Could indirect decompression occur for cord compression by the ligamentum flavum with anterior cervical discectomy and fusion?

OBJECTIVE Cord compression by the ligamentum flavum (CCLF) has been reported to adversely affect the clinical outcomes of anterior cervical discectomy and fusion (ACDF). While indirect decompression does occur for foraminal stenosis with ACDF, whether ACDF could improve CCLF with the distraction of disc space remains unclear. This study aimed to identify 1) whether indirect decompression occurs for CCLF with ACDF, and 2) risk factors that hinder the improvement of CCLF. METHODS This retrospective cohort study included 119 patients who underwent ACDF for the treatment of cervical myelopathy and CCLF was detected on preoperative MRI. Patients who demonstrated improvement in CCLF grade after ACDF were included in the improved group, while those who did not show improvement were classified as the unimproved group. Patient characteristics, cervical sagittal parameters, neck and arm pain visual analog scale score, and Japanese Orthopaedic Association (JOA) score were assessed. A comparison between the improved and unimproved groups was performed. Regression analyses were performed to identify factors associated with CCLF grade improvement. RESULTS Overall, 58.0% (69/119) of patients showed improvement in CCLF grade after ACDF. CCLF grade did not improve in the remaining 42.0% (50/119) of patients, and 3.4% (4/119) of patients experienced aggravation of CCLF after ACDF. Preoperative spondylolisthesis (OR 0.252, 95% CI 0.090–0.711; p = 0.009) and greater segmental lordosis 3 months postoperatively (OR 0.835, 95% CI 0.731–0.953; p = 0.008) were the factors that hindered the improvement of CCLF after ACDF. Furthermore, patients with higher pre- or postoperative CCLF grades showed significantly less improvement in JOA score 2 years postoperatively. CONCLUSIONS Indirect decompression for CCLF with ACDF is not reliable because 42.0% of patients did not demonstrate improvement in CCLF grade after the operation. Preoperative spondylolisthesis and postoperative increased segmental lordosis were risk factors for failure of CCLF improvement. Both pre- and postoperative higher CCLF grades were associated with poor neurological recovery 2 years postoperatively.