Background: Some surgeons presently reconstruct both the anteromedial and posterolateral bundles of the anterior cruciate ligament. The purposes of this study were to measure the abilities of single-bundle and anatomic double-bundle reconstructions to restore anteroposterior laxities and rotational kinematics to intact knee levels and to compare graft forces in reconstructed knees with forces in the native anterior cruciate ligament for the same loading conditions.
Methods: Native anterior cruciate ligament force and tibial rotations were recorded during passive knee extension tests with and without applied tibial loads. The anteromedial and posterolateral bundles were reconstructed with patellar tendon tissue sized to fit tightly within 7-mm femoral tunnels. Testing was repeated with the anteromedial graft alone (single bundle), tensioned to restore anteroposterior laxity at 30° of flexion, and with double-bundle grafts. For double-bundle reconstructions, the anteromedial graft was first tensioned as above and then the posterolateral graft was tensioned with use of one of four protocols: posterolateral tension = anteromedial tension at 10° (DB1), posterolateral tension = anteromedial tension at 30° (DB2), posterolateral tension = (anteromedial tension + 30 N) at 10° (DB3), and posterolateral tension = (anteromedial tension + 30 N) at 30° (DB4).
Results: The posterolateral graft underwent a greater length change than the anteromedial graft between 0° and 90°. This difference in elongation patterns produced high forces in the posterolateral graft at 0° when both grafts were tensioned and fixed at 30°. The mean laxities for single-bundle reconstructions were within 1.1 mm of those of the intact knee between 0° and 90°; the mean graft force at 0° was 76 N. The mean laxities for DB4 reconstructions were from 0.9 to 2.8 mm less than those of the intact knee, and the mean graft force at 0° was 264 N. Coupled internal tibial rotations from valgus moment were normal with the single-bundle graft. Internal rotations from tibial torque were approximately 2° to 4° greater than normal with a single-bundle graft. DB3 and DB4 reconstructions overcorrected the coupled tibial rotations from valgus moment and restored tibial rotations from internal torque to normal from 0° to 45°. The graft forces from tibial torque and valgus moment were normal with the single-bundle graft. The mean double-bundle graft forces at 0° were 57 N to 143 N and 34 N to 171 N greater than normal for internal torque and valgus moment, respectively.
Conclusions: The single-bundle reconstruction produced graft forces, knee laxities, and coupled tibial rotations that were closest to normal. Adding a posterolateral graft to an anteromedial graft tended to reduce laxities and tibial rotations, but the reductions were accompanied by markedly higher forces in the posterolateral graft near 0° that occasionally caused it to fail during tests with internal torque or anterior tibial force.
Clinical Relevance: The relatively small improvements in anteroposterior laxities and tibial rotations from adding a posterolateral graft may not be worth the high graft forces necessary to achieve them. The high forces in the posterolateral graft recorded during our tests present cause for concern and may help to explain the posterolateral graft ruptures that have been reported clinically. The need for a double-bundle reconstruction to restore anteroposterior laxity and rotatory stability is questioned.