Increased oxidative protection by high active vitamin E content and partial radiation crosslinking of UHMWPE

Vitamin E Cup Cross-linked Polyethylene in Total Hip Arthroplasty: A Meta-analysis of Randomized Controlled Trials

INTRODUCTION

The goal of this study was to assess the efficacy and safety of vitamin E cup cross-linked polyethylene (VEPE) liners compared with standard polyethylene (PE) liners in total hip arthroplasty.

METHODS

A systematic search of the PubMed, EMBASE, Scopus, and Cochrane Collaboration Library databases was conducted. The evaluated outcomes were radiological parameters, functional scores (Harris Hip Score, Numeric Rating Scale, and Activity Scale from the University of California), and adverse events. Odds ratios and mean differences (MD) were calculated for the dichotomous and continuous variables. Meta-analysis was done using Review Manager.

RESULTS

Seven randomized controlled trials (n = 990) were included. VEPE liners showed markedly lower penetration at the last follow-up (MD, -0.15; 95% confidence interval [CI], -0.18 to -0.11) and penetration rate at last follow-up (MD, -0.01; 95% CI, -0.01 to -0.00) than standard PE liners. However, no notable differences were observed in cup migration, inclination, anteversion, or patient-reported outcomes. The complication rate was not markedly different between the groups (odds ratio, 1.07; 95% CI, 0.42 to 2.73).

DISCUSSION

This meta-analysis found that while VEPE demonstrated decreased penetration rates in total hip arthroplasty, no differences were observed in patient outcomes or complications compared with standard PE. However, the clinical relevance of penetration rate reduction remains uncertain, given the short follow-up period.

Computational nodal displacement analysis of acetabulum fossa for injection molded cemented polyethylene acetabular liner

The acetabular liner (AL) is one of the key components that determine the functionality and durability of the total hip joint replacement (THR) device. The performance of Ultra high molecular weight polyethylene (UHMWPE)-based AL depends critically on the manufacturing route and its properties, which are evaluated pre-clinically using a host of experimental and computational analyses. The conventional manufacturing of an AL involves multiple stages, including extrusion/compression molding followed by machining, which is time/cost intensive and leads to material loss. In such a scenario, injection molding is a promising alternative, yet its feasbility remains unexplored for the manufacturing of AL for THA applications. Against this backdrop, the two-fold objectives of this work are to report our recent efforts to establish the efficacy of the injection molding of new generation UHMWPE biomaterial; HU (60 wt% HDPE- 40 wt% UHMWPE blend) for manufacturing AL prototype and to present the key biomechanical response analysis of this prototype, in silico. A range of manufacturing relevant material properties, as well as customized mold design to manufacture HU-based AL with external design features, are discussed. Such guidelines are particularly relevant to mold polymeric parts with a higher thickness (>8 mm). As part of the pre-clinical validation of AL with new design features, a less explored in silico approach to assess biomechanical micro-strain in the acetabulum fossa is presented, and the results are analysed in accordance with the mechanostat theory. The outcomes revealed that for a 100 kg subject weight, average micro-strain in the remodelling region was 1132, while it was determined as 723 for a 55 kg subject weight. Such results highlight the influence of subject weight on micro-strain generation and distribution in the acetabulum fossa. The von Mises stress in AL also increased with subject weight from 17 MPa in a subject weight of 55 kg to 28 MPa in a subject weight of 100 kg. Taken together, this work demonstrates the feasibility and competence of this new generation biomaterial in terms of implant manufacturing via injection molding with a clinically desired biomechanical response.

Cup positioning and its effect on polyethylene wear of vitamin E- and non-vitamin E-supplemented liners in total hip arthroplasty: radiographic outcome at 5-year follow-up

BACKGROUND

Aseptic loosening remains a challenging problem after total hip arthroplasty. Accurate cup placement and supplementation of antioxidants in acetabular liners might reduce material failure rates. The aim of this study is to assess the effect of the cup position on the wear behaviour of UHMWPE-XE and UHMWPE-X liners in vivo using virtual radiographs.

METHODS

We conducted a prospective, randomized, controlled, multicenter trial. Clinical data of 372 probands were analyzed. Anteroposterior pelvic X-rays of 324 patients immediately postoperatively and after 1 and 5 years were evaluated by the RayMatch® analysis software regarding cup position and wear behaviour.

