medial collateral ligament

**Anatomy** - Origin: medial femoral epicondyle. Insertion: medial tibia, about 5-7 cm below the joint line (pes anserinus region). - Superficial (tibial) layer is the main valgus restraint. The deep layer is a thickening of the joint capsule that attaches firmly to the medial meniscus. - Function: primary restraint to valgus stress and a secondary restraint to anterior tibial translation (after the ACL) and to external rotation.

**Mechanism of injury** - Valgus force to the lateral knee (e.g., a clipping tackle in football) with or without rotation. - Because of the deep-layer attachment to the medial meniscus, MCL tears can be accompanied by medial meniscus injury.

**"Unhappy (terrible) triad" (O'Donoghue)** - ACL + MCL + medial meniscus tear. Classically described this way, although studies show the lateral meniscus is more often injured with ACL tears.

**Clinical features** - Medial knee pain and tenderness along the ligament, swelling, and a feeling of instability or giving way. - Valgus stress test: laxity or pain with the knee at 0° and 30° of flexion. Laxity at 30° alone suggests an isolated MCL injury. Laxity at 0° suggests involvement of the posteromedial capsule and possibly the cruciates.

**Grading** - Grade I: sprain with microscopic tears, pain, no laxity. - Grade II: partial tear with mild to moderate laxity and a definite endpoint. - Grade III: complete tear with gross laxity and no firm endpoint.

**Diagnosis** - Clinical diagnosis. X-ray is used to rule out fracture. MRI is used to confirm the injury and evaluate associated injuries (ACL, meniscus). - Chronic MCL injury can calcify and produce a Pellegrini-Stieda lesion on X-ray, which is calcification near the medial femoral condyle.

**Management** - Isolated grade I-II injuries: nonoperative (RICE, NSAIDs, hinged knee brace, early range of motion, rehabilitation). The MCL has good healing capacity because it is extracapsular and well vascularized. - Grade III or combined injuries (e.g., with ACL tear): bracing first, with possible surgical repair or reconstruction for persistent instability or multiligament injury.

**Board pearls** - Valgus stress → MCL. Varus stress → LCL (fibular collateral ligament). - The MCL is attached to the medial meniscus, but the LCL is not attached to the lateral meniscus. - Anterior drawer or Lachman → ACL. Posterior drawer → PCL. - MCL = most commonly injured knee ligament. ACL = most commonly injured ligament requiring surgery. - Pes anserinus (sartorius, gracilis, semitendinosus) inserts near the MCL insertion. Pes anserine bursitis causes similar medial pain, so consider it in the differential.