In Vivo Length Changes of the Anterolateral Ligament and Related Extra-articular Reconstructions

Abstract

Background: Both anatomic anterolateral ligament (ALL) and nonanatomic anterolateral reconstructions are performed to improve the stability of anterior cruciate ligament (ACL)–deficient patients. However, the in vivo length change patterns and isometry of these anterolateral reconstructions are unknown. Purpose: To measure the theoretical length change patterns of the ALL and various anterolateral extra-articular reconstructions in healthy and ACL-deficient knees during in vivo weightbearing flexion. Study Design: Controlled laboratory study. Methods: Ten patients with an ACL injury in 1 knee and the contralateral side intact were included. By use of magnetic resonance and dual fluoroscopic imaging techniques, the changes in length of the ALL, modeled with its femoral attachment either anterior or posterior-proximal to the fibular collateral ligament (FCL) attachment, and nonanatomic extra-articular reconstructions were measured as a function of knee flexion and were compared between the intact and ACL-deficient knees. Results: The ALL, with its femoral attachment anterior to the FCL attachment, showed a consistent length increase of approximately 50% from 0° to 90° of knee flexion. The length change of the ALL was 20% ± 6% when its femoral attachment was placed posterior-proximal to the FCL. ACL deficiency did not affect ALL length. Even minor shifts in position around the rotational axis of the femur resulted in contrary ligament kinematic patterns. An extra-articular reconstruction with the femoral attachment proximal to the lateral epicondyle and the tibial attachment on the Gerdy tubercle increased 15% ± 4% in length from 0° to 60° and shortened at 90° of flexion. When the tibial fixation of the anatomic ALL with its femoral attachment posterior to the FCL was moved to the Gerdy tubercle, a 30% ± 4% length increase over 90° occurred, without the decrease in length at 90°. A significant length increase of both theoretical reconstruction grafts was seen at 0° in ACL-deficient knees. Conclusion: An anatomic ALL reconstruction as modeled based on recent anatomic studies was not isometric during in vivo knee flexion and was not affected by ACL deficiency. The nonanatomic extra-articular reconstructions demonstrated more biomechanically favorable length change patterns with the smallest percentage increase in elongation during knee flexion. Clinical Relevance: This study presents the first in vivo biomechanical data on the ALL, in both healthy and ACL-deficient knees, and provides surgical information that may be valuable for restoring normal anterolateral stability.