 Degrees of Freedom Kinematics of the Knee after Anterior Cruciate Ligament Deficiency

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.