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


CONCLUSIONS
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.
Ehmke
Larry W
LW
Legacy Biomechanics Laboratory, Portland, Oregon, USA.
Polzin
Britton M I
BM
Madey
Stephen M
SM
Bottlang
Michael
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001858:Bone Nails; D002102:Cadaver; D005260:Female; D005269:Femur / Q000601:surgery*; D006801:Humans; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*