Biomechanical evaluation of anterolateral ligament anatomical variants in anterior cruciate ligament-injured and reconstructed knee joints.

BACKGROUND

The anterolateral ligament (ALL) has structural diversity and is often injured concurrently with anterior cruciate ligament (ACL) tears. At present, the effect of ALL structural diversity on combined injury and associated reconstruction remains unclear.

METHODS

A finite element model of the knee joint with combined ACL-ALL injuries was established and validated against experimental data from the pig knee joints. Three distinct ALL types (I, II, and III), classified by their femoral insertion site relative to the lateral collateral ligament (LCL), were modeled. Simulations were performed under ACL-intact, ACL-injured, ACL-deficient, and ACL-reconstructed conditions during tibial loading in flexion/extension, internal/external rotation, and varus/valgus to assess kinematics and ligament stresses.

FINDINGS: ALL function was type-dependent. Following ACL deficiency, tibial internal rotation posed the highest risk of ALL injury. During ACL-ALL reconstruction, Type III ALL most effectively enhanced internal rotation stability and reduced peak stress in the hamstring tendon graft.

INTERPRETATION: The ALL is a key stabilizer against internal rotation. ACL failure makes internal rotation a primary mechanism for ALL injury. For reconstruction, placing the ALL femoral insertion postero-proximal to the LCL optimizes biomechanical outcomes by improving stability and load-sharing.