clinical features

Last reviewed 01/2018

Generally there is a history of a twisting or wrenching injury. The patient may claim that they heard the tissues snap. The knee is painful. Usually the knee becomes swollen almost immediately (this is in contrast to meniscal injuries where swelling appears some time after the injury).

On examination tenderness is most acute over the side of the torn ligament. If either side of the joint is stressed then this may cause excruciating pain.

The clinical presentation will differ depending on whether a tear is complete or partial. A patient with a partial tear is likely to be lame and have a very painful knee. In a complete tear the patient may have little or no pain. Also swelling is worse in a partial tear because haemorrhage remains confined within the joint whereas in a complete tear the ruptured capsule permits leakage of fluid. Any attempted movement is painful in a partial tear. This contrasts with an often painless abnormal knee movement that may occur (if not restricted by muscle spasm) in a complete tear.

It is essential to distinguish between a partial and a complete tear because the management differs for these two conditions. Thus if there is any doubt with respect to the diagnosis then it is essential to undertake an examination under anaesthesia.

A plain radiograph of the joint may reveal that the ligament has avulsed a small piece of bone.