Femoral nailing through the trochanter: the reamer pathway indicates a helical nail shape.

OBJECTIVES This biomechanical study captured the reamer pathway in human femurs reamed through a greater trochanteric entry portal. The spatial pathway of the reamed intramedullary canal was analyzed to determine how closely a helix can match the dimensions of this canal. METHODS Twenty-one human cadaveric femurs were reamed through a trochanteric entry portal 12 mm lateral to the superior trochanteric border. The pathway of the reamer canal was measured with a 3-dimensional motion tracking sensor. The magnitude and direction of curvature along the reamed canal was calculated and an average canal pathway was determined. Finally, a best-fit helix was derived by comparing the average canal pathway with 90 different computer-generated helix pathways. RESULTS The reamed canal exhibited a medially directed curvature of 1.97 +/- 0.30 m(-1) magnitude proximally and an anteriorly directed curvature of 1.21 +/- 0.27 m(-1) magnitude in the midsection. This multiplanar curvature could best be approximated by a helix with 1000 mm radius and 0.6 degree/mm pitch. This helix coincided within +/- 1 mm with the reamed canal over 59% of the canal length. It deviated 4 mm medial and 7 mm posterior at the entry portal and 7 mm medial and 3 mm posterior at the distal end of the reamed canal. CONCLUSION These results provide a scientific rationale for the design of helically shaped intramedullary nails. Helical nails introduced through a trochanteric entry site may offer reduced bone stresses, ease insertion, and facilitate removal. This in turn may reduce the likelihood of iatrogenic intraoperative fracture.