Natural history of an anterior cruciate ligament injury: associated injuries and consequences of rotational instability

Background: Anterior cruciate ligament (ACL) injuries represent a significant clinical and economic burden, with high incidences observed in young athletes participating in pivotal sports. While ACL reconstruction (ACLR) is common, the complex pathophysiology of rotatory instability and the long-term risk of post-traumatic osteoarthritis (OA) remain critical challenges in orthopedic management.

Objective: This review examines the epidemiology, biomechanical properties, and injury mechanisms of the ACL, while evaluating the impact of associated intra-articular and extra-articular lesions on knee stability and long-term joint health.

Key Points: The ACL functions as a primary restraint against anterior tibial translation and internal rotation, characterized by a ribbon-like anatomy and distinct functional bundles. Non-contact ruptures typically occur under valgus stress and quadriceps-induced anterior force, resulting in significant tibial displacement. Rotational instability, quantified by the pivot shift, is exacerbated by concomitant injuries to the medial meniscal ramp, lateral meniscal roots, and anterolateral structures. Bony factors, including increased lateral tibial slope, further influence laxity. Although ACLR restores gross stability and reduces the relative risk of secondary OA compared to non-operative management, it does not fully prevent degenerative changes. Meniscal preservation is identified as a primary factor in mitigating OA progression, as meniscectomy significantly increases the risk of Kellgren-Lawrence stage ≥2 changes.

Conclusion: Successful ACL management requires a comprehensive diagnostic approach that addresses both the primary ligamentous deficit and associated peripheral lesions. Restoring normal knee kinematics through anatomical reconstruction and meniscal repair is essential to delay the onset of post-traumatic osteoarthritis.