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

Disclosures

Spine. 2014;39(23):1975-1980. 

In This Article

Results

Lumbar Spinal Stenosis

The SpS arm included 373 patients with BMI less than 30, 167 with BMI between 30 and 35, and 94 with BMI 35 or more. Baseline differences are noted in Supplemental Digital Content, Appendix A—Table 1 available at http://links.lww.com/BRS/A901. Mean age was significantly different among the groups with the nonobese group being oldest and the highly obese group being youngest. Other significant differences included disabled work status, rates of hypertension, diabetes, depression, heart problems, and bowel or intestinal problems. Baseline outcome scores were not significantly different except for SF-36 vitality scores where the obese cohort reported lower mean scores, and the highly obese cohort reported lowest. Highly obese patients had the highest rate of asymmetric sensory decrease.

Supplemental Digital Content, Appendix B—Table 1 available at http://links.lww.com/BRS/A901 demonstrates operative details, complications and events. There were no significant differences between groups. Although mean operative time was highest in highly obese patients, the difference was not significant. Supplemental Digital Content, Appendix C—Table 1 and Figure 1 available at http://links.lww.com/BRS/A901 note change in scores and treatment effects in primary and secondary outcomes. No significant difference was observed in treatment effect among the groups for any of the outcomes.

Degenerative Spondylolisthesis

In the DS arm, 376 patients had BMI less than 30, 129 had BMI between 30 and 35, and 96 had BMI 35 or more. Supplemental Digital Content, Appendix A—Table 2 available at http://links.lww.com/BRS/A901 notes significant baseline differences in demographics, comorbidities, and health status. Again, mean age was significantly different with the highly obese youngest patients. This group also had a higher percentage of female patients. Notable socioeconomic differences existed. Highly obese patients had the highest percentage with income less than $50,000 and the lowest rates of marriage. Rates of hypertension, diabetes, depression, stomach problems, kidney problems, and other comorbidities were highest for the highly obese group.

The highly obese group had the lowest SF-36 scores in all categories indicating more severe symptoms. Except for the mental component summary, the symptom severity was directly correlated with level of obesity. ODI scores were also highest for the most obese group, indicating more severe symptoms. This group had the highest percentage of patients reporting worsening symptoms. Preference for surgery was highest in the highly obese group. In contrast, the rate of severe stenosis as indicated by imaging was higher in nonobese patients (63%) versus obese patients (55%) and highly obese patients (56%).

Supplemental Digital Content, Appendix B—Table 2 available at http://links.lww.com/BRS/A901 describes operative treatments, complications, and events. Mean operative times were longest in the highly obese group. Interestingly, intraoperative complication rate was highest in the nonobese group. The obese group experienced more wound issues. Only one wound dehiscence occurred; this was in an obese patient. The only wound hematoma was in a highly obese patient. The rate of wound infection was directly correlated with BMI with the highest occurrence in the highly obese group (8%) versus the obese group (3%) and the nonobese group (1%). The rate of additional surgical procedures within 1 year was highest in the highly obese group; however, at 3 and 4 years it was highest in the moderately obese group. Reoperation rate was nearly double for both obese groups compared with that of nonobese group throughout the study.

Supplemental Digital Content, Appendix C—Table 2 and Figure 2 available at http://links.lww.com/BRS/A901 show change in scores and treatment effects. In year 1, the SF-36 mental component summary score had a greater treatment effect for the highly obese group (6.5) versus the obese group (1.2) and the nonobese group (0.4); P = 0.015. The 4-year SF-36 physical function score had greater treatment effect in the highly obese group (26) versus obese group (25.4) and nonobese group (13.9), P = 0.016. Although the differences may not have come to significance, greater surgical treatment effect is noted for highly obese patients in nearly all of the primary outcome measures. This is likely attributable to the significantly poorer outcomes with nonoperative treatment for the highly obese group.

Intervertebral Disc Herniation

In the IDH arm, 854 patients had BMI less than 30, 207 had BMI between 30 and 35, and 129 had BMI 35 or more. Baseline demographics, comorbidities, and health status are reported in Supplemental Digital Content, Appendix A—Table 3 available at http://links.lww.com/BRS/A901. No significant difference in age was noted among the groups; however, the highly obese group had a higher percentage of females. Socioeconomic differences were apparent.

The highly obese group had the highest percentage with income less than $50,000 and the lowest percentage with some college. Again, highly obese patients experienced highest rates of hypertension, diabetes, stomach problems, and other comorbidities. The highly obese group had the lowest SF-36 scores indicating worse bodily pain, physical functioning, vitality, and physical component summary. The ODI scores were highest for the highly obese group, indicating greater disability. This group also reported the highest percentage of patients reporting getting worse (51%) versus the nonobese group (38%) and the obese group (40%). The obese group and highly obese group had higher preference for surgery (56% and 54%, respectively) in comparison with the nonobese group (48%).

Supplemental Digital Content, Appendix B—Table 3 available at http://links.lww.com/BRS/A901 describes operative treatments, complications, and events among the 3 groups in this arm of the study. Mean operative time was directly related to BMI: 90.5 minutes for the highly obese group versus the obese group (84 min) and the nonobese group (72.3 min). Blood loss was higher for the obese group (84.8 mL) and highly obese group (80.7 mL) than the nonobese group (56.1 mL). Significantly longer lengths of stay were observed for the obese group (1.2 d) and highly obese group (1.1 d) versus the nonobese group (0.89 d). The only nerve root injury occurred in a highly obese patient. No differences existed in the rate of wound complications after discectomy.

Supplemental Digital Content, Appendix C—Table 3 and Figure 3 available at http://links.lww.com/BRS/A901 show change in scores and treatment effects. SF-36 physical function change with surgery was lower for the obese group and highly obese group than for the nonobese group at each year. However, the difference in change scores among the cohorts was of greater magnitude for nonsurgical management. Although all showed improvement, nonobese patients had the highest positive change, whereas obese patients had less, and highly obese patients had the least. Therefore, surgical treatment effect was greatest for highly obese patients, followed by nonobese patients, and finally obese patients. This trend came to significance particularly in years 2 and 3 for the SF-36 physical function variable.

Change in ODI for nonoperative treatment was indirectly related to BMI; highly obese patients had least improvement in each year. Although this trend persisted, it came to significance in years 1 and 3. Because this difference was not as drastic for surgical management, treatment effect for surgery was greatest for highly obese patients each year. This was significant only in year 1. Although similar trends existed for other outcomes, differences were not consistently significant.

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