An accessory navicular is an extra bone on the inner side of your foot, just above the arch. It’s present from birth and sits next to the navicular, one of the small bones in the midfoot. Roughly 4 to 21 percent of people have one, with a large meta-analysis putting the overall prevalence at about 17.5 percent. Most people never know it’s there. It only becomes a problem when it starts causing pain, a condition called accessory navicular syndrome.
Three Types of Accessory Navicular
Not all accessory naviculars are the same. They’re classified into three types based on size and how they connect to the main navicular bone.
- Type 1 is a small, round bone that sits entirely within the tendon running along the inner foot (the posterior tibial tendon). It’s the least likely to cause problems.
- Type 2 is larger and connects to the navicular through a bridge of cartilage. This is the type most commonly associated with pain, because that cartilage junction is vulnerable to stress and inflammation.
- Type 3 is the most prominent. It connects to the navicular through a bony bridge, essentially forming an enlarged navicular. It can create a visible bump on the inner foot.
Why It Causes Pain
The posterior tibial tendon is the key player here. This tendon runs from the calf down through the inner ankle and attaches to the navicular, then fans out to bones on the sole of the foot. Its main job is supporting your arch and controlling how your foot rolls inward when you walk or run.
When an accessory navicular is present, that tendon’s attachment gets disrupted. Cadaver dissections have shown that in many cases, the posterior tibial tendon inserts directly into the accessory navicular rather than extending to its normal attachment points on the sole. Pulling on one section of the tendon produces no movement in the other, meaning the tendon effectively loses its mechanical advantage. This can weaken arch support and contribute to a flat foot posture, which in turn puts more strain on the inner foot with every step.
Type 2 accessory naviculars are particularly problematic because the cartilage bridge connecting the two bones absorbs repetitive stress. Over time, that cartilage can break down, inflame, or partially separate, producing localized pain along the inner midfoot.
Symptoms and Common Triggers
The hallmark symptom is a dull, aching pain on the inner side of the foot, right where the bump is. You might also notice redness or swelling over the bony prominence. The pain typically gets worse with activity and improves with rest.
Common triggers include shoes that press against the bump (especially stiff or narrow shoes, ski boots, or cleats), increased physical activity, and ankle sprains or direct trauma to the area. Adolescents often develop symptoms during growth spurts or when they ramp up sports participation, since the cartilage bridge in a Type 2 accessory navicular hasn’t yet fused and is more vulnerable to stress. People with flat feet are also more prone to symptoms because the flatter arch increases tension along the inner foot.
How It’s Diagnosed
A doctor can often suspect an accessory navicular just by feeling the bony bump on the inner foot and pressing on it to reproduce pain. Standard X-rays will show the extra bone and help identify which type you have. Comparing X-rays of both feet can also help distinguish the accessory navicular from a fracture, since the extra bone is usually present on both sides.
When X-rays aren’t conclusive, or when the pain doesn’t match what’s expected, an MRI provides much more detail. On MRI, a painful Type 2 accessory navicular typically shows a pattern of bone marrow swelling in the extra bone and inflammation within the cartilage bridge. These findings point to chronic stress, cartilage breakdown, or even small areas of bone damage. MRI can also reveal whether the posterior tibial tendon itself is damaged, which changes the treatment approach.
This imaging distinction matters because the symptoms of accessory navicular syndrome overlap with navicular stress fractures and posterior tibial tendon injuries. A stress fracture tends to produce vague, nagging pain over the top of the midfoot with a longer buildup, while accessory navicular pain is usually well localized to the inner bump.
Non-Surgical Treatment
Most people with a symptomatic accessory navicular improve without surgery. The first step is switching to wider, more comfortable shoes that don’t press against the inner foot. Activity modification helps too: cutting back on running, jumping, or other high-impact activities gives the inflamed area time to settle down. Over-the-counter anti-inflammatory medications can reduce pain and swelling during flare-ups.
Custom orthotics or cushioned shoe inserts can redistribute pressure away from the bump and provide better arch support, reducing the strain on the posterior tibial tendon. For more stubborn cases, a walking boot or short-leg cast may be used for several weeks. Immobilization enforces rest and prevents the repetitive micro-trauma that keeps the cartilage bridge irritated. The goal of all these approaches is the same: get you back to your normal activities or sports without pain.
When Surgery Is Considered
If months of conservative treatment don’t resolve the pain, surgery becomes an option. The most well-known procedure is the Kidner procedure, which involves removing the accessory navicular and reattaching the posterior tibial tendon to the remaining navicular bone. The idea is to eliminate the source of irritation while restoring more normal tendon function and arch support.
Variations exist. A simple excision removes the extra bone without rerouting the tendon, while modified versions of the Kidner procedure use different techniques to secure the tendon in a position that better supports the arch. The choice depends on the type of accessory navicular, how much the tendon is involved, and whether flatfoot is part of the picture.
Recovery after the Kidner procedure typically involves crutches for the first several days, followed by a gradual return to weight-bearing. Most patients resume normal activities within 10 to 12 weeks, though returning to competitive sports may take longer.
The Flatfoot Connection
The relationship between accessory navicular and flatfoot runs in both directions, and researchers still debate which one drives the other. What’s clear is that they frequently coexist. A weakened posterior tibial tendon, whether caused by the accessory navicular’s disruption of its attachment or by the increased load of a flat arch, creates a cycle: the flatter the foot, the more stress on the inner midfoot, and the more symptomatic the accessory navicular becomes.
This connection also matters after surgery. Studies of patients who needed revision surgery after an initial Kidner procedure found that nearly all of them had persistent flatfoot or inward-tilting heel alignment. These structural issues kept pulling on the reattached tendon and eventually caused the pain to return. For this reason, some surgeons address the flatfoot deformity at the same time as the accessory navicular removal, particularly in patients with significant arch collapse.