Sinus Tarsi Syndrome (STS) is a condition characterised by pain and tenderness in the anterior-lateral aspect of the ankle and the sinus tarsi (outside of the ankle, in front of the lateral malleolus). Patients with STS present with diffuse pain in the sinus tarsi when weightbearing (standing or walking) or on pressing the area the the fingers (palpation). In some, often chronic cases, the patient may also feel that their ankle is unstable and “giving way” (subtalar instability).
This condition results from damage to the tissues in the synovial recesses of the sinus tarsi, causing bleeding and/or inflammation, with or without ligament injuries. STS often arises from one or more acute inversion injuries of the foot (going over on your ankle), but can also arise from chronic foot pronation / subtalar joint pronation, being overweight, or taking part in certain sports, such as basketball, running, dancing, and volleyball. Untreated STS can lead to chronic instability of the subtalar joint due to changes in the local ligaments of the sinus tarsi with possible scar tissue formation and synovitis (inflammation of the synovial membrane of the joint).
Diagnosis of this condition is usually made by taking a clinical history and by palpation. In some cases, a guided injection of local anaesthetic into the sinus tarsi may be used to confirm STS. Swelling is rarely seen. Some cases may experience pain when inverting and everting the foot at the subtalar joint, but this does not occur in all cases. MRI is probably the best form of imaging for this condition, as it allows the clinician to determine soft tissue changes or injuries, such as inflammation, ligament injuries, ganglion cysts, or scar tissue. CT scans may show any fractures or bony changes earlier than plain radiographs (X-rays).
Treatment for this condition often includes periods of rest or reduced activity / altered activity, therapeutic in-shoe orthotics (insoles), physical exercises to address underlying or co-morbid muscle imbalances (stretching and strengthening), acupuncture, changes in footwear, losing weight in heavy individuals, and in some cases, corticosteroid injections. If such conservative methods do not help, then surgery may be indicated.