Body Mass Index Does Not Drive the Risk for Early Postoperative Instability After Total Hip Arthroplasty: A Matched Cohort Analysis.

INTRODUCTION: Instability remains the leading cause of revision following total hip arthroplasty (THA). The objective of the present investigation was to determine whether an elevated body mass index (BMI) is associated with an increased risk of instability after primary THA.

METHODS: An administrative claims database was queried for patients undergoing elective, primary THA for osteoarthritis between 2010 and 2022. Patients who underwent THA for a femoral neck fracture were excluded. Patients who had an elevated BMI were grouped into the following cohorts: 25 to 29.9 (n = 2,313), 30 to 34.9 (n = 2,230), 35 to 39.9 (n = 1,852), 40 to 44.9 (n = 1,450), 45 to 49.9 (n = 752), and 50 to 59.9 (n = 334). Patients were matched 1:1 based on age, sex, Elixhauser Comorbidity Index (ECI), as well as a history of spinal fusion, neurodegenerative disorders, and alcohol abuse, to controls with a normal BMI (20 to 24.9). A multivariate logistic regression controlling for age, sex, ECI, and additional risk factors for dislocation was utilized to evaluate dislocation rates at 30-days, 90-days, 6-months, 1-year, and 2-years. Rates of revision for instability were similarly compared at 1-year and 2-years post-operatively.

RESULTS: No significant differences in dislocation rate were observed between control patients and each of the evaluated BMI classes at all evaluated post-operative intervals (all P-values > 0.05). Similarly, the risk of revision for instability was comparable between the normal weight cohort and each evaluated BMI class at 1-year and 2-years post-operatively (all P-values > 0.05).

DISCUSSION: Controlling for comorbidities and known risk factors for instability, the present analysis demonstrated no difference in rates of dislocation or revision for instability between normal-weight patients and those in higher BMI classes.