Experimental study of subtalar and ankle joint in hind foot motion

To investigate the properties of hind foot motion and its changes in ankle or subtalar joint arthrodesis.Methods Eight fresh frozen adult leg-foot specimens were mounted in a coordinated system,a Steinann pin was perforated across the calcaneus as a marker.The displacements of the marked points in the coordinated system were recorded when subtalar or ankle joint was fixed respectively.Through matrix translation and Euler equation,the angle of the calcaneus rotation were calculated,representing the motion of the subtalar and ankle joints in different condition,Statistical analysis were also taken between different conditions.Results Three dimensional (3-D) motion was observed in hind foot motion.The range of motion with ankle joint fixation was:inversion 15.99°±2.81°,eversion 8.62°±1.90°,dorsiflexion 3.70°±1.00°,plantar flexion 5.87°±1.39°,5.52°±0.85°,17.09°±2.87°30.75°±5.04°,10.77°±1.56°,and 6.54°±1.88° respectively.While they were 22.62°±3.21°,40.88°±5.77°,18.87°±3.89°,9.12°±2.05°,17.48°±2.26° and 11.47°±2.29°,when no joint was fixed.Arthrodeses of ankle or subtalar joint would affect the hindfoot motion significantly (P< 0.01 ),especially the ankle joint in all three planes,and subtalar joint in coronal plane.Conclusion The motion of subtalar and ankle joint makes up the three dimensional movements of the hind foot.The motion of coronal plane of hind foot occurres mainly at subtalar joint,while sagittal plane motion occurres at ankle joint.The motions of ankle and subtalar joint are compensative each other in coronal plane,while in sagittal plane they act in cooperation.18 refs,1 fig,2 tabs.