Erector spinae muscle changes on magnetic resonance imaging following lumbar surgery through a posterior approach

Study Design. Prospective randomized study of patients undergoing lumbar arthrodesis. Objectives. To quantify MRI changes of the erector spinae following lumbar surgery through a posterior approach and the possible protection of these muscles during surgery by the use of cholinergic blockade. Summary of Background Data. It has been shown that lumbar spine surgery through a posterior approach can induce iatrogenic lesions in the erector spinae. We have shown in a previous study that histologic changes on muscular biopsy performed in the multifidus at the end of the surgical procedure were not modified by the use of cholinergic blockade during surgery. Methods. Twenty patients scheduled to undergo pedicle-screw enhanced L4-L5 arthrodesis were enrolled in this study. Ten patients received curare during anesthesia and 10 patients did not. MRI was obtained the day before the operation and at 6 months of follow-up on the same MR scanner. T1-weighted images were obtained in the axial plane. The 2 slices immediately proximal and distal to the pedicle screw construct on the postoperative MRI were selected. The corresponding slices were selected on the preoperative MRI. Each erector spinae on the 4 slices was surrounded using a mouse-guided tool. The contractile component of the cross- sectional area (CCSA) was calculated from the number of pixels surrounded and the signal intensity of each pixel. Results. There was only slight changes in the erector spinae CCSA proximal to a posterior lumbar arthrodesis. Erector spinae CCSA decreased by 27% distal to the arthrodesis. Curare showed no efficacy in preventing muscle damage. Conclusions. Erector spinae muscle alterations mainly occur distal to posterior lumbar surgical procedures.