- The accessory navicular is an extra bone on the inner midfoot, present in roughly 1 in 10 people and usually asymptomatic.
- It becomes painful when the bone or the posterior tibial tendon attached to it is irritated by activity, footwear pressure, or an ankle injury.
- It often shows up in adolescence as the bone matures, or in adults after an ankle sprain or tendon injury.
- Most cases respond to immobilization, supportive footwear, custom orthotics, and PT.
- Surgery — removing the accessory bone and reattaching the posterior tibial tendon — is reserved for symptomatic cases that don't respond to conservative care.
What is accessory navicular syndrome?
The accessory navicular (also called os tibiale externum) is an extra bone or piece of cartilage that develops on the inside of the midfoot, just above the arch. It's a normal anatomic variant — present in 4 to 14 percent of people — and most carry it through life without ever knowing. The bone sits adjacent to or within the posterior tibial tendon, the tendon that helps hold up the arch of the foot.
When the bone becomes painful, the condition is called accessory navicular syndrome. The most common triggers are adolescent growth, footwear that rubs against the bony prominence, overuse from sports, or an ankle sprain that pulls on the posterior tibial tendon. People with flat feet are particularly prone because the posterior tibial tendon works harder in a flat foot, which transmits more force through the accessory bone.
At Northwest Extremity Specialists, we treat accessory navicular syndrome conservatively first — and that approach works for the vast majority of patients. Our podiatrists confirm the diagnosis with examination and X-ray, build a stepped plan to settle the inflammation, and reserve surgical removal for the cases that genuinely need it.
See it in motion
Animations licensed from ViewMedica · Swarm Interactive
The navicular is a wedge-shaped bone in the middle of the foot, sitting between the talus (ankle bone) and the cuneiforms (which connect to the toes). The posterior tibial tendon attaches to it and is one of the main supports of the arch. An accessory navicular is an extra piece — sometimes a separate bone connected by cartilage, sometimes a bony hook extending off the main bone. Because the tendon attaches there, any pull on the tendon pulls on the extra piece, which is what generates pain.
What it feels like
Accessory navicular syndrome typically presents with a recognizable triad:
- A visible, hard bony bump on the inside of the midfoot, just above the arch
- Redness and swelling over the bump, especially after activity or in close-fitting shoes
- Vague aching pain in the midfoot and along the arch, worst during or after activity
- Pain when shoes press directly against the prominence
- Pain that may radiate down the arch or up toward the inner ankle
- Symptoms that often first appear during adolescence
- Worsening symptoms after an ankle sprain
Why it develops
You're born with the accessory navicular — but several things can make it become symptomatic:
- Trauma — ankle or midfoot sprains that pull on the posterior tibial tendon
- Chronic irritation from tight or rigid shoes rubbing the bony bump
- Overuse from running, hiking, dancing, or sports with repetitive foot loading
- Flat feet — the posterior tibial tendon works harder, increasing stress on the bone
- Adolescence — when the bone matures and surrounding cartilage hardens
How we diagnose accessory navicular syndrome
A first visit takes about 30 minutes. Your podiatrist will ask about the pain pattern, examine the inside of the foot for the bony prominence, redness, and tenderness, and check the integrity of the posterior tibial tendon. Standard X-rays usually confirm the accessory bone and reveal its specific type (the most painful type is the one connected to the main navicular by a cartilage bridge). MRI is reserved for cases where the diagnosis is unclear or where tendon injury is suspected. Most patients leave the same day with a clear diagnosis and a written plan.
Non-surgical care
Most accessory navicular syndrome settles with structured conservative care. Our typical plan:
- Short period of immobilization — walking boot or below-knee cast — for an acutely inflamed bone
- Ice and anti-inflammatory medication during the first 1–2 weeks
- Custom orthotics with arch support to offload the posterior tibial tendon
- Footwear modifications — soft uppers, padding, and avoiding shoes that press the bump
- Physical therapy for posterior tibial tendon strengthening once the acute inflammation has settled
- A graduated return to activity guided by symptoms
- Steroid injection in selected cases (used cautiously — repeated injections can weaken the tendon)
Surgical care
Surgery is reserved for symptomatic accessory navicular that has not responded to a thorough conservative trial of at least 3–6 months. The goal is to remove the accessory bone and restore the normal pull of the posterior tibial tendon.
- Kidner procedure — excision of the accessory bone with reattachment or advancement of the posterior tibial tendon
- Tendon repair when there is associated posterior tibial tendinopathy
- Concomitant flatfoot reconstruction in patients whose accessory navicular is part of a larger arch-collapse problem
Recovery from a Kidner procedure typically involves 4–6 weeks of protected weight-bearing in a boot, transition to athletic shoes over the following month, and return to higher-impact activity by 3 months. Custom orthotics are usually worn after surgery to support the reattached tendon.
When to see a specialist
- A painful bony bump on the inside of your midfoot that has lasted more than a couple of weeks
- Adolescent foot pain in the arch or inner midfoot, especially with new sport activity
- Worsening midfoot pain after an ankle sprain
- Pain plus redness or swelling over the inner midfoot
- Difficulty fitting shoes because of the bump
Accessory navicular syndrome is evaluated by any of our board-certified podiatrists. Surgical management — the Kidner procedure — is performed by Dr. Mia Horvath, Dr. Thomas Melillo, Dr. Denny Le, and Dr. Yama Dehqanzada, all of whom handle reconstructive foot procedures regularly.