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

Abstract

Background 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 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, 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 (R²=0.81). The values of Nsurg, Nvid and Nd were similar for all configurations. 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.

Detection of periprosthetic fractures around the femoral stem by resonance frequency analysis: An in vitro study

“…The decrease of pre-stressed state of the bone-implant system due to the fracture 19,37 leads to a decrease of the system rigidity, 4,17,18 which is responsible for a substantial change of the system vibro-acoustic response. In particular, the shift of the FRF to lower frequencies is consistent with a loss of rigidity of the system 24,26,38 due to the periprosthetic bone fracture. However, the change of press-fit due to the fracture should be high enough in order to be detected on the FRF’s measurement.…”

“…3,[19][20][21] Quantitative methods have widely been studied in the literature for FS insertion monitoring into the host bone. Most of them are based on impact force analysis, [22][23][24] vibration analysis, [25][26][27][28][29] or acoustics measurements. [30][31][32][33] Among these studies aiming at assessing the insertion of the FS, a limited number has been tested to detect periprosthetic fractures.…”

Small design modifications can improve the primary stability of a fully coated tapered wedge hip stem

“…This might affect the forces and will be investigated in further studies. The analysis of the stroke dynamics similar to [ 44 , 45 ] might increase the understanding of the impaction process.…”