Semimembranosus-tibial collateral ligament bursitis: MR imaging findings.

PURPOSE: The purpose of this paper is to describe the MR imaging characteristics of semimembranosus-tibial collateral ligament (SMTCL) bursitis.

MATERIALS AND METHODS: Fifteen patients (37-68 years old) with medial joint pain and presumed internal derangements of the knee underwent MR imaging. Fluid collections around the SMTCL were found prospectively in five patients. Our retrospective evaluation of recent MR imaging cases that had been previously diagnosed as pes anserinus bursitis revealed 10 additional cases with similar findings.

RESULTS: We believe that SMTCL bursitis clinically explained the patients' medial pain in all cases diagnosed prospectively. We gave the additional cases the same diagnosis presumptively.

CONCLUSIONS: SMTCL bursitis has a characteristic MR imaging appearance of fluid draped over the semimembranosus tendon in the shape of an inverted U. This entity can clinically mimic internal derangement of the knee, typically causing pain more superior and posterior to that of pes anserinus bursitis. MR imaging is useful in diagnosing SMTCL bursitis and avoiding unnecessary knee arthroscopy.