RESULTS

Mean cup anteversion was 20.3° (± 7.4) and inclination was 41.9° (± 7.0) postoperatively. 62.3% of all patients had an anteversion and inclination within the Lewinnek safe zone. Anterior and anterolateral approaches led to significantly higher cup anteversion compared to lateral approaches (27.3° ± 5.5; 20.9° ± 7.2; 17.5° ± 6.6; p < 0.001 and p = 0.001, respectively). Mean anteversion increased to 24.6° (± 8.0) after 1 year (p < 0.001). Only one revision occurred because of implant dislocation. Wear rates from UHMWPE-X and UHMWPE-XE did not differ significantly. Anteversion angles ≥ 25° correlated to increased polyethylene wear (23.7 µm/year ± 12.8 vs. 31.1 µm/year ± 22.8, p = 0.012) and this was amplified when inclination angles were ≥ 50° (23.6 µm/year ± 12.8 vs. 38.0 µm/year ± 22.7, p = 0.062).

CONCLUSION

Anterior approaches lead to the highest inaccuracy of cup placement, but cup positioning outside the Lewinnek safe zone does not necessarily cause higher dislocation rates. Moreover, mean anteversion increased by approximately four degrees within the first year after operation, which is expected to be functional due to a regularization of pelvic tilt after intervention. Mid-term wear rates of UHMWPE-X and UHMWPE-XE liners are comparable, but steep cup positions lead to significantly increased polyethylene wear. In summary, a re-evaluation of target zones for intraoperative cup positioning might be considered. In the long-term reduced oxidative embrittlement could lead to superior wear behaviour of vitamin E-blended liners.

Chemical stability of oil-infused polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) can be made radiopaque for medical imaging applications through the diffusion of an iodised oil-based contrast agent (Lipiodol Ultra Fluid). A similar process is used for Vitamin E incorporated polyethylene which provides antioxidant properties. This study aimed to investigate the critical long-term properties of oil-infused medical polyethylene after 4 weeks of accelerated thermal ageing. Samples treated with an oil (Vitamin E or Lipiodol) had a higher oxidation stability than currently used medical grade polyethylene, indicated by a smaller increase in oxidation index after ageing (Vitamin E + 36%, Lipiodol +40%, Untreated +136%, Thermally treated +164%). The tensile properties of oil treated polyethylene after ageing were significantly higher than the Untreated and Thermally treated controls (p<0.05) indicating less mechanical degradation. There was also no alteration in the percentage crystallinity of oil treated samples after ageing, though the radiopacity of the Lipiodol treated samples reduced by 54% after ageing. The leaching of oil with time was also investigated; the leaching of Lipiodol and Vitamin E followed the same trend and reached a steady state by two weeks. Overall, it can be concluded that the diffusion of an oil-based fluid into polyethylene not only increases the oxidative and chemical stability of polyethylene but also adds additional functionality (e.g. radiopacity) providing a more suitable material for long-term medical applications.

Controlled bacteriostasis of tea polyphenol loaded ultrahigh molecular weight polyethylene with high crosslink density and oxidation resistance for total joint replacement

To avoid catastrophic bacterial infection in prosthesis failure, ultrahigh molecular weight polyethylene (UHMWPE), a common bearing material of artificial joints, has been formulated with antibiotics to eliminate bacteria locally at the implant site. However, the pressing issues regarding cytotoxic effects and evolution of drug resistant bacteria necessitates the development of bio-friendly bacteriostat with long bacteriostatic efficacy. Herein, tea polyphenol extracted from nature source was introduced in UHMWPE as a biogenic antimicrobial. Controlled antimicrobial activity was achieved by chemical crosslinking to regulate the release of the tea polyphenol. In addition, the crosslinking efficiency of UHMWPE blends with high loaded tea polyphenol was significantly improved in comparison to radiation crosslinking. The immobilized tea polyphenols also enhanced the oxidation stability of the UHMWPE, which is essential to prolong the service life in vivo and the storage time in vitro. The blends presented good biocompatibility, despite cell repellent on the highly crosslinked surface. Chemically crosslinked tea polyphenol/UHMWPE exhibited feasible properties for total joint implants, which is promising for clinical application.

Polyphenol-Assisted Chemical Crosslinking: A New Strategy to Achieve Highly Crosslinked, Antioxidative, and Antibacterial Ultrahigh-Molecular-Weight Polyethylene for Total Joint Replacement

