Os-Trigonum Syndrome
Patient Information
Os-Trigonum Syndrome is a condition of the posterior ankle caused by an accessory bone (the os trigonum) located behind the ankle joint. This small extra bone, present in approximately 7–14% of the population, can become a source of pain and dysfunction — particularly in dancers, footballers, and athletes who repeatedly perform movements involving the pointed foot. Mr Matthew Welck offers specialist diagnosis and surgical treatment for os trigonum syndrome in London at the RNOH Stanmore, The Wellington Hospital North London, and private clinics in Hertfordshire.
Useful resource: Posterior Ankle Impingement – PhysioWorks
What is Os-Trigonum Syndrome?
An os trigonum is a congenital accessory bone situated behind the talus (the main ankle bone). In most people, this accessory bone causes no symptoms and is discovered incidentally on X-ray. However, in some individuals — particularly athletes — it can become impinged between the ankle bones during plantarflexion (pointing the foot downward), leading to pain and inflammation. This is known as os trigonum syndrome or posterior ankle impingement syndrome.
Causes and Predisposing Factors
- Forced or repetitive plantarflexion (pointing the foot), as seen in ballet dancers, gymnasts, and footballers
- Acute injury causing stretching or tearing of the fibrocartilaginous connection between the os trigonum and the talus
- Fracture of the os trigonum following a sudden forced plantarflexion injury
- Differential diagnoses include Achilles tendon pathology, FHL (flexor hallucis longus) tendinopathy, and posterior talus fracture
Symptoms of Os-Trigonum Syndrome
- Deep pain at the back of the ankle, particularly on pushing off or pointing the foot
- Localised tenderness and swelling behind the ankle joint
- Pain that worsens with repeated plantarflexion activities such as walking downstairs, dancing, or kicking
- Restricted range of motion at the ankle in severe cases
GP Information
Investigation Guidelines
- Diagnosis may be confirmed with plain lateral radiographs of the ankle, which will show the os trigonum behind the talus.
- MRI or ultrasound can assess soft tissue involvement including FHL tendon pathology and surrounding inflammation.
- A diagnostic local anaesthetic injection into the posterior ankle can confirm the diagnosis by temporarily relieving symptoms.
Conservative Management
Initial treatment is normally conservative and should be trialled for a minimum of 3 months before considering surgical referral:
- PRICE – Protection, Rest, Ice, Compression, Elevation to manage acute flare-ups
- NSAIDs – Short-term use of anti-inflammatory medication to reduce pain and swelling
- Corticosteroid injection – appropriate if the clinician is skilled in posterior ankle injection technique and diagnosis is confirmed
- Physiotherapy – stretching, strengthening, and proprioceptive exercises for the ankle
- Activity modification – reducing or temporarily stopping the provocative activity
Referral Indications
- Diagnostic uncertainty — particularly to exclude other posterior ankle pathology
- Failure of conservative measures after a minimum of 3 months
- Referral for formal physiotherapy assessment and rehabilitation programme
- Consideration of steroid injection, arthroscopic excision, or open excision of the os trigonum
Surgical Treatment
When conservative treatment fails, Mr Matthew Welck offers minimally invasive arthroscopic excision of the os trigonum. This keyhole procedure removes the offending bone through small incisions, resulting in rapid recovery and return to sport. Open excision is also available where indicated. Most patients experience significant improvement in symptoms following surgery.
Book an Appointment
For expert evaluation and treatment of os trigonum syndrome in London, please contact us to book a consultation with Mr Matthew Welck at one of his clinic locations across London and North London.