Primary Hip Stem Micromotion Assessment: Correlation between Rasp and Stem Stability

INTRODUCTION Primary stability achieved by press-fit is critical for the longterm success of cementless hip stems [1]. It is recognized that micromotions over 30-150 micron prevent osteointegration and lead to implant failure [2]. Conversely, excessive press-fit can cause intra-op fractures [3]. A device able to intraoperatively assess stem stability was developed and validated [4]. It consists of an angular sensor and a torsional load cell, which are embedded in a real-time torque wrench. The device is manually operated by the surgeon, who can use this quantitative information to decide whether more press-fit is needed. This device could successfully discriminate between stable and unstable stems intra-operatively [4]. The goal of the present work was to find a correlation between rasp and stem stability. This could provide the surgeon with a quantitative information concerning the quality of the femoral canal just prepared before inserting the stem, thus enabling a prediction of the implant stability possibly achievable.