The anatomic variations of the posterior talofibular ligament associated with os trigonum and pathologies of related structures.

Purpose: The aim of this study is to investigate the detailed anatomy of the posterior talofibular ligament (PTFL) on MR images in patients with os trigonum. We also evaluated the pathological conditions of the PTFL, anterior talofibular ligament (ATFL), flexor hallucis longus (FHL) tendon, talus and os trigonum.

Methods: Ankle MRIs of 70 patients with os trigonum (study group) and 70 patients without it (control group) were reviewed for the anatomy of the anterior and posterior fibers of PTFL. The prevalence of PTFL and ATFL pathologies was also compared between two groups. Additionally FHL tenosynovitis and osseous pathologies were evaluated.

Results: The posterior fibers inserted into the lateral tubercule of the posterior process of the talus in the control group whereas if an os trigonum was present, the posterior fibers of PTFL were inserted only into the os trigonum. The origins of anterior and posterior fibers were the medial surface of the lateral malleolus and the insertion of the anterior fibers was lateral surface of the talus posterior to the lateral malleolar facet in both groups. There was a significant association between an abnormal PTFL, ATFL and the presence of os trigonum. FHL tenosynovitis was higher in the study group but it did not meet the statistical significance. The most common pathology of the talus and os trigonum was subchondral edema along the synchondrosis.

Conclusions: In patients with os trigonum, the posterior fibers of the PTFL were inserted herein. In the case of an os trigonum signal alterations of ligaments were more common, which may reflect chronic instability.