The effect of high obesity on outcomes of treatment for lumbar spinal conditions: Subgroup analysis of the Spine Patient Outcomes Research Trial

Study Design. Spine Patient Outcomes Research Trial subgroup analysis. Objective: To evaluate the effect of high obesity on management of lumbar spinal stenosis, degenerative spondylolisthesis (DS), and intervertebral disc herniation (IDH). Summary of Background Data: Prior Spine Patient Outcomes Research Trial analyses compared nonobese and obese patients. This study compares nonobese patients (body mass index <30 kg/m²) with those with class I obesity (body mass index = 30.35 kg/m²) and class II/III high obesity (body mass index ≥ 35 kg/m²). Methods: For spinal stenosis, 250 of 634 nonobese patients, 104 of 167 obese patients, and 59 of 94 highly obese patients underwent surgery. For DS, 233 of 376 nonobese patients, 90 of 129 obese patients, and 66 of 96 highly obese patients underwent surgery. For IDH, 542 of 854 nonobese patients, 151 of 207 obese patients, and 94 of 129 highly obese patients underwent surgery. Outcomes included Short Form-36, Oswestry Disability Index, stenosis/sciatica bothersomeness index, low back pain bothersomeness index, operative events, complications, and reoperations. Operative and nonoperative outcomes were compared by change from baseline at each follow-up interval using a mixed effects longitudinal regression model. An as-treated analysis was performed because of crossover between surgical and nonoperative groups. Results: Highly obese patients had increased comorbidities. Baseline Short Form-36 physical function scores were lowest for highly obese patients. For spinal stenosis, surgical treatment effect and difference in operative events among groups were not significantly different. For DS, greatest treatment effect for the highly obese group was found in most primary outcome measures, and is attributable to the significantly poorer nonoperative outcomes. Operative times and wound infection rates were greatest for highly obese patients. For IDH, highly obese patients experienced less improvement postoperatively compared with obese and nonobese patients. However, nonoperative treatment for highly obese patients was even worse, resulting in greater treatment effect in almost all measures. Operative time was greatest for highly obese patients. Blood loss and length of stay was greater for both obese cohorts. Conclusion: Highly obese patients with DS experienced longer operative times and increased infection. Operative time was greatest for highly obese patients with IDH. DS and IDH saw greater surgical treatment effect for highly obese patients due to poor outcomes of nonsurgical management.