Os Tibiale Externum Syndrome

Os Tibiale Externum

🦶 Introduction

Os Tibiale Externum Syndrome (OTES)—also known as accessory navicular syndrome—is a painful condition that arises when an accessory ossicle (the os tibiale externum) located medial to the navicular bone becomes symptomatic. While present congenitally in approximately 4–14% of the population, symptoms typically manifest later due to mechanical irritation or increased stress on the posterior tibialis tendon (PTT), often contributing to medial foot pain and sometimes to dysfunctional biomechanics like flatfoot or tendon insufficiency 

✅ Structured Scientific Summary

1. Definition

  • An extra ossicle adjacent to the navicular bone (inside the arch), usually integrated into the distal PTT 

  • Symptoms—medial arch pain, swelling, and PTT irritation—collectively define os tibiale externum syndrome 

2. Cause

  • Congenital persistence of a secondary ossification center that fails to fuse by adolescence 

  • Symptom onset triggers include: trauma (e.g., ankle sprains), overuse, ill‑fitting footwear, and flatfoot biomechanics placing increased strain on the PTT 

  • Os classification types (Geist):

    • Type I: small sesamoid in PTT—rarely symptomatic.

    • Type II: triangular ossicle connected via cartilage—most symptomatic.

    • Type III: fused cornuate tuberosity—prominent and occasionally painful 

3. Classification

  • Geist classification outlines three types—as above 

  • Type II is most clinically significant: the cartilaginous synchondrosis allows motion and pain, and portions of PTT may insert on it 

4. Signs & Symptoms

  • Medial arch pain, often dull or throbbing, exacerbated by: weight-bearing, running, footwear pressure 

  • Palpable bony prominence with localized swelling an

  • Tenderness along PTT, possible weakened midfoot posture or PTT dysfunction 

  • Associated flatfoot (pes planovalgus) is common, often contributing to symptom development 

  • Onset typically in adolescence or adulthood after ossification or increased activity 

5. Current Treatment Trends

A. Conservative Management (≈70–80% success)

  • Rest, NSAIDs, ice, and activity modification—initial strategy 

  • Immobilisation: short leg cast or boot for 4–6 weeks during acute flares 

  • Physical therapy:

    • Strengthening PTT and intrinsic foot muscles

    • Stretching calf and posterior tibialis

    • Proprioception and gait retraining

    • Orthotic management (arch support, shoe modifications) 

  • Imaging-confirmed interventions: guided corticosteroid injections, shockwave therapy (supported by recent case success) 

B. Surgical Intervention (~20–30% of cases)

  • Indications: persistent pain, failed conservative management, Type II/III prominence, or PTT dysfunction 

  • Procedures: excision of ossicle ± repair of PTT, Kinder procedure (osteotomy + tendon realignment) 

  • Post-op rehab: early ROM; progressive strengthening and proprioception; return to activity typically in 8–12 weeks.