Classification

O'Donoghue classification [1]

Isolated grade I MCL injury (mild)

• MCL has few torn fibres but no loss of ligamentous integrity.

Isolated grade II MCL injury (moderate)

• MCL is partially torn. However, the fibres are still opposed. There might be mild pathological laxity, which may or may not be symptomatic.

Isolated grade III MCL injury (severe)

• Integrity of the MCL is completely disrupted. There is significant pathological laxity of the knee with valgus stress.

AMA Committee on the Medical Aspects of Sports standard nomenclature of athletic injuries [2]

MCL injuries are classified based on the amount of medial joint opening when a valgus load is applied at 20° to 30° of knee flexion: View image

• Grade I: 0 to 5 mm of opening

• Grade II: 5 to 10 mm of opening

• Grade III: >10 mm of opening

Other forms of MCL injury

MCL + anterior cruciate ligament (ACL) injury

• The ACL is the most commonly injured ligament along with the MCL.

MCL + multiligament injury

• The posterior cruciate ligament, lateral collateral ligament, and menisci are frequently simultaneously injured.

Recurring MCL injury

• Recurring, or chronic, MCL injury is a complication of acute MCL injury.