Sinus Tarsi Syndrome

Subtalar instability and sinus tarsi syndrome. The tarsal sinus and tarsal canal are a cone shaped region, which is the boundary between the posterior subtalar joint, and the talo-calcaneo-navicular joint.  The origin of the extensor digitorum brevis is in this area. As well as joint capsule, nerve endings, and several ligaments. Sinus tarsi syndrome is an abnormality of the canal and sinus.  It consists of lateral foot pain , focal pain over sinus tarsi on palpation, perceived hindfoot instability and usually history of inversion trauma. Studies of the ankle could be normal because the injury is in the ligaments of the subtalar joint.
 
Klein MA, Spreitzer AM: MR Imaging of the Tarsal Sinus and Canal: Normal Anatomy and Pathologic Findings, and Features of the Sinus tarsi Syndrome. Radiology 1993; 186: pp. 233-240.
Meyer JM, Lagier R: Post-traumatic sinus tarsi syndrome: an anatomical and radiologic study. Acta Orthopaedica Scandinavia 1977;48: pp. 121-128