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.

Ref:

1. Sella EJ, Lawson JP, Ogden JA. The accessory navicular synchondrosis. Clin Orthop Relat Res 1986;209:280–285