Biomechanics of the hindfoot joints in response to degenerative hindfoot arthrodeses

Objective. The aim of this study is to understand how the different single and combined hindfoot arthrodeses affect the biomechanics of the hindfoot. Design. The range of rotation of each hindfoot bone in in vitro specimens were measured and compared before and after prescribed arthrodeses. Background. Single and combinations of single arthrodeses in the hindfoot are used by surgeons to correct hindfoot deformities. Clinical reports of both successful and less successful procedures are reported in the clinical literature, backed by unfounded statements as to the biomechanics of the hindfoot. Methods. Eight fresh frozen specimens were mounted in a frame and loaded to induce maximal dorsiflexion, plantarflexion, and rotation about the long axis of the foot, defined as supination and pronation. The three dimensional motion of the talus, calcaneus, navicular, and cuboid was tracked using an ultrasonic positioning system. The resulting range of rotation (RoR) of each bone in dorsiflexion to plantarflexion and supination to pronation about the calculated helical axis was then compared. Arthrodeses were then systematically introduced and the measurements repeated. Results. Significant differences in RoR were found at each joint corresponding to specific combinations of arthrodeses, P<0.05. At the calcaneocuboid joint, statistically normal rotations were calculated when the subtalar joint was arthrodized. At both the talonavicular and subtalar joints, statistically normal rotations were found when the calcaneocuboid joint was fused. In all of the other arthrodesis conditions, statistically stable joints were found. Conclusions. The results show that the mobility of each hindfoot joint is dependent on the mobility of the other hindfoot joints, and that the function of the talonavicular joint has the greatest influence on overall hindfoot function. Relevance This study provides meaningful biomechanical data that demonstrates the changes in hindfoot mechanics are a result of each of the possible hindfoot arthrodeses. Specific results provide a biomechanical rationale for the use of a double calcaneocuboid, talonavicular arthrodesis over a triple arthrodesis, as well as grounds for the use of the calcaneocuboid arthrodesis. (C) 1998 Elsevier Science Ltd. All rights reserved.