The Accessory Navicular Bone

What is an accessory Navicular Bone?

accessoryAn Accessory Navicular Bone is an extra bone that may be attached or detached from the navicular bone. It is considered a normal variant and is present in approximately 10% of people. This accessory bone is usually located under the plantar medial aspect of the navicular and is often associated with a pes planus (flatfoot) deformity. Ossification of the navicular bone occurs at three years of age in females and five years of age in males. However, the accessory navicular bone does not begin ossification before eight years of age.

flatfoot

The majority of patients are asymptomatic but, females tend to be more symptomatic. The patient may present with an activity related limp and pain in the arch area. The condition may also be bilateral. During examination, there may be swelling, tenderness, warmth, or redness in the plantar medial aspect of the arch. Relative to a normal foot, a plain x-ray AP view can detect the accessory navicular. An external oblique view is considered to be the best imaging position to detect an accessory navicular bone. An MRI may also be obtained in order to determine the size and type of the accessory navicular as well as assess the posterior tibial tendon.

radiologyThe accessory navicular is classified into three types. In Type I classifications, the accessory ossicle is mainly in the substance of the posterior tibial tendon and is not attached to the navicular. In Type II, the accessory bone resides very close to the navicular tubercle and is connected to the navicular by a thick layer of cartilage. In Type III classifications, the accessory bone is considered an enlarged navicular tubercle. Type IIIs are essentially a type II that is fused with the navicular by a bony bridge.

accessory typesIn regards to prognosis, when skeletal maturity has been reached, almost all patients become asymptomatic.

Treatment

Nonoperative treatment usually consists of activity modification, orthotics, or a short leg walking cast. Surgical excision is indicated only after all conservative treatment options have failed.

 

 

Tarsal Coalition

Tarsal coalition is a congenital anomaly in which the tarsal bones fuse together, leading to a rigid flat foot, foot pain, and multiple ankle sprains. There are two types of tarsal coalition. The first is known as a Talocalcaneal Coalition, which is a coalition between the talus and the calcaneus. The second is referred to as a calcaneonavicular coalition which is a coalition between the calcaneus and the navicular. When talocalcaneal coalition occurs, it usually happens around 12-15 years of age. The calcaneonavicular coalition presents at an earlier age. About 50% of coalitions are bilateral, and around 20% have multiple coalitions in the same foot. Coalition may be fibrous, cartilaginous, or bony and occurs due to failure of segmentation. It could be associated with fibular hemimelia or Apert’s syndrome.

tarsal anatomy

Symptoms typically consist of patient’s complaining of a painful foot, a history of repeated ankle sprains, and a flat foot deformity. Tarsal coalition may result in a peroneal spastic flat foot. During the physical examination, the physician may find hindfoot valgus. On toe standing, the arch does not reconstitute and heel cord contracture may also be evident during the exam. Furthermore, there may be restriction in the subtalar joint’s range of motion. It is important to check both feet as the condition may be bilateral.

hindfoot

The best imaging study is a CT scan. It can determine the size and location of the coalition. And MRI is also useful in detecting a fibrous or cartilaginous coalition. AP, Lateral, and Oblique view x-rays should be ordered. On a lateral view x-ray, the Calcaneonavicular Coalition can be identified by the “anteater nose sign” and the elongation of the anterior calcaneal process.

ant

A lateral view of a Talocalcaneal Coalition may show talar beaking which is a traction spur that occurs due to the limited motion of the subtalar joint. Additionally, the C sign may be seen which is a radiological sign outlining the talar dome and the sustentaculum. A 45° oblique view is the best for showing calcaneonavicular coalitions.

45oblique

Nonoperative treatment usually consists of anti-inflammatory drugs, modified activities, or the use of a brace or cast. Surgical treatment for the calcaneonavicular coalition usually consists of resection with an interposition of the extensor digitorum brevis muscle or a fat graft no matter the size of the coalition. Similarly, Talocalcaneal coalitions that involve less than 50% of the subtalar joint are also resected. A triple arthrodesis procedure is performed for large coalitions, failed resections, or advanced conditions.

Posterior Tibial Tendon Dysfunction

A tendon is a band of fibrous tissue that connects muscle to bone allowing the joint to bend. Tendons enable participation in physical activities such as running, jumping and other movements. The posterior tibial tendon starts in the calf and descends down the leg behind the inside of the ankle and attaches to the foot’s arch. Its function is to support the medial arch and sub-talar joint as the body passes over the foot. When the posterior tibial tendon becomes inflamed or is overstretched, the ability to support the arch is impaired resulting in flattening of the foot.

Posterior tibial tendon (Figure 1) dysfunction, as this phenomenon is called, can be attributed to several factors:

  • Tendon overuse.
  • exposing the foot to a significant load
  • Obesity
  • Hypertension
  • Trauma
  • Diabetes
  • Inflammatory diseases such as rheumatoid arthritis.

    post-tibial-tendon
    Figure 1

Patients with posterior tibial tendon dysfunction will often present with pain and swelling on the inside of the ankle, loss of the foot’s arch (flatfoot), tenderness over the mid-foot and an inability to stand on the toes.

To diagnose posterior tibial tendon dysfunction, physicians will likely use the “too many toes” test (Figure 2). Here, the physician measures abduction of the forefoot. If the

posterior-tibial
Figure 2

posterior tibial tendon is damaged, the forefoot will deviate outwards in relation to the rest of the foot and will appear to have too many toes when viewed from behind. In addition to the “too many toes” test, the physician may ask patients to do a single heel rise. Here, patients are asked to stand with their hands on the wall and lift the unaffected foot off the ground and raise the toes on the affected foot. If the heel does not rotate inward, there is posterior tibial tendon dysfunction.

 

 

Posterior tibial tendon dysfunction can be classified in four stages:

 STAGE I – characterized by an inflamed posterior tibial tendon with normal strength. Upon examination, the patient will be tender to palpation but may show little or no change in the arch of the foot. While X-rays will most likely show no changes, an MRI will likely reveal mild to moderate tenosynovitis.

 STAGE II – characterized by a partially torn tendon or degenerative changes. Here, the physician will note considerable flattening of the arch without arthritic changes and will have a positive too many toes sign. X-rays will reveal abduction of the forefoot while an MRI will reveal a partial tear.

 STAGE III – characterized by severe tendon degeneration with a rupture likely. Patients with stage III posterior tibial tendon dysfunction will present with rigid flatfoot. X-rays will likely reveal abduction of the forefoot and collapse of the talo-navicular joint while an MRI will show a tear in the tendon.

 STAGE IV – is similar to stage III with the addition of an arthritic ankle joint.

Treatment for posterior tibial tendon dysfunction can range from conservative to surgical depending on how far the condition has progressed. In its early stages, physicians will often utilize rest, anti-inflammatory medications, and immobilization. If the foot fails to respond to conservative treatment or the condition has progressed too far, there are several surgical procedures that can be utilized. First, physicians may perform a tenosynovectomy. Here, the surgeon will debride and excise inflamed tissue surrounding the tendon. A second option is an osteotomy. Here, the surgeon changes the alignment of the calcaneus and may remove a portion of the bone. A third option is a tendon transfer where fibers from another tendon are used to repair the posterior tibial tendon. Finally, surgeons may fuse one or more bone together, eliminating movement in the joint through a process called arthrodesis. During this procedure, the forefoot is stabilized.