Function and strain of the anterolateral ligament part I: biomechanical analysis.

Purpose: Because reconstruction of the anterior cruciate ligament (ACL) in a double-bundle technique did not solve the problem of persistent rotatory laxity after surgery, new potential answers to this issue are of great interest. One of these is an extraarticular stabilization based on the rediscovery of the anterolateral ligament (ALL). Knowledge about its biomechanical function and benchmark data for an optimal reconstruction remain lacking. Therefore, the purpose of this study was to assess the function of the ALL under passive motion, anterior tibial translation and tibial rotational moments.

Methods: Continuous passive motion (0°-120° flexion), ap-translation and static pivot shift tests were performed on eight cadaveric knees. The knees were measured in intact, ACL-resected (ACL) and ACL + ALL-resected (ALL) conditions. Ap-translation and static pivot shift under 134 N anterior shear load were determined at 0°, 30°, 60° and 90° flexion. Strain of the ALL was recorded in intact and ACL conditions.

Results: During continuous passive motion under unloaded conditions, no significant difference in internal rotation between ACL and ALL was observed. With an additional internal tibial torque of 1-4 Nm, internal rotation increased significantly between 60° and 120° after resection of the ALL (p ≤ 0.05). Anterior tibial translation was significantly higher at 30° in ALL (p = 0.01) and for a simulated pivot shift at 60° and 90° in ACL (p ≤ 0.01). The ALL was not strained under unloaded passive motion. Adding different internal tibial torques led to strain starting at 60° flexion (1 N m internal torque) and 15° flexion (4 N m internal torque) in intact ligaments. In ACL, significantly greater ALL strains under lower flexion angles were seen for each condition (p ≤ 0.05).

Conclusions: This study demonstrated the ALL to be without function under passive motion and with no influence on tibial rotation. On application of extrinsic loads, the ALL had a low but significant stabilizing effect against anterior tibial shear load at low flexion angles. For this reason, it can be concluded that the ALL is supporting the ACL against internal tibial loads to a minor degree. A relationship between the ALL and the pivot shift cannot be concluded. With these results ALL-reconstruction cannot be recommended at the moment without further biomechanical investigations.