Ex vivo estimation of cementless femoral stem stability using an instrumented hammer

TL;DR

This study validates a force-sensing hammer method to assess femoral stem stability during cementless hip arthroplasty, potentially aiding surgeons in optimizing insertion and preventing fractures.

Contribution

Introduces a novel instrumented hammer technique to quantify femoral stem stability, correlating force signals with insertion quality in bovine models.

Findings

Force indicator I correlates strongly with pullout force (R^2=0.81)

Impact number indicators (Nsurg, Nvid, Nd) are consistent across configurations

Method can identify optimal stopping point during stem insertion

Abstract

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