LCL

**Lateral collateral ligament (LCL; fibular collateral ligament) – knee**

**Anatomy** - Extracapsular ligament from the lateral femoral epicondyle to the head of the fibula (conjoined with the biceps femoris tendon insertion). - Not attached to the lateral meniscus (unlike the MCL, which attaches to the medial meniscus). This is why isolated LCL injuries rarely involve meniscal tears. - Primary function: resists varus (adduction) stress. Secondary: resists posterior tibial translation and external rotation, as part of the posterolateral corner (PLC). - The PLC includes the LCL, popliteus tendon and popliteofibular ligament.

**Mechanism of injury** - Direct blow to the anteromedial knee that forces the knee into varus. This is less common than MCL injury, which follows a lateral blow (valgus). - Hyperextension or a non-contact varus force can also cause it. - Often occurs with ACL/PCL tears or PLC injury.

**Clinical presentation** - Lateral knee pain, swelling and instability, especially with cutting or pivoting. - Positive varus stress test: laxity or opening of the lateral joint line at 0° and 30° of flexion. - Opening at 30° only suggests an isolated LCL injury. - Opening at both 0° and 30° suggests combined cruciate/PLC injury. - Common peroneal nerve injury is a key association because the nerve wraps around the fibular neck. It causes foot drop and sensory loss over the dorsum of the foot and lateral leg.

**Diagnosis** - Clinical exam first, then plain films to rule out fracture (e.g., Segond or arcuate fracture). - MRI is the imaging modality of choice for ligament and associated injuries.

**Management** - Grade I–II: conservative treatment (RICE, bracing, rehab). - Grade III or PLC involvement: surgical repair or reconstruction, since LCL/PLC injuries heal poorly.

**High-yield comparisons** - MCL: valgus stress, lateral blow, attached to the medial meniscus, injured more often. - Unhappy triad (O'Donoghue): ACL + MCL + medial meniscus, from a lateral blow to a planted foot. - ACL: anterior drawer/Lachman, prevents anterior tibial translation. - PCL: posterior drawer, dashboard injury.

**Other abbreviation notes** - LCL can also stand for lymphocytic... but this is not standard. On boards, "LCL" almost always means lateral collateral ligament. In lipid contexts the standard term is LDL, not LCL.