BackgroundPolyetheretherketone (PEEK) and its composites are polymers resistant to fatigue strain, radiologically transparent, and have mechanical properties suitable for a range of orthopaedic applications. In bulk form, PEEK composites are generally accepted as biocompatible. In particulate form, however, the biologic response relevant to joint replacement devices remains unclear. The biologic response to wear particles affects the longevity of total joint arthroplasties. Particles in the phagocytozable size range of 0.1 µm to 10 µm are considered the most biologically reactive, particularly particles with a mean size of < 1 µm. This systematic review aimed to identify the current evidence for the biologic response to PEEK-based wear debris from total joint arthroplasties.Questions/purposes(1) What are the quantitative characteristics of PEEK-based wear particles produced by total joint arthroplasties? (2) Do PEEK wear particles cause an adverse biologic response when compared with UHMWPE or a similar negative control biomaterial? (3) Is the biologic response affected by particle characteristics?MethodsEmbase and Ovid Medline databases were searched for studies that quantified PEEK-based particle characteristics and/or investigated the biologic response to PEEK-based particles relevant to total joint arthroplasties. The keyword search included brands of PEEK (eg, MITCH, MOTIS) or variations of PEEK types and nomenclature (eg, PAEK, CFR-PEEK) in combination with types of joint (eg, hip, knee) and synonyms for wear debris or immunologic response (eg, particles, cytotoxicity). Peer-reviewed studies, published in English, investigating total joint arthroplasty devices and cytotoxic effects of PEEK particulates were included. Studies investigating devices without articulating bearings (eg, spinal instrumentation devices) and bulk material or contact cytotoxicity were excluded. Of 129 studies, 15 were selected for analysis and interpretation. No studies were found that isolated and characterized PEEK wear particles from retrieved periprosthetic human tissue samples.ResultsIn the four studies that quantified PEEK-based particles produced using hip, knee, and spinal joint replacement simulators, the mean particle size was 0.23 µm to 2.0 µm. The absolute range reported was approximately 0.01 µm to 50 µm. Rod-like carbon particulates and granular-shaped PEEK particles were identified in human tissue by histologic analysis. Ten studies, including six animal models (rat, mouse, and rabbit), three cell line experiments, and two human tissue retreival studies, investigated the biologic response to PEEK-based particles. Qualitative histologic assessments showed immunologic cell infiltration to be similar for PEEK particles when compared with UHMWPE particles in all six of the animal studies identified. However, increased inflammatory cytokine release (such as tumor necrosis factor-α) was identified in only one in vitro study, but without substantial suppression in macrophage viability. Only one study tested the effects of par...

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Total Knee Replacement has been under development for over 50 years. Its primary objectives are for normal articulation of a diseased joint, to relieve pain and restore function. Over the years three main surgical types of alloys have been used: 316L stainless steel, titanium and cobalt-chrome based alloys. Titanium, despite its superior biocompatibility, closest to bone’s Young’s modulus and lack of nickel in its composition, has poor resistance to wear. This major disadvantage of titanium alloys is the reason for which their use in load bearing prostheses is limited. Various methods of surface modifications have been investigated in order to improve wear performance by improving mechanical and tribological properties of medical grade titanium alloys. In this work, the effect of nitrogen ion implantation on micro- and nano-hardness and surface roughness of medical grade titanium alloy (Ti6Al4V ELI) has been investigated, and compared to those of unimplanted Ti6Al4V ELI, cast and wrought CoCrMo alloys. Due to the formation of a smooth and hard nitride layer on the surface of the ion implanted Ti6Al4V ELI alloy significant improvement in micro- and nano-hardness was achieved. This hardened layer is thought to improve the wear resistance of Ti-based alloys and hence can maximise their use for more demanding prosthetic applications.

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