MRI diagnosis of partial tears of the anterior cruciate ligament.

In an attempt to define the magnetic resonance imaging (MRI) features of partial tears of the anterior cruciate ligament (ACL) we retrospectively analysed the MRI scans of 30 patients with a recent arthroscopic finding of a normal, a partial or a completely torn ACL. On review of the original reports MRI correctly predicted 9/9 (100 per cent) complete ACL tears, 11/12 (92 per cent) normal ACLs but only 1/9 (11 per cent) partial ACL tears. On analysis of the MRI there were four features which helped to differentiate partial ACL tears from either complete ACL tears or normal ligaments. These were the appearance of some intact fibres, thinning of the ligament, a wavy or curved ligament and the presence of an inhomogeneous mass posterolateral to the ACL. We propose that these findings may be indicators of partial ACL tear.