Measurement outcomes from hip simulators

Abstract

Simulation of wear in total hip replacements has been recognised as an important factor in determining the likelihood of clinical success. However, accurate measurement of wear can be problematic with factors such as number and morphology of wear particles produced as well as ion release proving more important in the biological response to hip replacements than wear volume or wear rate alone. In this study, hard-on-hard (CoCr alloy, AgCrN coating) and hard-on-soft (CoCr alloy and CrN coating on vitamin E blended highly cross-linked polyethylene) bearing combinations were tested in an orbital hip simulator under standard and some adverse conditions. Gravimetric wear rates were determined for all bearings, with cobalt and where applicable, silver release determined throughout testing. Isolation of wear particles from the lubricating fluid was used to determine the influence of different bearing combinations and wear conditions on particle morphology. It was found that cobalt and silver could be measured in the lubricating fluid even when volumetric wear was not detectable. In hard-on-hard bearings, Pearson's correlation of 0.98 was established between metal release into the lubricating fluid and wear volume. In hard-on-soft bearings, coating the head did not influence the polyethylene wear rates measured under standard conditions but did influence the cobalt release; the diameter influenced both polyethylene wear and cobalt release, and the introduction of adverse testing generated smaller polyethylene particles. While hip simulators can be useful to assess the wear performance of a new material or design, measurement of other outcomes may yield greater insight into the clinical behaviour of the bearings in vivo.

Wear testing of a canine hip resurfacing implant that uses highly cross‐linked polyethylene

“…27 Third, the size of the polyethylene wear debris was not measured in this study, and the size of these particulates is an important factor in determining host response and risk of osteolysis. 58 Finally, only one implant size was investigated in this study, so it is currently unknown how different implant sizes would affect wear rates.…”

Characterization of wear debris from metal‐on‐metal hip implants during normal wear versus edge‐loading conditions

“…To estimate total volumetric wear, cobalt and chromium levels in hip simulator lubricant fluid were determined by ICP‐MS and assumed to comprise approximately 92% of total metal in the alloy according to ASTM standards for wrought CoCr alloys used for surgical implants . Previous studies have indicated that the cobalt concentration in hip simulator fluid is highly correlated with wear rates …”

“…51,52 Previous studies have indicated that the cobalt concentration in hip simulator fluid is highly correlated with wear rates. 47,52,53…”

Tribocorrosion of hard-on-hard total hip replacements with metal and ceramic counterfaces under standard and adverse loading conditions

“…Saikko [30] demonstrated that under adverse loading conditions the gravimetric wear rate was not able to show a difference in performance of simulator tested hard-on-hard bearings unless the testing conditions passed a so-V et al [31] have also shown evidence of material degradation in hard-on-hard bearings with AgCrN coatings, despite no visible damage or gravimetric mass loss. Changes of the sliding regime to anything representing less than ideal conditions (i.e.…”

“…As discussed, the industry and research community are becoming increasingly interested in the effects of adverse loading situations and daily living activities on the performance of total hip replacements [23,24,30,31]. A continuous simple twin-peak profile may not be the best method for assessing these devices before they are implanted in patients.…”