Uncertainty determination for X-ray computed tomography wear assessment of polyethylene hip joint prostheses

Hip joint replacements have been successfully used in the field of orthopaedic medicine for over fifty years. Whilst clinical studies have shown encouraging long-term clinical performance, failure of these devices due to wear still occurs. The laboratory determination of wear rate is an important part of the pre-clinical validation of prostheses. The most commonly applied method for wear evaluation of prosthetic joint components is the gravimetric method. It is generally accurate and reliable but has certain limitations. In particular, gravimetric measurements cannot provide information about localization of wear damage and deformation over the component’s surface. As an alternative, tactile coordinate measuring machines are used to evaluate both volumetric wear and wear damage distribution over the worn surface. However, considering polymeric prosthetic components, these machines could induce unwanted damages and/or deformations due to clamping and probing forces leading to a large measurement uncertainty. X-ray computed tomography recently emerged as an advanced non-contact technique capable of performing dimensional measurements with high accuracy. Moreover, X-ray computed tomography can be used for volumetric wear measurement as well as for determination of local distribution of wear and deformations without any risk of further damaging or deforming polymeric components. Nevertheless, the uncertainty of such measurements has yet to be investigated. The purpose of the work was to determine the uncertainty in both volumetric wear measurements and assessment of local distribution of wear and deformations using X-ray computed tomography. More in depth, in this work, tomographic measurements were conducted on nine hip joint components made from three different types of ultrahigh molecular weight polyethylene. This investigation identified and quantified the main individual uncertainty contributions.