An accessory navicular bone is a common finding on many foot x-rays. Most accessory naviculars are asymptomatic. However, in some patients the prominent bone on the inside of foot will create discomfort leading to difficulty with shoe fitting. Alternatively, the fibrous union between the navicular bone and the “extra” accessory part may become irritated and create discomfort. Physical examination combined with plain x-rays of the foot will be diagnostic. Treatment is usually non-operative with a change in shoe wear, and activity modification. However, it is not uncommon for patients to have ongoing symptoms and in these individuals patients may consider surgery to remove the prominent accessory navicular and reattach the posterior tibial tendon if necessary.
Figure 1: Normal Navicular compared to “Accessory” Navicular
Many people have accessory (“extra”) naviculars (figure 1) – a prominent extra bone extending form the navicular bone. Most accessory naviculars are completely asymptomatic. However, some individuals will develop pain on the inside of their hindfoot. This pain occurs either from the prominent extra bone rubbing against a shoe; from irritation at the fibrous junction where the accessory bone meets the regular navicular; or for both of these reasons. Often individuals will be asymptomatic for years until a new pair of shoes or a change in their activity level precipitates symptoms. The accessory navicular itself typically develops during adolescence when the two areas of the navicular bone fail to fuse together.
On examining a foot with a symptomatic accessory navicular there will often be a bony prominence on the inside of the foot, just below and in front of the ankle. The size of this prominence will vary from small to quite large. Pressing over this area will often produce discomfort. There may be an associated flat foot deformity as this is common (but not universal!) in patients with accessory naviculars. Stressing the posterior tibial tendon by raising the heel up and down on one foot or by forcing the foot to the inside against resistance may aggravate the symptoms as these maneuvers stress the posterior tibial tendon which attaches (inserts) on the inside of the accessory navicular bone. Patients may walk with a slight limp due to pain.
Accessory naviculars can be seen on plain X-rays. These x-rays will allow the size of the accessory navicular to be determined. Occasionally if the status of the posterior tibial tendon needs to be assessed or other problems are suspected (ex. Navicular stress fracture) it may be necessary to perform an MRI although this is not considered routine.
Many individuals with symptomatic accessory naviculars can be managed successfully without surgery. Standard non-surgical treatment includes:
Appropriate Comfortable Shoes
Shoes that are soft around the inside of the ankle can allow for any excess prominence of bone. This can be achieved by purchasing shoes with plenty of padding and space in this area or by having a shoemaker create extra space in this area. For example many patients will get their ski boots expanded in the area around the prominence to minimize irritation. In addition a shoe with a stiff sole will help disperse force away from the arch of the foot during walking and thereby minimize the force on the posterior tibial tendon.
Application of local Padding
Often applying local foam or gel padding such as can be purchased at many pharmacies can help improve symptoms.
If symptoms have been aggravated by an increase in activity level then backing off on activities in the short term can be helpful. The foot is subject to a lot of repetitive loading during walking and minimizing this force will often help symptoms to settle. After symptoms have settled the activity level can then be gradually increased.
Excess weight will increase the force on the posterior tibial tendon as it inserts into the accessory navicular and will tend to precipitate or aggravate symptoms. If a patient with a symptomatic accessory navicular is overweight then losing weight can be very helpful. Even losing 5-10lbs will decrease by 15-30 lbs the amount of force going through the foot with each step. This is because the foot acts like a lever serving to magnify the force absorbed by the foot with each step.
If a patient truly fails non-operative treatment then surgical intervention may be warranted. The standard operative treatment of an accessory navicular is a Kidner procedure.
Modified Kidner Procedure (Resection of the Prominent Accessory Navicular)
The Kidner procedure involves resecting the prominent accessory navicular and ensuring that the posterior tibial tendon is still attached to the bone. Often the prominent bone can simply be shelled out from its position relative to the posterior tibial tendon leaving the tendon intact. However, often the tendon is loose and floppy once the extra bone has been remove and therefore requires suturing or tother means of attaching it into the remaining navicular bone.
In the original Kidner procedure the entire posterior tibial tendon was released from the navicular and then rerouted through a drill hole placed through the navicular, As a means of treating isolated accessory naviculars the original Kidner procedure is rarely done anymore. This is because the recovery time is much more prolonged than for the Modified Kidner and the results are no better and in some instances may be worse.
In most instances a patient’s recovery will be as follows:
0-6 weeks: Immobilization (in case or cast boot) non-weight-bearing or touch weight-bearing
6-10 weeks: Increasing activity in a cast boot. Physical therapy to work on strength and balance
Full recovery after 9-2 months
In some patients (where the posterior tibial tendon is still intact and functioning) the treating surgeon may allow weight-bearing as tolerated in a cast boot immediately after surgery.
Edited January 3rd, 2010