Accessory Navicular Syndrome: Causes & Treatment | Podiatrist Howell MI

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A painful bump on the inside of your foot — between the arch and the ankle — that seems to rub against every shoe you own may be an accessory navicular. It’s one of the most common normal anatomical variants of the foot, yet it causes significant pain and disability when it becomes inflamed or when the posterior tibial tendon attached to it is stressed.

Dr. Tom Biernacki, DPM explains what the accessory navicular is, why it causes pain, and the conservative and surgical options available at Balance Foot & Ankle.

What Is the Accessory Navicular?

The accessory navicular (also called os tibiale externum) is a small extra bone or cartilaginous fragment on the medial (inner) aspect of the navicular — the keystone bone of the medial arch. It’s present in 10–15% of the population and is usually bilateral. In most people, it never causes any symptoms. Problems arise when the accessory bone is prominent enough to irritate footwear, or when the posterior tibial tendon — which attaches partly to it — is overloaded.

The Geist classification describes three types: Type 1 is a small, rounded os within the posterior tibial tendon (most common, rarely symptomatic). Type 2 is a larger accessory bone connected to the navicular by a fibrocartilaginous synchondrosis — this type is the most commonly symptomatic. Type 3 represents a fused accessory bone that creates a prominent “cornuate navicular” — visible as a large bump on the medial foot.

Symptoms of Accessory Navicular Syndrome

• Medial midfoot pain — aching or tenderness over the inner foot prominence
• Visible or palpable bump on the inner side of the foot at the navicular
• Redness or swelling over the prominence — from shoe friction
• Pain with activity — standing, walking, running, or sports
• Worsening with flat footwear — shoes without arch support load the posterior tibial tendon more
• Onset often in adolescence — when bone maturation finalizes and activity levels peak

Diagnosis

Diagnosis begins with palpation of the medial midfoot — tenderness directly over the navicular prominence is the key clinical sign. Weight-bearing X-rays demonstrate the accessory bone and classify its type. MRI is used when symptoms are severe or surgery is being considered, demonstrating synchondrosis edema (bone marrow signal changes indicating stress or micro-fracture), posterior tibial tendon integrity, and associated plantar fascia involvement. Ultrasound can assess the posterior tibial tendon dynamically for tendinosis or tearing.

Accessory Navicular Treatment

Conservative Treatment

The vast majority of accessory navicular syndrome cases respond to conservative care. The primary goals are reducing pressure on the prominent bone and offloading the posterior tibial tendon.

Footwear modification: wide, soft shoes that don’t press against the medial midfoot bump. A small donut pad around the prominence creates a pressure-free zone and is often the most immediately effective intervention. Custom orthotics with medial arch support reduce posterior tibial tendon stress by supporting the arch and controlling pronation — this is essential for patients with flat feet, who make up the majority of symptomatic cases.

For acute flare-ups: a short leg cast or CAM walker boot for 4–6 weeks offloads the synchondrosis completely and resolves active inflammation. Ice and NSAIDs manage pain. Physical therapy focuses on posterior tibial tendon strengthening and proprioceptive training once the acute phase resolves.

Surgical Treatment (Kidner Procedure)

When conservative care fails after 3–6 months of consistent treatment, surgery is indicated. The Kidner procedure — originally described in 1929 and still the gold standard — involves excision of the accessory navicular bone and advancement of the posterior tibial tendon to a more plantar insertion point on the navicular, improving its mechanical advantage for arch support.

Modern modifications of the Kidner procedure achieve excellent results — 80–90% of patients report significant pain reduction and high satisfaction. Recovery involves 6 weeks non-weight-bearing followed by progressive rehabilitation; return to sports typically takes 3–6 months. A simple excision without tendon advancement (for Type 1 or 3) has an even faster recovery.

Frequently Asked Questions

Is the accessory navicular normal?

Yes — it’s a normal anatomical variant present in 10-15% of people. Most people with an accessory navicular never experience any pain from it. It becomes symptomatic in a subset of people, usually those with flat feet, who are very active, or who wear narrow footwear. Having an accessory navicular doesn’t automatically mean you’ll need treatment.

Does the accessory navicular cause flat feet?

The accessory navicular doesn’t cause flat feet directly, but the two conditions are strongly associated. Flat feet increase posterior tibial tendon loading, which stresses the synchondrosis of a Type 2 accessory navicular — making symptomatic disease much more likely. Treating the flat foot with orthotics reduces stress on the accessory navicular and is often the key to resolving symptoms without surgery.

Sources

1. Kidner FC. The prehallux (accessory scaphoid) in its relation to flat-foot. J Bone Joint Surg Am. 1929;11(4):831-837.
2. Sullivan JA, Miller WA. The relationship of the accessory navicular to the development of the flat foot. Clin Orthop Relat Res. 1979;144:233-237.
3. Scott AT, et al. Accessory navicular syndrome. Foot Ankle Clin. 2009;14(4):711-722.

Related Care at Balance Foot & Ankle

Clinical navicular services at our Howell and Bloomfield Hills offices.

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