Lateral collateral ligament (LCL)

What it is

Unlike the broad MCL, the LCL is a narrow, round cord that you can sometimes feel on the outer side of a bent knee, particularly when sitting cross-legged. It lies outside the joint capsule and is not attached to the lateral meniscus. It is one of the key parts of the posterolateral corner, a group of structures that together control outward bowing and rotation of the tibia.

Why it matters for patients

The LCL is injured less often than the MCL. It usually tears from a blow to the inner side of the knee or a forceful twist, as in a football tackle, wrestling or a fall. Symptoms include pain and swelling on the outer knee and a feeling that the knee wobbles outwards when walking, especially on uneven ground.

Mild sprains often heal with a brace and physiotherapy. Complete tears, particularly when other posterolateral corner structures or the cruciate ligaments are also torn, heal poorly on their own and often need surgical repair or reconstruction, ideally planned within the first weeks.

How it is examined

A surgeon stresses the knee outwards and performs rotational tests, and checks the peroneal nerve. MRI and stress X-rays show the extent of injury.