Accessory Navicular

Quick answer

An accessory navicular is an extra small bone or piece of cartilage located on the inner side of the midfoot, just behind the arch — next to the regular navicular bone. About 4–14% of people have one, most of whom never know it. When it becomes painful, it typically presents as arch pain in adolescents or active adults.

How to recognize it

When symptomatic:

• Pain on the inside of the arch, just in front of the medial ankle
• A visible bony bump at the inner arch
• Tenderness when pressing on the bump
• Pain with activity, especially running, jumping, or dancing
• Worse in tight shoes or shoes that rub against the prominence
• Sometimes pain after a twisting injury that strained the connection
• Can mimic posterior tibial tendon dysfunction — and the two often coexist

The bump is usually visible to the naked eye, especially when standing — it sits about a thumb’s width forward and slightly downward from the inner ankle bone.

The three types

Accessory naviculars are classified by anatomy:

• Type I — a small sesamoid bone within the posterior tibial tendon. Usually asymptomatic. About 30% of accessory naviculars.
• Type II — connected to the navicular by a fibrocartilaginous bridge (synchondrosis). The most commonly symptomatic type. About 50–60% of cases.
• Type III — fused to the navicular as a bony prominence (sometimes called “cornuate navicular”). Symptoms when the prominence rubs on shoes.

The type matters because it influences treatment — Type II responds best to surgery if needed; Type III is more about footwear modification.

Why this becomes painful

Most accessory naviculars are silent. Pain typically develops because:

• Adolescent growth spurt — the connection between accessory and main navicular is stressed
• Trauma — an inversion injury sprains or breaks the synchondrosis
• Increase in activity — new sport or training intensity
• Posterior tibial tendon strain — the tendon attaches to or near the accessory bone, transmitting force
• Footwear pressure — narrow or stiff shoes rub the prominence
• Flat feet — the posterior tibial tendon works harder, stressing the attachment

Because the posterior tibial tendon plays such a central role in arch support, an unstable accessory navicular can contribute to flat feet — and vice versa.

Diagnosis

• Physical exam — tenderness over the prominence, sometimes pain with resisted foot inversion
• X-rays — show the accessory bone and its type
• MRI — looks for inflammation at the synchondrosis (a Type II that’s “hot”) and posterior tibial tendon involvement
• Bone scan — occasionally used to confirm the accessory is the source of pain

Treatment

Conservative care (first-line for most)

• Activity modification — reduce activities that aggravate pain
• Wider shoes with soft padding over the prominence — eliminate direct pressure
• Custom orthotics with arch support and a medial post — unloads the posterior tibial tendon
• NSAIDs for inflammation
• Walking boot for 4–6 weeks for severe pain or after acute injury — often allows the synchondrosis to settle
• Physical therapy — posterior tibial tendon strengthening, calf stretching
• Cortisone injection in selected cases

A significant majority of symptomatic accessory naviculars settle with conservative care, especially after a flare related to growth or new activity.

Surgery

For pain that doesn’t respond to 3–6 months of dedicated conservative care:

• Kidner procedure — the classic surgery: removes the accessory bone and reattaches the posterior tibial tendon to the main navicular. Generally well-tolerated.
• Modified Kidner — variations on the above
• Synchondrosis fusion — joins the accessory to the main navicular as a single bone
• Recovery typically 6–12 weeks; non-weight-bearing initially, then progressive
• Outcomes are generally good in well-selected patients

If posterior tibial tendon dysfunction has developed alongside the accessory navicular, surgery may need to address both.

Bottom line

Most accessory naviculars are anatomic curiosities that never cause trouble. When they do, it’s usually in adolescence or after a change in activity. Footwear modification, orthotics, and a course of relative rest resolve most symptomatic cases. Surgery (the Kidner procedure) is well-established for cases that don’t respond — but it’s reserved for genuinely persistent pain after a real trial of conservative care.