A Painful Bony Bump on the Inner Arch — Especially in Active Adolescents
An accessory navicular is an extra bone — or, more precisely, an extra ossification center — located on the inner side of the foot just above the arch, adjacent to the navicular bone. It is a congenital anatomical variant present in approximately 4–14% of the population, the majority of whom have no symptoms from it at all. When it does become painful, the condition is called accessory navicular syndrome.
Symptoms most commonly appear in adolescence, when the bone is finishing its development (typically ages 8–13), often triggered by a new activity, a change in footwear, or a minor injury. Adults can also develop or redevelop symptoms, particularly with new footwear that rubs directly on the prominent bump. Our podiatrists evaluate and treat accessory navicular syndrome at our Coon Rapids and Golden Valley offices, serving patients across the north and west metro including Maple Grove, Ham Lake, Andover, Champlin, Blaine, Plymouth, Wayzata, Minnetonka, St. Louis Park, and Edina.
Most accessory navicular bones cause no symptoms and require no treatment. If your child has a visible or palpable bony bump on the inside of the foot but no pain or activity limitation, evaluation is usually not necessary unless symptoms develop. An accessory navicular discovered incidentally on an X-ray in an otherwise asymptomatic child does not require treatment or routine follow-up.
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The Three Types of Accessory Navicular
Healthcare providers classify accessory navicular bones into three types based on their anatomy and connection to the main navicular bone. Type determines the likelihood of symptoms and guides treatment:
| Type | Anatomy | Symptoms | Clinical Significance |
| Type I (Sesamoid) | A small, rounded ossicle embedded within the posterior tibial tendon (PTT), fully separate from the navicular. Present in approximately 30% of accessory navicular cases. | Rarely symptomatic. If pain occurs, it is from direct pressure of footwear on the ossicle. | Conservative treatment (padding, footwear modification) almost always sufficient. Surgery rarely needed. |
| Type II (Synchondrosis) | A larger accessory bone connected to the true navicular by a fibrocartilaginous synchondrosis (a fibrous joint). The posterior tibial tendon inserts primarily into the accessory bone rather than the true navicular. Present in approximately 55% of cases. | The most commonly symptomatic type. Pain at the medial arch from stress on the synchondrosis cartilage joint, Posterior Tibial Tendon tension, and shoe pressure on the prominent medial bump. Often associated with flatfoot. | The Type II synchondrosis can become inflamed from repetitive Posterior Tibial Tendon stress, direct trauma, or shoe friction. This is the type that most commonly requires treatment, including surgical excision when conservative care fails. |
| Type III (Cornuate navicular) | The accessory bone has fused completely to the true navicular, creating an enlarged, irregular navicular shape (“cornuate navicular”). Present in approximately 15% of cases. | Variable. The enlarged navicular may protrude medially and rub against shoes, causing bursitis or skin irritation. No synchondrosis pain because the bones are fused. | When symptomatic, management is similar to Type I — padding and footwear modification usually sufficient. Surgical shaving of the prominence occasionally needed. |
Why Type II is the most important: in Type II, the posterior tibial tendon — the primary tendon supporting the medial arch — inserts into the accessory bone rather than its normal attachment on the true navicular. This means contraction of the posterior tibial tendon loads the fibrocartilaginous synchondrosis between the accessory and true navicular. When this joint becomes inflamed or disrupted, it produces the characteristic medial arch pain of accessory navicular syndrome.
What Causes Symptoms to Develop?
The accessory navicular itself is present from childhood, but symptoms typically develop in response to a trigger that increases stress on the bone or surrounding tissue:
New or tight footwear: shoes that press directly on the prominence are one of the most common triggers. Athletic cleats, skating boots, ski boots, and narrow dress shoes are frequent offenders.
Acute injury: a sprain, direct blow to the foot, or fall can disrupt the fibrocartilaginous synchondrosis in Type II, triggering an inflammatory cycle that becomes chronic.
Adolescent growth and activity surge: symptoms commonly begin when an adolescent significantly increases their activity level or starts a new sport during the period when the accessory bone is ossifying (ages 8–13).
Flatfoot: a flat or pronated foot dramatically increases the tensile load on the posterior tibial tendon and, by extension, on the synchondrosis in a Type II accessory navicular. Children and adolescents with both flat feet and an accessory navicular are at significantly higher risk of developing symptoms.
Symptoms
A visible or palpable bony prominence on the inner side of the foot, just behind and above the arch, at the level of the navicular
Pain and tenderness directly over the prominence, typically worsened by activity, prolonged standing, or footwear pressure
Redness, swelling, or a callus/bursa over the medial prominence from chronic shoe friction
Pain with activities that load the posterior tibial tendon — running, jumping, push-off, walking uphill
Concurrent flatfoot — many patients with symptomatic Type II accessory navicular have a flat or pronated foot that is part of the same biomechanical picture
In adolescents: a history of a sprain or awkward step that initiated or acutely worsened the pain, followed by pain that does not resolve as expected
Diagnosis
Diagnosis is clinical, with imaging to classify the type and exclude other causes of foot pain. We assess the location and character of tenderness, the presence and size of the medial prominence, flatfoot deformity and Posterior Tibial Tendon (PTT) function, and whether the pain is reproduced by resisted inversion (testing the PTT directly).
X-ray — weight-bearing views of the foot identifies the accessory navicular, classifies the type, and assesses foot alignment and arch height. Most accessory navicular bones are readily visible on standard foot X-rays.
MRI — most useful when Type II synchondrosis inflammation is suspected or when the degree of PTT involvement needs to be characterized before surgical planning.
Treatment at Family Foot & Ankle Clinic
The majority of symptomatic accessory navicular cases — particularly in adolescents during a first episode — resolve with conservative management. Surgery is reserved for cases that have failed an adequate conservative trial.
