Biomechanical analysis of a distally interlocked press-fit femoral total hip prosthesis

This study was undertaken to compare the stability of a distally interlocked femoral prosthesis to a standard press-fit implant (Cementless Spotorno, Protek Co., Toronto, Canada). Five human femora were studied with each acting as its own control. All were tested in the locked mode followed by unlocked testing modes. The MTS 858 Biomaterials Testing System was used to test the implanted femoral stems under both pure torsional and pure axial loading. Distal interlocking increased the torsional stability by 320% (locked 4.05 Nm/degree; unlocked 1.25 Nm/degree) (P < .01) and the axial stability by 230% (locked 1,236.26 N/mm; unlocked 527.44 N/mm) (P < .01). the use of temporary distal interlock in cases where the initial stability of a press-fit implant is suboptimal should allow for improved biological fixation by minimizing micromotion at the stem-bone interface.