Preoperative Weight Loss is Not Beneficial in Obese Patients Undergoing Cervical or Lumbar Fusion - A National Cohort Study of 57,961 Patients.

Abstract

Morbid obesity is a known risk factor for worse outcomes after spinal fusion. Preoperative weight loss is routinely advocated for obese spinal fusion candidates based on the assumption that postoperative risk in patients with lower body mass index (BMI), after recent weight loss, is equivalent to that in weight-stable patients. However, this assumption has not been directly tested in the literature. To compare obese patients who lost ≥5% of body weight within two years prior to undergoing cervical or lumbar fusion with obese patients who maintained a stable weight prior to surgery. Retrospective cohort study with propensity score matching. EPIC COSMOS was used to identify obese patients (BMI 30-50 kg/m²) undergoing cervical or lumbar fusion between 2017 to 2023. Patients were divided into two cohorts: (a) weight loss (WL): patients with 5-30% body weight loss within two years preoperatively, (b) No weight loss (NoWL): controls with stable weight. Patients with pathological weight loss were excluded. At 90 days, length of stay (LOS), Healthcare utilization (HCU), severe adverse events (SAEs), and minor adverse events (MAEs) were assessed. At the two-year follow-up, surgical failure (SF) was assessed. Cohorts were matched on demographics, pre-weight-loss BMI, comorbidities, diagnoses, and operative factors using propensity score matching. Analyses for cervical and lumbar fusions were run independently. Multivariable linear or logistic regression was used to determine the odds ratio of outcomes, adjusting for age, sex, race, pre-weight-loss BMI, comorbidities, diagnoses, and operative factors. Sensitivity analysis was conducted by excluding myelopathic patients and additionally adjusting the regression models for BMI at surgery. After matching, the cervical fusion groups consisted of 10,201 patients per cohort, with a mean age of 59.4 years, 52.6% females, and 75.3% white patients. The WL cohort had higher rates of HCU (11.5% vs. 8.8%), SAEs (10.7% vs. 9.0%), MAEs (14.0% vs. 10.9%), and surgical failure (11.6% vs. 9.7%). The lumbar fusion groups consisted of 10,755 patients per cohort, with a mean age of 62.4 years, 56.1% female, and 77.7% white patients. The WL cohort also had higher rates of HCU (12.2% vs. 11.6%), SAEs (11.0% vs. 10.0%), MAEs (24.9% vs. 22.8%), and surgical failure (13.8% vs. 12.9%). In multivariable regression analysis, the cervical fusion WL cohort had higher odds of HCU (adjusted odds ratio (aOR): 1.28, p < 0.001), MAEs (aOR: 1.26, p < 0.001), and surgical failure (aOR: 1.20, p < 0.001), as well as increased LOS (adjusted beta-coefficient (aβ): 0.53, p < 0.001) compared to cervical fusion NoWL cohort. Statistical significance was no longer observed after removing myelopathic patients. In the lumbar fusion cohorts, there were no statistical differences in the outcomes in WL and NoWL cohorts for all measured outcomes. In obese patients, lowering BMI through recent weight loss does not confer the same benefits as a weight-stable lower BMI and may increase the odds of some complications after spinal fusion. Loss of muscle mass and nutritional deficiencies may explain the lack of benefits from low BMI immediately after weight loss. Pre-habilitation and nutritional optimization of these patients may be reasonable until more data is available.