The optimum location and diameter of an entry hole in the proximal femur

The optimum location and diameter, of an entry hole for an intramedullary nail, in the upper proximal femur, is investigated in this article. A comparative study for five different entry hole positions and seven different hole diameters at each position, has been pursued. The entry holes were located at the tip of the trochanter, at the superior, anterior and posterior parts of the lateral neck close to the trochanter and at the superior, anterior and posterior, medial parts of the neck close to the femoral head. Finite element analyses of the proximal femur, with and without the open holes, have been performed. The third generation standardized femur model was used in these finite element calculations. Results were obtained for the maximum principal stresses, the maximum principal strains and the maximum strain energy densities, on the uppermost, entry hole perimeters, for the estimation of a secondary fracture risk. All results indicated that the preferred entry locations are the tip of the greater trochanter and the lateral, superior, anterior part of the neck, independent of the hole diameter. Holes with diameters less than 12mm, emanating from the trochanteric fossa, sustain a fracture risk, among the highest. For a hole emanating from the trochanteric fossa, a lower fracture risk seems to exist for hole diameters greater than 12mm, than for hole diameters less than 12mm. For holes starting at the trochanteric fossa and at the anterior, medial upper neck, the fracture risk seems to decrease, with increasing hole diameters between 9mm and 11mm. For the entry locations, at the tip of the trochanter, the anterior, lateral, upper neck and the posterior, medial, upper neck, the fracture risk seems to increase, with increasing hole diameters between 9mm and 11mm.