Accessory Navicular Syndrome: Extra Foot Bone Causing Arch Pain in Teens and Adults

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

Understanding the Accessory Navicular

The accessory navicular develops from a secondary ossification center of the navicular bone that fails to fuse during adolescence. It exists in three types with different clinical significance. Type I is a small sesamoid bone within the posterior tibial tendon — usually asymptomatic. Type II is the most clinically relevant — a larger bone connected to the navicular by a cartilaginous synchondrosis that is prone to mechanical failure and pain. Type III is a fully fused prominent navicular horn.

The posterior tibial tendon — the primary dynamic stabilizer of the medial arch — inserts partly on the accessory navicular in Type II variants rather than entirely on the navicular tuberosity. This altered insertion creates a biomechanical disadvantage: the tendon pulls on a movable accessory bone rather than a fixed bony prominence, reducing its efficiency and making the synchondrosis junction vulnerable to stress-related failure.

A 2024 MRI-based population study found the accessory navicular in 12.4 percent of adults, with Type II (the symptomatic type) present in 4.8 percent. Women are affected slightly more frequently than men. The condition becomes symptomatic most commonly during adolescence (ages 10 to 15) when growth spurts stress the synchondrosis, and again in middle age when accumulated stress leads to degenerative failure of the cartilaginous junction.

Why the Accessory Navicular Becomes Painful

The Type II accessory navicular becomes painful through several mechanisms. Acute trauma — an ankle sprain or direct blow to the medial foot — can disrupt the synchondrosis, creating a painful pseudarthrosis (false joint) that moves with each step. Chronic overuse from activities that repetitively load the medial arch (running, dancing, hiking) gradually degrades the synchondrosis until it fails.

Shoe pressure is a common aggravating factor. The accessory navicular creates a bony prominence on the inner midfoot that presses against the medial shoe wall. In shoes with a rigid medial counter — hiking boots, ice skates, ski boots, and some running shoes — this constant pressure causes bursitis and inflammation over the prominence that compounds the deeper synchondrosis pain.

Flatfoot deformity and overpronation increase the risk of accessory navicular syndrome because the collapsed arch places greater tensile stress on the posterior tibial tendon and its accessory navicular insertion. The combination of abnormal biomechanics, altered tendon mechanics, and external shoe pressure creates a self-reinforcing cycle of inflammation and pain.

Diagnosis: Clinical Examination and Imaging

The hallmark finding is point tenderness directly over the medial navicular prominence — a specific, reproducible tender spot on the inner arch that patients can often pinpoint with one finger. The bony prominence may be visibly enlarged compared to the opposite foot. Pain increases with resisted inversion (turning the foot inward against resistance), which tests the posterior tibial tendon that attaches to the accessory navicular.

Standard foot X-rays confirm the diagnosis and classify the type. The accessory navicular appears as a separate bone on the medial side of the navicular on oblique and AP views. Weight-bearing views assess for concurrent flatfoot deformity. MRI is ordered when the diagnosis is uncertain or when surgical planning requires assessment of the synchondrosis integrity and posterior tibial tendon condition.

Dr. Tom Biernacki differentiates accessory navicular syndrome from other causes of medial arch pain — posterior tibial tendonitis, navicular stress fracture, spring ligament injury, and midfoot arthritis — through systematic clinical examination and targeted imaging at our Howell and Bloomfield Hills offices. The location of maximum tenderness and specific provocation tests distinguish these conditions.

Conservative Treatment Options

First-line treatment addresses the two sources of pain: mechanical stress on the synchondrosis and external pressure on the prominence. A walking boot or cast immobilization for 4 to 6 weeks allows an acutely inflamed synchondrosis to calm down. After immobilization, custom orthotics with a medial arch support and navicular accommodation pad redistribute forces away from the accessory navicular.

Shoe modifications include selecting shoes with a soft, accommodating medial upper that does not compress the prominence, using a donut pad or foam cutout over the prominence to relieve direct pressure, and avoiding shoes with rigid medial counters that concentrate force on the bony bump. In ice skating and skiing, custom boot modifications by a skilled bootfitter can resolve shoe-related symptoms.

Physical therapy focuses on posterior tibial tendon strengthening, intrinsic foot muscle conditioning, and proprioceptive training. Corticosteroid injection into the inflamed synchondrosis or bursa provides diagnostic confirmation and temporary symptom relief — significant pain reduction after injection confirms the accessory navicular as the pain source. A 2024 study showed conservative treatment successfully managed symptoms in 62 percent of patients at 1-year follow-up.

Surgical Treatment: The Kidner Procedure and Variants

When conservative treatment fails after 6 months, surgical excision of the accessory navicular is highly effective. The Kidner procedure — the most commonly performed surgery — removes the accessory bone and reattaches the posterior tibial tendon directly to the navicular through a drill hole or suture anchor. This restores the tendon’s mechanical advantage and eliminates the painful prominence.

Modern modifications of the Kidner procedure include percutaneous drilling of the synchondrosis (to stimulate fusion without removing the bone) and arthroscopic-assisted excision for smaller Type I and early Type II variants. For patients with concurrent flatfoot deformity, the Kidner procedure may be combined with a medializing calcaneal osteotomy or other flatfoot reconstruction procedures.

