SPINE Volume 40, Number 1, pp 56-61 ©2014, Lippincott Williams & Wilkins

OUTCOMES

The Impact of Obesity on Short- and Long-term Outcomes After Lumbar Fusion Rafael De la Garza-Ramos, MD,*† Mohamad Bydon, MD,*† Nicholas B. Abt, BS,*† Daniel M. Sciubba, MD,*† Jean-Paul Wolinsky, MD,*† Ali Bydon, MD,*† Ziya L. Gokaslan, MD,*† Bruce Rabin, MD, PhD,‡ and Timothy F. Witham, MD*†

Study Design. Retrospective cohort study. Objective. To compare short- and long-term outcomes in obese versus nonobese patients undergoing instrumented posterolateral fusion of the lumbar spine. Summary of Background Data. Obesity is an important public health issue due to the negative effects on quality of life. Some studies have shown an association between obesity and higher rates of complications and unfavorable outcomes after spine surgery. Methods. We retrospectively reviewed medical records for all adult patients undergoing 1- to 3-level posterolateral fusion for degenerative spine disease between 1992 and 2012 at a single institution. Patients were divided into obese (body mass index > 30 kg/m2) and nonobese cohorts to compare complications, reoperation rates, and symptom resolution at the last follow-up. A regression model was used to estimate relative risk ratios. Results. During the study period, 732 patients underwent lumbar fusion, with 662 (90.44%) nonobese patients and 70 (9.56%) obese patients in the cohort. Obese patients had significantly higher blood loss intraoperatively (P = 0.002) and a longer average length of stay (P = 0.022). Moreover, obesity was independently associated with a significantly increased risk of developing a postoperative complication (risk ratio 2.14; 95% confidence interval, 1.10–4.16) and surgical site infection (risk ratio 3.11; 95% confidence interval, 1.48–6.52). At the last follow-up, a higher proportion of obese patients had radiculopathy (P = 0.018), motor deficits (P = 0.006), sensory deficits (P = 0.008), and bowel or bladder dysfunction (P = 0.006) than nonobese patients.

From the *The Spinal Column Biomechanics and Surgical Outcomes Laboratory; †Department of Neurosurgery, and ‡Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD. Acknowledgment date: May 13, 2014. First revision date: July 31, 2014. Second revision date: September 11, 2014. Acceptance date: September 13, 2014. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: consultancy, grants, payment for lectures, stocks. Address correspondence and reprint requests to Timothy F. Witham, MD, The Johns Hopkins Hospital, 600 North Wolfe St, Meyer 5-109, Baltimore, MD 21287; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000655

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Conclusion. In this study, obese patients undergoing lumbar fusion had higher blood loss, longer lengths of stay, higher complication rates, and worse functional outcomes at the last follow-up than nonobese patients. These findings suggest that both surgeons and patients should acknowledge the significantly increased morbidity profile of obese patients after lumbar fusion. Key words: obesity, lumbar, fusion, degenerative, outcomes, complications, spine, surgery, wound, infection. Level of Evidence: 4 Spine 2015;40:56–61

O

besity (defined as a body mass index [BMI] ≥ 30 kg/m2) is a concerning public health issue due to the numerous adverse effects on quality of life and overall increased morbidity and mortality.1 In 2012, it was estimated that 34.9% of adults older than 20 years in the United States were obese.2 Importantly, obesity has been associated with a higher prevalence of chronic back pain3 and intervertebral disc degeneration,4 and some studies have reported a higher rate of perioperative complications and unfavorable outcomes after spine surgery in this population.5–7 Nonetheless, other studies have not shown a significantly increased risk of postoperative complications or worsened outcomes.8–10 The purpose of this study is to compare short- and long-term outcomes between obese and nonobese patients undergoing instrumented posterolateral fusion (PLF) in the lumbar spine.

MATERIALS AND METHODS Study Design and Patient Selection All adult patients undergoing an instrumented PLF of the lumbar spine from 1992 to 2012 in the neurosurgery department at a single institution were identified. Only patients who underwent a 1- to 3-level lumbar fusion for degenerative spine disease were included; patients who underwent surgery for infectious, traumatic, neoplastic, or other causes were excluded.

