Yes, a 12-mm os trigonum can absolutely cause posterior ankle pain after running a 10-km race
An os trigonum is a well-established cause of posterior ankle impingement syndrome, particularly in athletes who engage in repetitive plantar flexion activities like running, and a 12-mm ossicle is sufficiently large to cause mechanical impingement and pain. 1
Understanding Os Trigonum Syndrome in Runners
The os trigonum is the most common accessory bone of the foot and, while often asymptomatic, becomes problematic when subjected to mechanical overload 2. In runners, the repetitive push-off phase during running—especially over 10 km—involves forced plantar flexion that can compress the os trigonum between the posterior tibia and calcaneus, causing pain 1, 2.
Why This Occurs After a 10K Race
- Repetitive loading: The cumulative stress from thousands of push-off cycles during a 10-km run can trigger acute-on-chronic overload of a previously asymptomatic os trigonum 3
- Post-activity inflammation: The os trigonum can undergo mechanical stress, remain structurally intact, but become acutely painful due to surrounding soft tissue inflammation 3
- Size matters: A 12-mm os trigonum is substantial enough to create significant impingement during maximal plantar flexion 4
Clinical Presentation to Confirm
The runner should have:
- Posterior ankle pain localized behind the talus, worsened by plantar flexion or push-off movements 2
- Pain reproduction with forced plantar flexion on examination 2
- Tenderness over the posterolateral ankle, specifically at the os trigonum location 5
- Pain during or immediately after the running activity, particularly during the propulsive phase 1
Diagnostic Confirmation
While the provided evidence focuses primarily on ankle trauma and tibial stress injuries (which are not relevant here [@1-12@]), the research on os trigonum is clear:
- Radiographs will show the os trigonum 2, 5
- MRI can demonstrate bone marrow edema in the os trigonum and surrounding soft tissue inflammation if symptomatic 6, 7
- Diagnostic injection with local anesthetic under fluoroscopic guidance can confirm the os trigonum as the pain source 3
Important Differential Consideration
Don't miss concomitant flexor hallucis longus (FHL) tenosynovitis, which travels between the posterior tubercles of the talus and can be simultaneously affected 1, 8. The FHL muscle morphology, particularly a lower musculotendinous junction, may predispose to os trigonum syndrome 8. If pain persists despite appropriate treatment, consider subtalar joint pathology as well 7.
Initial Management Approach
- Activity modification: Reduce or temporarily cease running, particularly avoiding push-off intensive activities 1
- NSAIDs: Can reduce pain and swelling, though use cautiously as they may suppress natural healing 9
- Corticosteroid injection: Under fluoroscopic or ultrasound guidance into the os trigonum region—this resolves symptoms in approximately 84% of cases, though 32% may require a second injection 3
When Conservative Treatment Fails
If symptoms persist beyond 3 months of conservative management, surgical excision through posterior ankle endoscopy is highly effective 4, 5:
- Pain typically resolves within 3 weeks post-operatively 4
- Return to light running at 8 weeks 4
- Full return to sport at 3 months 4, 6
- Excellent long-term outcomes with average AOFAS scores of 87.6 points 5
Critical Timing Factor
Patients with symptoms lasting ≤2 years before surgery have significantly better outcomes (average AOFAS score 90 points) compared to those with >2 years of symptoms (78 points, p=0.011) 5. This emphasizes not delaying definitive treatment if conservative measures fail.
Key Pitfall to Avoid
Do not assume this is simply a "running overuse injury" requiring only rest. The os trigonum will continue to cause impingement with return to activity unless the underlying mechanical problem is addressed through either successful conservative management or surgical excision 2, 3.