A 17-year-old female representative football player presented with lateral ankle pain. She described experiencing a minor inversion injury three months prior to her visit. She was initially diagnosed with a lateral ankle sprain and had three weeks off football training. At this point she was able to return to training but had continued to be bothered by ongoing lateral ankle pain. This was typically worse at the start of a session but would warm up and largely resolve during training. It would then ache afterwards and would also feel stiff in the mornings.
On examination she was able to walk comfortably. There was no gross ankle swelling or other deformity. She had mild restriction in subtalar movements and localized tenderness over the lateral ankle and sinus tarsi region. Her foot and ankle examination were otherwise normal.
An x-ray series of the ankle does not show any acute abnormality. There is a ganglion within the sinus tarsi which measures approximately 20 x 6 x 10 mm. This appears to arise from the anterior aspect of the posterior subtalar joint. No other abnormality is identified in the sinus tarsi.
Due to the ongoing symptoms the player elected to have a guided steroid injection into the sinus tarsi. This was done under fluoroscopic guidance. After a short lived post-injection flare there was a dramatic improvement in the player’s symptoms. She was able to resume training five days after the injection and reported being pain-free at this time. She remains symptom-free four months after the injection.
The sinus tarsi is a small cone-shaped bony tunnel running from an opening anterior and inferior to the lateral malleolus. The tunnel runs in a posteromedial direction to a point just posterior to the medial malleolus. It is lined with synovial tissue and can become chronically inflamed leading to a low-grade synovitis. Patients with sinus tarsi syndrome generally present with localised lateral ankle pain, but in some cases this can be more generalised and difficult to diagnose. In the majority of cases there is a history of an inversion injury however it can also be caused by poor biomechanics and repeated loading. Most patients will have localised tenderness over the lateral ankle.
While in this case there are clear MRI findings that support the sinus tarsi as being the pain generator, in many patients this is not the case. Imaging studies are however important to help exclude other potential causes of lateral ankle pain. In cases where there is a high degree of suspicion, a diagnostic local anaesthetic test is often the most useful diagnostic tool. Injecting 1ml of lignocaine will generally improve the player’s pain, improve their clinical examination findings and allow them to hop or run without pain. When there is an improvement with local anaesthetic a corticosteroid injection can often be a very effective treatment. Surgery is not generally needed.
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