The effects of external compression by three 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 lumbar spine surgery.
OBJECTIVES: To study the relation between external compression and muscle strain induced by spinal retractors and intramuscular pressure in the dorsolumbar compartment during posterior spinal surgery. SUMMARY OF BACKGROUND DATA: Pressures were studied as a function of the distance between the retractor blades during surgery.
METHODS: Intramuscular pressure was measured bilaterally in the erector spinae muscle with intermittent microcapillary infusion technique in 12 patients undergoing posterior lumbar spine surgery during 271 (range 90-420) minutes. Three self-retaining retractors were tested; the McCulloch, 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. Intramuscular pressure varied between 61 mm Hg and 158 mm Hg depending on which retractor was used and on the distance between the retractor blades. Intramuscular pressure never exceeded 30 mm Hg at rest after the operation.
CONCLUSIONS: External compression and muscle strain from retractor blades during surgery increased intramuscular pressure in the paravertebral muscles to levels that, according to other studies, induce ischemia in the muscles.