Kinematic changes in patients with double arthrodesis of the hindfoot for realignment of planovalgus deformity.

Double fusion (i.e., fusion of the subtalar and talonavicular joint) represents a modification of triple arthrodesis preserving integrity of the calcaneocuboidal joint. Our aims were (1) to evaluate dynamic plantar pressure distribution in patients undergoing double arthrodesis, (2) to obtain a comparison of kinematic changes to healthy feet, (3) to evaluate the influence of radiographic alignment, and (4) to assess functional outcome. Sixteen feet (14 patients) treated by double fusion due to fixed planovalgus deformity were included. Dynamic plantar pressure distribution was assessed using a capacitive pressure platform. Results were compared with a demographically matched control group. Clinical assessment included the American Orthopaedic Foot and Ankle Society (AOFAS) score and radiographic assessment included measurement of talometatarsal, calcaneal pitch, and talocalcaneal (TC) angle on lateral radiographs. Significant differences in plantar pressure distribution were found for maximum force of the hindfoot, midfoot, and big toe region: While the hindfoot and hallux represented decreased load in the double arthrodesis patients, load increased in the midfoot region compared with healthy controls. The lateral talus-first metatarsal-angle increased from -16.3° to -8.2°, and the TC angle decreased from 41.3° to 35.8° (p < 0.05). The pre- and post-operative AOFAS score increased from 37 points (SD, 16.3) to 70 points (SD, 16.7). These results revealed that double arthrodesis represents a reliable method for correction of planovalgus deformity. Compared with healthy feet, force transmission of the midfoot is increased whereas push-off force decreases.