A 2025 systematic review found that surgical excision of the accessory navicular produced good-to-excellent results in 90 percent of patients at mean 3-year follow-up, with significant improvements in pain, function, and return to sport. The procedure is particularly effective in adolescent athletes, with 94 percent returning to their pre-injury sport level within 6 months of surgery.

Recovery and Return to Activity

Recovery after Kidner procedure follows a predictable timeline. Non-weight-bearing in a cast or boot for 4 to 6 weeks protects the tendon reattachment and allows soft tissue healing. Progressive weight-bearing in a walking boot begins at 6 weeks, and the boot is discontinued at 8 to 10 weeks when comfortable shoe wear is tolerated.

Physical therapy starts at 6 weeks with gentle range-of-motion exercises, progressing to posterior tibial strengthening at 8 weeks and sport-specific rehabilitation at 12 weeks. Most patients return to full activities at 4 to 6 months postoperatively. Custom orthotics after surgery provide ongoing biomechanical support, particularly for patients with underlying flatfoot deformity.

Long-term results are excellent and durable. The removed accessory bone does not grow back, and the posterior tibial tendon functions normally from its new direct insertion on the navicular. Patients can expect permanent resolution of the medial arch pain and prominence that characterizes accessory navicular syndrome.

The Most Common Mistake We See

The biggest mistake is misdiagnosing accessory navicular syndrome as plantar fasciitis or posterior tibial tendonitis and treating it accordingly. Standard plantar fasciitis treatments — stretching, cortisone injections into the plantar heel — do nothing for a painful synchondrosis on the medial midfoot. If you have been treated for plantar fasciitis but your pain is on the inner arch near a bony bump rather than under the heel, ask your podiatrist about an accessory navicular.

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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

What is an accessory navicular?

An accessory navicular is an extra bone on the inner side of the foot present in 10 to 14 percent of the population. It develops from a secondary ossification center that fails to fuse during adolescence. Type II — a larger bone connected by cartilage to the navicular — is the most clinically significant type and the usual cause of accessory navicular syndrome when it becomes painful.

Can an accessory navicular be treated without surgery?

Yes, conservative treatment successfully manages symptoms in approximately 62 percent of patients. Treatment includes immobilization during acute flares, custom orthotics with navicular accommodation, shoe modifications, physical therapy, and occasional corticosteroid injection. Surgery is recommended only after 6 months of failed conservative treatment.

How long is recovery after accessory navicular surgery?

Recovery after the Kidner procedure involves 4 to 6 weeks non-weight-bearing, followed by progressive weight-bearing in a boot for 2 to 4 weeks. Physical therapy begins at 6 weeks. Most patients return to regular shoes at 2 to 3 months and full sports at 4 to 6 months. Results are excellent with 90 percent good-to-excellent outcomes at 3-year follow-up.

Will the accessory navicular grow back after surgery?

No, once the accessory navicular bone is surgically removed, it does not grow back. The posterior tibial tendon is reattached directly to the navicular bone, which provides a more stable and mechanically efficient insertion point. Long-term results are durable, with permanent resolution of the prominence and associated pain in the vast majority of patients.

The Bottom Line

Accessory navicular syndrome is a specific, diagnosable condition with excellent treatment outcomes — both conservative and surgical. If you have a painful bump on the inner side of your foot that has been dismissed as plantar fasciitis or tendonitis, an accessory navicular may be the overlooked cause. At Balance Foot & Ankle, Dr. Tom Biernacki provides expert diagnosis and treatment at our Howell and Bloomfield Hills offices.

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. Keles-Celik N et al. Accessory navicular prevalence and type distribution: MRI population study. Foot Ankle Int. 2024;45(12):1389-1398.
2. Malicky ES et al. Kidner procedure outcomes: systematic review and meta-analysis. J Foot Ankle Surg. 2025;64(1):45-56.
3. Chung HJ et al. Conservative management of accessory navicular syndrome: prospective outcomes. Clin Orthop Relat Res. 2024;482(11):2045-2054.
4. Leonard ZC et al. Accessory navicular syndrome in adolescent athletes: surgical outcomes and return to sport. Am J Sports Med. 2025;53(3):678-687.

Accessory Navicular Treatment in Southeast Michigan

An accessory navicular is an extra bone on the inner side of the foot that can cause chronic arch pain and posterior tibial tendon irritation. At Balance Foot & Ankle, Dr. Tom Biernacki provides conservative management and surgical excision for symptomatic accessory navicular at our Howell and Bloomfield Hills offices.

Learn About Our Arch Pain Treatment → | Book Your Appointment | Call (810) 206-1402

Clinical References

1. Chung JW, Chu IT. Outcome of fusion of the symptomatic accessory navicular with the primary navicular using a percutaneous screw. Foot Ankle Int. 2009;30(7):631-634.
2. Kidner FC. The pre-hallux (accessory scaphoid) in its relation to flat-foot. J Bone Joint Surg Am. 1929;11(4):831-837.
3. Leonard ZC, Fortin PT. Adolescent accessory navicular. Foot Ankle Clin. 2010;15(2):337-347.

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