ANATOMY OF THE ENDOSTEAL CANAL OF THE PROXIMAL FEMUR

Abstract

Purpose: The anatomy of the endosteal canal of the proximal femur varies greatly in the general population. This variability can compromise total hip arthroplasty when a femoral stem is inserted without cement. While the secondary fixation of the implant is dependent on several parameters, the predominant factor is the primary stability and the large contact between the bone and the treatment surface of the apposed prosthesis. These two conditions, necessary but insufficient to guarantee an excellent clinical result, are obtained if there is a correct bone-implant morphology match. We analysed the morphology of the endosteal canal of the proximal femur to determine whether there is a standard anatomic conformation justifying the use of line prostheses.

Material and methods: We examined 30 femurs harvested from 30 individuals in a consecutive series in our anatomy laboratory. We made 12 scanner slices parallel to the knee joint line starting 1 cm above the apex of the lesser trochanter going up to 11 cm above the lesser trochanter. For each slice, we assimilated the canal to an ellipsoid surface to characterise its barycentre, the angle of the greater axis relative to the reference plane of the posterior condyles, and its dimensions defined with length (greater axis), and width (perpendicular to the greater axis).

Results: For each femur, the AP projections of the barycentres fell on a straight line (anatomic axis) and the lateral projections on a parabole. Helitorsion, i.e. the difference in the torsion angles between the first slice and the last slice was constant (57±8.5°). The dimensions were recorded for each slice.

Discussion: This method can be criticised. We were able to confirm the tridimensional data reported by Noble and confirmed the notion of a somatotype. We defined the normal (statistical) equation of the endosteal canal for the proximal end of the femur (barycentre, dimensions).

Conclusion: The anatomy of the endosteal canal of the upper extremity of the femur is not variable but standardised. It is thus possible to adapt the bone to the prosthesis.