Preventive measures of back muscle injury after posterior lumbar spine surgery in rats

Study Design. Postoperative back muscle injury was studied in rats. Postoperative findings were compared among three groups: 2-hour continuous back muscle retraction. 5-minute retraction release after 1 hour of retraction, and 5-minute release at every 40 minutes of retraction. Objective. To determine whether intermittent release of the retractor during surgery is effective to prevent severe muscle injury. Summary of Background Data. In surgery performed on the extremities using a tourniquet, intermittent reperfusion intervals can permit extended tourniquet application when the operation is prolonged. However, there have been no specific studies on the effects of intermittent retraction release for postoperative back muscle injury. Methods. The back muscle of rats was retracted using a self- retaining retractor for 2 hours. The 36 rats were divided equally into the following three groups: Group 1, 2 hours of continuous retraction; Group 2, two 1-hour retractions interposed with a 5-minute retraction release; and Group 3, three 40-minute retractions interposed with a 5-minute retraction release. In each group, the multifidus muscle was histologically analyzed at 48 hours, 1 week, and 6 weeks after surgery. The muscles were stained by a variety of histochemical methods. The level of serum CPK-MM isoenzyme was measured 48 hours after surgery. Results. Postoperative back muscle degeneration was the most severe in Group 1. The concentration of CPK-MM in Group 1 was significantly higher than that in Groups 2 and 3. One week after surgery, the lesser diameter of regenerated fibers in Group 1 was smaller than that in Groups 2 and 3. The incidence of neurogenic muscle damage was the highest in Group 1. Conclusions. During posterior lumbar spine surgery, 5-minute retraction release after 1 hour or after 40 minutes of retraction was effective in preventing severe back muscle injury after surgery.