gms | German Medical Science

Objectives: Bone marrow (BM) is increasingly getting into focus in the course of investigating pathomechanisms of adverse effects related to periprosthetic inflammation induced by local exposure to particles released from arthroplasty implants. Particles released from cobalt-chromium-molybdenum (CoCrMo) alloys are considered common elicitors of chronic inflammatory local and systemic adverse effects. So far, there is a lack of data demonstrating particle numbers, size distribution and elemental composition of BM resident particles which would allow to implement clinically relevant in vitro and in vivo test strategies at different degrees of exposure. Thus, the aim of this study was to analyse CoCrMo-containing micro-, submicron-, and nanoparticles from different arthroplasty implants in terms of particle numbers, particle size distribution and elemental ratios with respect to particle size by synchrotron-based nano-X-ray fluorescence (nano-XRF).

Methods: Periprosthetic BM from eight patients with hip arthroplasty implant (CoCrMo dual modular neck junction), knee arthroplasty implant, or with hip resurfacing implant were analysed. Data were collected at beamline ID16B of the European Synchrotron (ESRF) by nano-XRF. A pink beam of a centre energy of 25.6 keV was selected and focused to 60 nm x 60 nm spot size. The Co intensity maps were used for input for a subsequent top-hat transformation with a disk-shaped structuring element. A mask was obtained through thresholding of the top-hat transformed Co maps for subsequent particle analyses.

Results and conclusion: Nano-XRF analyses revealed a detectable presence of CoCrMo particles in periprosthetic BM in all cases of TKA, mTHA and HR implants. Analyses of particle sizes revealed lognormal particle size distribution patterns predominantly towards the nanoscale indicating a natural system where particles are formed or broken up. Quantitative analyses of particle numbers and normalisation to BM volume and BM cell number indicated particle concentrations of up to 1 x 10^11 particles / ml BM or 2 x 10^4 particles / BM cell, respectively. Analyses of elemental ratios of CoCrMo particles showed that particularly the particles' Co content depends on particle size. Smaller particles are characterized by lower Co to Cr and Co to Mo ratios.

The obtained data point towards Co release from arthroprosthetic particles. The lognormal size-frequency distribution of the particles suggests degradation processes of particles within periprosthetic BM. This is the first study providing data of arthroprosthetic CoCrMo particle numbers and characteristics in human periprosthetic BM to be used for clinically relevant dosimetry in future in vitro and in vivo studies, in particular for the evaluation of the toxicity and carcinogenicity of CoCrMo.