[The biomechanical study of rotating-arm self-locking intramedullary nails in comminuted femoral shaft fractures].

This study was sought to compare and evaluate the biomechanical properities of rotating-arm self-locking intramedullary nails (RSIN) with domestic femoral intramedullary nail (DFIN) in communited femoral shaft fractures. A 2 cm midshaft defect was created on seven pairs of cadaver femur, and fixed with two kinds of intramedullary nails. Then the torsion, four-point bending and axial loading to failure were tested on these models. The load versus deformation curve was generated from the load recorded by the load cell and the deformation simultaneously recorded by the linear variable displacement transducer. The mean torsional stiffness of the femora fixed with RSIN was 0.98 Nm/degree, which was significantly less than that fixed with the similar nails reported in documents, and the mean value of bending stiffness of the femur fixed with DFIN was larger than that of the femur fixed with RBIN, but there was no significant statistic difference. For use in fracture models under compression load beyond 1200 N, the RBIN was more rigid than DFIN, which provided the biggest load. All the parameters of the test with nails were greater than that for femur fixed with nails. In conclusion, FBIN probably provides enough strength and rigidity for use in communited femoral shaft fractures.