36-year-old male patient with complaints of chronic pain in the lateral aspect of the left foot for nearly 5 years especially on weight bearing. A previous history of twisting injury (ankle sprain) was noted.
CT images of the left ankle revealed irregularity with erosions and subchondral cysts involving the inferior aspect of the talus and superior and anterior aspects of the calcaneus.
MRI of the left ankle revealed effacement of the normal fat in the tarsal canal and sinus tarsi at the level of the subtalar joint with loss of definition of the sinus tarsi ligaments. Hypointensity on T1W and ill defined hyperintensity on T2W images was noted in the sinus tarsi. Post contrast images revealed minimal enhancement in the sinus tarsi. Degenerative changes were noted in the inferior talus (roof of sinus tarsi) and superior calcaneus with subchondral cysts. The intrinsic ligaments of the sinus tarsi appeared intact.
CT and MRI findings were diagnostic of sinus tarsi syndrome.
The sinus tarsi is a lateral anatomical space located between the talus superiorly and the calcaneus inferiorly. The anterior and posterior boundaries of this space are the anterior and posterior subtalar joints respectively. This space is medially continuous with the much narrower tarsal canal. The sinus tarsi and tarsal canal mainly contain five ligaments, namely - the cervical ligament, the three roots of the inferior extensor retinaculum (medial, intermediate and lateral roots) and the interosseous talocalcaneal ligament. In addition to these structures both sinus tarsi and tarsal canal contain neurovascular structures and fat. [1, 2]
Sinus tarsi syndrome was first described by O’Connor in 1958, however, its pathogenesis remains unclear. [2] This syndrome is mainly caused by haemorrhage or inflammation of the synovial recesses of the sinus tarsi with or without ligament injuries. It frequently occurs after repetitive ankle sprains or following trauma. It is more commonly seen in young males in the 3rd and 4th decades. Patients usually present with pain in the lateral side of the hind foot at the sinus tarsi. [2]
Pathological examination of the involved tissue has shown features of chronic inflammatory changes, fat necrosis, fibrosis and synovial cysts. [2]
Plain radiographs are usually normal in early stages; however, in advanced cases changes of degenerative arthritis may be evident. Subtalar arthrography was a modality used before the advent of MRI but the sensitivity is low. The value of CT lies in demonstrating secondary osteoarthritic changes in advanced cases. Currently MRI is the imaging modality of choice for diagnosing sinus tarsi syndrome. Sagittal T1W/ PD fat suppressed images are the best images for evaluation. The characteristic MRI feature of sinus tarsi syndrome is obliteration of fat in the sinus tarsi. Imaging findings include hypointensity on T1W and hyperintensity on T2W images (corresponding to inflammatory changes) or hypointensity on both T1W and T2W images (corresponding to fibrosis) with or without ligament injuries. Osteoarthritis and subchondral cysts may be seen in advanced cases. Contrast enhancement is useful in identifying hypertrophied synovium but is non-specific. [2, 3]
Sensitivity of MRI to pick up cervical and interosseous talocalcaneal ligament injuries is variable. [4]
Majority of the patients respond to conservative treatment including physical therapy, NSAIDs and local steroid injections. When there is failure of conservative therapy, surgical measures like synovectomy, ligament reconstruction or arthrodesis with fusion of subtalar joint may be necessary. [5]
Sinus tarsi syndrome
The patient has complained of lateral pain in the left foot for almost 5 years, which worsens with weight-bearing. There is a history of ankle sprain. Based on the provided CT and MRI images, the notable findings are as follows:
1. CT Scan: In the region between the talus and the calcaneus (the sinus tarsi), the local fat density is blurred or absent. In some cases, mild bone sclerosis or marginal joint sclerosis may be seen.
2. MRI Scan: The sinus tarsi fat is often replaced, showing low signal on T1 and high signal on T2 or PD sequences, suggesting inflammatory exudation or effusion. In some patients, there may be abnormal signal or disrupted continuity in the surrounding ligaments (e.g., the cervical ligament, interosseous talocalcaneal ligament). If necessary, mild bone marrow edema or soft tissue edema signals can also be observed.
3. Some patients may also present with osteophytic changes or subchondral cystic lesions of the subtalar joint, indicating the possibility of chronic inflammatory or degenerative changes.
Overall, these imaging manifestations are consistent with chronic inflammation, fibrosis, or potential ligamentous injury leading to replacement of the sinus tarsi fat density/signal.
Based on the patient's history and imaging features, the possible diagnoses or differential diagnoses include:
Combining the patient’s age, history of chronic lateral foot and ankle pain, previous sprain episodes, and imaging findings demonstrating abnormal sinus tarsi fat density or signal, the most likely diagnosis is: Sinus Tarsi Syndrome.
If clinical presentations remain atypical or there is doubt about the diagnosis, a high-resolution MRI sequence for ligament evaluation or a diagnostic injection (local anesthetic with steroid) could be considered to assess symptom relief.
Once sinus tarsi syndrome is confirmed or strongly suspected, the following treatment approaches may be considered:
A rehabilitation/exercise prescription should follow an individualized, gradual progression. The following plan can be considered:
Throughout the rehabilitation process, adherence to the “FITT-VP Principle” is recommended:
Disclaimer: This report provides a reference for medical analysis and cannot replace face-to-face consultation or professional medical advice. If you have any questions or changes in your condition, please seek medical attention promptly for a personalized treatment plan.
Sinus tarsi syndrome
