The accessory navicular (os navicularum or os tibiale externum) is an extra bone or piece of cartilage located on the inner side of the foot just above the arch. It is incorporated within the posterior tibial tendon, which attaches in this area. An accessory navicular is congenital (present at birth). It is not part of normal bone structure and therefore is not present in most people. People who have an accessory navicular often are unaware of the condition if it causes no problems. However, some people with this extra bone develop a painful condition known as accessory navicular syndrome when the bone and/or posterior tibial tendon Where are the femur tibia and fibula
? aggravated. This can result from any of the following. Trauma, as in a foot or ankle sprain. Chronic irritation from shoes or other footwear rubbing against the extra bone. Excessive activity or overuse. Many people with accessory navicular syndrome also have flat feet (fallen arches). Having a flat foot puts more strain on the posterior tibial tendon, which can produce inflammation or irritation of the accessory navicular.Causes
Most of the time, this condition is asymptomatic and people may live their whole lives unaware that they even have this extra bone. The main reason the accessory navicular bone becomes problematic is when pain occurs. There is no need for intervention if there is no pain. The accessory navicular bone is easily felt in the medial arch because it forms a bony prominence there. Pain may occur if the accessory bone is overly large causing this bump on the instep to rub against footwear.Symptoms
The main symptom of an aggravated accessory navicular is pain, particularly in the instep. Walking can sometimes be difficult, and tight shoes may worsen the condition.Diagnosis
Typically, accessory navicular syndrome isn?t hard to diagnose. Our podiatrists will examine the lower limb and check the hard prominence, as well as use X-rays to confirm the presence of extra bone tissue. Other diagnostic images may be able to identify inflammation and specific damage to the midfoot. Depending on the severity of your discomfort, conservative measures may be enough to resolve the condition.Non Surgical Treatment
Patients with a painful accessory navicular may benefit with four to six physical therapy treatments. Your therapist may design a series of stretching exercises to try and ease tension on the posterior tibial tendon. A shoe insert, or orthotic, may be used to support the arch and protect the sore area. This approach may allow you to resume normal walking immediately, but you should probably cut back on more vigorous activities for several weeks to allow the inflammation and pain to subside. Treatments directed to the painful area help control pain and swelling. Examples include ultrasound, moist heat, and soft-tissue massage. Therapy sessions sometimes include iontophoresis, which uses a mild electrical current to push anti-inflammatory medicine to the sore area.Surgical Treatment
The original procedure advocated by Kidner involved shelling out of the accessory navicular bone from within the insertional area of the posterior tibial tendon and rerouting this tendon under the navicular bone in hopes of restoring a normal pull of this tendon. When treating younger children, history has shown us that simply shelling out of the accessory navicular bone from within the tendon and remodeling the tuberosity of the navicular bone can give you satisfactory results.
In general, you want to reserve advancement of the posterior tibial tendon for adults or those who have a more significant flatfoot deformity. You may also use this approach after determining that quality custom orthotics are only resulting in a slight decrease of symptoms.