The Effect of High Obesity on Outcomes of Treatment for Lumbar Spinal Conditions

Subgroup Analysis of the Spine Patient Outcomes Research Trial

Kevin J. McGuire, MD, MS; Mohammed A. Khaleel, MD, MS; Jeffrey A. Rihn, MD; Jon D. Lurie, MD, MS; Wenyan Zhao, PhD; James N. Weinstein, DO, MS


Spine. 2014;39(23):1975-1980. 

In This Article

Abstract and Introduction


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.


Several modern health care initiatives focus on the obesity epidemic due to associated comorbidities, including hypertension, heart disease, diabetes, and osteoarthritis.[1,2] Obesity is associated with an increased prevalence of low back pain as well as seeking care for it.[3] Being overweight increases the risk of lumbar disc degeneration, particularly at a young age.[4]

Obesity has been associated with inferior results of surgery for lumbar spinal stenosis (SpS)[5] as well as increased complication rates,[6] particularly with regard to surgical site infections.[7] Nonetheless, the literature is conflicted regarding the effect of obesity on outcomes of lumbar surgery. With appropriate indications, obese patients may benefit from surgical treatment.[8,9] The Spine Patient Outcomes Research Trial (SPORT) represents one of the largest studies of operative and non-operative care of patients with lumbar SpS, degenerative spondylolisthesis (DS), and intervertebral disc.herniation (IDH).

A previous subgroup analysis of SPORT comparing surgical and nonsurgical outcomes for nonobese patients (body mass index [BMI] < 30 kg/m2) and obese patients (BMI ≥30 kg/m2) demonstrated significant treatment effects of surgery for all groups. Obesity did not affect outcome of surgery for SpS. For DS, it was associated with higher rates of infection, twice the reoperation rate, and less improvement in Short Form-36 (SF-36) physical function scores.[10] For IDH, obese patients experienced less benefit from both operative and nonoperative treatment, particularly with SF-36 physical function scores and Oswestry Disability Index (ODI). Both groups benefited from surgery over nonsurgical management.[11]

Obesity represents a heterogeneous classification. The International Classification of Obesity, shown in Table 1, was adapted from the World Health Organization and adopted by the Expert Panel on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, a group assembled by the National Heart, Lung, and Blood Institute of the National Institutes of Health.[12,13]

The severely obese patients have more comorbidities and higher health care demands than the moderately obese patients.[14] From 1986 to 2000, although the prevalence of obesity (BMI ≥30 kg/m2) doubled from 1 in 10 to 1 in 5, the prevalence of BMI 40 or more quadrupled from 1 in 200 to 1 in 50, and that of BMI 50 or more quintupled from 1 in 2000 to 1 in 400.[15] High obesity rate is fast growing and represents the greatest disability and cost.

The severely obese patients face further risks of comorbidities and lifestyle limitations. The purpose of this study was to use SPORT to assess the impact of high obesity (BMI ≥35 kg/m2) on outcomes of surgical and nonsurgical management of lumbar pathology. Table 2 indicates the frequency of BMI classifi - cations within each arm of the study group.

Similar to the group studied by Katzmarzyk et al,[14] our study population had a low rate of patients with class III obesity (BMI ≥40 kg/m2). We, likewise, combined class II and III obesity into a high obesity group with BMI 35 or more. We hypothesized that this group would experience poorer outcomes of both surgical and nonsurgical treatment for SpS, DS, and IDH.