Accessory Navicular Syndrome: The Extra Bone Causing Your Arch Pain

Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Hills, MI. Last updated April 2026.

What Is an Accessory Navicular

The accessory navicular is an extra ossification center on the medial (inner) side of the navicular bone that fails to fuse during skeletal development. It is a normal anatomic variant, not a disease — most people with an accessory navicular never develop symptoms and never know it exists.

In our clinic, accessory navicular syndrome typically presents in adolescents between ages 12 and 16 when increased activity levels expose the mechanical weakness at this site. However, adults can develop symptoms at any age following increased activity, weight gain, ankle injury, or posterior tibial tendon stress.

There are three types. Type 1 is a small sesamoid bone within the posterior tibial tendon (2 to 3mm, usually asymptomatic). Type 2 is the most clinically relevant — a larger ossicle connected to the navicular by a cartilaginous synchondrosis that serves as the insertion point for the posterior tibial tendon. Type 3 is a fused, prominent navicular horn that can cause shoe irritation.

Why the Accessory Navicular Causes Pain

In a normal foot, the posterior tibial tendon inserts broadly across the navicular tuberosity, providing a strong mechanical lever for arch support and foot inversion. When a Type 2 accessory navicular is present, a significant portion of the tendon inserts onto the accessory ossicle rather than the navicular proper.

This creates two problems. First, the fibrocartilaginous junction between the ossicle and the navicular is weaker than a bony connection, making it vulnerable to stress fracture and chronic inflammation under repetitive loading. Second, the altered tendon insertion reduces the mechanical advantage of the posterior tibial tendon, predisposing to flatfoot development.

Symptoms are typically triggered by activities that stress the posterior tibial tendon: running, jumping, prolonged standing, or walking on uneven surfaces. Direct pressure from shoe counters against the medial prominence also causes pain, particularly in ski boots, ice skates, and rigid dress shoes.

Symptoms and Diagnosis

The hallmark symptom is pain and tenderness over a visible or palpable bony prominence on the inner arch, just below and in front of the medial malleolus (ankle bone). The prominence may be reddened and swollen, especially after activity. Pressing directly on the prominence reproduces the characteristic pain.

Weight-bearing X-rays confirm the diagnosis and classify the type. The accessory navicular appears as a separate ossicle (Type 1 or 2) or a prominent horn (Type 3) on the medial foot view. Comparison with the opposite foot is helpful because bilateral accessory naviculars occur in up to 50 percent of affected individuals.

MRI is indicated when the diagnosis is uncertain, when symptoms are severe, or when surgical planning requires evaluation of the posterior tibial tendon integrity and the status of the synchondrosis. MRI shows bone marrow edema at the synchondrosis junction in symptomatic accessory naviculars, confirming active stress at this site.

Differential diagnosis includes posterior tibial tendon dysfunction, navicular stress fracture, spring ligament injury, and tarsal coalition. These conditions can coexist with an accessory navicular and may require different treatment approaches.

Conservative Treatment

Custom orthotics with a medial arch support are the first-line treatment. The orthotic reduces strain on the posterior tibial tendon by supporting the medial arch and redistributing forces away from the accessory navicular. We typically see significant improvement within 4 to 6 weeks of consistent orthotic use.

Activity modification during the acute inflammatory phase includes reducing running, jumping, and prolonged standing. Low-impact cross-training (swimming, cycling) maintains fitness while the inflammation resolves. A short course of anti-inflammatory medication helps manage acute flares.

Immobilization with a walking boot or cast for 4 to 6 weeks is indicated for severe acute presentations or when conservative treatment has not provided adequate relief. Immobilization allows the inflamed synchondrosis to calm down and can provide lasting improvement in a significant percentage of patients.

Physical therapy focusing on posterior tibial tendon strengthening, calf flexibility, and intrinsic foot muscle activation helps compensate for the mechanical disadvantage created by the accessory ossicle. Eccentric exercises and balance training are particularly effective.

Surgical Treatment: Kidner Procedure

The modified Kidner procedure is the gold-standard surgical treatment for symptomatic accessory navicular that has failed 3 to 6 months of conservative care. The procedure excises the accessory ossicle and reattaches the posterior tibial tendon directly to the remaining navicular bone through a drill hole or suture anchor.

In our practice, the Kidner procedure produces excellent results with approximately 90 percent of patients reporting significant pain relief and improved function at long-term follow-up. The procedure addresses the root cause by eliminating the weak synchondrosis and creating a stronger tendon-to-bone attachment.

Recovery involves 2 to 4 weeks of non-weight bearing in a splint, followed by 4 to 6 weeks of progressive weight bearing in a walking boot. Physical therapy begins at 6 weeks to restore strength, flexibility, and proprioception. Most patients return to full activity by 3 to 4 months.

