Function and strain of the anterolateral ligament part II: reconstruction

Anterolateral rotatory instability (ALRI) may result from isolated ruptures of the anterior cruciate ligament (ACL) or combined lesions with the anterolateral ligament (ALL). Biomechanical studies have demonstrated that the ALL contributes to the overall rotational stability of the knee. The purpose of this study was to investigate the biomechanical function of anatomic ALL reconstruction (ALL_rec) in the setting of a combined ACL and ALL injury and reconstruction. The hypothesis was that combined ACL reconstruction (ACL_rec) and ALL_rec (ACL/ALL_rec) significantly reduces internal rotation and shows load sharing between both reconstructions compared with isolated ACL_rec.

Eight fresh-frozen cadaveric knees were evaluated using a six degrees of freedom knee simulator. Continuous passive motion and external loads were tested. Kinematic differences between ACL_rec and combined ACL/ALL_rec were compared. Additionally, ACL graft tension and ALL graft strain were measured continuously throughout the testing protocol.

Combined anatomic ACL/ALL_rec significantly improved the internal rotatory stability compared with isolated ACL_rec at 30°-90° under an internal rotation moment. During a static pivot-shift test, additional ALL_rec showed no significant reduction of ap-translation. ALL_rec resulted in an increase in ACL graft tension during continuous passive motion and with additional internal rotation moment.

In the case of a combined ACL and ALL deficiency, concurrent ACL_rec and ALL_rec significantly improved the rotatory stability of the knee compared with solely reconstructing the ACL at flexion angles ≥ 30°. Nevertheless, additional ALL_rec with fixation at 60° and with low tension could not restore extension-near rotatory stability. For that reason, ALL_rec with fixation at 60° flexion cannot be recommended in clinical application.