Metal wear particle characterization from metal on metal total hip replacements: Transmission electron microscopy study of periprosthetic tissues and isolated particles

Abstract

The less intense tissue reaction around metal on metal total hip replacements (THRs) compared to metal on polyethylene (PE) THRs may be explained by the differences in the characteristics of metal wear particles. In this study, transmission electron microscopy was used to study metal wear particles that were either in situ in cells or had been extracted from the cells by a new technique based on enzymatic tissue digestion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearing couples. Most of the CoCrMo wear particles were smaller than 50 nm (range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE particles. While even a small volume of metal wear will produce high numbers of particles, the apparently less severe local tissue reaction to metal particles may be due to the possibility that corrosion, dissolution, and dissemination of metal particles may result in fewer local biological effects than the long-term retention of PE particles in the periprosthetic tissues.

Effects of digestion protocols on the isolation and characterization of metal-metal wear particles. I. Analysis of particle size and shape

“…When using high concentrations of serum (in the present study 95%) as a lubricant, a digestion protocol is required to be able to isolate and characterize wear particles. Based on preexisting protocols used for the isolation of various particle types, [21][22][23][24]27,28,31-33 we tested protocols using 2N and 12N KOH, as well as 5N NaOH. However, since Campbell et al 31,32 postulated that strong alkaline solutions might affect metal particle characteristics, new enzymatic protocols were designed for quantitative comparison with alkaline treatments.…”

“…These protocols were adapted from those commonly used for polyethylene particle isolation. [21][22][23][24]27,28,[31][32][33] In addition, a new enzymatic protocol was developed based on a combination of enzymes previously used by others to isolate particles from tissues. 22 All solutions in all protocols were passed through 0.1-or 0.2-m pore size filters to minimize possible contamination.…”

“…Metal wear particles are known to be much smaller than polyethylene particles, [21][22][23][24][25][26] and digestion reagents, used in isolation protocols, can potentially damage the metal. To provide realistic measurements of size, shape, and composition of metal particles, it is important to optimize particle isolation and minimize particle changes due to the effects of the protocol reagents.…”

“…In addition to treatments with alkaline solutions, 23,24,27 there have also been efforts to use enzymes for particle isolation from tissues. 18,22,28 However, if these protocols are to be used to isolate particles generated by simulator testing of metalmetal implants, a systematic study of their effects on these particles is required. In the present study, three types of CoCrMo metal particles were chosen to help in understanding the science involved in particle damage by reagents.…”

“…22 Part I of the present study focused on the effects of the isolation protocols on the size and shape of the particles. Part II focused on ion release and particle composition.…”