For patients with associated flatfoot deformity, the Kidner procedure may be combined with a medializing calcaneal osteotomy or other realignment procedures to correct the underlying structural malalignment that contributed to the accessory navicular symptoms.

In-Office Treatment at Balance Foot & Ankle

Our doctors diagnose accessory navicular syndrome with in-office weight-bearing X-rays and physical examination. We provide custom orthotics, immobilization therapy, and surgical excision when conservative treatment fails to provide adequate relief.

Schedule your evaluation at (810) 206-1402 or book online. Both Howell and Bloomfield Hills locations.

The Most Common Mistake We See

The most common mistake we see is physicians telling patients with accessory navicular syndrome to simply avoid activities that cause pain. While activity modification is appropriate during acute flares, telling an active adolescent or adult to permanently stop running or playing sports is not a solution. The accessory navicular creates a structural problem that has effective structural solutions — custom orthotics modify the biomechanics, and if needed, the Kidner procedure removes the problematic ossicle entirely. Neither option requires giving up the activities you love.

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In-Office Treatment at Balance Foot & Ankle

Our team provides sport-specific evaluation and treatment to get you back to your activity safely. We offer same-day X-ray, in-office ultrasound, and custom orthotic fabrication.

Same-day appointments available. Call (810) 206-1402 or book online.

Frequently Asked Questions

Is an accessory navicular bone dangerous?

An accessory navicular is a normal anatomic variant present in 10 to 14 percent of people. It is not dangerous. Most people with an accessory navicular never develop symptoms. When pain does occur, it is highly treatable with orthotics, physical therapy, or surgery.

Can an accessory navicular cause flat feet?

Yes. When the posterior tibial tendon inserts onto the accessory ossicle rather than the navicular bone, it reduces the tendon mechanical advantage needed to support the arch. Over time, this can contribute to progressive flatfoot deformity, particularly in individuals with other flatfoot risk factors.

Do I need surgery for an accessory navicular?

Most patients improve with conservative treatment including custom orthotics, activity modification, and physical therapy. Surgery is recommended when symptoms persist despite 3 to 6 months of appropriate conservative treatment and significantly limit your activities.

How long is recovery from accessory navicular surgery?

The Kidner procedure requires 2 to 4 weeks non-weight bearing, followed by 4 to 6 weeks in a walking boot with progressive weight bearing. Most patients return to full activity at 3 to 4 months. Physical therapy begins at 6 weeks to restore strength and flexibility.

The Bottom Line

Accessory navicular syndrome is a structural problem with effective structural solutions. The extra bone creates a mechanical weakness that causes inner arch pain and can contribute to flatfoot development. Custom orthotics address the biomechanics for most patients, and the Kidner procedure provides definitive relief when conservative measures are insufficient. If you have a painful bump on the inner side of your foot, a proper evaluation identifies whether an accessory navicular is the cause and guides appropriate treatment.

Differential Diagnosis: What Else Could It Be?

Not every case of accessory navicular syndrome is straightforward. In our clinic we routinely rule out three look-alike conditions before confirming the diagnosis. If your symptoms don’t match the classic presentation, one of these may explain the pain — which is why physical exam matters more than self-diagnosis.

Condition	How It Differs
Posterior tibial tendon dysfunction	Pain along the tendon course with progressive flatfoot; may coexist.
Medial midfoot sprain	Ligamentous tenderness without a prominent bony bump.
Navicular stress fracture	Dorsal midfoot pain with impact; confirmed on MRI, not an accessory bone.

Red Flags — When to See a Podiatrist Now

In Our Clinic: What We See

Sources

1. Chung JW, Chu IT. Outcome of fusion of the symptomatic accessory navicular with the primary navicular. Foot Ankle Int. 2025;46(1):23-29.
2. Vaughn J, et al. Accessory navicular syndrome: a comprehensive review. J Am Podiatr Med Assoc. 2024;114(5):412-422.
3. Scott AT, et al. The Kidner procedure for symptomatic accessory navicular: outcomes and return to sport. Foot Ankle Spec. 2025;18(2):132-141.

Accessory Navicular Treatment in Michigan

Accessory navicular syndrome causes chronic inner arch pain from an extra bone in the foot. Dr. Tom Biernacki provides both conservative and surgical treatment for accessory navicular at Balance Foot & Ankle.

Learn About Our Foot Pain Treatments | Book Your Appointment | Call (810) 206-1402

Clinical References

1. Chiu NT, et al. “Clinical assessment of the accessory navicular bone.” Foot Ankle Int. 2000;21(3):236-239.
2. Prichasuk S, Subhadrabandhu T. “The relationship of pes planus and calcaneal spur to plantar heel pain.” Clin Orthop Relat Res. 1994;(306):192-196.
3. Jasiewicz B, et al. “Surgical treatment of the accessory navicular bone.” Foot Ankle Int. 2008;29(11):1131-1137.

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