Mechanical effects of different localization of the point of entry in femoral nailing

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Abstract
Twenty pairs of human femora were reamed alternatively on the right or left side, with the opposite side serving as the unreamed control. The fossa piriformis (group I) or tip of the greater trochanter (group II) were chosen for introduction of the intramedullary reamer (Howmedica type). The femora were tested in vertical compression in a NITS mechanical testing machine until failure. In group I, all femora fractured through the entry portal. This happened in only 3 out of 10 in group II, where 7 fractured through the medial part of the femoral neck remote from the portal. The difference is statistically significant. Reduction in strength between the unreamed control side and the reamed femur was median 1486 (23%) in group I and 506 N (11%) in group II. Reduction in energy absorption between the control side and reamed side was median 9786 Nm (44.5%) in group I and 1142 Nm (10.5%) in group II. The difference in energy absorption reduction between groups I and II was statistically significant (P = 0.04). We conclude that reaming through an entry point (portal) in the piriformis fossa weakens the femoral neck and creates a localizing point for fracture. frontal plane, but might weaken the femoral neck and become the origin of secondary fractures [2–4]. The present study was undertaken to examine the effect on the mechanical properties of the proximal end of the femur by the localization of entry portals at either the top of the trochanter or the trochanteric fossa.

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