An accessory bone is an extra bone that isn’t typically present in most people, but is found in some due to a natural variation during bone development in the womb. Many accessory bones are found coincidentally while having no symptoms and investigating a different injury, while others may produce uncomfortable symptoms.
The most common accessory bones in the body include:
As mentioned above, an accessory navicular is an extra bone that is found near your existing navicular bone (see diagram for reference).
Accessory naviculars are estimated to be present in approximately 10% of the population. Interestingly, in studies looking at the prevalence
of patients presenting to a foot and ankle clinic, this rose to almost one quarter of patients. Additionally, in Asian populations, this
rose even further to 34% for an accessory navicular, with one in two people having an accessory bone of some sort.
Accessory navicular bones are formed from an additional ossification centre, which fails to fuse with the rest of the navicular bone during development. It can be connected to the main navicular bone by a fibrous tissue or a cartilage joint. Having an accessory navicular bone doesn’t mean you’ll experience any pain or problems - however it may increase your risk of developing other foot problems such as posterior tibial tendonitis, a flatfoot deformity, or an accessory navicular syndrome.
Accessory navicular syndrome is a condition where the fibrous tissue connecting the accessory navicular to the navicular bone is irritated or damaged, leading it to become inflamed or torn, causing pain, swelling, and tenderness in the midfoot. We see this most in those who participate in high-impact activities that involve running, jumping, or sudden changes in direction, and that have an accessory navicular bone - though many don’t know it at the time.
Leaving accessory navicular syndrome untreated poses similar risks to leaving any injury untreated. You may experience ongoing pain and swelling that can worsen or remain constant. The pain and discomfort may interfere with your ability to walk properly and participate in exercise and other physical activities. In some cases, where ongoing inflammation damages the joint, arthritis may occur, contributing to pain and stiffness in the midfoot. If the accessory navicular bone (and any related inflammation) places excess pressure on the posterior tibial tendon, it may also increase the likelihood of developing a flat foot deformity, given the posterior tibial tendon is important in maintaining the shape and integrity of your arch.
Signs and symptoms to look out for include:
While our podiatry team may get an idea of whether it’s likely that you have an accessory navicular based on your physical examination, the only way to confirm this diagnosis is with x-ray imaging to detect the size and location of your accessory bone. Many of our patients actually unexpectedly learn about the presence of an accessory bone during an x-ray that is evaluating a completely separate injury or problem.
If your accessory navicular bone is asymptomatic and does not cause you any pain, discomfort or other interferences to your daily life, then it’s likely you won’t need any treatment.
For symptomatic accessory naviculars, after your diagnosis is confirmed, the first stage of treatment focuses on reducing any painful symptoms (if present) including inflammation. Resting the foot, avoiding movements that place further pressure on the accessory bone, using ice, keeping the foot elevated and taking non-steroidal anti-inflammatories (NSAIDs) can help temporarily reduce the swelling and pain at home. For effective symptom relief, the best treatment is using the MLS laser, an innovative and safe laser that is able to painlessly and effectively reduce pain without creating any heat or other side effects.
Next, we want to let the damaged structures heal while reducing the risk of future irritation. This may include the use of foot mobilisation therapy, other physical therapies, custom foot orthotics, good footwear, immobilisation devices like a brace or walker and lifestyle and exercise modifications.
If your symptoms do not show significant improvement, surgery may be considered to remove the navicular bone and repair any damage to the posterior tibial tendon, if present. This is not a treatment we see often, as the aforementioned treatment options typically have good outcomes and pain alleviation.
We often see a notable difference in symptoms following our management plan within a few weeks of treatment, with complete symptom resolution within a few months.
There is no guaranteed way to prevent this syndrome, however wearing comfortable and supportive footwear, avoiding footwear that is too tight, avoiding going too hard too fast during exercise, stretching well prior to physical activity and maintaining a healthy weight to reduce the pressure on the feet can all work to help support good foot health.