THE EFFECTS OF EXTERNAL COMPRESSION BY 3 DIFFERENT RETRACTORS ON PRESSURE IN THE ERECTOR SPINE MUSCLES DURING AND AFTER POSTERIOR LUMBAR SPINE SURGERY IN HUMANS

Study Design, An experimental study on patients undergoing posterior l umbar spine surgery. Objectives, To study the relation between externa l compression and muscle strain induced by spinal retractors and intra muscular pressure in the dorsolumbar compartment during posterior spin al surgery. Summary of Background Data. Pressures were studied as a fu nction of the distance between the retractor blades during surgery. Me thods. Intramuscular pressure was measured bilaterally in the erector spinae muscle with intermittent microcapillary infusion technique in 1 2 patients undergoing posterior lumbar spine surgery during 271 (range 90-420) minutes. Three self-retaining retractors were tested; the McC ulloch, the Viking, and the Richard retractors. Results. Intramuscular pressure was 7.7 mm Hg before surgery. It varied between 35 mm Hg and 69 mm Hg during surgical exposure of the laminas and facet joints. In tramuscular pressure varied between 61 mm Hg and 158 mm Hg depending o n which retractor was used and on the distance between the retractor b lades. Intramuscular pressure never exceeded 30 mm Hg at rest after th e operation. Conclusions. External compression and muscle strain from retractor blades during surgery increased intramuscular pressure in th e paravertebral muscles to levels that, according to other studies, in duce ischemia in the muscles.