The initial safe range of motion of the ankle joint after three methods of internal fixation of simulated fractures of the medial malleolus

Background Previous studies have demonstrated the safe passive range of ankle motion for inter-bone stiffness after internal fixation under load but there is a lack of information about the safe range of ankle motion for early rehabilitation in the absence of loading. The present study was designed to assess the effect of ankle movement on inter-bone displacement characteristics of medial malleolus fractures following three types of internal fixation to determine the safe range of motion. Methods Five lower legs obtained during autopsy were used to assess three types of internal fixation (two with Kirschner-wires alone; two with Kirschner-wires plus tension band wiring; and, one with an AO/ASIF malleolar screw alone). Following a simulated fracture by sawing through the medial malleolus the displacement between the fractured bone ends was measured during a passive range of movement with continuous monitoring using omega (Ω) shaped transducers and a biaxial flexible goniometer. Statistical analysis was performed with repeated measures analysis of variance. Findings Inter-bone displacement was not proportional to the magnitude of movement throughout the range of ankle motion as, when separation exceeded 25 μm, there was increasingly wide separation as plantar-flexion or dorsal-flexion was increased. There was no statistical significant difference between the small amount of inter-bone displacement observed with three types of fixation within the safe range of dorsal-flexion and plantar-flexion for early rehabilitation. However the inter-bone separation when fixation utilized two Kirschner-wires alone tended to be greater than when using the other two types of fixation during dorsal-flexion and eversion. Interpretation The present study revealed a reproducible range of ankle motion for early rehabilitation which was estimated to be within the range of 20° of dorsal-flexion and 10° of plantar-flexion without eversion. Also, internal fixation with two Kirschner-wires alone does not seem to provide stability achieved by the other two forms of fixation.