The impact of self-retaining retractors on the paraspinal muscles during posterior spinal surgery

Study Design. This was a prospective pilot study examining pre-, intra- and postoperative measures. Objectives. The aim of the study was to investigate the effect of muscle retractors on the posterior spinal muscles during posterior spinal surgery. Summary of Background Data. Previous studies have identified changes in the structure and function of the back extensor mechanism as a result of low back pain. However, the effect of surgery on the functioning of these muscles, particularly surgical retraction, has received less attention. Methods. Twenty patients undergoing posterior spinal surgery were recruited into this study, and recordings of intramuscular pressure during surgery were performed using a pressure-monitoring system before insertion of retractors, 5, 30, and 60 minutes into surgery, and on removal of retractors. Before and following use of the retractors, muscle biopsies were taken from the multifidus muscle for analysis using birefringence techniques. Results. A significant increase in intramuscular pressure (P < 0.001) was observed during surgery. On removal of retractors, this pressure returned to or near to the original value. Analysis of muscle biopsies using calcium activated adenosine triphosphatase birefringence revealed a reduction in muscle function following prolonged use of self-retaining retractors. Conclusions. A substantial rise in pressure in the erector spinae muscle during posterior spinal surgery was observed, and this appeared to be associated with marked changes in the function of the muscles. This could be an important factor in the generation of operative scar tissue and postoperative dysfunction of the spinal muscles.