Abstract
BackgroundThe identification of implant wear particles and non-implant related particles and the characterization of the inflammatory responses in the periprosthetic neo-synovial membrane, bone, and the synovial-like interface membrane (SLIM) play an important role for the evaluation of clinical outcome, correlation with radiological and implant retrieval studies, and understanding of the biological pathways contributing to implant failures in joint arthroplasty. The purpose of this study is to present a comprehensive histological particle algorithm (HPA) as a practical guide to particle identification at routine light microscopy examination.MethodsThe cases used for particle analysis were selected retrospectively from the archives of two institutions and were representative of the implant wear and non-implant related particle spectrum. All particle categories were described according to their size, shape, colour and properties observed at light microscopy, under polarized light, and after histochemical stains when necessary. A unified range of particle size, defined as a measure of length only, is proposed for the wear particles with five classes for polyethylene (PE) particles and four classes for conventional and corrosion metallic particles and ceramic particles.ResultsAll implant wear and non-implant related particles were described and illustrated in detail by category. A particle scoring system for the periprosthetic tissue/SLIM is proposed as follows: 1) Wear particle identification at light microscopy with a two-step analysis at low (× 25, × 40, and × 100) and high magnification (× 200 and × 400); 2) Identification of the predominant wear particle type with size determination; 3) The presence of non-implant related endogenous and/or foreign particles. A guide for a comprehensive pathology report is also provided with sections for macroscopic and microscopic description, and diagnosis.ConclusionsThe HPA should be considered a standard for the histological analysis of periprosthetic neo-synovial membrane, bone, and SLIM. It provides a basic, standardized tool for the identification of implant wear and non-implant related particles at routine light microscopy examination and aims at reducing intra-observer and inter-observer variability to provide a common platform for multicentric implant retrieval/radiological/histological studies and valuable data for the risk assessment of implant performance for regional and national implant registries and government agencies.
Highlights
The identification of implant wear particles and non-implant related particles and the characterization of the inflammatory responses in the periprosthetic neo-synovial membrane, bone, and the synovial-like interface membrane (SLIM) play an important role for the evaluation of clinical outcome, correlation with radiological and implant retrieval studies, and understanding of the biological pathways contributing to implant failures in joint arthroplasty
The most frequently used bearing surface couplings are: metal-on-polyethylene (MoP), ceramic on polyethylene (CoP), metal-on-metal (MoM), and ceramic-on-ceramic (CoC); a metallic adapter sleeve, made of CoCrMo or Ti has been added to large metallic heads (≥32 mm) and of Ti to large ceramic heads (≥32 mm)
PE particles of variable size are detected at light microscopy examination under polarized light: Microparticles: PE microparticles are usually located in the cytoplasm of the macrophages; they measure between 1 and 10 μm and are predominantly globular, elongated, and fibrillary/needle-shaped showing variable birefringent reactivity under polarized light (Fig. 3a)
Summary
The identification of implant wear particles and non-implant related particles and the characterization of the inflammatory responses in the periprosthetic neo-synovial membrane, bone, and the synovial-like interface membrane (SLIM) play an important role for the evaluation of clinical outcome, correlation with radiological and implant retrieval studies, and understanding of the biological pathways contributing to implant failures in joint arthroplasty. The identification of particulate wear material of orthopaedic implants and its differential diagnosis with endogenous crystalline and non-crystalline materials in the periprosthetic capsular neo-synovial membrane, bone, and the synovial-like interface membrane (SLIM) is important for the evaluation of clinical outcome, correlation with radiological and implant retrieval studies, and understanding of the biological adverse reactions associated with implant failures. Particulate material can be generated by tribochemical wear (tribocorrosion) mechanism and by other modality at the head-neck tapers such mechanically assisted crevice/fretting corrosion, pitting and intergranular corrosion, and etching which depend on the material, material couple, and alloy microstructure [3, 4]
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