• The purpose of this study was to determine if obesity affects outcomes following treatment of symptomatic lumbar disc herniation.

This publication by Rihn et al represents a retrospective analysis of data collected from the Spine Patient Outcomes Research Trial (SPORT).   As has been previously published describing the SPORT trial, participants were either randomized or placed in an observational cohort. This data presented was taken from the as-treated analysis and therefore the randomization effect was removed, making it a retrospective review.

For the purposes of this publication, obesity was defined as a body mass index (BMI) of less than 30.   The nonobese group included 854 patients while the obese group included 336.  The primary outcome measure was the physical function and bodily pain domain of the SF-36 and the American Academy of Orthopaedic Surgeons Musculoskeletal Outcomes Data Evaluation and Management System (MODEMS) version of the Oswestry Disability Index (ODI).  Secondary measures included work status, patient reported self improvement, and  satisfaction.  The authors utilized the Low Back Pain Bothersomeness Index and Sciatica Bothersomeness Index to measure symptom severity. All of the these are validated outcome measures.

The overall results shows that patients classified in the obese group were more likely to undergo surgical management for a lumbar disc herniation than those in the nonobese group. Additionally, statistically significant differences were noted in operation time, blood loss, and length of stay between the two groups, with the obese patients having higher measures for all three variables.  Obese patients who underwent surgery had less improvement in the Sciatica Bothersomeness Index and Low Back Bothersomeness Index than nonobese patients. No significant differences were noted in satisfaction levels.

The authors concluded that the benefit of surgery over non-surgical treatment was not affected by body mass index.

Taking a critical look at the supplementary material that accompanied this publication,  it should be noted that there were significant differences in baseline characteristics for a number of variables including sex, education level, income, compensation, and the presence of several medical co-morbidities. Furthermore, significant differences in several domains of the SF36 and ODI scores were presented at baseline between the two groups.    Lastly, BMI status was not reassessed over the four year course which has the potential to change several point estimates. Any conclusions drawn from this should be cautious due to these aforementioned study limitations along with the fact that this was a secondary analysis of data from the SPORT trial in which the effect of obesity on outcomes was not among the primary question to be answered.

Within the last 7 years, at least 5 other investigations, looking specifically at the effect obesity on the outcome of surgical treatment of a lumbar disc herniation, has been published.  The findings from Yoo et al (Korean J Spine 2014) found that operating time and blood loss were significantly increased in those with obesity, much like the analysis by Rihn et al.   Unlike Rihn et al, other retrospective cohort studies have concluded that obesity  is a strong, independent predictor of recurrent lumbar disc herniation for patients who underwent minimally invasive techniques for initial discectomy.