Muscle-preserving interlaminar decompression for the lumbar spine: a minimally invasive new procedure for lumbar spinal canal stenosis.

STUDY DESIGN: Outcomes of muscle-preserving interlaminar decompression (MILD) for the lumbar spine are reported.

OBJECTIVE: To verify the clinical findings of lumbar MILD.

SUMMARY OF BACKGROUND DATA: A preliminary short-term follow-up study of lumbar MILD demonstrated satisfactory neural recovery and reduced invasiveness. METHODS.: The initial 105 consecutive patients with lumbar spinal canal stenosis were included in this study. A total of 210 intervertebral levels were decompressed. There were 48 women and 57 men, and the mean patient age was 68.8 years. The postoperative follow-up period ranged from 8 to 44 months (mean 21.3 months). Eighty-one patients showed cauda equina claudication, and 75 patients complained of radicular pain. Preoperative imaging studies demonstrated that all patients had moderate-to-severe spinal canal stenosis, 75 patients had degenerative spinal canal stenosis, and the remaining 30 had degenerative spondylolisthesis. Pre- and postoperative Japanese Orthopedic Association scores, intraoperative blood loss, surgical complications, and postoperative ambulation were recorded. RESULTS.: One hundred five patients underwent lumbar MILD procedure for 210 interspinous levels, 42 patients for 2 levels, 37 patients for 1 level, 17 for 3 levels, 7 for 4 levels, and 2 for 5 levels. Cerebrospinal fluid leakage due to dural tear occurred in 2 patients. Expansion of the operative field was not necessary to repair the dura mater. The mean operation time was 104.9 minutes per level, and mean intraoperative blood loss was 29.4 g per level. Neurologic improvement was demonstrated in all patients. The mean recovery rate calculated with pre- and postoperative Japanese Orthopedic Association scores was 64.9%. Patients started to stand or walk an average of 2.5 days after surgery. None of the patients presented with wound infection. There was no neurologic complication in this series.

CONCLUSION: In MILD for the lumbar spine, damage to the posterior stabilizing structures such as the intervertebral facet joints, paravertebral muscles, thoracolumbar fascia, supra- and interspinous ligaments, can be minimized, while preserving the function of the spinous processes as lever arms for lumbar extension.