Estimation of cementless femoral stem stability using an impact hammer

International audienceThe success of cementless hip arthroplasty depends on the primary stability of the femoral stem (FS). It remains difficult to assess the optimal number of impacts to guarantee the FS stability while avoiding bone fracture. The aim of this study is to validate a method using a hammer instrumented with a force sensor to monitor the insertion of FS in bovine femoral samples. Cementless FS of different sizes were impacted into five bovine femur samples, leading to 99 configurations. Three methods were used to quantify the insertion endpoint of the FS: the impact hammer, video motion tracking and the surgeon proprioception. For each configuration, the number of impacts performed by the surgeon until he felt a correct insertion was noted Nsurg. The insertion depth E was measured through video motion tracking, and the impact number Nvid corresponding to the end of the insertion was estimated. Two indicators, noted I and D, were determined from the analysis of the time variation of the force, and the impact number Nd corresponding to a threshold reached in D variation was estimated. The pullout force of the FS was significantly correlated with I (R�=0.81). The values of Nsurg, Nvid and Nd were similar for all configurations. The results validate the use of the impact hammer to assess the primary stability of the FS and the moment when the surgeon should stop the impaction procedure for an optimal insertion, which could lead to the development of a decision support system