Extraarticular Subtalar Arthrodesis for Pes Planovalgus: An Interim Result of 50 Feet in Patients with Spastic Diplegia

BACKGROUND: There are no reports of the pressure changes across the foot after extraarticular subtalar arthrodesis for a planovalgus foot deformity in cerebral palsy. This paper reviews our results of extraarticular subtalar arthrodesis using a cannulated screw and cancellous bone graft. METHODS: Fifty planovalgus feet in 30 patients with spastic diplegia were included. The mean age at the time of surgery was 9 years, and the mean follow-up period was 3 years. The radiographic, gait, and dynamic foot pressure changes after surgery were investigated. RESULTS: All patients showed union and no recurrence of the deformity. Correction of the abduction of the forefoot, subluxation of the talonavicular joint, and the hindfoot valgus was confirmed radiographically. However, the calcaneal pitch was not improved significantly after surgery. Peak dorsiflexion of the ankle during the stance phase was increased after surgery, and the peak plantarflexion at push off was decreased. The peak ankle plantar flexion moment and power were also decreased. Postoperative elevation of the medial longitudinal arch was expressed as a decreased relative vertical impulse of the medial midfoot and an increased relative vertical impulse (RVI) of the lateral midfoot. However, the lower than normal RVI of the 1st and 2nd metatarsal head after surgery suggested uncorrected forefoot supination. The anteroposterior and lateral paths of the center of pressure were improved postoperatively. CONCLUSIONS: Our experience suggests that the index operation reliably corrects the hindfoot valgus in patients with spastic diplegia. Although the operation corrects the plantar flexion of the talus, it does not necessarily correct the plantarflexed calcaneus and forefoot supination. However, these findings are short-term and longer term observations will be needed.