Association of body mass index with lower extremity long bone fracture location

Obesity is becoming more prevalent and has unique associations with fracture risk. Prior research has extensively focused on fracture incidence, yet how body mass index (BMI) is associated with the anatomic distribution of lower extremity long bone fractures remains less understood. This study aimed to evaluate the relationship between BMI and lower extremity fracture location in the femur, tibia, fibula, and malleoli in a national cohort.

Design : Retrospective cohort study. Setting : National Inpatient Sample (NIS) database, 2016-2019. Patient Selection Criteria : Patients with lower extremity fractures involving the femur, tibia, fibula, or malleoli were identified using ICD-10 diagnosis codes and were included if a BMI diagnosis code was present in the record. Outcome Measures and Comparisons : The primary outcome was fracture location, categorized as proximal, shaft, distal, pertrochanteric, subtrochanteric, tibial pilon, bimalleolar, or trimalleolar. Fracture location proportions were compared across BMI categories. Multivariable logistic regression was used to evaluate the association between BMI category and fracture location after adjusting for age, sex, race, and comorbidities.

A total of 262,535 patients with lower extremity long bone fractures and documented BMI were included in this cohort. As BMI increased, there was a shift towards subtrochanteric, shaft, and distal femoral fractures, as well as distal fibular fractures and tibial pilon fractures. In multivariable analyses, obesity was associated with increased odds of most distal fracture locations and ankle fractures, whereas underweight BMI was associated with increased odds of proximal and pertrochanteric femur fractures.

BMI is independently associated with lower extremity fracture location. Increasing BMI shifts fracture patterns distally along the bone, whereas underweight status is associated with proximal and pertrochanteric femoral fractures. These findings support incorporating BMI into fracture pattern assessment and clinical decision-making.

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