Recorded Variables A total of 732 patients met our inclusion criteria. The neurosurgical preoperative, operative, and postoperative clinical January 2015

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OUTCOMES notes were assessed to record patient demographics such as age, comorbidities, preoperative diagnosis, and presenting symptoms. Intraoperative data on number of levels fused, bone morphogenetic protein use, and estimated blood loss (EBL) were also collected from operative notes. Postoperative data on length of stay, complications, and need for reoperation were also assessed. Patients in this study were divided into 2 cohorts: nonobese and obese. Obesity was defined as a BMI 30 kg/m2 or more, in accordance with the definition provided by the World Health Organization.11

Outcome Variables This study evaluated short- and long-term outcomes. Shortterm outcomes included average length of stay, EBL, development of at least 1 postoperative complication (surgical site infection, pneumonia, deep vein thrombosis (DVT), pulmonary embolism, hematoma, wound dehiscence, myocardial infarction, paralysis, or death). Long-term outcomes included symptom improvement at the last follow-up, need for revision surgery and development of pseudarthrosis. Clinical notes were used to assess the presence of symptoms (back pain, radiculopathy, and neurological deficits) at each follow-up visit.

Treatment Protocol All patients underwent an instrumented PLF of the lumbar spine. Of the total cohort, 305 (41%) also received an interbody graft, but the proportion of patients who received this was not significantly different between groups (39% in the nonobese cohort vs. 42% in the obese cohort; P = 0.404). All patients received preoperative antibiotics (single-dose cefazolin). Patients received a fusion either due to multilevel disease and signs of instability or to prevent iatrogenic instability from wide decompression. Prior to the year 2000, most implants were stainless steel based, and after 2000, most instrumentation was titanium based. All patients received pedicle screws and rods.

Statistical Analysis A descriptive statistical analysis was performed and data are presented as mean ± standard deviation for parametric data and as median (interquartile range) for nonparametric data. Characteristics were compared between groups using the Student t test and χ2 test for continuous and noncontinuous data, respectively. A univariate analysis was first performed to identify possible confounding variables, and afterwards a logbinomial model was conducted to estimate adjusted relative risk ratios (RRs) with their 95% confidence intervals (CIs). Statistical significance was defined as P < 0.05. All analyses were performed using STATA 12 SE (StataCorp LP, College Station, TX).

RESULTS

Obesity and Lumbar Fusion • De la Garza-Ramos et al

nonobese patients and 70 (9.56%) obese patients (Table 1). The mean age for all patients was 55.11 ± 14.21 years, with no significant difference between groups; more than 50% of patients in both groups were females. When analyzing comorbidities, obese patients had significantly higher rates of coronary artery disease (20.00% vs. 10.73% in nonobese; P = 0.021), diabetes (22.86% vs. 9.97% in nonobese; P = 0.001), hypertension (47.17% vs. 30.06% in nonobese; P = 0.003), chronic obstructive pulmonary disease (8.57% vs. 1.06% in nonobese; P < 0.001), and depression (24.29% vs. 11.18% in nonobese; P = 0.002). The majority of patients were operated on because of spinal stenosis, and a higher proportion of patients in the nonobese group had this diagnosis (62.84% in nonobese vs. 50.00% in obese; P = 0.036). In terms of presenting symptoms, there were no statistically significant differences between cohorts.

TABLE 1. Demographics of All Patients

Undergoing PLF Based on Body Habitus

Characteristic

Nonobese

Obese

Cases, no. (%)

662 (90.44)

70 (9.56)

Age, (mean ± standard deviation) Sex, male, no. (%)

P

55.45 ± 14.30 51 ± 12.94

0.068

304 (45.92)

25 (35.71)

0.103

CAD

71 (10.73)

14 (20.00)

0.021

Diabetes

66 (9.97)

16 (22.86)

0.001

Hypertension

199 (30.06)

33 (47.14)

0.003

Smoker

131 (19.79)

20 (28.57)

0.084

COPD

7 (1.06)

6 (8.57)

The Impact of Obesity on Short- and Long-Term Outcomes following Lumbar Fusion.

Study Design. Retrospective cohort study.Objective. To compare short and long-term outcomes in obese versus non-obese patients undergoing instrumented...
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