Oxidative stress and heat shock protein response in human paraspinal muscles during retraction

Object. The need for wide dissection and forceful retraction of paraspinal muscles often required for posterolateral lumbar fusion and fixation may severely jeopardize the muscles, structurally and functionally. The underlying pathophysiology of muscle damage may involve both mechanical and ischemic mechanisms. On the other hand, the surgery-related stress may trigger certain protective responses within the insulted paraspinal muscles. This study was conducted to assess the relationship between the oxidative stress and the stress response mediated by heat shock protein 70 (HSP70) induction within paraspinal muscles being retracted. Methods. Multifidus muscle specimens were surgically obtained before, during, and after retraction in patients with lumbar spondylolisthesis undergoing posterolateral lumbar fusion, pedicle fixation, and laminectomy. Muscle samples were analyzed to determine HSP70 and malondialdehyde (MDA) levels. Both HSP70 expression and MDA production within multifidus muscle cells were increased significantly by retraction. Expression of HSP70 then decreased after a peak at 1.5 hours of retraction, whereas MDA levels remained elevated even after release of retractors for reperfusion of the muscles. Analysis of histopathological and immunohistochemical evidence indicated that the decline of HSP70 synthesis within muscle cells after prolonged retraction was the result of severe muscle damage. Conclusions. Results of this study highlight the deleterious effect of intraoperative retraction on human paraspinal muscles at the cellular and molecular levels. The authors also found that intraoperative maneuvers aimed at reducing the oxidative stress within the paraspinal muscles may help to attenuate surgery-related paraspinal muscle damage.