Os Trigonum Syndrome

OS Trigonum Syndrome

🦶 Introduction

Os Trigonum Syndrome (OTS) is a posterior ankle impingement condition stemming from an accessory ossicle—the os trigonum—located on the posterior aspect of the talus. Present in about 5–30% of individuals, this extra bone typically fuses during adolescence. However, when fused formation fails, repetitive or acute plantarflexion movements can compress the ossicle between the talus and calcaneus (the so-called “nutcracker phenomenon”), triggering pain, inflammation, and posterior ankle impingement, especially in athletes and dancers

✅ Structured Scientific Summary

1. Definition

Os Trigonum Syndrome is a form of posterior ankle impingement caused by a retained os trigonum that becomes symptomatic due to mechanical compression, often involving soft tissues such as the joint capsule or flexor hallucis longus tendon

2. Cause

  • Congenital origin: Failure of the secondary ossification center of the posterior talus to fuse (~7–15% prevalence)

  • Mechanism: Acute forced plantarflexion or repetitive overuse leads to pinching between talus and calcaneus, injuring surrounding soft tissue (capsule, FHL tendon)

  • Risk groups: Ballet dancers, soccer players, downhill runners, gymnasts due to extreme or frequent plantarflexion

3. Classification

  • OTS is one type of posterior ankle impingement syndrome (PAIS), which also includes impingement from bony spurs (Stieda’s process), soft tissue hypertrophy, or combined causes

  • Some cases originate from an unfused Stieda process or fracture of the lateral talar tubercle presenting similarly to an os trigonum

4. Signs & Symptoms

  • Pain: Deep ache at posterior ankle exacerbated by active or passive plantarflexion (e.g., pointe ballet, push-off, downhill walking)

  • Tenderness: Localized posterolateral midline, often palpable swelling or small lump

  • Limited ROM: Reduced plantarflexion due to mechanical block

  • Additional: Occasional clicking; symptoms may mimic Achilles tendon or posterior tibial issues, sometimes misdiagnosed

5. Current Treatment Trends

A. Conservative Management (≈60% success)

  • Initial phase: Rest, ice, NSAIDs, activity modification to reduce irritation

  • Immobilisation: Use of CAM boot or brace for 2–4 weeks in acute/refractory cases

  • Physiotherapy: Targeted to restore ROM, strengthen ankle stabilizers, normalize gait, proprioception, and modify biomechanics

  • Guided injections: Ultrasound-guided corticosteroids into posterior impingement space for severe cases

B. Surgical Intervention (~40%)

  • Indicated when conservative care fails or mechanical impingement severe (large ossicle, loose body, symptomatic Stieda’s process)

  • Typically performed arthroscopically to excise the os trigonum or resect Stieda’s process and debride hypertrophic soft tissue

  • Post-op rehab involves early ROM, proprioception, gradual strengthening; full return to sport ~2–3 months

6. Prognosis

  • Conservative: Many recover within 4–6 weeks, especially non-athletes; success rates ≈60%

  • Surgical: Excellent outcomes; most athletes return fully within 8–12 weeks; low recurrence rates

  • Complications rare, include persistent swelling or scar; effective post-op rehab mitigates these