KSSTA - 2026-09-25 - Journal Article
Current concepts in isolated and combined injuries of the medial collateral ligament complex, part II: The anteromedial knee instability classification.
Runer A, Bouguennec N, Wierer G, Robinson J, Amis A, Herbst E, Kittl C, Cristiani R, Hoser C, Willinger L, Abermann E, D'Ambrosi R, Senorski EH, Getgood A, Musahl V, Ball S, Williams A, Siebenlist S, Moatshe G, Smigielski R, Lind M, Strauss M, Herbort M, Samuelsson K, Fink C
Topics
Key Takeaway
The AMKI classification introduces a three-letter grading system for anteromedial knee instability that stratifies medial and anteromedial laxity into Grades A (isolated dMCL), B (combined dMCL+sMCL ± ACL), and C (complete medial stabilizer disruption) to guide individualized treatment.
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Summary
This expert consensus/current concepts paper introduces the Anteromedial Knee Instability (AMKI) classification to address the inadequacy of existing grading systems for isolated and combined MCL complex injuries. The three-letter system grades laxity using valgus stress testing at 20–30° flexion and external rotation testing, with Grade A indicating isolated dMCL injury, Grade B indicating combined dMCL/sMCL injury with or without ACL involvement, and Grade C indicating complete medial stabilizer failure. The classification is designed to individualize operative versus nonoperative decision-making based on both clinical examination findings and biomechanical principles.
Key Limitation
The classification lacks prospective clinical validation with outcome data, inter-rater reliability coefficients, or defined thresholds (in millimeters or degrees) for each grade, limiting its immediate reproducibility across surgeons.
Original 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.