OBJECTIVETo investigate possible causes of micromotion in distal femoral prosthesis.

METHODSBased on the assumption that the femur and prosthesis were considered as concentric cylinders with completely bonded interface, a theoretical model simulating the interfacial stress transfer was established. The distributions of the interfacial shear and radial stresses with the changing of z were obtained through mathematics and mechanics deducing.

RESULTSThe maximum interfacial shear stress occurred at the position of z=0, namely, the cross section of the femur neck. The interfacial shear stress sharply decreased with the increasing of z and came to nearly zero at the range of z> 0.1 m. While the interfacial radial stress increased with the increasing of z,at the range of z >0.05 m it was constant and reached the maximum.

CONCLUSIONThe micromotion in distal prosthesis is caused by the interfacial radial stress.