Assessment of the geometry of proximal femur for short cephalomedullary nail placement: An observational study in dry femora and living subjects

Background: Intramedullary devices have increasingly become popular and are widely used for fixation of unstable intertrochanteric and subtrochanteric fractures as well. These implants have been designed taking into consideration the anthropometry of the western population whose anthropometry varies from those of other ethnic groups. This study was carried out to assess the geometry of proximal femur for the placement of short cephalomedullary nails in our subset of patients and suggest suitable design modifications based on these parameters. Materials and Methods: The study was conducted in the following three groups: (1) Anthropometric study of 101 adult human dry femora, (2) radiographs of the same femora, and (3) radiographs of the contralateral uninjured limb of 102 patients with intertrochanteric or subtrochanteric fractures. In Group 1, standard anthropometric techniques were used to measure neck shaft angle (NSA), minimal neck width (NW), trochanteric offset, and distance from the tip of greater trochanter (GT) to the lower border of lesser trochanter on the femoral shaft axis (distance X). In Group 2 and 3, the NSA, minimal NW, NW at 130 degrees and 135 degrees, trochanteric shaft angle (TSA), trochanteric offset, distance X, distance between the tip of GT and the point where the neck axis crosses the line joining the tip of the GT to the lower border of the lesser trochanter on the femoral shaft axis (distance Y), and canal width at 10, 15, and 20 cm from tip of GT were measured on standard radiographs. The values obtained in these three groups were pooled to obtain mean values. Various parameters of commonly used short cephalomedullary nails available for fixation of pertrochanteric fractures were obtained. These were compared to the results obtained to suggest suitable modifications in the nail designs for our subset of patients. Results: The mean parameters observed were as follows: NSA 128.07 degrees 4.97 (range 107 degrees u141 degrees), minimum NW 29.0 2.8 mm (range 22u42 mm), NW at 130 degrees 30.12 2.86 mm (range 22.2u42.5 mm), NW at 135 degrees 30.66 3.02 mm (range 22.8u40.3 mm), TSA 10.45 degrees 2.34 degrees (range 3 degrees u15.5 degrees), distance x 65.73 6.45 mm (range 28.6u88.4 mm), distance Y 38 4.91 mm (range 16.6u55.3 mm), and canal width at 10, 15, and 20 cm from the tip of GT 13.46 2.34 mm, 11.40 2.27 mm, and 11.64 2.04 mm, respectively. Conclusion: The measurements of the proximal femur are not significantly different from other ethnic groups and are adequate to accept the current commonly available short cephalomedullary nails. However, certain modifications in the presently available short cephalomedullary nail designs are recommended for them to better fit the anatomy of our subset of population (a) two nails of 125 degrees and 135 degrees, (b) the medio-lateral angle at the level of 65 mm from the tip of the nail, (c) two femoral neck screw placements (35 and 45 mm from the tip of the nail), and (d) five different sizes of distal width for better fit in canal (9u13 mm).