FATIGUE PROPERTIES OF A 12-HOLE VERSUS A 5-HOLE INTRAMEDULLARY SUPRACONDYLAR NAIL

Objectives: To evaluate a design change intended to improve fatigue pr operties of Intramedullary Supracondylar nails (IMSC). Design: Fatigue testing was performed on 12-hole and 5-hole IMSC nails in 18 plastic- fiber composite femurs. Fractures were simulated by a 1 cm wide osteot omy. Nails were cycled until failure with femoral loads ranging from 1 33 N to 1869 N (30 to 420 Ib.) for the 12 mm nails and 133 N to 1335 N (30 to 300 Ib.) for the 11 mm nails. A simple finite element computer model (FEM) was also created to determine the difference in stress di stribution between the two designs. Setting: All mechanical testing wa s performed using a servohydraulic test fram (MTS Systems, Minneapolis , MN). The FEM was performed using I-DEAS software (SDRC, Milford, OH) running on an Apollo 9000/735 workstation (Hewlett-Packard, Pale Alto , CA). Intervention: The nails were locked proximal and distally. Main Outcome Measurement: The number of cycles to failure and the maximum tensile stress (FEM) was measured and compared between the two designs . Results: The 11 mm and 12 mm 12-hole nails failed at an average of 5 3,514 cycles and 102,433 cycles respectively. No nail failures were se en in the 5-hole design. The FEM showed a 400% increase in maximum ten sile stress due to the transverse screw hole in the cannulated nail. C onclusions: Elimination of screw holes at the level of a supracondylar metaphyseal defect significantly improves the fatigue life of the IMS C nail.