The impact of intermittent retraction on paraspinal muscle function during lumbar surgery.

Study Design. Prospective cohort study. Objective. To study the effect of surgical retraction on paraspinal muscle function and investigate the effect of intermittent muscle retraction. Summary of Background Data. Paraspinal muscle retraction leads to increased intramuscular pressure with a reduction in local blood flow resulting in ischemic damage. This may lead to muscle dysfunction and increased back pain after surgery. Methods. Two groups of 20 patients underwent one-level decompressive lumbar surgery. Group A underwent continuous muscle retraction, group B underwent intermittent muscle retraction. All patients completed pain questionnaires and underwent spinal strength assessment, paraspinal needle electromyography (EMG) before and after surgery, and had intraoperative muscle biopsy analysis using the technique of birefringence. Results. Pain questionnaires revealed a reduction in back pain in all patients following surgery; patients with shorter retraction times had less pain (P < 0.05). Paraspinal muscle histochemistry revealed patients with shorter muscle retraction times and patients who underwent intermittent muscle retraction has less damage (P < 0.05). Isometric strength testing revealed patients in the intermittent retraction group had a less profound reduction in strength after surgery (P < 0.05). Needle EMG data and pain questionnaires showed no differences between the continuous and intermittent groups, although EMG data did show that muscle shows evidence of reinnervation after surgery. Conclusion. Although histologically there was a reduction in muscle damage in patients that underwent intermittent retraction, there was no benefit on clinical outcome. Paraspinal muscle shows evidence of reinnervation after surgery.