An accessory navicular is an extra bone found on the inner side of the foot, just above the arch. Present in approximately 4% to 21% of the population, this congenital anomaly is often an incidental finding that causes no issues. However, for a small percentage—less than 1%—this extra bone becomes painful, leading to a condition known as accessory navicular syndrome (ANS). This pain typically arises in adolescence when the bone fully ossifies, or following an injury that disrupts the cartilaginous connection between the extra bone and the main navicular bone. The primary driver of pain is often inflammation at the attachment site of the posterior tibial tendon, a crucial structure that supports the foot’s arch.
The approach to treating an accessory navicular is a stepwise journey. It begins with simple, non-invasive measures, progresses to more structured conservative care, and, in a minority of cases where symptoms persist, culminates in surgical intervention. The vast majority of patients find relief without needing an operation.
Step 1: First-Line Conservative Management
For the vast majority of patients, the first line of defense against accessory navicular pain is conservative management. The primary goal at this stage is to reduce inflammation and offload the painful area. The foundational approach is often summarized by the RICE protocol: Rest, Ice, Compression, and Elevation. This is particularly effective for acute flare-ups or symptoms triggered by a specific activity. Modifying or ceasing activities that exacerbate the pain is a critical first step.
Beyond initial symptom management, treatment focuses on reducing friction and mechanical stress. The bony bump on the inside of the foot can be irritated by tight or poorly fitting shoes, so switching to wider, more supportive footwear is a simple but effective change. Over-the-counter arch supports or custom-made orthotics can also be beneficial. These inserts support the foot’s arch, reducing the workload on the posterior tibial tendon and, consequently, the friction and movement at the painful accessory navicular site. For many, this simple change can provide significant relief.
Step 2: Advanced Non-Surgical Interventions
If initial shoe changes and rest are insufficient, a more aggressive conservative approach is warranted. The cornerstone of this phase is immobilization. Placing the foot in a short leg walking boot or cast for 4 to 6 weeks provides complete rest to the area, allowing the acute inflammation to subside. Studies show that immobilization, often in conjunction with orthotics, can be effective, with one pediatric study finding that 40% of patients treated with immobilization alone achieved pain relief.
Physical therapy plays a pivotal role in this stage. A supervised, customized strengthening and stretching program is crucial for a full recovery, particularly for active individuals and athletes. Key components include calf stretching and exercises to strengthen the ankle and foot stabilizers, which help support the arch and reduce stress on the posterior tibial tendon. A structured rehabilitation program, as demonstrated in a case study of a young boxer, can be instrumental in facilitating a safe and timely return to high-level competition without the need for surgery.
For symptom management, nonsteroidal anti-inflammatory drugs (NSAIDs) can be used to reduce both pain and swelling. If pain is severe and unresponsive to oral medications, a healthcare provider might consider a cortisone injection. However, this is typically approached with caution, as injections can have undesirable side effects, including weakening the posterior tibial tendon.
The success of this entire non-operative phase often takes time. One study highlighted that patients who achieved complete pain relief did so after an average of 8 months of conservative treatment, and many require an average of over two trials of different therapies. Overall, conservative management can be highly effective. Research indicates that while only about 28% of patients experience complete pain relief with non-operative care, the majority can avoid surgery, with some studies showing that up to 70% of patients will not require an operation.
Step 3: Surgical Options for Refractory Cases
When symptoms persist after a thorough course of conservative management—typically 6 to 12 months—surgery becomes a viable option. The primary indications for surgery are persistent pain, recurrent inflammation of the posterior tibial tendon, and significant interference with daily life or athletic performance.
Several surgical techniques exist, each with its own nuances. The two most common are simple excision and the Kidner procedure.
- Simple Excision: This procedure involves the straightforward removal of the extra bone. It is often considered for smaller accessory naviculars that are not associated with significant flatfoot deformity.
- Kidner Procedure: This is the most frequently performed surgery, considered a gold standard for treating all subtypes of symptomatic accessory navicular. It involves not only the removal of the accessory bone but also the reattachment of the posterior tibial tendon to the main navicular bone, which addresses the underlying mechanical dysfunction that often causes pain.
A systematic review found that both procedures lead to satisfactory improvements in pain and function. Postoperative outcomes for the Kidner procedure are often rated as excellent, with one review finding a 58% excellent rate. It’s important to note that the Kidner procedure can involve a more complex recovery.
The Surgical Journey and Recovery
Surgery for an accessory navicular is typically performed as an outpatient procedure, and the patient is placed in a non-weight-bearing cast for about 6 to 8 weeks. The recovery timeline is gradual:
- 0-8 Weeks: Non-weight-bearing in a cast.
- 8 Weeks: Transition to partial weight-bearing with crutches and a rigid-soled shoe.
- 10 Weeks: Can begin full weight-bearing and gentle return to normal activities.
- 4 Months: Swelling is still noticeable, especially after activity.
- 6 Months: The healing process continues, with swelling and discomfort diminishing.
- 12 Months: Complete healing is expected.
While surgery is effective, it is not without risks. Potential complications include infection, delayed wound healing, nerve injury, and DVT. A significant consideration is that about 20% of patients can still experience arch pain following surgery, a condition that might require further conservative care. The overall complication rate is considered moderate, with one systematic review finding an 11% complication rate for the Kidner procedure.
A Glimpse into the Future: Novel Treatments
Emerging research offers a potential future option. Transarterial microembolization (TAME) is a minimally invasive technique that targets the inflammatory neovessels responsible for chronic pain. A recent study on 75 patients with refractory ANS showed a significant and durable reduction in pain, with the average pain score dropping from 6.9 to 1.4 out of 10 at the final follow-up, with no major complications. While promising, TAME is an emerging technique and not yet a standard of care.
The treatment of an accessory navicular is a testament to the principle of “start low and go slow.” The journey begins with simple, non-invasive interventions like rest, shoe modifications, and orthotics. For those who need more, a structured program of immobilization and supervised physical therapy often provides significant relief. Only when these measures fail after many months is surgery considered, with the Kidner procedure being the most established and effective option. Understanding this hierarchy empowers patients to work with their physicians to navigate their treatment path effectively, with the goal of returning to a pain-free, active life.