Sagittal imbalance in patients with lumbar spinal stenosis and outcomes after simple decompression surgery.

BACKGROUND CONTEXT Lumbar spinal stenosis (LSS) is the most common lumbar degenerative disease, and sagittal imbalance is uncommon. Forward-bending posture, which is primarily caused by buckling of the ligamentum flavum, may be improved via simple decompression surgery. PURPOSE The objectives of this study were to identify the risk factors for sagittal imbalance and to describe the outcomes of simple decompression surgery. STUDY DESIGN This is a retrospective nested case-control study PATIENT SAMPLE: This was a retrospective study that included 83 consecutive patients (M:F=46:37; mean age, 68.5±7.7 years) who underwent decompression surgery and a minimum of 12 months of follow-up. OUTCOME MEASURES The primary end point was normalization of sagittal imbalance after decompression surgery. METHODS Sagittal imbalance was defined as a C7 sagittal vertical axis (SVA) ≥40 mm on a 36-inch-long lateral whole spine radiograph. Logistic regression analysis was used to identify the risk factors for sagittal imbalance. Bilateral decompression was performed via a unilateral approach with a tubular retractor. The SVA was measured on serial radiographs performed 1, 3, 6, and 12 months postoperatively. The prognostic factors for sagittal balance recovery were determined based on various clinical and radiological parameters. RESULTS Sagittal imbalance was observed in 54% (45/83) of patients, and its risk factors were old age and a large mismatch between pelvic incidence and lumbar lordosis. The 1-year normalization rate was 73% after decompression surgery, and the median time to normalization was 1 to 3 months. Patients who did not experience SVA normalization exhibited low thoracic kyphosis (hazard ratio [HR], 1.04; 95% confidence interval [CI], 1.02-1.10) (p<.01) and spondylolisthesis (HR, 0.33; 95% CI, 0.17-0.61) before surgery. CONCLUSIONS Sagittal imbalance was observed in more than 50% of LSS patients, but this imbalance was correctable via simple decompression surgery in 70% of patients.