title: Effect of e-beam sterilization on the in vivo performance of conventional UHMWPE tibial plates for total knee arthroplasty.
abstract: Although the introduction of highly cross-linked polyethylene is effective in reducing the amount of wear, there are still major concerns regarding the use of this material in total knee arthroplasty (TKA), essentially due to the reduction of fatigue resistance and toughness. Monitoring the in vivo performance of different types of UHMWPE is a much needed task to tackle the lack of information on which should be the most reliable choice for TKA. The present study was aimed at investigating the mid-term degradation of electron beam sterilized conventional UHMWPE tibial plates. Visual inspection enabled to grade the surface damage of 12 retrievals according to the Hood's score: the total wear damage correlates to the in vivo time (Spearman's ρ=0.681, p<0.05) and BMI (ρ=0.834, p<0.001). Surface degradation was less severe than that quantified in similar studies on γ-sterilized UHMWPE. Raman and infra-red spectroscopies were utilized to unfold the microstructural modifications. In the load zone, polyethylene whitened damage regions were noticed in the inserts implanted longer than 1year, in which oxidation index (OI) is clearly higher than 1 (max 8). The maximum OI (ρ=0.802, p<0.005) and αc(ρ=0.816, p<0.005) correlate to the implantation time in the load zone. The crystallinity increased along with the extent of oxidation. Concentration of absorbed species from synovial fluid is higher in the contact zone and correlates to maximum OI (Spearman's ρ=0.699, p=0.011). Absorption was promoted in the contact area by the mechanical action of the femoral counterpart and it exacerbated the oxidative degradation in retrievals with high concentration of absorbed species. In the non-load zone, mild but detectable oxidation was observed, probably due to free radicals trapped after sterilization.
  
  
  
  Although several clinical studies on retrieved tibial bearings have been published so far, monitoring and comparing the in vivo performance of different types of UHMWPE is still a much needed task. The present study reports for the first time results on the effect of sterilization by electron beam on the mid-term in vivo performance of conventional UHMWPE tibial plates. In the present investigation, visual inspection of wear damage based on the Hood's scoring method, Raman micro-spectroscopy and Fourier-transformed infrared spectroscopy were utilized to unveil the damage, the microstructural modifications and the oxidation occurred during implantation. The findings of this investigation have been discussed and compared to previous clinical studies on γ-air sterilized, γ-inert sterilized tibial bearings.
authors.affiliation: Department of Orthopaedic Surgery, Mie University, Graduate School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan.
authors.forename: Shine
authors.initials: S
authors.lastname: Tone
authors.affiliation: Department of Orthopaedic Surgery, Mie University, Graduate School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan. Electronic address: masahase@clin.medic.mie-u.ac.jp.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hasegawa
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pezzotti
authors.affiliation: Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine, Kamigyo-ku Hirokoji Agaru, Kawaramachi-dori, 602-8566 Kyoto, Japan.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Puppulin
authors.affiliation: Department of Orthopaedic Surgery, Mie University, Graduate School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Sudo
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D001860:Bone Plates; D004583:Electrons; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011095:Polyethylenes; D013242:Sterilization / Q000379:methods*; D013977:Tibia / Q000601:surgery*
chemical_list: D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene
keywords: E-beam sterilization; FT-IR; Oxidation; Raman spectroscopy; Surface damage; Total knee arthroplasty; UHMWPE