Treatment of Prominent Os Trigonum on X-ray
For a prominent os trigonum identified on X-ray, begin with conservative management including activity modification, NSAIDs, and physical therapy for 3-6 months; if symptoms persist despite conservative treatment, proceed to surgical excision via arthroscopic or open approach. 1
Initial Clinical Assessment
When an os trigonum is identified on radiographs, determine whether it is symptomatic or an incidental finding:
- Symptomatic presentation: Posterior ankle pain exacerbated by plantar flexion activities (ballet, soccer, push-off maneuvers), tenderness over the posterior ankle, and pain reproduction with forced plantar flexion 1
- Mechanism: Repetitive plantar flexion causing compression of the os trigonum between the posterior tibial lip and calcaneus 1, 2
- Associated pathology: Flexor hallucis longus tendon pathology is commonly present and should be evaluated 1
Diagnostic Imaging Algorithm
Initial Imaging
- Standard radiographs are appropriate for initial evaluation, including a lateral view in maximal plantar flexion to visualize the os trigonum position 1
Advanced Imaging (When Indicated)
- MRI without contrast is the preferred next study if symptoms persist and radiographs are equivocal, as it allows visualization of bone marrow edema within the ossicle, assessment of the synchondrosis, and evaluation of associated tendon pathology 3
- CT scan offers multiplanar characterization of the ossicle and synchondrosis, and can be used with arthrography to demonstrate disruption of the synchondrosis 3
- Bone scan can show increased radiotracer uptake at the synchondrosis in symptomatic cases, though positive findings lack specificity 3, 4
Treatment Algorithm
Conservative Management (First-Line)
All patients should begin with non-operative treatment:
- Activity modification: Avoid repetitive plantar flexion activities for 3-6 months 1
- Physical therapy: Focus on ankle strengthening and flexibility 1
- NSAIDs: For pain control 1
- Corticosteroid injection: Under fluoroscopic guidance into the synchondrosis can provide diagnostic confirmation and therapeutic benefit; 84% success rate with one or two injections 5
Surgical Management (When Conservative Treatment Fails)
Indications for surgery:
- Persistent symptoms after 3-6 months of conservative treatment 1
- Athletes requiring unavoidable plantar flexion for their sport 1
- Confirmed symptomatic os trigonum by diagnostic injection 5
Surgical options:
- Arthroscopic excision (preferred): Performed in prone position using posterolateral portals; allows complete excision with visualization of flexor hallucis longus tendon, no immobilization required postoperatively, full weight-bearing as tolerated 6
- Open excision: Alternative approach when arthroscopic technique is not feasible 1
Special Considerations
Acute Fracture of Os Trigonum
- Mechanism: Hyperplantar flexion injury causing compression fracture 2
- Diagnosis: CT is the imaging modality of choice when fracture is suspected 2
- Treatment: Conservative management is usually successful; immobilization and protected weight-bearing 2
Post-Traumatic Overload Syndrome
- Occurs after ankle sprain in inversion/plantar flexion where the os trigonum undergoes mechanical overload and becomes painful 5
- Corticosteroid injection resolves symptoms in 84% of cases 5
- Surgical excision reserved for the 16% who fail injection therapy 5
Critical Pitfalls to Avoid
- Do not assume all os trigonum findings are symptomatic: The os trigonum is present in 7% of the normal population and is often asymptomatic 4
- Do not proceed directly to surgery: Conservative management should always be attempted first, as most cases respond to non-operative treatment 1, 5
- Do not miss associated flexor hallucis longus pathology: This tendon is commonly involved and should be assessed during evaluation and surgical excision 1
- Do not confuse with posterior process fracture: CT imaging helps differentiate true fractures from os trigonum 2