Muscle-Preserving Interlaminar Decompression for the Lumbar Spine

Abstract

In Brief 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 21.3months). 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. Partial drilling of the spinous processes and split of the supra- and interspinous ligaments brought a minimally invasive interspinous approach. This lumbar procedure is performed through a midline incision, providing ample exposure of the bilateral intracanalicular space with minimal invasion to the paravertebral muscles and facet joints. It can preserve the function of the spinous processes as levers for the lumbar extension mechanism.