Current concepts in isolated and combined injuries of the medial collateral ligament complex, part II: The anteromedial knee instability classification.

Abstract

The medial collateral ligament (MCL) has a strong self-healing capacity; nevertheless, not every MCL injury heals adequately. Persisting medial and anteromedial knee laxity should be avoided as it may lead to increased strains and wear of the surrounding tissue, including the anterior cruciate ligament (ACL), meniscus and cartilage. Better understanding of MCL anatomy and biomechanics, especially in combined ACL-MCL injuries, has necessitated the need for updated clinical examination, classification and treatment approaches. The newly introduced anteromedial knee instability (AMKI) classification is a clinically and biomechanically based classification system designed to grade medial and anteromedial knee laxity using a structured three-letter-based system. First, an injury to the posteromedial complex and the posterior oblique ligament needs to be ruled out by testing valgus laxity in full individual knee extension. The inability to fully extend the knee might lead to a false positive result. Medial laxity is then assessed at 20°-30° of knee flexion. A Grade A injury is defined by a normal clinical valgus stress test indicating an intact superficial MCL (sMCL), but a positive external rotation test, suggesting an isolated injury to the deep MCL (dMCL). Grade B is characterised by a nearly normal or abnormal valgus laxity, combined with a nearly normal or abnormal external rotation test, indicating mild to moderate injuries to both the dMCL and sMCL with or without additional ACL injury. A Grade C injury represents a high-grade injury pattern, with both severely abnormal valgus laxity and external rotation testing, suggesting a complete injury to the medial stabilisers, often but not necessarily in combination with ACL insufficiency. Treatment of isolated MCL or combined ACL-MCL injuries is complex and multifactorial, but can be individualised based on the AMKI classification. LEVEL OF EVIDENCE: Level V.