Os Trigonum Syndrome – Pain From an Extra Bone Behind the Ankle
Os trigonum syndrome causes posterior ankle pain in dancers and athletes. Learn about this extra bone, diagnosis, and treatment options at CFFAI.
By Dr. Carli Hoover, DPM
Os Trigonum Syndrome – Pain From an Extra Bone Behind the Ankle
You feel sharp pain deep behind your ankle, especially when pointing your toes downward or pushing off to jump. The pain doesn't match typical ankle sprain symptoms, and standard ankle treatments haven't helped. You might have os trigonum syndrome—a condition caused by an extra bone fragment that develops in some people and can cause significant pain, especially in dancers, runners, and athletes. If you're experiencing mysterious ankle pain in Central Florida, this could be your answer.
What Is Os Trigonum?
Os trigonum is an extra bone—or more accurately, a bone fragment—located behind the ankle joint. Present in about 7-14% of the general population, this small accessory bone sits between the talus (ankle bone) and calcaneus (heel bone).
In most people, this bone causes no problems at all. They live their entire lives unaware it's there. However, in dancers, runners, and athletes who repeatedly point their toes or push off powerfully, the repeated motion can irritate or inflame the os trigonum, causing pain—a condition called os trigonum syndrome.
Who Develops Os Trigonum Syndrome?
This condition is particularly common in:
- Ballet dancers—the profession with the highest prevalence due to constant pointing and plantarflexion movements
- Runners—especially sprinters and distance runners
- Football and soccer players—activities involving explosive push-off movements
- Gymnasts and divers—sports requiring powerful ankle movements
- Rock climbers—who repeatedly point their feet and place weight on toes
While most people with os trigonum never experience problems, those who engage in high-impact or repetitive ankle movements risk developing irritation and inflammation.
Causes of Symptoms
Os trigonum syndrome develops through several mechanisms:
Repetitive Irritation
- Plantarflexion stress—repeatedly pointing the foot can irritate the bone
- Direct compression—pointing the foot compresses the space around the os trigonum
- Inflammation—chronic irritation triggers inflammatory response
Acute Injury
- Ankle sprain—trauma that irritates the bone and surrounding tissues The AAOS sprained-ankle page notes that a hard twist can injure more than the ligaments—cartilage and nearby bone can take a hit in the same event, which is why lingering posterior pain after a “simple sprain” deserves a second look.
- Direct blow—impact to the back of the ankle
- Sudden increase in activity—ramping up training intensity without proper progression
Anatomical Factors
- Large os trigonum—larger fragments are more likely to cause problems
- Tight surrounding tissues—limited space increases pressure on the bone
- Biomechanical issues—foot mechanics that increase stress on the posterior ankle
Symptoms: Posterior Ankle Pain with Purpose
If you have os trigonum syndrome, you'll experience:
- Pain deep behind the ankle—in the posterior ankle space
- Pain with plantarflexion—pointing your foot downward increases discomfort
- Pain with push-off movements—especially walking, running, or jumping
- Swelling and tenderness in the back of the ankle
- Difficulty with athletic activities—particularly those requiring explosive movements or toe-pointing
- Morning stiffness—pain that improves somewhat with activity
- Radiating discomfort—sometimes felt along the bottom of the foot
The pain typically worsens with activities and improves with rest, distinguishing it from other ankle conditions.
Diagnosis: Why Standard Ankle Imaging Might Miss It
At Central Florida Foot & Ankle Institute in Orlando, Altamonte Springs, Longwood, Lake Mary, and Sanford, Dr. Carli Hoover uses specialized diagnostic protocols:
Physical Examination
We assess your posterior ankle for tenderness, perform specific maneuvers that reproduce the pain with plantarflexion, and evaluate your overall ankle mechanics.
Imaging
- Lateral foot X-rays—may show the os trigonum clearly, though some people have anatomical variants that are harder to visualize
- Specialized ankle X-rays—taken at specific angles to better visualize posterior ankle structures
- MRI or CT imaging—definitively shows the os trigonum and any inflammation around it
- Ultrasound—dynamic imaging showing the relationship between the bone and surrounding tissues
Diagnostic Injection
If diagnosis remains unclear, we may perform a diagnostic injection around the os trigonum. If pain resolves with the injection, it confirms the bone is causing your symptoms.
Treatment Options: Conservative First, Surgery if Needed
Conservative Management (First-Line Treatment)
Most cases of os trigonum syndrome respond well to conservative care:
- Rest and activity modification—reducing repetitive plantarflexion activities
- Anti-inflammatory medications—NSAIDs to manage pain and inflammation
- Ice therapy—reducing inflammation and pain after activities
- Custom orthotics—shoe inserts that reduce plantarflexion stress and support foot mechanics
- Proper footwear—avoiding shoes that increase plantarflexion or put pressure on the posterior ankle
- Physical therapy—gradual strengthening and flexibility work
- Corticosteroid injections—targeted anti-inflammatory therapy around the os trigonum
Most athletes successfully manage os trigonum syndrome with these approaches, continuing to perform at high levels.
Surgical Excision
When conservative treatment fails after 2–3 months:
- Os trigonum excision—removing the bone fragment surgically
- Soft tissue repair—addressing any associated tendon or ligament damage
Surgical removal of the os trigonum provides excellent results for patients with persistent symptoms, with 90%+ satisfaction rates. Recovery typically involves 6–8 weeks of modified activity, followed by gradual return to full athletics.
When to Seek Care
If you have persistent posterior ankle pain, especially with plantarflexion or in the context of athletic activity, seek evaluation promptly. The earlier we diagnose and treat os trigonum syndrome, the faster you can return to pain-free activity.
Get Back to Your Sport
At Central Florida Foot & Ankle Institute, we understand that athletes need practical, effective solutions. Dr. Carli Hoover specializes in managing conditions that sideline performers and help them return to peak performance.
Call (407) 307-0006 or book at https://floridafai.intakeq.com/booking. Let's get you back to doing what you love.