Simultaneous and multisite measure of micromotion, subsidence and gap to evaluate femoral stem stability

Abstract

a b s t r a c tThe initial stability of cementless femoral components is crucial for the long-term success of total hip arthroplasty. This has been reported in animal and clinical studies. Until now, the stability was evaluated by the measurement of relative micromotion on a few simultaneous locations around the stem in cadaveric experiments. This paper presents an extended experimental setup to measure simultaneously local micromotion, subsidence and gap on hundreds of points at the bone-stem interface. This technique we applied to anatomical and straight stems in three pairs of cadaveric femurs. Measurements were in agreement with typically reported values. Conversely to other methods, which measure micromotion between implant and bone anchoring points of the measuring device, our method provides local micromotion between stem surface and adjacent bone surface. The observed variation of micromotion at the peri-implant surface confirms the importance of this simultaneous measure on a lot of points around the implant.

Biomechanical evaluation of the helica femoral implant system using traditional and modified techniques

“…We speculate that the lateralized osteotomy in the modified technique may result in more cancellous bone at the calcar or cortical bone at the interface with the femoral stem and collar that contributed to greater implant‐bone motion. The macromotion we found (i.e., >40–150 µm) has been shown clinically to produce fibrous tissue and fibrocartilage deposition rather than bone ingrowth …”

“…Micromotion is defined as the amount of movement capable of producing stable bony ingrowth and is considered <20 mm (0.02 mm); macromotion is the degree of motion that prevents bone ingrowth and allows fibrocartilage and fibrous tissue to form instead-occurs with motion >40-150 mm (0.04-0.15 mm). 20,21 One goal in femoral implant design is to reduce the incidence of stress shielding. 13,14,18 Stress shielding manifests as bone resorption in regions of bone tissue that experience a reduction in load bearing secondary to redistribution of load from the femoral cortex to the stiffer femoral implant.…”

“…Mechanical loosening is further divided into micro‐ and/or macromotion. Micromotion is defined as the amount of movement capable of producing stable bony ingrowth and is considered <20 µm (0.02 mm); macromotion is the degree of motion that prevents bone ingrowth and allows fibrocartilage and fibrous tissue to form instead—occurs with motion >40–150 µm (0.04–0.15 mm) …”

Full-field measurement of micromotion around a cementless femoral stem using micro-CT imaging and radiopaque markers

“…The compression device was modified from an existing one (Gortchacow et al, 2012). The distal part of the femur was cut away at approximately 220 mm from the tip of the greater trochanter.…”

“…More recently, micromotion measurement techniques based on micro-computed tomography (micro-CT) imaging were introduced, and demonstrated great potential. Notwithstanding the very high number of measurement points they can collect, they were limited to measurement around non-metallic implants due to imaging artifacts (Sukjamsri et al, 2015) or confined to a small portion of the implant (Gortchacow et al, 2012(Gortchacow et al, , 2011.…”