Accessory Bones and Sesamoid Problems in the Foot and Ankle
Overview
Accessory bones are small extra bones (ossicles) that occur as normal developmental variations. Most are painless and need no treatment. Symptoms arise only when an ossicle is stressed, rubs in footwear, irritates a tendon or is injured. The sesamoids beneath the big-toe joint are normal bones rather than accessory bones and can develop overload, fracture, arthritis or loss of blood supply. Imaging must be matched carefully to the site and pattern of symptoms.
Common symptomatic patterns
- Accessory navicular: pain and shoe pressure over the inner midfoot, sometimes associated with flatfoot or posterior tibial tendon irritation.
- Os trigonum: pain at the back of the ankle with repeated pointing of the foot, ballet, kicking or downhill activity.
- Os peroneum: pain along the outer midfoot related to the peroneus longus tendon.
- Os subfibulare or other lateral ossicle: may represent a developmental bone or old avulsion injury and can coexist with ankle instability.
- Sesamoid disorder: pain beneath the big-toe joint from overload, stress injury, fracture, arthritis or avascular necrosis, which means loss of blood supply to the bone.
Assessment
The presence of an accessory bone on X-ray does not prove it is painful. Assessment localises tenderness, reproduces symptoms with movement or tendon loading and reviews foot alignment, footwear and activity. A recent injury may make it difficult to distinguish an accessory ossicle from a fracture.
Weight-bearing X-rays are usually the first investigation. CT defines bone shape and whether bones have joined; MRI shows bone stress and problems affecting cartilage, tendons or other soft tissues; ultrasound can assess nearby tendons during movement. Comparison with the other foot is occasionally useful.
Non-surgical treatment
- Temporary modification of the movement or activity that loads the painful region.
- Footwear change, padding or relief of direct pressure.
- An insole to redistribute load or support an associated flatfoot or high-arched foot.
- A short period in a Moonboot for acute bone or tendon irritation in selected cases.
- Physiotherapy to restore strength, control and gradual return to activity.
- Pain-relieving or anti-inflammatory medicine after checking that it is suitable for your health and current medicines.
- A precisely targeted injection may be used selectively for diagnostic clarification or temporary relief. Injection into vulnerable tendon tissue is avoided, and injection around a sesamoid or soft-tissue structure requires careful technique.
When may surgery be considered?
Surgery is considered only when symptoms remain clearly localised and limiting despite appropriate non-surgical treatment. The operation depends on the specific structure and any associated tendon, ligament or alignment problem.
Examples include excision of a symptomatic accessory navicular with treatment of the posterior tibial tendon, removal of an os trigonum, treatment of an os peroneum with peroneal tendon repair, or excision or fixation of a symptomatic lateral ossicle with ligament stabilisation. Sesamoid surgery is used cautiously because removing a sesamoid can alter big-toe mechanics and alignment.
Recovery
Recovery depends on whether the procedure is isolated bone excision or includes tendon repair, ligament reconstruction, bone fixation or foot realignment. A postoperative shoe, splint or Moonboot may be required and weight-bearing restrictions vary.
Swelling and local sensitivity can persist after the wound has healed. Rehabilitation restores movement, tendon strength and sport-specific loading.
Risks and limitations
- Persistent pain if the accessory bone was incidental rather than the main pain source.
- Infection, wound problems, numbness or scar sensitivity.
- Tendon weakness, instability or recurrence when associated pathology remains.
- Failure of bone healing after fixation or fracture treatment.
- Altered big-toe alignment or transfer pain after sesamoid excision.
- Need for further surgery.
Frequently asked questions
Does an accessory bone need removal?
No. Most are normal variants and require no treatment unless they clearly match persistent symptoms.
Is an os trigonum the same as a fracture?
No. It is usually developmental, but a recent injury can disrupt it or mimic a posterior talar fracture, so clinical context matters.
Why can an accessory navicular hurt?
It may rub in shoes, become stressed at its connection to the navicular or irritate the posterior tibial tendon.
Can a sesamoid fracture heal without surgery?
Many can be treated with prolonged off-loading, footwear modification and gradual rehabilitation. Displacement, failure of bone healing or persistent symptoms may require specialist review.
Can one sesamoid simply be removed?
Sometimes, but excision changes the balance of the big-toe joint and can cause deformity or transfer pain, so it is reserved for selected cases.
General information
This page provides general information only. It cannot diagnose your condition or replace advice from a clinician who has assessed you. Your treatment and recovery plan may differ from the examples described here. Follow the instructions from your treating team. In an emergency, call 000 or attend the nearest emergency department.