Highly crosslinked ultrahigh-molecular-weight polyethylene (UHMWPE) bearings are wear-resistant to reduce aseptic loosening but are susceptible to oxidize in vivo/in vitro, as reported in clinical studies. Despite widespread acceptance of antioxidants in preventing oxidation, the crosslinking efficiency of UHMWPE is severely impacted by antioxidants, the use of which was trapped in a trace amount. Herein, we proposed a new strategy of polyphenol-assisted chemical crosslinking to facilitate the formation of a crosslinking network in high-loaded tea polyphenol/UHMWPE blends. Epigallocatechin gallate (EGCG), a representative of tea polyphenol, was mixed with UHMWPE and peroxide. Multiple reactive phenolic hydroxyl groups of tea polyphenol coupled with the nearby free radicals to form extra crosslinking sites. The crosslinking efficiency was remarkably enhanced with increasing tea polyphenol content, even at a concentration of 8 wt %. Given by the hydrogen donation principle, the high-loaded tea polyphenol also enhanced the oxidation stability of the crosslinked UHMWPE. The antioxidative performance was preserved even after tea polyphenol elution. Moreover, superior antibacterial performance was achieved by the in situ tea polyphenol release from the interconnected pathways in the present design. The strategy of polyphenol-assisted chemical crosslinking is applicable for producing highly crosslinked, antioxidative, and antibacterial UHMWPE, which has promising prospects in clinical applications.

Vitamin E-blended highly cross-linked polyethylene liners in total hip arthroplasty: a randomized, multicenter trial using virtual CAD-based wear analysis at 5-year follow-up

BACKGROUND

Progressive oxidation of highly cross-linked ultra-high molecular weight (UHMPWE-X) liners is considered to be a risk factor for material failure in THA. Antioxidants such as vitamin E (alpha-tocopherol) (UHMWPE-XE) were supplemented into the latest generation of polyethylene liners. To prevent inhomogenous vitamin E distribution within the polymer, blending was established as an alternative manufacturing process to diffusion. The purpose of the present study was to investigate the in vivo wear behavior of UHMWPE-XE in comparison with conventional UHMWPE-X liners using virtual CAD-based radiographs.

METHODS

Until now, 94 patients from a prospective, randomized, controlled, multicenter study were reviewed at 5-year follow-up. Of these, 51 (54%) received UHMWPE-XE and 43 (46%) UHMWPE-X liners. Anteroposterior pelvic radiographs were made immediately after surgery and at 1 and 5 years postoperatively. The radiographs were analyzed using the observer-independent analysis software RayMatch^® (Raylytic GmbH, Leipzig, Germany).

RESULTS

The mean wear rate was measured to be 23.6 μm/year (SD 13.7; range 0.7-71.8 μm). There were no significant differences between the two cohorts (UHMWPE-X: 23.2 μm/year vs. UHMWPE-XE: 24.0 μm/year, p = 0.73). Cup anteversion significantly changed within the 1st year after implantation independent from the type of polyethylene liner [UHMWPE-X: 18.2-23.9° (p = 0.0001); UHMWPE-XE: 21.0-25.5° (p = 0.002)]. No further significant changes of cup anteversion in both groups were found between year 1 and 5 after implantation [UHMWPE-X (p = 0.46); UHMWPE-XE (p = 0.56)].

CONCLUSION

The present study demonstrates that the addition of vitamin E does not adversely affect the midterm wear behavior of UHMWPE-X. The antioxidative benefit of vitamin E is expected to become evident in long-term follow-up. Cup anteversion increment by 5° within the 1st year is likely a result of the released hip flexion contracture resulting in an enhanced posterior pelvic tilt. Therefore, a reassessment of target values in acetabular cup placement might be considered.

Elastoplastic behavior of highly cross-linked and vitamin E-stabilized polyethylene - A biomechanical study

BACKGROUND

Vitamin E-stabilized cross-linked polyethylene has been touted to alleviate the negative effects of oxidation. Although it has demonstrated significant improvements in wear resistance, bio-tribology, and oxidative resistance, little is known about the effect of antioxidants and dosage of cross-linking on the mechanical strength. This study aimed to evaluate the mechanical properties of these novel materials, which are commonly used in orthopedic implants.

METHODS

Samples of different polymers were prepared with various levels of cross-linking and with or without vitamin E-stabilization and then tested according to ASTM D695 and D638. The elastoplastic characteristics under compression and tension were compared between the groups.

FINDINGS

Vitamin E-stabilized cross-linked polyethylene showed a significant increase in elastic modulus over other groups, with a maximum increase of 26% in compression and 40% in tension when compared to the highly cross-linked group without vitamin E stabilization. The elastoplastic behavior under compression differed to that in tension for all polymers, demonstrating the anisotropic characteristics of these polymers.

INTERPRETATION

The lower mechanical strength of highly cross-linked polyethylene has been a complication with the use of this polymer in orthopedic liners. This current study suggests that vitamin E-stabilized cross-linked polyethylene could be a suitable alternative material for knee implants because of its improved strength in resisting external forces.