What is sinus tarsi syndrome?
The sinus tarsi is a space in the hindfoot between the talus and calcaneus that normally contains fat and neurovascular structures. The sinus tarsi syndrome typically presents with lateral hindfoot pain and a subjective feeling of instability. The most common cause of sinus tarsi syndrome is prior ankle sprain, which over time results in scarring within the tarsal sinus. This scarring can be identified on MRI as replacement of the normal high T1-weighted signal intensity fat with low signal intensity fibrous tissue. Other less common causes of sinus tarsi syndrome include inflammatory arthritis, ganglion cysts, and neoplasms.