Noninvasive ankle distraction: relationship between force, magnitude of distraction, and nerve conduction abnormalities.

Seven healthy volunteers (14 ankles; four males, 3 females) with no history of ankle or foot pathology were placed in a modified beach chair position on an operating table for ankle distraction using a noninvasive ankle distractor. In-line traction of 0 to 225 N (50 lb) in 22.5-N (5-lb) increments was applied to the ankle. A direct lateral radiograph was obtained at each distraction force. The joint space was measured on the lateral radiographs using electronic microcalipers. Surface recordings of the superficial peroneal, deep peroneal dorsal digital cutaneous, and sural nerves were obtained. The ankle joint space increased progressively from an average 3.1 mm with no force applied to an average 4.2 mm with 225 N (50 lb) distraction force applied. The maximum joint distraction averaged 1.3 mm (range, 0.35 to 2.35 mm). The sensory amplitudes were diminished or absent with increasing time and force of distraction. The decreased amplitudes were most marked after 1 hour of distraction with 135 N (30 lb) or greater distraction force. This correlated with symptoms of paresthesias. The superficial and deep peroneal cutaneous nerves were affected to a much greater extent than the sural nerve. The amplitudes quickly returned to normal values with the weight being released from the ankle. The noninvasive ankle distractor safely increased ankle joint space by more than 1 mm. Distraction with 135 N (30 lb) or more for 1 hour is associated with reversible nerve conduction changes. Based on these findings, we recommend using the noninvasive ankle distraction apparatus for ankle arthroscopy, with up to 135 N (30 lb) of traction applied to the foot for up to 1 hour. Greater force, applied for longer periods, is associated with increasing nerve conduction abnormalities.