The in vivo assessment of tibial motion in the transverse plane in anterior cruciate ligament-reconstructed knees

Twenty-one knees with acutely injured anterior cruciate ligaments were reco nstructed with patellar tendon autografts. Eight of the knees had concomita nt medial ligament injuries that were not addressed surgically. Follow-up e valuation (average, 25 months) included computed tomography measurements to analyze transverse-plane laxity in both translation and rotation. These me asurements were performed with the patient's leg in a load cell device that stabilizes the distal femur and applies known anterior translational force to the proximal tibia at approximately 20 degrees of flexion. A torque app aratus was used to apply internal and external rotational torque to the leg . Images of the tibial plateau in neutral, internal, and external rotation were performed, with and without an anterior translational force. Both knee s of each patient were tested and categorized as group I (anterior cruciate ligament-reconstructed) or group II (uninjured). Translation as measured b y computed tomography averaged 1 mm side-to-side difference. Internal rotat ion averaged 8.7 degrees in group I knees and 10.8 degrees in group II knee s. External rotation averaged 9.1 degrees in group I knees and 7.4 degrees in group II knees. The eight knees with concomitant medial ligament injurie s were analyzed separately; external rotation without anterior load in grou p I was 9.5 degrees, compared with 5 degrees in group II. This difference w as significant (P < 0.01).