The lateral collateral ligament (LCL / fibular collateral ligament) of the knee runs from the lateral femoral epicondyle to the fibular head, forming the primary lateral restraint against varus stress. It is a cord-like structure (unlike the broad MCL) with no direct meniscal attachment. The LCL is part of the posterolateral corner complex alongside the popliteus tendon and popliteofibular ligament.
Resists varus stress and prevents the lateral side of the knee from opening — critical during stance phase of gait.
Isolated LCL tears are uncommon — most LCL injuries occur as part of posterolateral corner (PLC) disruption from combined varus and external rotation trauma. The figure-of-four test and varus stress at 30 degrees assess LCL integrity. Combined PLC injuries require surgical reconstruction of the LCL, popliteus complex, and popliteofibular ligament using tendon grafts. Missed PLC injuries lead to chronic varus instability that predisposes to ACL graft failure. MRI identifies the LCL tear location and associated PLC injury.
Varus impact or hyperextension injury producing lateral knee pain, fibular head tenderness, and instability on varus stress testing.
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