Limb alignment after total knee replacement has been demonstrated to be one of the most influential in determining long-term survival of the implants. Malalignment can contribute to early prosthesis failure through point loading and premature polyethelene wear. Alignment guides have been developed to improve the accuracy of femoral and tibial cuts during surgery. Recently, there are at least two groups of femoral intramedullary reamer. The first group uses step reamer (8 mm drill with 10 mm step) and another one uses non-step reamer (8 mm drill). The purpose of this cadaveric study was to analyse the accuracy of both design by compared with computer navigation system. Eight cadaveric lower extremities were used for the present study in four cadaveric bodies. The step reamer was applied on the left side and the non-step reamer was applied on the right side of the same cadaver. The distal femoral cuts, using femoral valgus angle 6°, were performed. The resection angles between the cutting surface and the mechanical axis were measured and collected by means of computer navigation system. The results show that the step reamer resulted in 0.125° + 0.25° of varus, whereas the non-step reamer resulted in 0.5° + 1.08° of varus compared with the calculated mechanical axis by computer-assisted navigation. These data suggest that step reamer has the accuracy more than non-step reamer when evaluated by computer-assisted navigation.

Keywords: Intramedullary guide, Femoral alignment system, Total knee arthroplasty, Step reamer, Entry point, Computerassisted navigation