NONINVASIVE ANKLE DISTRACTION - RELATIONSHIP BETWEEN FORCE, MAGNITUDEOF DISTRACTION, AND NERVE-CONDUCTION ABNORMALITIES

Seven healthy volunteers (14 ankles; four males, 3 females) with no hi story of ankle or foot pathology were placed in a modified beach chair position on an operating table for ankle distraction using a noninvas ive ankle distracter, In-line traction of 0 to 225 N (50 Ib) in 22.5-N (5-lb) increments was applied to the ankle. A direct lateral radiogra ph was obtained at each distraction force. The joint space was measure d on the lateral radiographs using electronic microcalipers, Surface r ecordings of the superficial peroneal, deep peroneal dorsal digital cu taneous, and sural nerves were obtained. The ankle joint space increas ed progressively from an average 3.1 mm with no force applied to an av erage 4.2 mm with 225 N (50 Ib) distraction force applied. The maximum joint distraction averaged 1.3 mm (range, 0.35 to 2.35 mm). The senso ry amplitudes were diminished or absent with increasing time and force of distraction. The decreased amplitudes were most marked after 1 hou r of distraction with 135 N (30 Ib) or greater distraction force. This correlated with symptoms of paresthesias. The superficial and deep pe roneal cutaneous nerves were affected to a much greater extent than th e sural nerve. The amplitudes quickly returned to normal values with t he weight being released from the ankle. The noninvasive ankle distrac ter safely increased ankle joint space by more than 1 mm. Distraction with 135 N (30 Ib) or more for 1 hour is associated with reversible ne rve conduction changes, Based on these findings, we recommend using th e noninvasive ankle distraction apparatus for ankle arthroscopy, with up to 135 N (30 Ib) of traction applied to the foot for up to 1 hour. Greater force, applied for longer periods, is associated with increasi ng nerve conduction abnormalities.