INTRA-OPERATIVE TESTS ON CEMENTLESS HIP STEM MECHANICAL STABILITY

The aim of the present investigation was to develop a new device that enables the stability achieved by a cementless stem to be assessed intra-operatively. The angle of the stem/femur rotation under torsion and the torque are acquired and compared in real time to a pre-set stability threshold inferred from the literature. The device indicates whether the stem is stable or not. A calibration was needed to convert angular into linear shear displacements. For this reason, repeated tests in vitro were made on both cadaveric and composite femurs, chosen so as to host the same kind and size of prostheses, all implanted with different levels of press-fitting. The device was then validated. The overall accuracy, 21%, which takes into account the interfemur variability, was deemed sufficient to assess the stability.