E2241. Demystifying the Sinus Tarsi
  1. Blake Marmie; Baylor Scott & White
  2. John Wallace; Baylor Scott & White
  3. Ricardo Garza-Gongora; Baylor Scott & White
  4. Connie So; Baylor Scott & White
  5. Barrett Luce; Baylor Scott & White
Sinus tarsi syndrome (STS) is a frequently neglected diagnosis in cases of subtalar joint instability and pain. Its complex anatomy lends itself to being frequently involved with other more common ankle ligamentous injuries. Additionally, its complex anatomy makes delineating its features and identifying pathology difficult. Therefore, this exhibit’s purpose is to provide clarity and a systematic understanding of a clinically significant and often overlooked area of ankle injury and instability.

Educational Goals / Teaching Points
The exhibit will first give an anatomic overview of the boundaries and components of the sinus tarsi and canalis tarsi. Diagrams and radiologic images will highlight the ligamentous system contained within the sinus tarsi as well as the nerves, vasculature, and surrounding structures. Key pathologic processes and predispositions will then be explained. Common and uncommon pathologies will be annotated on multiple imaging modalities and MR sequences. Finally, the exhibit will focus on sinus tarsi syndrome and subtalar instability. Our image rich platform will provide information on the clinical presentation, imaging features, and the spectrum of medical and surgical management available for STS.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The sinus tarsi (ST) and the canalis tarsi comprise the conical interosseous cavity that exists between the common concave surfaces of the talus and the calcaneus. The canalis consists of a narrow channel posteromedially and connects to an expanded ST anterolaterally. Within this funneled cavity lies a complex and often variable ligamentous complex. Magnetic resonance imaging (MRI) is the preferred modality for visualization of this complex system and for the evaluation of STS. Assessment of the ST following an acute injury may also be accomplished with computed tomography (CT). Most STS cases are posttraumatic. Chronic inversion injuries and instability may lead to rupture of the cervical ligament, interosseous talocalcaneal ligament or any other of the supporting structures. This is often preceded by calcaneofibular and anterior talofibular ligament injuries. The resulting scar tissue can cause pain and subjective feelings of instability. ST encroachment may also occur with lesions such as cysts /neoplasms, osseous overgrowth from tarsal coalition and pes cavus /planus deformities. Inflammatory conditions also implicated in STS include gout, osteoarthritis and synovitis related diseases such as rheumatoid arthritis.

Proper evaluation of the components of the ST and canalis is a difficult task and is often an area of neglected diagnostic attention. Educating radiologists and providing a systematic approach for identifying pathology and diagnosing STS will allow for proper classification of acute and chronic ankle injuries with subtalar joint instability. This heightened understanding and confidence for the diagnosis of STS may provide added options for medical and surgical therapy otherwise not offered to the patient.