MECHANICAL EFFECTS OF DIFFERENT LOCALIZATION OF THE POINT OF THE POINT OF ENTRY IN FEMORAL NAILING

Twenty pairs of human femora were reamed alternatively on the right or left side, with the opposite side serving as the unreamed control. Th e fossa piriformis (group I) or tip of the greater trochanter (group I I) were chosen for; introduction of the intramedullary reamer (Howmedi ca type). The femora were tested in vertical compression in a MTS mech anical 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 remo te from the portal. The difference is statistically significant. Reduc tion in strength between the unreamed control side and the reamed femu r was median 1486 (23%) in group I and 506 N (11%) in group II. Reduct ion 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 throug h an entry point (portal) in the piriformis fossa weakens the femoral neck and creates a localizing point for fracture.