The medial collateral ligament (MCL) is the most commonly injured ligament about the knee. The ligament is attached to the medial epicondyle of the femur 3cm above the joint line and passes downward to attach to the antero-medial aspect of the tibia. It is typically injured following an acute valgus stress.
The ligament is the primary restraint to valgus stress and also internal tibial rotation. It provides a secondary restraint to anterior tibial translation.
MCL injuries are usually the result of a valgus stress to a partially flexed knee. Patients report an acute onset of localised medial knee pain. With isolated injuries, there may be some localised medial swelling – but patients rarely report generalised swelling.
Traditionally, the injuries are graded based on the degree of laxity present with a valgus stress. This should be assessed both in 30 degrees of knee flexion and in extension. When there is laxity in full knee extension, this implies a more significant injury.
In general, there is no significant effusion or other clinical signs. When the examination findings are more than just localised knee pain and tenderness, other diagnoses should be considered.