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AAOS Now

Published 12/1/2013
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Peter Pollack

Outcomes Trend Down for Extremely Obese Patients

Study data offers granulation among BMI groups

“Extreme obesity is a unique, separate population among patients with higher body mass index (BMI),” said Mohammed A. Khaleel, MD, speaking at the 2013 annual meeting of the North American Spine Society. “Such patients have a BMI greater than or equal to 35. It’s the fastest growing group within the obese population, and the condition is associated with greater disability and healthcare expenditures.”

Dr. Khaleel presented findings from an analysis of data from the Spine Patient Outcomes Research Trial (SPORT)—a multi-institutional randomized clinical trial and concurrent observational cohort—in his paper, “The Effect of Extreme Obesity on Outcomes of Treatment for Lumbar Spinal Conditions.” The research team evaluated the effect of extreme obesity on three conditions: lumbar spinal stenosis (n = 634), degenerative spondylolisthesis (n = 601), and disk herniation (n = 1,190).

“Previous analyses of the SPORT database have suggested that patients who are obese have higher rates of infection and reoperation after surgery for degenerative spondylolisthesis,” said Dr. Khaleel, “but have not differentiated between those who are obese and those who are extremely obese.”

Spinal stenosis
Overall, 373 patients with spinal stenosis were classified as nonobese (BMI < 30); 167 patients were classified as obese (BMI = 30 to < 35) and 94 patients were classified as extremely obese (BMI ≥ 35). Within each of these categories, approximately two thirds of patients were treated surgically: 250 nonobese patients (67 percent); 104 obese patients (62 percent); 59 extremely obese patients (63 percent).

According to Dr. Khaleel, surgery for spinal stenosis consisted primarily of decompression, with very few fusions being performed. At baseline, patients in the extremely obese cohort tended to have greater disability and more comorbidities, and to report lower physical component scores.

“Regarding outcomes, we found no significant difference in the surgical treatment effect among the groups at any point from 1 year to 4 years after surgery,” said Dr. Khaleel. “Operative times tended to be longer as patient BMI increased, but the effect did not reach statistical significance.”

Degenerative spondylolisthesis
Of the 601 patients with degenerative spondylolisthesis, 376 were classified as nonobese, 129 were obese, and 96 were extremely obese. Surgical intervention consisted primarily of fusion, and rates of surgery ranged from 62 percent in the nonobese group, to 70 percent in the obese group, and 69 percent in the extremely obese group.

“Baseline differences suggested that extremely obese patients have lower self-reported physical function and mental component scores,” said Dr. Khaleel. “They also reported getting worse at a faster rate, even though imaging suggested that stenosis was most severe in the nonobese group. Additionally, comorbidities and negative socioeconomic factors were highest in the extremely obese group.”

Dr. Khaleel noted that there was a significantly greater treatment effect in the 4-year SF-36 physical function scores for the extremely obese patients compared to obese and nonobese patients.

“When we take a closer look at this finding,” he explained, “we see that much of this greater treatment effect can be attributed to worse outcomes for nonsurgical treatment among patients in the extremely obese group. If we examine the surgical change scores, they’re actually pretty similar between the obese and the extremely obese, but some extremely obese patients actually reported getting worse with nonsurgical treatment.”

In addition, operative times were longer for the extremely obese patients (mean 222.7 minutes), compared to those for obese patients (218.4 minutes) and nonobese patients (197.2 minutes). Wound infection rates were highest in the group of extremely obese patients (8 percent), compared to the obese (3 percent) and nonobese (1 percent) groups. The obese and extremely obese patient groups also had nearly double the rate of additional surgery at 3- and 4-year follow-up than the nonobese group.

“Interestingly, dural tear rates were highest with the nonobese group,” noted Dr. Khaleel.

Disk herniation
Among patients with disk herniation, 854 were classified as nonobese, 207 as obese, and 129 as extremely obese; 63 percent of the nonobese patients had surgery, as did 73 percent of the obese patients and 73 percent of the extremely obese patients. According to Dr. Khaleel, diskectomy was the primary surgical intervention.

“Similar to the other groups, baseline differences demonstrated lower self-reported scores among extremely obese patients, higher comorbidity rates, lower socioeconomic scores, and greater likelihood for the extremely obese group to report getting worse,” said Dr. Khaleel. “Extremely obese patients experienced less improvement after surgery than obese and nonobese patients. Nonsurgical treatment outcomes were even worse, resulting in a significantly greater treatment effect for extremely obese patients compared to nonobese patients.”

In addition, operative times were greater for patients in the extremely obese cohort (90.5 minutes) compared to the obese cohort (84 minutes) and the nonobese cohort (72.3 minutes). Patients in the obese cohort displayed greater blood loss (84.8 mL) compared to the extremely obese cohort (80.7 mL) and the nonobese cohort (56.1 mL).

“In conclusion, we recognize that the extremely obese group had a big impact on previously recognized differences between the obese and the nonobese for outcomes for surgical versus nonsurgical treatment of these conditions,” said Dr. Khaleel. “The extremely obese had the highest rates of comorbidity, lowest baseline measures, and the most negative socioeconomic characteristics. For degenerative spondylolisthesis in particular, extremely obese patients had longer operative times and higher infection rates.

“The treatment effect was positive in all groups,” he concluded, “but surgical treatment effect was largest for the extremely obese for the treatment of spondylolisthesis or disk herniation, and that effect was largely attributable to much poorer outcomes from nonsurgical interventions.”

Dr. Khaleel’s coauthors include Kevin J. McGuire, MD; Katiri Wagner, BS; Jeffrey A. Rihn, MD; Jon D. Lurie, MD; Wenyan Zhao, PhD; James N. Weinstein, DO, MS.

Disclosure information: Dr. Khaleel, Dr. Zhao—no conflicts; Dr. Rihn—Pfizer, DePuy, The Spine Journal, North American Spine Society; Dr. Lurie—NewVert, Foundation for Informed Medical Decision Making, FzioMed, Baxano, Spine, The Spine Journal, ISRN Orthopaedics, National Institutes of Health, Agency for Healthcare Research & Quality, Blue Cross Blue Shield, FzioMed; Dr. Weinstein—Spine/Lippincott Williams & Wilkins; Dr. McGuire, Ms. Wagner—no information available.

Peter Pollack is electronic content specialist for AAOS Now. He can be reached at ppollack@aaos.org

Bottom Line

  • Extreme obesity is linked to lower baseline scores in physical function.
  • Extreme obesity is associated with more comorbidities, longer operative times, and negative outcome trends.
  • Positive treatment effect for surgery among extremely obese patients may be attributable to more negative treatment effect for nonsurgical interventions.