BIOMECHANICS OF THE HINDFOOT JOINTS IN RESPONSE TO DEGENERATIVE HINDFOOT ARTHRODESES

Objective. The aim of this study is to understand how the different si ngle and combined hindfoot arthrodeses affect the biomechanics of the hindfoot. Design. The range of rotation of each hindfoot bone in in vi tro specimens were measured and compared before and after prescribed a rthrodeses. 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 a s to the biomechanics of the hindfoot. Methods. Eight fresh frozen spe cimens were mounted in a frame and loaded to induce maximal dorsiflexi on, plantarflexion, and rotation about the long axis of the foot, defi ned as supination and pronation. The three dimensional motion of the t alus, calcaneus, navicular, and cuboid was tracked using an ultrasonic positioning system. The resulting range of rotation (RoR) of each bon e in dorsiflexion to plantarflexion and supination to pronation about the calculated helical axis was then compared. Arthrodeses were then s ystematically introduced and the measurements repeated. Results. Signi ficant differences in RoR were found at each joint corresponding to sp ecific combinations of arthrodeses, P<0.05. At the calcaneocuboid join t, statistically normal rotations were calculated when the subtalar jo int was arthrodized. At both the talonavicular and subtalar joints, st atistically normal rotations were found when the calcaneocuboid joint was fused. In all of the other arthrodesis conditions, statistically s table joints were found. Conclusions. The results show that the mobili ty of each hindfoot joint is dependent on the mobility of the other hi ndfoot joints, and that the function of the talonavicular joint has th e greatest influence on overall hindfoot function. Relevance This stud y provides meaningful biomechanical data that demonstrates the changes in hindfoot mechanics are a result of each of the possible hindfoot a rthrodeses. Specific results provide a biomechanical rationale for the use of a double calcaneocuboid, talonavicular arthrodesis over a trip le arthrodesis, as well as grounds for the use of the calcaneocuboid a rthrodesis. (C) 1998 Elsevier Science Ltd. All rights reserved.