Conservative Management
Activity modification. Reducing the aggravating activities — particularly those requiring forceful push-off, uphill walking, or prolonged running — while the inflammation settles. Complete rest is rarely necessary; relative rest and cross-training maintain fitness while protecting the inflamed synchondrosis.
Immobilization. For acute or severe episodes, a short-leg walking boot for 4–6 weeks effectively offloads the posterior tibial tendon and allows the synchondrosis to calm down. This is particularly effective after an acute traumatic event that has disrupted the synchondrosis.
Custom orthotics. The most important sustained conservative intervention. A custom orthotic with a medial arch support reduces the tensile stress on the posterior tibial tendon and the synchondrosis with every step. For patients with concurrent flatfoot, the orthotic also addresses the underlying biomechanical driver. More on our Custom Orthotics page.
Padding and footwear modification. A horseshoe pad or cut-out placed over the medial prominence reduces direct shoe pressure on the accessory navicular. Footwear with a wider last and no rigid medial seam eliminates shoe-on-bone friction. Cleats and skating boots should be modified with padding or replaced with better-fitting alternatives.
Physical therapy and stretching. Posterior tibial tendon strengthening (resisted inversion exercises) and calf flexibility work (gastrocnemius and soleus stretching) reduce the dynamic load on the synchondrosis during activity. See our Calf Stretching Guide below.
NSAIDs and ice. Anti-inflammatory medications and ice (15 minutes, wrapped in a thin towel, after activity) manage acute pain and inflammation. Adjunctive and not definitive.
Surgical Treatment — The Kidner Procedure
Surgery is considered when symptoms persist despite a thorough course of conservative treatment—typically at least 3–6 months of activity modification, supportive footwear, orthotics, physical therapy, and one or more periods of immobilization. The choice of procedure depends on the type of accessory navicular, the condition of the posterior tibial tendon, and whether a symptomatic flatfoot deformity is also present.
The Modified Kidner Procedure: The accessory navicular is excised (removed) and the posterior tibial tendon is advanced and securely reattached to the native navicular. This removes the painful accessory bone while restoring the tendon to its normal insertion.
Concomitant flatfoot correction: Many patients with a symptomatic accessory navicular also have a flexible flatfoot that contributes to ongoing strain of the posterior tibial tendon. In these cases, removing the accessory navicular alone may not adequately address the underlying biomechanical problem. Depending on the severity of the deformity, flatfoot reconstruction procedures may be performed at the same time to improve foot alignment, reduce stress on the posterior tibial tendon, and optimize long-term outcomes.
Simple excision (without PTT advancement): In selected patients—particularly those with a symptomatic Type I or Type III accessory navicular and otherwise normal foot alignment—simple excision of the accessory bone without posterior tibial tendon advancement or flatfoot reconstruction can provide excellent results.
When the procedure is appropriately matched to the patient’s anatomy and biomechanics, surgical outcomes are excellent.
See our Foot & Ankle Surgery Overview for general information on surgical care at our clinic.
Frequently Asked Questions
Does my child need surgery for an accessory navicular?
Not necessarily, and not as a first step. The majority of symptomatic accessory navicular cases respond to conservative management — particularly a well-fitted orthotic, activity modification, and a period in a walking boot during acute flares. Surgery is reserved for cases that have genuinely failed an adequate conservative trial. A single episode managed conservatively does not indicate surgery; recurrent episodes that consistently respond inadequately to non-surgical care do.
My child’s accessory navicular was found on X-ray after an ankle sprain. Does it need treatment?
Only if it is causing symptoms. An accessory navicular discovered incidentally on imaging — without pain directly at the site— does not require specific treatment. Many people have accessory naviculars that are found on X-ray without the patient ever having known about them. Focus management on the ankle sprain; the accessory navicular is managed only if it becomes independently symptomatic.
Not directly, but the two conditions are closely related. The posterior tibial tendon, which is the primary support for the medial arch, inserts into the accessory navicular rather than its normal attachment point in Type II cases. This abnormal insertion weakens the arch-supporting function of the PTT, predisposing to flat foot or worsening an existing flatfoot. Conversely, flatfoot increases PTT tension and makes the accessory navicular more symptomatic. Treating both the accessory navicular and the flatfoot — with appropriate orthotics for the flatfoot and management of the accessory navicular symptoms — typically produces better outcomes than managing them in isolation.
Will the accessory navicular come back after surgery?
No. Once the accessory navicular is removed, it does not regrow. Most patients experience lasting pain relief after surgery. However, persistent or recurrent pain can occur if scar tissue develops, the posterior tibial tendon remains irritated, or an underlying flatfoot deformity continues to place excessive stress on the tendon and inner foot. In patients with symptomatic flatfoot, correcting the accessory navicular alone may not fully address the underlying biomechanical problem. Long-term outcomes are generally excellent when the procedure is appropriately matched to the patient’s anatomy and foot alignment. If you have had accessory navicular surgery and continue to experience pain, our Second Opinion / Foot Pain Not Improving evaluation can help determine the cause and discuss treatment options.
Medial Arch Pain or a Painful Bony Bump on the Inner Foot? Let’s Find Out What’s Going On.
Accessory navicular syndrome is highly treatable, particularly when evaluated early and managed with the right combination of orthotics and activity modification. Surgery produces excellent outcomes for the cases that need it. Book an appointment at our Coon Rapids or Golden Valley office.
Call 763-421-7300 | Book online
Serving Coon Rapids, Golden Valley, Maple Grove, Ham Lake, Andover, Champlin, Blaine, Plymouth, Wayzata, Minnetonka, St. Louis Park, Edina, and all Twin Cities communities.