The biomechanical evaluation of intramedullary nails in distal femoral shaft fractures.

The biomechanical parameters (torsional rigidity and compressive strength) for three different intramedullary femoral nails, Küntscher (K), Brooker-Wills (BW), and Küntscher Interlocking (KI) were compared in this study. Fractures were created in the femoral shaft distal to the isthmus with sections removed so that pure torsional rigidity and resistance to compression could be measured. The standard K nail provided no torsional rigidity and only minimal resistance to longitudinal compression. The KI was significantly more rigid under compression than either the BW or the K. In torsional resistance the K nail was significantly weaker than either the BW or KI. The K nail does not provide significant resistance to compression or torsion for use in oblique or comminuted fractures. The BW nail probably provides enough resistance to rotation for use in distal fractures, but probably does not provide enough resistance to compression for use in fractures that are prone to shortening.