Raman spectroscopy reveals creep and wear rate of e-beam-sterilized conventional UHMWPE tibial inserts

Linear and Volumetric Polyethylene Wear Patterns after Primary Cruciate-Retaining Total Knee Arthroplasty Failure: An Analysis Using Optical Scanning and Computer-Aided Design Models

(1) Background: Analyses of retrieved inserts allow for a better understanding of TKA failure mechanisms and the detection of factors that cause increased wear. The purpose of this implant retrieval study was to identify whether insert volumetric wear significantly differs among groups of common causes of total knee arthroplasty failure, whether there is a characteristic wear distribution pattern for a common cause of failure, and whether nominal insert size and component size ratio (femur-to-insert) influence linear and volumetric wear rates. (2) Methods: We digitally reconstructed 59 retrieved single-model cruciate-retaining inserts and computed their articular load-bearing surface wear utilizing an optical scanner and computer-aided design models as references. After comprehensively reviewing all cases, each was categorized into one or more of the following groups: prosthetic joint infection, osteolysis, clinical loosening of the component, joint malalignment or component malposition, instability, and other isolated causes. The associations between volumetric wear and causes of failure were estimated using a multiple linear regression model adjusted for time in situ. Insert linear penetration wear maps from the respective groups of failure were further processed and merged to create a single average binary image, highlighting a potential wear distribution pattern. The differences in wear rates according to nominal insert size (small vs. medium vs. large) and component size ratio (≤1 vs. >1) were tested using the Kruskal-Wallis test and the Mann-Whitney test, respectively. (3) Results: Patients with identified osteolysis alone and those also with clinical loosening of the component had significantly higher volumetric wear when compared to those without both causes (p = 0.016 and p = 0.009, respectively). All other causes were not significantly associated with volumetric wear. The instability group differentiated from the others with a combined peripheral antero-posterior wear distribution. Linear and volumetric wear rates showed no significant differences when compared by nominal insert size (small vs. medium vs. large, p = 0.563 and p = 0.747, respectively) or by component (femoral-to-insert) size ratio (≤1 vs. >1, p = 0.885 and p = 0.055, respectively). (4) Conclusions: The study found increased volumetric wear in cases of osteolysis alone, with greater wear when combined with clinical loosening compared to other groups. The instability group demonstrated a characteristic peripheral anterior and posterior wear pattern. Insert size and component size ratio seem not to influence wear rates.

Ultra-High-Molecular-Weight Polyethylene in Hip and Knee Arthroplasties

Ultra-high-molecular-weight polyethylene (UHMWPE) wear and particle-induced osteolysis contribute to the failure of total hip arthroplasty (THA) and total knee arthroplasty (TKA). Highly crosslinked polyethylene (HXLPE) was developed in the late 1990s to reduce wear and has shown lower wear rates and loosening than conventional UHMWPE in THA. The irradiation dose for crosslinking is up to 100 kGy. However, during crosslinking, free radical formation induces oxidation. Using HXLPE in THA, the cumulative revision rate was determined to be significantly lower (6.2%) than that with conventional UHMWPE (11.7%) at a mean follow-up of 16 years, according to the Australian Orthopaedic Association National Joint Replacement Registry. However, HXLPE does not confer to TKA the same advantages it confers to THA. Several alternatives have been developed to prevent the release of free radicals and improve polymer mechanical properties, such as thermal treatment, phospholipid polymer 2-methacryloyloxyethyl phosphorylcholine grafting, remelting, and vitamin E addition. Among these options, vitamin E addition has reported good clinical results and wear resistance similar to that of HXLPE without vitamin E, as shown by short-term clinical studies of THA and TKA. This review aims to provide a comprehensive overview of the development and performance of UHMWPE in THA and TKA.

Failure Analysis of Ultra-High Molecular Weight Polyethylene Tibial Insert in Total Knee Arthroplasty

Knee osteoarthritis is treated based on total knee arthroplasty (TKA) interventions. The most frequent failure cause identified in surgical practice is due to wear and oxidation processes of the prothesis' tibial insert. This component is usually manufactured from ultra-high molecular weight polyethylene (UHMWPE). To estimate the clinical complications related to a specific prosthesis design, we investigated four UHMWPE tibial inserts retrieved from patients from Clinical Hospital Colentina, Bucharest, Romania. For the initial analysis of the polyethylene degradation modes, macrophotography was chosen. A light stereomicroscope was used to estimate the structural performance and the implant surface degradation. Scanning electron microscopy confirmed the optical results and fulfilled the computation of the Hood index. The oxidation process in UHMWPE was analyzed based on Fourier-transform infrared spectroscopy (FTIR). The crystallinity degree and the oxidation index were computed in good agreement with the existing standards. Mechanical characterization was conducted based on the small punch test. The elastic modulus, initial peak load, ultimate load, and ultimate displacement were estimated. Based on the aforementioned experimental tests, a variation between 9 and 32 was found in the case of the Hood score. The oxidation index has a value of 1.33 for the reference sample and a maximum of 9.78 for a retrieved sample.

Comparative Raman study on the molecular structure and IN VIVO wear of poly(methyl methacrylate)-based devices used as temporary knee prostheses: Effect of the antibiotic

The infection rate of total knee arthroplasty is still high, in spite of the high success of this surgical procedure. The use of an antibiotic-loaded temporary spacer made of poly(methyl methacrylate) (PMMA) has been proposed to treat infected knee arthroplasties. This study was aimed at comparatively investigating, on a molecular scale, two types of spacers from the same manufacturer (Spacer K and Vancogenx-space knee, Tecres, Italy), which differ for the added antibiotic (gentamicin sulphate in Spacer K and gentamicin sulphate + vancomycin hydrochloride in Vancogenx). Raman spectroscopy was used to gain more insights into the possible effects of the antibiotic on the spacer composition and polymer structure both in the new components and after in vivo use. Vancogenx was found to contain a lower residual MMA content than Spacer K (about 0.15% versus 0.4%). The former contained a higher amount of isotactic stereosequences than the latter, while the syndiotactic content (the prevailing component) was not significantly different in the two prostheses. The presence of vancomycin hydrochloride influenced not only the degree of polymerization and PMMA tacticity and crystallinity, but in turn also the wear behavior. Actually, Spacer K retrievals were found more affected by in vivo implantation than Vancogenx-space knee ones, revealing slight variations in polymer tacticity and crystallinity and relative radiopacifier content, besides release of MMA and additives of polymerization. However, these changes did not appear worrisome, due to the temporary nature of the prosthesis. In view of these results, the addition of vancomycin hydrochloride could offer an advantage, in spite of the higher costs requested and the potential risks of its unselective use.