The medial collateral ligament (MCL / tibial collateral ligament) of the knee is a broad flat ligament running from the medial femoral epicondyle to the medial tibial flare. It has a superficial component (primary valgus restraint) and a deep component (meniscofemoral and meniscotibial ligaments attached to the medial meniscus). It is the primary restraint to valgus knee stress and is the most commonly injured knee ligament.
| Origin | Medial femoral epicondyle |
|---|---|
| Insertion | Medial surface of the proximal tibia deep to the pes anserinus, about 4-6 cm below the joint line (superficial layer), and the medial meniscus and tibial rim just below the joint line (deep layer) |
Resists valgus stress and provides static medial stability, preventing the knee from buckling inward. It also helps resist external rotation of the tibia and acts as a secondary restraint to anterior tibial translation.
MCL injuries are graded I (sprain, intact), II (partial tear, lax but firm endpoint), III (complete tear, no endpoint). Isolated MCL tears are managed conservatively with functional bracing; even complete tears heal reliably without surgery due to the excellent blood supply, unlike the ACL. Because the deep layer is attached to the medial meniscus, medial meniscal tears can accompany MCL injury. MCL repair or reconstruction is reserved for combined ligament injuries (e.g., ACL + MCL, posterolateral corner + MCL). Valgus stress testing at 30 degrees of flexion isolates the MCL; opening in full extension suggests additional posteromedial capsule or cruciate injury. MRI grades the injury and identifies associated pathology.
Valgus force injuries ranging from tender without instability (Grade I) to complete tear with valgus opening at 30° flexion (Grade III).
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