Diagnosing the acutely locked knee.

A prospective cross-sectional study was undertaken to observe the management of acutely locked knees and identify features predictive of causes remediable by surgical intervention. A total of 50 consecutive patients presented for orthopaedic opinion with an acutely locked knee. In all, 48 underwent examination and arthroscopy under general anaesthesia. Among them, 43 were found to have distinct pathology causing a mechanical block to full extension. Four were found to have only degenerative changes, two "unlocked" without any surgical intervention, and one was entirely normal. A mechanical cause of the "locked" knee can be identified consistently using three key components from the history and examination: a history of a definite injury, localised joint line tenderness and the presence of an effusion. The use of such criteria would assist in the prompt, appropriate triage and referral of patients with an acutely locked knee.