Anterolaterale Rotationsinstabilität: Vorderes Kreuzband, anterolateraler Komplex oder lateraler Meniskus?

Background: Injuries of the anterior cruciate ligament (ACL), Kaplan fibers (KF), anterolateral capsule/anterolateral ligament (C/ALL), and lateral meniscus posterior root (LMPR) have been separately linked to anterolateral instability. The aim was to investigate the importance of these structures for knee stability. Methods: In this study 10 fresh-frozen human knees were robotically tested from 0° to 90° of flexion. An anteroposterior force of 88 N, an internal-external rotational torque of 5 N/m, and a valgus-varus torque of 8 N/m were applied and the kinematics of the intact knee were recorded. Another 10 knees were tested in a kinematics rig with optical tracking to measure knee laxity after sequentially severing the structures over 0°–110° of flexion. Results: The ACL was the primary restraint for anterior tibial translation (ATT); other structures were insignificant (< 10%). The KF and C/ALL resisted internal rotation (IR), achieving 44 ± 23% (p < 0.01) and 14 ± 13% (p < 0.05) at 90°, respectively. The LMPR resisted valgus rotation but not IR. The ATT increased from 70° to 100° (p < 0.05) after ACL insufficiency (p < 0.001) and after severing the lateral structures. The pivot-shift maneuver increased anterolateral rotational instability after ACL transection from 0° to 40° (p < 0.05) and further after severing the lateral structures from 0° to 100° (p < 0.01). Conclusion: The anterolateral complex acts as a functional unit to provide rotational stability. The ACL is the primary stabilizer for ATT. The KFs are the most important IR restraint above 30° of flexion. A combined KF and C/ALL injury substantially increased anterolateral rotational instability, while an isolated injury of the KF or C/ALL did not. An LMPR insufficiency did not cause significant instability with an intact ACL.