Cavovarus foot deformity with multiple tarsal coalitions: functional and three-dimensional preoperative assessment.

In rare instances, tarsal coalition leads to cavovarus foot deformity, although the pathologic mechanism leading to this deformity is not clear. This article reports a case of a 14-year-old boy presenting a severe cavovarus deformity of the right foot with talocalcaneal and calcaneonavicular coalitions, and a mild cavus deformity of the left foot with a single talocalcaneal coalition. Computed tomography and postoperative histologic analysis demonstrated a synostosis between talus and calcaneus and a fibrous calcaneonavicular coalition with partial ossification. Instrumented gait analysis revealed a limited range of ankle plantar flexion and increased external rotation of the ankle. Associated skeletal malformations including incomplete hemimelia of the forearm and scoliosis raised the possibility of a teratologic condition, but neurologic examination, spinal magnetic resonance imaging, and nerve conduction velocities were normal. The progressive ossification of combined coalitions during growth of the foot may have been one factor leading to this complex foot deformity. The fine-wire electromyogram showed normal tibialis anterior and posterior muscle activity. Small soft tissue tears in the sinus tarsi may have led to a mild reflexive increase of the muscle tone and tendon shortening, which pulled the forefoot into adduction and the heel into varus, and raised the medial arch. Mechanical alterations of the ankle appear secondary to the heel varus and to the progressive deformity of the talus. Three-dimensional computed tomography reconstruction and gait analysis appeared to be helpful additional parameters to understanding the pathomechanics of this complex foot deformity and for preoperative planning of triple arthrodesis.