Pain at the back of the ankle when you point your toes can come from posterior ankle impingement. An os trigonum, a small extra bone behind the ankle, can contribute in some people. But seeing an extra bone on an X-ray does not prove that it is causing your symptoms. The examination, movement pattern and surrounding tendons all matter before deciding on treatment.
What is an os trigonum?
An os trigonum is an accessory bone at the back of the talus, one of the main ankle bones. Some people have it without any symptoms. Problems may arise when tissues at the back of the ankle become pinched or irritated, particularly during repeated pointing of the foot. Dancers, footballers and other active people may notice symptoms during specific movements.
Posterior ankle pain has other causes too. An enlarged bony process, tendon irritation, an injury or another ankle condition may produce a similar complaint. A foot and ankle assessment should establish the likely pain source rather than treating an incidental scan finding.
What does the assessment look for?
A clinician asks where the pain is, how it began and which activities provoke it. They examine movement, swelling, tenderness and function, including the tendons that pass around the ankle. The flexor hallucis longus tendon, which helps move the big toe, is one of the nearby structures that may need consideration.
Tell the clinician whether there was a single injury, a recent increase in training or a gradual loss of tolerance. Pain with ordinary walking may require a different approach from discomfort only at the extreme of a dance position. Explain your goals, but do not repeatedly force the painful movement to demonstrate it before assessment.
Ask about a diagnosis-led assessment
Which scans can help?
An X-ray can show an os trigonum or an enlarged posterior talar process. MRI may provide more information about the surrounding soft tissues and whether there are other relevant changes. A specialist selects imaging according to the clinical question and what is already known.
A report should be interpreted with the examination. The presence of an accessory bone alone is not an instruction to remove it or inject around it. Bring previous images and reports, not just the phrase os trigonum from a summary. Understanding what a scan does and does not explain helps keep treatment focused.
Can it improve without surgery?
Non-operative treatment is usually considered first. Depending on the diagnosis, this can include reducing provocative loading, a rehabilitation plan and sometimes a period of support or immobilisation. Medicines or a selected local injection may be discussed after assessment of the risks and the intended target.
The aim is to reduce symptoms while restoring useful function, not to avoid movement forever. A therapist or specialist may help you adjust training and progress back to the movements you need. Ask what can safely continue, which activities should pause and what findings would change the plan.
When is surgery considered?
Persistent, well-localised symptoms despite appropriate non-surgical care may lead to a foot and ankle surgical opinion. Posterior ankle arthroscopy or endoscopy can be used for selected problems at the back of the ankle. The operation and recovery depend on the structures involved and the work required.
Surgery is not selected from the X-ray alone, and recovery is not identical for every athlete or dancer. Discuss risks, rehabilitation, time away from work and the criteria for returning to performance. A published recovery range is not a personal guarantee. The specialist should explain why an operation is or is not appropriate for your case.
Discuss an assessment route with our team
Can PRP remove an os trigonum or stop impingement?
PRP cannot remove an accessory bone or create space where a structural impingement remains. The sources reviewed here do not establish PRP as a standard treatment for os trigonum syndrome. Research on other tendons or joints does not demonstrate that it will solve this particular mechanical problem.
If there is a separate tendon diagnosis, that requires its own assessment and evidence discussion. It should not be used to imply that every posterior ankle symptom is a PRP indication. A useful treatment conversation explains the suspected pain source, the role of rehabilitation and whether a specialist referral is the more appropriate next step.
Which symptoms need prompt assessment?
After a significant injury, seek prompt help if you cannot bear weight, have major swelling, deformity or severe pain. A hot, red ankle with fever needs urgent medical advice. New numbness, a cold or discoloured foot, or a sudden marked loss of function should not wait for a routine clinic review.
Calf swelling and pain, especially with breathlessness or chest pain, require urgent assessment for causes outside a local ankle impingement. Do not assume that every symptom in the same leg comes from an os trigonum. Follow the urgent care advice appropriate to your symptoms.
What should you ask before treatment?
Ask whether the extra bone is considered symptomatic and what supports that conclusion. Find out whether tendon problems or other injuries have been excluded, what a non-operative plan involves and how progress will be measured. If an injection is offered, ask about the target, evidence, risks and alternatives.
The London PRP Clinic can help discuss a diagnosis-led assessment route for ankle pain. Bring imaging and describe the movements you want to regain. The value is in a clear, proportionate plan, including referral when needed, rather than selecting an injection before the mechanical problem has been understood.
Contact The London PRP Clinic about your symptoms
Evidence and further reading
FootCareMD, American Orthopaedic Foot & Ankle Society: posterior ankle endoscopy or arthroscopy
2024 review: minimally invasive surgery for os trigonum syndrome
Information reviewed 4 November 2026. This article is general information, not a diagnosis or personal treatment advice. Seek urgent care for severe or rapidly worsening symptoms. Assessment and treatment depend on your individual circumstances.