Clinical and Radiological Outcomes of Microscopic Lumbar Foraminal Decompression: A Pilot Analysis of Possible Risk Factors for Restenosis

A single-center retrospective comparative study was designed to identify the risk factors for restenosis of lumbar foraminal stenosis (LFS) after microscopic foraminal decompression (MFD). 21 consecutive patients who underwent single-level MFD with an average of 19-month follow-up were divided into two study groups based on clinical outcomes; group 1 (7 patients with poor outcomes requiring revision surgery), group 2 (14 patients with good outcomes with no revision surgery required). Changes of lumbar spinal alignment on plain standing radiographs were compared and analyzed between two study groups to investigate the pathology and risk factors associated with restenosis after MFD. Preoperative disc wedging (DW) angle was significantly larger in group 1 than in group 2 (3.5 ± 1.0° vs 1.1 ± 0.2°, P < 0.01). Postoperatively, disc height (DH) and foraminal height (FH) decreased (P < 0.05), and DW deteriorated (P < 0.01) significantly in group 1, while there were no significant changes in group 2. Lumbar lordosis (LL) remarkably improved postoperatively in group 2 (24.7 ± 8.0 to 32.0 ± 7.0, P < 0.001), contrary to limited improvement in group 1 (25.1 ± 9.2 to 27.0 ± 12.0, P = 0.45). Postoperative LL is a predictive factor for restenosis after MFD. Decrease in DH or progression of DW was contributing to restenosis. LFS presenting with large DW and lumbar degenerative kyphosis should be excluded from surgical indications for MFD without instrumented fusion, considering the high recurrence rate.