Effect of functional neuromuscular stimulation on anterior tibial compartment pressure

Intramuscular pressures in the anterior tibial compartment were measured in five paraplegic subjects who used functional neuromuscular stimulation (FNS) by percutaneous intramuscular electrodes for exercise and walking. Effects of two types of stimulation pattern were tested: continuous stimulation for 15 minutes and cyclic stimulation for 60 minutes, with duty cycle and stimulation levels similar to that used in walking. Resting compartment pressure levels before stimulation were less than 7 mm Hg in all subjects. Continuous stimulation at maximum parameters produced compartment pressure levels up to 116 mm Hg, but these were not sustained. They decreased to below 40 mm Hg within one minute in all except one subject, who was having repeated spasms. Cyclical stimulation raised mean muscle pressure to between 70 and 80 mm Hg in two patients. Muscle contraction pressure increased to 153 mm Hg in one patient, but was below 100 mm Hg in all patients after two minutes, except during spasms. Muscle relaxation pressure stayed below 30 mm Hg in four subjects. After stimulation, the pressure returned to prestimulation levels within 15 minutes. These results suggest that FNS subjects are not in danger of developing compartment syndrome. Nevertheless, occasional testing of compartment pressures is recommended, especially when activity levels rise significantly.