Date of Award

January 2021

Document Type


Degree Name

Medical Doctor (MD)



First Advisor

Jonathan N. Grauer


Introduction: Body Mass Index (BMI) is a weight-for-height metric that is used to quantify tissue mass and weight levels. Existing literature investigating the correlation of Body Mass Index (BMI) with surgical complications has focused on those with elevated BMI. These investigations have reported mixed conclusions, possible due to insufficient power, poor controlling of confounding variables, and inconsistent definitions of BMI categories (e.g. underweight, overweight, varying classifications of obese). Additionally, few studies have considered outcomes of patients with low BMI.

Objectives: The aim of this thesis is to analyze the spectrum of categories for BMI with 30-day perioperative adverse events to better assess where along the BMI spectrum patients are at risk for complications, readmission, and mortality across several orthopaedic procedures namely: anterior cervical spine surgery, posterior cervical spine surgery, and total shoulder arthroplasty (TSA).

Methods: Patients undergoing elective anterior cervical spine surgery, posterior cervical spine surgery, or total shoulder arthroplasty were abstracted from the 2005-2016 National Surgical Quality Improvement Program (NSQIP) databases. Patients were aggregated into pre-established WHO BMI categories and adverse outcomes were normalized to average risk of normal-weight subjects (BMI 18.5-24.9 kg/m2). Risk-adjusted multivariate analyses were then performed on aggregated adverse outcome categories controlling for demographics (age, sex, functional status) and overall health as measured by the American Society of Anesthesiologists (ASA) classification.

Results: A total of 51,149 anterior cervical surgery patients, 16,806 posterior cervical patients, and 15,717 TSA patients met inclusion criteria. Odds for adverse events for underweight patients (BMI<18.5 kg/m2) were the highest among any category of patients along the BMI spectrum. These patients experienced increased odds of any adverse event for anterior cervical (Odds Ratio (OR)=1.62, p=0.036, posterior cervical (OR)=1.67, p=0.008, and TSA (OR)=2.22, p=0.034. Underweight patients also experienced elevation in serious adverse events, post-operative infection, and reoperation. Relative to normal BMI patients, there was no consistent significant elevation for adverse outcomes for any of the other overweight/obese categories across the three procedures.

Conclusions: The current thesis found underweight patients to have the highest risk of adverse events – a BMI subpopulation that has not previously received significant focus. Increased pre-surgical planning and resource allocation for this population should be considered by physicians and healthcare systems, as is often already done for patients on the other end of the BMI spectrum.


This thesis is restricted to Yale network users only. This thesis is permanently embargoed from public release.