  Background 15 The success of cementless hip arthroplasty depends on the
primary stability of the femoral stem. It remains difficult to assess the
optimal number of impacts to guarantee the femoral stem 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 femoral
stem in bovine femoral samples. Methods 20 Different cementless femoral stem
were impacted into five bovine femur samples, leading to 99 configurations.
Three methods were used to quantify the insertion endpoint: 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, 25 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. Findings The
pullout force of the femoral stem was significantly correlated with I
(R${}^2$=0.81). The values of Nsurg, Nvid and Nd were similar for all
configurations. 30 Interpretation The results validate the use of the impact
hammer to assess the primary stability of the femoral stem 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. Abstract: 248
words. Main text: 4658 words
