Histologic and electrophysiological changes of the paraspinal muscle after spinal fusion: An experimental study

Abstract

Study design.: Experimental study evaluated electrophysiological and histologic changes in the paraspinal muscle after spinal fusion. Objective.: To determine the effect of posterior spinal fusion on paraspinal muscle by means of electrophysiological and histologic evaluation, using a rabbit model. Summary of background data.: Posterior lumbar spinal fusion is a common spinal surgery. Paraspinal muscular dysfunction is postulated to be due to injury inflicted by the surgery, either during exposure or from disuse of the fused segment. The effect of spinal fusion on paraspinal muscular function remains unclear. Methods.: Thirty New Zealand white rabbits were divided into 2 groups: 2-level posterior spinal fusion with instrumentation (group F) and the sham control group (group S). Preoperative and follow-up electromyography tests, as well as histologic assessments, were performed in 6-month intervals. Results.: In group F, 14 of 15 surgeries resulted in a solid fusion, as judged by postmortem examination. In group S, the root mean square of electromyography did not present a significant difference at 6-month follow-up when compared with preoperative status (P > 0.05). At 6-month follow-up, group F presented a significantly lower root mean square in the fused region than in adjacent regions (P < 0.05). Group S did not demonstrate significant differences in the median frequency between the preoperative and postoperative periods (P < 0.05). Group F resulted in a significant decrease of median frequency in the fusion region. However, increases were observed in the adjacent caudal region and the cranial region. The histologic analysis demonstrated a significant reduction in muscle fiber size (P < 0.05) in the fusion region of group F, when compared with the preoperative status, whereas group S did not present any significant differences (P > 0.05). Conclusion.: These results demonstrated that spinal fusion resulted in atrophy and reduced adjacent paraspinal muscle activity. Muscular activity was greater in the adjacent regions after spinal fusion, which may indicate muscle hypertrophy. © 2008, Lippincott Williams & Wilkins.