Long-term outcomes of microendoscopic laminoplasty in patients with lumbar spinal stenosis: impact of the surgical approach and facet tropism
Microendoscopic laminoplasty (MEL) is the surgical procedure of choice at our institution for decompressing nerve roots in lumbar spinal stenosis (LSS). This minimally invasive procedure allows for bilateral decompression via unilateral endoscopic surgical access and maximum preservation of the lumbar zygapophyseal (facet) joints at the level (s) of interest. For this procedure, the surgical approach is generally made on the ipsilateral side of the stenosis. However, this rule of thumb is not always applicable because of lumbar facet joint degeneration and variations in the long-axis orientation of the spinous processes. Few studies to date have proposed criteria about the surgical approach for MEL. Surgeons use their clinical judgment to decide on a case-by-case basis. Facet tropism is frequently encountered in patients with LSS undergoing MEL. Long-term postoperative changes in spinal alignment parameters could guide selection of the side for the surgical approach in MEL. This retrospective study included 45 patients who underwent MEL for single-level LSS between April 1, 2010 and June 30, 2014. The mean age of the patients was 74.8 ± 8.2 years; 23 (51%) were male. FT was defined as a bilateral facet joint angle difference of ≥10 degrees. Study variables included lumbar lordosis angle, Cobb angle, and vertebral slippage based on standing radiographic images. The study population was divided into two groups based on the degree of facet joint sagittal orientation on the side of the incision. Specifically, patients in whom the surgical approach was made on the side of the more sagittally oriented facet joint were categorized into Group S. The other patients were categorized into Group N. The percent change in mean Cobb angle between preoperative and postoperative assessments was 124 ± 164% for Group S and 45.6 ± 62.5% for Group N (P < 0.05), indicating postoperative progression of scoliosis in Group S. Considering the postoperative risk of scoliosis and related complications, approaching from the side of the less sagittally oriented facet joint is preferable in MEL for the treatment of LSS in patients with FT.