Three-dimensional correlation between trochanteric fossa and the ideal entry point for antegrade femoral nailing

To verify the practical correlation between the topographical features of the femur neck base and the ideal entry point by analyzing three-dimensional (3D) models virtually implanted with an antegrade femoral nail.

A total of 103 cadaveric femurs (50 males and 53 females) were enrolled. Specimens underwent continuous 1.0mm slice computed tomography (CT) scans. CT images were rendered into 3D images using image-processing software (Mimics^®) to reconstruct the geometry of the cortex and medullary canal. A real cannulated femoral nail (CFN)^® was processed into a 3D image using a 3D sensor at the actual size and optimally placed in the femur model using Mimics^® for virtual implantation. The correlation between the ideal entry point in the cranial view of the proximal femur and the trochanteric fossa was assessed and overlap of trochanter overhang was verified.

The entry point of 68 models (66.0%) was the trochanteric fossa, while the others were placed around the anterior border of the trochanteric fossa. The proximal end of the nail overlapped in 50 models (48.1%), and among them, the central point of 23 models (22.3%) was obscured by trochanteric overhang. There was a statistically significant risk associated with female gender (6.02 times) and type IV overhang of Grenchenig's classification (4.56 times). Despite the precise positioning of the trochanteric fossa, 11 models (10.7%) had the entry point covered by trochanteric overhang.

The ideal entry point was over the trochanteric fossa in just half of the models, and could be hindered by trochanteric overhang even though the CFN was ideally positioned.