Over the years, I have had a number of patients who come in with complaints of pain in the inner center part of their arch. Typically, these patients tend to be athletic, however not all are. Oftentimes, these patients have a bump in this inner center arch area. What is this bump and why is it painful?
As infants and children, many of our bones start off as cartilage. These cartilage “bones” are difficult to see on x-ray until they become calcified. The calcification process occurs at a variety of different times in life depending on the bone.
An accessory navicular is an extra bone that is on the inner center arch of the foot. Up to 2.5% of individuals are born with the accessory navicular. Throughout early childhood, this condition is not noticed. However, in adolescence, when the accessory navicular begins to calcify, the bump on the inner aspect of the arch becomes noticed. For most, it is never symptomatic. However, for some, there is some type of injury, whether a twist, stumble, or fall, that makes the accessory navicular symptomatic.
There are three different types of accessory navicular. This extra cartilage, which is turned into bone, is found attached to the posterior tibial tendon, just medial (inside) the navicular bone. The accessory navicular can affect the insertion of the posterior tibial tendon. This tendon has a job of keeping your foot aligned and helping to maintain an arch. The accessory navicular can be associated with a normal foot posture and alignment, or sometime with a flat (pes planus) foot.
An initial assessment is an orthopaedic office begins with a thorough history and complete physical exam, including an assessment of the posterior tibial tendon and areas of tenderness. Associated misalignments of the ankle and foot should be noted. Finally, weight-bearing x-rays of the foot will help in making the diagnosis. Sometimes, an MRI may be needed to see if the posterior tibial tendon is involved with the symptoms or getting more clarity on the anatomy of the accessory navicular.
Initial treatment is conservative. With the first episode of symptoms, a medial heel wedge, anti-inflammatories, and physical therapy can be helpful. If very painful, a cast or boot may be needed for a short period time before the wedge and physical therapy can be initiated. Very rarely is a steroid injection warranted or recommended. As the pain improves, patients can resume activities. For a minority of patients, an arch support or custom orthotic can help to take some of the extra pressure off of the accessory navicular and the posterior tibial tendon.
For patients who have failed conservative care or who have had recurrent symptoms, surgery can be considered. Surgical intervention requires an excision of the accessory navicular and reattachment of the posterior tibial tendon to the navicular. Often times, this is the only procedure necessary. However, if there are other deformities such as a flat foot or forefoot that is abducted, other procedures may be required.
In summary, an accessory navicular is a fairly uncommon condition which is rarely symptomatic. Oftentimes non-surgical treatment is successful. In the minority of cases, surgical intervention is required. Patients typically do very well with conservative and surgical treatment. Athletic activities can usually be restarted once symptoms have improved or the patient has recovered from surgery.