Recovery of function in adjacent nerve roots after surgery for lumbar disc herniation: use of quantitative sensory testing in the exploration of different populations of nerve fibers.

Results from experimental and clinical studies indicate that adjacent nerve roots may be affected in sciatica because of lumbar disc hemiation. This may be caused by proinflammatory mediators in the epidural space being transported into nerve roots at the same or neighboring lumbar segments. The aim of the present study was to investigate the recovery of function of sensory nerve fibers in the adjacent noncompressed nerve roots. Thirty-nine patients undergoing microdiscectomy for monoradiculopathy were investigated with quantitative sensory testing immediately before surgery, and at 6 weeks, 4 months, and 12 months after the operation. Twenty-one healthy volunteers were used as controls. The patients were classified as having a good or a poor result at the 1-year follow-up according to a clinical score. Significant improvement of function in the noncompressed nerve roots were only observed in the 31 patients with a good result. The improvement in small myelinated nerve fibers came within 12 months in the adjacent nerve roots in both the symptomatic as well as the asymptomatic leg. The improvement of function in small unmyelinated fibers also came within 12 months after surgery; however, significant improvement was only observed in the ipsilateral neighboring nerve root. The function in large myelinated fibers did not improve in any of the adjacent nerve roots during the observation period. The observed recovery of function in adjacent noncompressed nerve roots after successful surgical decompression in monoradiculopathy may be because of less production of proinflammatory mediators when the disc herniation is removed.