Accessory Navicular Syndrome: Painful Extra Bone on the Inner Foot

Quick answer: Treatment for accessory navicular syndrome treatment follows a stepwise approach: 1) conservative care first (rest, ice, supportive footwear, OTC anti-inflammatories), 2) physical therapy and targeted exercises, 3) in-office treatments (injections, custom orthotics) if conservative fails at 4-6 weeks, 4) surgery for refractory cases. Most patients resolve at step 1 or 2. Call (810) 206-1402.

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?

An accessory navicular is an extra piece of cartilage or bone located on the inner side of the foot, just above the arch. It sits adjacent to the navicular bone—one of the key bones of the midfoot—and is present in approximately 10–14% of the population. While many people have an accessory navicular and never experience problems, a significant subset develop accessory navicular syndrome: a painful condition in which the extra bone causes irritation, inflammation, and arch dysfunction.

Types of Accessory Navicular

Podiatrists classify accessory naviculars into three types based on radiographic appearance. Type I is a small sesamoid bone embedded within the posterior tibial tendon, rarely symptomatic. Type II is the most clinically significant—a triangular or heart-shaped accessory bone connected to the main navicular by fibrocartilage; this synchondrosis (fibrocartilaginous junction) is prone to micro-motion and inflammation, causing the majority of symptomatic cases. Type III represents a fused accessory navicular that has become incorporated into the main navicular, creating a prominent navicular tuberosity—sometimes called a cornuate navicular.

Causes and Risk Factors

The accessory navicular is a congenital variant, meaning it forms during fetal development and is present from birth. Symptoms most commonly emerge during adolescence (ages 10–16) when rapid growth and increased sports participation stress the accessory bone. Adults may develop symptoms after trauma, prolonged standing occupations, or changes in footwear. Flat feet (pes planus) significantly increase risk because the posterior tibial tendon—which attaches to or near the accessory navicular—is placed under greater tension with every step in a flatfooted individual.

Symptoms

The hallmark presentation is a prominent, bony bump on the inner midfoot with overlying redness and tenderness. Pain worsens with activity, shoe pressure on the prominence, and prolonged weight-bearing. Many patients note arch fatigue and medial ankle weakness. Acute flares of swelling and sharp pain can occur following minor trauma or after starting a new sport or activity.

Diagnosis

Diagnosis is confirmed with weight-bearing foot X-rays that clearly demonstrate the accessory bone and its relationship to the navicular. MRI is valuable for assessing the integrity of the synchondrosis (looking for bone marrow edema and fibrocartilage disruption) and evaluating posterior tibial tendon health.

Conservative Treatment

Non-surgical management is successful in the majority of patients, particularly children and adolescents. Rest and activity modification reduce stress on the painful area. Custom foot orthotics with a medial arch support and navicular padding offload the accessory bone and correct the flatfoot biomechanics that perpetuate symptoms. Immobilization in a walking boot for 4–6 weeks allows the inflamed synchondrosis to calm. Physical therapy strengthens the posterior tibial tendon and intrinsic foot muscles. Corticosteroid injection may be used selectively to reduce acute inflammation.

Surgical Treatment: The Kidner Procedure

When conservative care fails to provide lasting relief, the Kidner procedure is the gold standard surgical treatment. Named for the surgeon who described it, this procedure involves excising the accessory navicular, reattaching the posterior tibial tendon firmly to the native navicular, and reshaping any bony prominence. Performed as an outpatient under ankle block anesthesia, the surgery has excellent outcomes with patient satisfaction rates consistently above 85%. Recovery involves 4–6 weeks non-weight-bearing followed by physical therapy, with return to sports typically achieved by 4–6 months postoperatively.

Accessory Navicular Treatment in Michigan

An accessory navicular — a painful extra bone on the inner arch — causes chronic arch pain and difficulty with footwear. Dr. Tom Biernacki provides custom orthotics, immobilization, and surgical excision (Kidner procedure) for symptomatic accessory navicular at Balance Foot & Ankle.

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

Clinical References

1. Kiter E, Erdag N. “Accessory navicular and clinical significance.” Foot Ankle Int. 2005;26(5):415-417.
2. Chiu NT, et al. “Clinical use of technetium-99m methylene diphosphonate bone scan to evaluate accessory navicular syndrome.” Clin Nucl Med. 2000;25(6):442-446.
3. Kidner FC. “The pre-hallux (accessory scaphoid) in its relation to flat-foot.” J Bone Joint Surg Am. 1929;11(4):831-837.

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.

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In Our Clinic: What We See

In-Office Treatment at Balance Foot & Ankle

If home treatment isn’t providing relief for your flat feet, our podiatry team at Balance Foot & Ankle can help with same-day evaluations and advanced in-office care.

Related Care at Balance Foot & Ankle

Clinical navicular services at our Howell and Bloomfield Hills offices.

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