Accessory Ossicle Navicular Pain

Overview
Accessory navicular syndrome occurs when a type II accessory navicular (or "os tibiale externum") becomes painful due to movement across the pseudojoint between the ossicle and the navicular bone. The syndrome presents on MRI with bone marrow oedema signal (hypointense T1, hyperintense T2/STIR) in both the accessory ossicle and navicular. It can be inferred on musculoskeletal ultrasound if a patient's pain is located at a type II accessory navicular and the patient is tender to transducer pressure. Ultrasound can also be useful to compare with the contralateral side.



Causes
People who have an accessory navicular often are unaware of the condition if it causes no problems. However, some people with disabilities with this extra bone develop a painful condition known as accessory navicular syndrome when the bone and/or posterior tibial tendon are 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.

Symptoms
Many people have accessory (?extra?) naviculars (figure 1) - a prominent extra bone extending from the navicular bone. Most accessory naviculars are completely asymptomatic. However, some individuals will develop pain on the inside of their midfoot. Pain may occur from the pressure of the shoe ware against the prominence, irritating either the bone itself or the fibrous junction where the accessory bone meets the regular navicular. Alternatively, the fibrous junction or interface may become painful as a result of tension applied by the posterior tibial tendon through its connection or insertion at that site. Often, individuals will be asymptomatic for years, however, a new pair of shoes or a change in their activity level can cause symptoms. The accessory navicular itself typically develops during adolescence, when the two areas of the navicular bone fail to fuse together.

Diagnosis
Diagnosis starts by speaking with the patient about symptoms. The physician will look at the foot and examine it for signs of an accessory navicular. By putting pressure on the area, the doctor may determine its presence simply by the presence of pain. The muscle, joint, and the overall structure of the foot may be considered, as well as the way in which the patient walks. If a diagnosis of accessory navicular syndrome is made, an X-ray or MRI may be ordered to confirm diagnosis.

Non Surgical Treatment
In order to strengthen your muscles to prevent further injury and to provide support to the foot, your podiatrist may also outline a physical therapy routine and prescribe orthotics. Orthotics will provide support to the arch of your foot, although they must be carefully crafted in order to make room for that pesky extra bone you?ve got poking about.



Surgical Treatment
If non-surgical treatment fails to relieve the symptoms of accessory navicular syndrome, surgery may be appropriate. Surgery may involve removing the accessory bone, reshaping the area, and repairing the posterior tibial tendon to improve its function. This extra bone is not needed for normal foot function.