Body Mass Index-Related Changes in Tibial Morphology: Considerations for Intramedullary Nailing

To evaluate the association between body mass index (BMI) and tibial morphological parameters, specifically focusing on medullary and cortical geometry.

This single-center retrospective observational study included adults aged 18-65 years with full-length AP and lateral tibial radiographs obtained within the prior 6 months. The participants were grouped as nonobese (BMI < 30 kg/m²) or obese (BMI ≥ 30 kg/m²). The outer tibial diameter (TD) and medullary canal diameter (MCD) were measured in both the anteroposterior (AP) and lateral planes at the level of the narrowest visible medullary canal within the middle third of the diaphysis, and the cortical thickness index (CTI) and canal-bone ratio (CBR) were calculated. Group comparisons, correlation analyses, and multivariable linear regression models (BMI, age, sex, and height) were performed for the AP and lateral CBRs.

Seventy-four individuals were analyzed (42 nonobese, 32 obese). The obese group demonstrated a significantly smaller MCD in both planes, a higher CTI, and a lower CBR. BMI was negatively correlated with the AP CBR and lateral CBR and with the AP and lateral MCD but was positively correlated with the AP CTI and lateral CTI. In the regression analysis, BMI remained an independent negative predictor of the AP CBR and lateral CBR.

A high BMI is associated with tibial medullary canal narrowing and a low CBR, accompanied by a high CTI, in both the AP and lateral planes. These findings support careful preoperative evaluation of internal tibial morphology in obese patients to optimize intramedullary implant planning.