Pedicle screw fixation and posterior fusion for lumbar degenerative diseases: effects on individual paraspinal muscles and lower back pain; a single-center, prospective study

BACKGROUND To the best of our knowledge, there have been no reports on the points at which the denervated multifidus and erector spinae muscles become reinnervated after pedicle screw fixation and posterior fusion in patients with lumbar degenerative diseases. Our study was designed to confirm reinnervation of denervated paraspinal muscles following pedicle screw fixation and posterior fusion and to confirm alleviation of the patients' lower back pain (LBP). METHODS In this prospective study, we enrolled 67 patients who had undergone pedicle screw fixation and posterior fusion. The surgery had alleviated their leg pain, but the patients complained of LBP at the L3-5 level 3 months after the surgery. The patients were divided into two groups (I and II) according to the level at which pain was experienced. Paraspinal mapping scores were recorded preoperatively and 3, 6, 12, and 18 months postoperatively. Oswestry Disability Index and visual analogue scale scores were determined. Regression analyses using a general linear model and a mixed model were performed. RESULTS Pedicle screw fixation and posterior fusion significantly denervated the multifidus and erector spinae not only in the surgical segment, but also in adjacent segments. Group I patients displayed reinnervation in the denervated erector spinae and multifidus muscles at 12 and 18 months, respectively. In contrast, group II showed reinnervation only in of the denervated erector spinae of the upper segment at 18 months, with no other areas of reinnervation. Postoperative LBP was significantly diminished at 12 months in group I and at 18 months in group II. There was also significantly less LBP at 6 months (prior to reinnervation of the paraspinal muscles). CONCLUSIONS The denervated multifidus and erector spinae muscles at L4-5, which had been denervated using pedicle screw fixation and posterior fusion, were significantly reinnervated at 18 months postoperatively, whereas patients with denervation at L3-5 had only a tendency to be reinnervated at follow-up. Postoperative LBP in these patients was significantly diminished at the follow-up visits.