Evidence & Methods
As complications following surgery receive increased scrutiny from the public, government and third-party payers, the ability to risk adjust and prognosticate outcomes in the setting of specific medical co-morbidities is becoming increasingly vital. At this time, the impact of obesity on outcomes after lumbar spine surgery remains controversial. The authors sought to address this issue by analyzing data from the National Surgical Quality Improvement Program (NSQIP).
The authors analyzed more than 10,000 cases of lumbar spine surgery. They classified obesity using the WHO graded scale and concluded that patients with WHO grade III obesity were at an increased risk of complications as well as extended length of hospital stay.
The authors’ findings add to a growing body of literature detailing the deleterious effect of obesity on outcomes following spine surgery. This is necessary information for patients, physicians, hospital administrators and third-party payers. At a minimum, the study’s findings can be used to better inform patients at the time of surgical consent regarding the anticipated impact of obesity on outcomes. As this information was derived from a national registry intended for quality improvement purposes, it suffers from the possibility of confounding due to errors in coding as well as missing data. In addition, the number of complication events as compared to the sample size is invariably restricted and, given the number of covariates the authors included in their regressions, the model may be overfit. Only scientifically rigorous, prospective, comparative research can truly provide high quality evidence to better inform this issue.
—The Editors
Several related single-institution and population-based studies have been conducted, but results have been mixed. Some studies have shown no increased risk after lumbar surgery in obese patients [5], [6], [7], particularly after minimally invasive surgery (MIS) [8], [9], [10], whereas most have noted an association between high BMI and an increased risk of complications [11], [12], [13], [14], [15]. Specifically, a few studies have found the obese population to have a higher rate of wound complications [11], [12], [14], [16], [17], deep vein thromboses (DVTs) [11], [13], reoperation [18], intraoperative blood loss [15], [16], [17], [19], extended hospital stays, and longer operative times [19].
Possible explanations for the inconsistency in the literature may lie in sample size differences and the fact that different BMI thresholds were used to define the obese and comparison cohorts. Most related studies defined obesity as BMI greater than or equal to 30 kg/m2, but some compared the obese group with a nonobese group (BMI less than 30 kg/m2) [16], [19], others with a normal weight group (BMI=18.5–24.9 kg/m2) [20], and others with both a normal group and an overweight group (BMI=25–29.9 kg/m2) [6]. One large-scale multi-institutional study compared a morbidly obese group (BMI greater than or equal to 40 kg/m2) with a normal-weight group (defined in their study by the absence of International Classification of Diseases, Ninth Revision [ICD-9] codes for obesity, overweight, or underweight) [11], whereas another study compared obese (BMI=30–39.9 kg/m2) and morbidly obese (BMI greater than or equal to 40 kg/m2) patients to a normal or overweight group (defined in their study by the absence of ICD-9 codes for obesity and morbid obesity) [17]. There was one study that used a nonstandard definition for obese (BMI greater than or equal to 35 kg/m2) and nonobese (BMI less than 35 kg/m2) [18]. Other smaller studies also differed in their definitions of obesity [2], [3], [10], [12], [14], [15], [21], [22].
Given the different BMI thresholds used for defining obesity and the mixed results of the studies, the question arises as to what degree of obesity is actually associated with which adverse outcomes. The World Health Organization (WHO) has a graded scale for obesity: Obese I (30–34.9 kg/m2), Obese II (35–39.9 kg/m2), and Obese III (greater than or equal to 40 kg/m2). Nonetheless, only one of the smaller studies has used this graded scale of obesity in the analysis of spinal fusion complications [14]. To our knowledge, no large lumbar surgery study has used this graded definition of obesity for this purpose. Furthermore, most studies have mostly focused on lumbar fusions, and there are limited data comparing complications for different types of lumbar surgery.
The present study is a large-scale multi-institutional database study using the American College of Surgeons National Surgery Quality Improvement Program (ACS NSQIP) database. National databases are increasingly being used to address clinical questions with degrees of randomization, speed, and power previously not possible. Each database measures different variables and has its specific advantages and limitations to answer clinical questions, particularly for short-term postoperative outcomes. With the use of ACS NSQIP, this study characterizes and compares the 30-day clinical outcomes of patients with graded levels of obesity after five common lumbar spine surgery procedures. Results are compared with currently available literature.
