Factors Predicting Cost-effectiveness of Adult Spinal Deformity Surgery at 2 Years

Abstract

Objective: To identify preoperative factors that lead to cost-effectiveness at 2 years' follow-up in the setting of surgical treatment for adult spinal deformity.

Methods: Retrospective analysis of a prospective, consecutive, multicenter database including 514 patients who underwent surgery for adult spinal deformity. The change in quality-adjusted life-years (QALY) was calculated from the 2-year change in Oswestry Disability Index (ODI). Medicare coding was used to determine the direct costs based on diagnosis-related group and Relative Value Unit reimbursement. Analysis was performed to determine which factors were associated with a cost/QALY less than $100,000, making the procedure cost-effective.

Results: The average QALY change for all patients in this study was 0.15 and the average cost/QALY was $243,761.97. A total of 56 patients (10.4%) had a cost/QALY of less than $100,000 at 2-year follow-up. Those patients were mostly female (89%), with a mean age of 60 years and the following diagnoses: 18 (32.1%) adult idiopathic scoliosis, 12 (35.7%) adult de novo scoliosis, 87 (14.3%) sagittal imbalance, and 10 (17.9%) other scoliosis. The Health-Related Quality of Life ODI and Scoliosis Research Society (SRS) instruments were all associated with cost-effectiveness except SRS-Mental. Factors associated with cost-effectiveness were age greater than 55 years, adult de novo scoliosis, prior surgery, higher preoperative sagittal vertical axis, lower maximum Cobb angles, 8 or fewer fusion levels, lower blood loss, worse global alignment classification, and global sagittal malalignment. Combined anterior-posterior surgeries were negatively associated with cost-effectiveness. Preoperative ODI scores between 60 and 70 and SRS Pain and Activity subscores more than 4 minimally clinically important difference points below the normative values had the highest percentage of cost-effective patients.

Conclusions: The QALY change is 0.15 and the cost/QALY of adult deformity surgery is $243,761.97 at 2 years. Patients with higher preoperative morbidity are more likely to be cost-effective with a cost/QALY less than $100,000.

Keywords: Adult spinal deformity; Cost-effectiveness; QALY; Spinal fusion.