Obesity does not impact clinical outcome but affects cervical sagittal alignment and adjacent segment degeneration in short term follow-up after an anterior cervical decompression and fusion

Abstract

BACKGROUND CONTEXTObesity increases complications and cost following spine surgery. However, the impact on sagittal alignment and adjacent segment degeneration (ASD) after anterior cervical decompression and fusion is less understood. PURPOSETo compare clinical and radiographic outcomes after anterior cervical decompression and fusion between obese and nonobese patients. STUDY DESIGNRetrospective cohort study. PATIENT SAMPLEIn all, 467 patients that underwent an anterior cervical decompression and fusion procedure from January 2008 through December 2015 were assessed. Surgery indications were radiculopathy, myelopathy, or myeloradiculopathy that had failed nonoperative treatments. Exclusion criteria included patients who had postoperative follow-up less than 6 months. Of 467 patients originally identified, 399 fulfilled the inclusion and exclusion criteria. OUTCOME MEASURESThe following patient-reported outcomes were obtained: Neck Disability Index and Visual Analog Scale scores for the neck and arm pain. Radiographic assessments included: C2–C7 lordosis, T1 angle, levels fused, sagittal vertical axis (SVA), fusion mass lordosis, proximal and distal adjacent segment lordosis, ASD, and presence of fusion. METHODSPlain radiographs were performed preoperatively, immediately postoperatively, and final follow-up. Demographic information was collected on all patients. Baseline patient characteristics were compared using chi-squared analysis and independent sample t tests for categorical and continuous data, respectively. For analysis, patients were divided into 4 groups based on obesity stratification as defined by Center for Disease Control: body mass index (BMI) <25 kg/m2 (normal weight), BMI≥25 kg/m2 to <30 kg/m2 (overweight), ≥30 kg/m2 to <35 kg/m2 (Class I obesity), BMI≥35 kg/m2 to <40 kg/m2 (Class II obesity), and BMI≥40 kg/m2 (Class III obesity). Additionally, obese (≥30 kg/m2) and nonobese (<30 kg/m2) patients were compared in a separate analysis. Multivariate analysis was used to compare clinical and radiographic outcomes among all BMI classes, as well as between BMI≥30 kg/m2 versus BMI<30 kg/m2 study groups. Multivariate analyses controlled for differences in baseline patient characteristics and included age, sex, smoking, American Society of Anesthesiologists Physical Status Score, diabetes mellitus, and number of levels. RESULTSOf the 399 patients assessed, 97 were identified as normal weight, 157 as overweight, 81 with Class I obesity, 45 with Class II obesity, and 19 with Class III obesity. On multivariate analysis, despite having similar SVA measurements on preoperative radiographs, increase in BMI was associated with increase in postoperative SVA (p=0.041) along with significantly larger SVA in immediate postoperative (p=0.004) and final follow-up radiographs (p=0.003) for patients with BMI≥30 kg/m2 versus BMI<30 kg/m2. Furthermore, patients with BMI≥30 kg/m2 had smaller preoperative (p=0.012), immediate postoperative (p=0.017), and final lordosis (p<0.001) in addition to smaller immediate postoperative (p=0.025) and final fusion segment lordosis (p=0.015) and smaller preoperative (p=0.024) and final distal lordosis (p=0.021) compared with patients with BMI<30 kg/m2. Additionally, greater BMI was associated with lower final Visual Analog Scale neck scores (p=0.008). Radiographic early ASD rates were higher in patients BMI≥30 kg/m2 versus BMI<30 kg/m2 (p=0.028). CONCLUSIONSOverall, obese patients who underwent anterior cervical decompression and fusion had similar patient-reported outcomes compared with nonobese patients but had worse radiographic parameters and higher rates of ASD development compared with nonobese patients. This underscores the importance of patient selection and surgical approach for both patient populations.