Os Naviculare (Accessory Navicular)

An os naviculare, or accessory navicular, is an extra small bone or piece of cartilage on the inner side of the foot, just above the arch. It is a common normal variant and usually causes no trouble. It can become painful after injury or overuse, especially in adolescence. Most cases settle with footwear, orthotics and physiotherapy.

The navicular is a boat-shaped bone in the middle of the foot. The tibialis posterior tendon, which supports the arch, attaches to its inner side. An accessory navicular sits next to this point and is often partly embedded in the tendon. It is joined to the main navicular by fibrous tissue or cartilage rather than solid bone.

How common is an accessory navicular?

It is one of the most common extra bones in the foot. A meta-analysis of 39 studies in Surgical and Radiologic Anatomy (Stolarz and colleagues) found an accessory navicular in about 12.6% of feet and 17.5% of people. Half of those affected had one in both feet. Men and women were affected at similar rates, but prevalence varied widely between populations, from about 8% to 38%.

Most people with an accessory navicular never know it is there. It is often found by chance on an X-ray taken for another reason.

What are the symptoms?

• Pain and swelling over the inner arch
• Tenderness when wearing tight shoes or boots that press on the bump
• Flattening of the arch or a flat-foot appearance
• Pain that worsens with activity

Why does it become painful?

• Repetitive stress or overuse, such as running, ballet or other sports
• Direct trauma or a sprain
• Tight or ill-fitting footwear rubbing over the prominence
• An underlying flat foot or tibialis posterior tendon dysfunction

A relatively minor injury can disrupt the cartilage or fibrous link between the extra bone and the navicular. The resulting small, painful movement at that junction can lead to wear, a swollen fluid sac (bursa) and a more prominent bump. Because the tibialis posterior tendon attaches here, an accessory navicular may also be associated with problems in that tendon.

Non-surgical treatment

Most painful accessory naviculars are treated without surgery at first:

• Activity modification to reduce repetitive stress
• Supportive, cushioned footwear
• Custom orthotics to support the arch and offload the bony prominence
• Ice and anti-inflammatory medication
• Physiotherapy to strengthen the surrounding muscles
• Immobilisation in a boot or cast for 2–4 weeks in severe cases
• A steroid injection for persistent cases

A systematic review in Current Reviews in Musculoskeletal Medicine (Wariach and colleagues) noted that published studies report a low success rate for non-surgical treatment in patients with a painful accessory navicular. Simple measures are still the right first step, and surgery is considered only when they have not helped.

When is surgery recommended?

When conservative management fails, the most commonly performed operation is the Kidner procedure. The accessory navicular is removed and the tibialis posterior tendon is reattached to the main navicular bone. In many cases, a calcaneal osteotomy (heel shift) is also performed to realign the foot and offload the inner arch. Surgery is performed as a day case under general anaesthetic.

The same systematic review found that both simple removal of the extra bone and the Kidner procedure are effective, with low complication rates and high patient satisfaction. It also reported cases in which people with a flat foot or an outward-tilting heel needed revision surgery for recurrent pain after a Kidner procedure. This is one reason why correcting the alignment of the heel may be recommended at the same time.

What is recovery like?

• 0–6 weeks: non-weight-bearing in a cast, with the foot elevated
• 6 weeks: cast removed, change to a walking boot and begin weight-bearing
• 6–12 weeks: progressive physiotherapy; swelling may persist
• 12 weeks onwards: return to full activity if pain-free

How Mr Hester can help

Mr Hester is a dual fellowship-trained foot and ankle surgeon (FRCS Tr&Orth), trained at Guy's and St Thomas' and in Toronto and Calgary, and a member of BOFAS and EFAS. He sees patients privately at The London Clinic, Cromwell Hospital, King Edward VII's Hospital and HCA The Shard. His NHS practice is at King's College Hospital.

Insured patients need a GP referral and an authorisation code from their insurer. Self-pay patients are welcome. To book, call 020 7046 8004.

Frequently Asked Questions

Sources

1. Stolarz K, Osiowski A, Preinl M, Osiowski M, Jasiewicz B, Taterra D. The prevalence and anatomy of accessory navicular bone: a meta-analysis. Surg Radiol Anat. 2024;46(10):1731–1743. PMID: 39136746. https://pubmed.ncbi.nlm.nih.gov/39136746/
2. Wariach S, Karim K, Sarraj M, Gaber K, Singh A, Kishta W. Assessing the outcomes associated with accessory navicular bone surgery: a systematic review. Curr Rev Musculoskelet Med. 2022;15(5):377–384. PMID: 35776339. https://pubmed.ncbi.nlm.nih.gov/35776339/
3. Flat feet. NHS. https://www.nhs.uk/conditions/flat-feet/