The effect of different interference fits on the primary fixation of a cementless femoral component during experimental testing

Esther Sánchez,Christoph Schilling,Thomas M Grupp,Alexander Giurea,Caroline Wyers,Joop Van Den Bergh,Nico Verdonschot,Dennis Janssen

doi:10.1016/j.jmbbm.2020.104189

Abstract

Cementless femoral total knee arthroplasty (TKA) components use a press-fit (referred to as interference fit) to achieve initial fixation. A higher interference fit could lead to a superior fixation, but it could also introduce more damage to the bone during implantation. The purpose of the current study was to investigate the effect of interference fit on the micromotions and gap opening/closing at the bone-implant interface. Experimental tests were performed in six pairs of cadaveric femurs implanted with femoral components using a low interference fit of 350 μm and a high interference fit of 700 μm. The specimens were subjected to the peak loads of gait and squat, based on the Orthoload dataset. Digital Image Correlation (DIC) was used to measure the micromotions and opening/closing in different regions of interest (ROIs). Two linear mixed-effect statistical models were created with micromotions and gap opening/closing as dependent variables. ROIs, loading conditions, and implant designs as independent variables, and cadaver specimens as random intercepts. The results revealed no significant difference between the two interference fit implants for micromotions (p = 0.837 for gait and p = 0.065 for squat), nor for the gap opening/closing (p = 0.748 for gait and p = 0.561 for squat). In contrast, significant differences were found between loading and most of the ROIs in both dependent variables (p < 0.0001). Additionally, no difference in bone deformation was found between low and high interference fit. Changing interference between either 350 μm or 700 μm did not affect the primary stability of a femoral TKA component. There could be an interference fit threshold beyond which fixation does not further improve.

Highlights

Primary fixation of the implant to the bone is crucial for the longterm performance of total knee arthroplasty (TKA) (Chong et al, 2010), in younger patients with a longer life expectancy (Kienapfel et al, 1999) and in older patients with low bone quality (Newman et al, 2017)
Animal studies have shown that if micromotions at the bone-implant interface are below 40 μm, bone will grow into the implant surface, while if micromotions are above 150 μm, a fibrous tissue formation will interfere with osseointegration and may eventually lead to aseptic loosening (Kienapfel et al, 1999; Abdul-Kadir et al, 2008; Reimeringer et al, 2013)
In our study we found no significant difference in stability between the two interference fits

Summary

Introduction

Primary fixation of the implant to the bone is crucial for the longterm performance of total knee arthroplasty (TKA) (Chong et al, 2010), in younger patients with a longer life expectancy (Kienapfel et al, 1999) and in older patients with low bone quality (Newman et al, 2017). The primary fixation depends, amongst other parameters, on the press-fit provided by the implant system and on the frictional properties of the surface coating, which allows for bone ingrowth on the long term (Campi et al., 2018; Witmer and Meneghini, 2018; Damm et al, 2015). Primary sta bility is often expressed as the amount of relative displacement between the implant and the bone under physiological loads, referred to as micromotions (Abdul-Kadir et al, 2008; Tissakht et al, 1995).

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