Accessory Navicular

Accesory Navicular

This anatomic variant consists of an accessory ossicle located at the medial edge of the navicular
Accessory ossicles are derived from unfused ossification centers.
90% bilateral
It is most commonly symptomatic in the 2nd decade of life and causes medial foot pain
Symptomatic in <1% of patients.

Classification

Type I occurs primarily as a round sesamoid within the substances of the distal posterior tibial tendon.

It is rarely associated with symptoms.

Small, 2–3-mm sesamoid bone in the PTT; referred to AS “os tibiale externum”

Type II is associated with a synchondrosis within the body of the navicular at risk for disruption either from traction injury or shear forces in the region.

Larger ossicle than type I

Secondary ossification center of the navicular bone

Most common variety (50%)

Type III, also known as a navicular beak or a cornuate navicular occurs with fusion of the accessory navicular bone to the body of the navicular.

Clinical Features:

– Pain may begin after wearing ill-fitting shoes, with weight bearing activities or athletics, or after trauma to the foot.

– Tenderness over the medial aspect of the foot and over the accessory navicular bone.

– Secondary Achilles tendon contracture can occur

– Flatfoot is common and with severe flatfoot, lateral pain may occur secondary to impingement of the calcaneus against the fibula.

X-rays:

– AP, lateral, internal oblique and external oblique

– The accessory ossicle may be best visualized on the internal oblique view(reverse oblique view)

Treatment

• Conservative measures: Shoe-wear modification, including use of a softer, wider shoe, NSAIDS

• Medial arch support for flatfoot.

• A below knee cast may be worn for 3 -6 weeks for persistent symptoms

• Surgery maybe employed for persistent pain not responding to conservative measures

• Kidner’s procedure: Consists of excising the accessory navicular and rerouting the tibialis posterior tendon into a more plantar position.

• Kidner’s operation will not correct sag at the metatarsocuneiform joint.

• Severe flatfoot deformity with lateral impingement symptoms may require concomitant osteotomy of the calcaneus and/or medial column of the foot to improve alignment and decrease mechanical stress of the PTT insertion.

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