Introduction to hip implants and biomarker testing
Ilona Świątkowska, ... Alister J. Hart, in Biomarkers of Hip Implant Function, 2023
1.2.1.2 Plastic polymers
Ultra-high-molecular-weight polyethylene (UHMWPE) is a semicrystalline polymer with a long history of use in orthopaedic applications, most notably in acetabular liners for THR implants. The material has a low coefficient of friction, is biocompatible, and inexpensive to produce.
However, when in contact with harder surfaces, UHMWPE releases micrometre-sized particles, which can lead to bone resorption around the implant (periprosthetic osteolysis), aseptic loosening (loss of implant fixation in the absence of infection), and early mechanical failure. To reduce the prevalence of these adverse effects, much effort has been made to increase the degree of crosslinking within the UHMWPE.
First-generation highly crosslinked UHMWPE (HXLPE) liners, clinically introduced in the 1990s, were gamma irradiated and then thermally processed (annealed or remelted) to improve their resistance to free radicals created during irradiation. Neither process yielded perfect results: annealing failed to eliminate all the free radicals, while remelting resulted in a material with undetectable free radicals but reduced crystallinity and increased susceptibility to fatigue cracking (Kurtz et al., 2011).
To try to address these drawbacks, the next generation of HXLPE liners aimed to achieve oxidative resistance while maintaining the high wear resistance of the first-generation material and the mechanical strength of conventional polyethylene; the two approaches used were sequential irradiation and annealing, and vitamin E doping (vitamin E acts as a free-radical scavenger) (D’Antonio et al., 2012; Oral and Muratoglu, 2011).
Despite initial concerns, first-generation HXLPE demonstrates excellent radiographic results and longevity, even in young and active patients (Lim et al., 2019). Second-generation HXLPE delivered promising short- to mid-term results, but long-term follow-up will be required to ascertain whether these designs have a clinical advantage over first-generation liners (Langlois and Hamadouche, 2020).
Post time: Jun-26-2023
