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.

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.