The MR imaging features of the posterior intermalleolar ligament in patients with posterior impingement syndrome of the ankle

Objective. To describe the MR imaging features of the posterior intermalleo lar ligament (IML) in patients with posterior impingement syndrome (PIS) of the ankle. Design and patients. Three patients (one male and two females, 13-25 years of age) are presented. Each patient presented clinically with symptoms of P IS of the ankle. Plain film examination was negative for a structural cause of the PIS in all patients. MR images were obtained with a 1.5 T scanner u sing an extremity coil. Clinical data and, in one patient, findings at ankl e arthroscopy, were correlated with the results of MR imaging. Results. Ankle MR images from the three patients with a clinical diagnosis of PIS are presented. Findings in all patients included: (1) absence of ano ther structural cause of the PIS (i.e., an os trigonum, trigonal process, f racture, loose bodies, etc.), (2) identification of the IML as a structure discrete from the posterior talofibular and tibiofibular ligaments, and (3) prominence of the IML as indicated by (a) identification of the IML in thr ee different imaging planes, and (b) a caliber of the IML comparable to tha t of the conventional posterior ankle ligaments visualized in the same imag ing plane. Arthroscopic resection of a meniscoid IML resulted in resolution of the PIS in one of the patients presented. Conclusions. MR imaging is an effective means of investigating the IML as a potential cause of PIS. The identification of a prominent IML in the absen ce of another structural cause of PIS indicates that impingement of the IML is the most likely cause of PIS.