A computed tomography-based analysis of proximal femoral geometry for lateral impingement with two types of proximal femoral nail anterotation in subtrochanteric fractures

ObjectiveTo evaluate and analyse the geometrical discrepancies between the proximal femur and two types of AO/Association for the Study of Internal Fixation (AO/ASIF) Proximal Femoral Nail Anterotation (PFNA/PFNA-II) using computed tomography (CT)-based analysis in Asian patients, and its implication in lateral cortical impingement during reduction intra-operatively in subtrochanteric fractures.Materials and methodsCoronal CT images of hips in 50 randomly selected healthy cases were analysed using a unique measurement method with respect to the height, diameter, bending angle and inclination angle of lateral cortex of proximal femur. The data were then compared with dimensions of PFNA and PFNA-II.ResultsThe average height of proximal femur was 61.1 ± 5.2 mm, diameter 18.1 ± 1.5 mm, bending angle 8.4 ± 2.2° and inclination angle of lateral cortex 11.9 ± 1.1°. The average impingement length of the lateral cortex was 54.2 ± 4.7 mm (range 41.4–64.2 mm), which was shorter than the height of the proximal femur. On comparison with dimensions of PFNA and PFNA-II, the lateral inclination angle and impingement length were found to be discrepant in PFNA; however, in the latter the flat lateral surface helps avoiding impingement with the lateral femoral cortex.ConclusionOur study provides clear evidence that the flat lateral shape of PFNA-II is better suited for the femur of Asian patients by reducing the chances of impingement with the lateral proximal femoral cortex during intra-operative reduction in subtrochanteric fractures.