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


Obesity is accepted to be a major risk factor for a number of health problems.[1,2] High obesity (BMI ≥ 35 kg/m2), however, is a unique subcategory with a singular set of health concerns. We hypothesized high obesity rate would be associated with poorer outcomes of surgical and nonsurgical treatment of lumbar pathology. Previous subgroup analysis of SPORT has suggested that obese patients and nonobese patients had similar outcomes from surgery for SpS. Obesity was associated with increased rates of infection and reoperation, as well as less-improved SF-36 physical scores in surgical management for DS.[10] Obese patients also had less improvement in SF-36 physical function scores and ODI from both operative and nonoperative treatment for IDH.[11]

This study reanalyzes the SPORT database to assess the impact of high obesity rate (BMI ≥35 kg/m2) on outcomes. A significant percentage of patients in each arm of the study were in this category—14.8% patients with SpS, 16% patients with DS, and 10.8% patients with IDH. High obesity rate has had an increased prevalence in recent years.[1] Patients in this cohort had the highest rates of hypertension, diabetes, and depression. Socioeconomic factors are known to play a role in lumbar surgical outcomes.[22] For DS and IDH, highly obese patients had the highest percentage of income less than $50,000, and for IDH, they had the lowest education. It is possible, that these factors may have played some role in differences in surgical treatment effect in these 2 arms.

For SpS, highly obese patients reported worse baseline physical scores for the SF-36. Nonetheless, there was no significant difference in treatment effect from surgery between the 3 groups for the primary or secondary patient-reported outcomes at any time point. Although some studies suggest a higher dis-satisfaction and poor outcomes after surgery for lumbar SpS among the obese patients,[8] our fi ndings for SpS are in agreement with studies that suggest no negative impact of obesity on the outcomes of spinal surgery.[8,9] The similar positive treatment effects for surgery among all groups imply that the nonobese group, obese group, and highly obese group may benefit equally from surgical treatment. The obese group and highly obese group do not seem to be at a significantly increased risk of complications from surgery.

For DS and IDH, operative time was significantly longest for the highly obese group. For DS, wound infection and reoperation within 1 year was highest for the highly obese group. It must be noted that the majority of surgical procedures for SpS and all surgical procedures for IDH involved only decompression. Conversely, nearly three-fourths of the surgical procedures for DS involved instrumented fusion. Average operative times were longer than in other arms of the study. Possibly, instrumentation and longer operative times may play a role in the increased adverse events for highly obese patients in the DS arm. The higher rate of intraoperative complications, including dural tear, vascular injury, and other complications in the nonobese group may simply be a function of the higher number of patients in this category. There were 233 nonobese patients who underwent surgery, whereas there were only 90 obese patients and 66 highly obese patients who underwent surgery for DS.

Despite longer operative times and reoperation rates at 1 year, treatment effect for surgical treatment of DS was greatest for the highly obese group. For both DS and IDH, differences were noted in change scores and surgical treatment effect for several primary and secondary outcome measures at different time intervals. Although all cohorts improved with either treatment over time, nonobese patients had better change scores with nonoperative treatment, suggesting that nonsurgical management may be a particularly viable option in this group. In contrast, nonoperative change score was actually negative for highly obese patients in some cases. Consequently, surgical treatment effect was greater for obese patients and greatest for highly obese patients. This implies that the high BMI cohorts may benefit more from surgical management, despite increased operative times and reoperation rates.

Limitations of this study include the preoperative differences between groups in such variables as socioeconomic factors and comorbidity. The preoperative preference for surgery was also higher for the highly obese group in all arms of the study. Although this difference was not significant, it could play a role in the higher treatment effect for surgery in the treatment of DS and IDH in highly obese patients. The SPORT study was not designed for subgroup analysis, and this study highlights this limitation by further separating the obese subcategory. Nonetheless, SPORT is the largest study to date analyzing outcomes of patients treated for SpS, DS, and IDH, making it more likely powered for subgroup analysis.