Purpose: We sought to clarify the ability of magnetic resonance imaging (MR) to show partial anterior cruciate ligament (ACL) ruptures and to allow distinction of partial from complete ACL ruptures.
Materials and methods: Eighty-eight patients were studied by arthroscopy and MR (36 with normal ACLs, 21 with partial ACL ruptures, and 31 with complete ACL ruptures). MR studies were interpreted by an experienced, blinded reader. MR examinations were also independently scored with respect to four primary and seven secondary signs, and these data were analyzed using discriminant analysis.
Results: The sensitivity of MR is lower for partial than for complete ACL ruptures. Most detected partial ACL ruptures resemble complete ruptures on MR. Secondary signs do not significantly improve detection of partial ACL ruptures, but they do help to distinguish partial from complete ACL ruptures. Displacement of the posterior horn of the lateral meniscus and popliteus muscle injury are indicative of complete ACL rupture.
Conclusions: The majority of partial ACL ruptures are shown by MR, but MR is less sensitive for partial than for complete ACL rupture. The distinction of partial from complete ACL rupture on MR examination, while problematic, is slightly improved by assessment of secondary signs.