Is High Body Mass Index Protective or Detrimental in Surgical Fixation of Hip Fractures?: A Spline Regression Analysis of 22,388 Patients

Objective:We aimed to characterize the association between BMI as a continuous variable and 30-day postoperative outcomes following hip fracture surgery through (1) 30-day readmission and reoperation; (2) local wound-related; and (3) systemic complications.Methods:The National Surgical Quality Improvement Program database (January 2016-December 2019) was queried for patients undergoing hip fracture open reduction and internal fixation. Baseline patient demographics, comorbidities, and patient outcomes were recorded. Multivariable regression models accounted for baseline demographics, comorbidities, and fracture patterns. Significant associations were analyzed using spline regression models to evaluate the continuous association between BMI and the aforementioned outcomes.Results:Spline models demonstrated a U-shaped curve for the odds of 30-day readmission and 30-day reoperation with nadirs at the BMI of 27.5 and 22.0 kg/m(2). The odd ratios of superficial infection, deep infection, any wound complication, and inability to weight bear on POD 1 rose progressively starting at a BMI of 25.6, 35.5, 25.6, and 32.7 kg/m(2) respectively. Odds of 30-day mortality, transfusion, pneumonia, and delirium were greatest at the lowest recorded BMI (11.9 kg/m(2)).Conclusion:BMI has a U-shaped association with 30-day readmission and reoperation. Conversely, the highest risk of mortality and systemic complications (transfusion, pneumonia, and delirium) were within the lower BMI range, with diminishing risk as BMI increased. Local wound complications and systemic sepsis exhibited a third unique pattern with progressive rise in odds as BMI increased. The odds of any complications demonstrated a U-shaped pattern with a nadir in the overweight to obese I categories, suggesting that patients may be at lowest risk within this range.