Gamma irradiation alters fatigue‐crack behavior and fracture toughness in 1900H and GUR 1050 UHMWPE

Background Highly crosslinked UHMWPE is associated with increased wear resistance in hip simulator and clinical studies. Laboratory and case studies, however, have described rim fracture in crosslinked acetabular liners. Controversy exists, therefore, on the relative merits of crosslinked liners over conventional liners in terms of wear performance versus resistance to fatigue cracking. Questions/purposes We asked whether crosslinked liners would show less surface damage than conventional liners but would be more susceptible to fatigue damage. Methods We examined 36 conventional UHMWPE and 39 crosslinked UHMWPE retrieved implants with similar patient demographics and identical design for evidence of wear damage, including articular surface damage, impingement, screw-hole creep, and rim cracks. Results We observed no difference in wear damage scores for the two liners. Conventional liners more frequently impinged but were more often elevated with smaller head sizes. We observed creep in approximately 70% of both types of liners. Incipient rim cracks were found in five crosslinked liners, and one liner had a rim fracture. Only one conventional liner had an incipient rim crack. Conclusions Contrary to our expectation, damage was similar between crosslinked and conventional UHMWPE liners. Moreover, the 15% occurrence (six of 39) of incipient or complete fractures in crosslinked liners as compared with a 3% occurrence (one of 36) in conventional liners may have implications for the long-term performance of crosslinked liners. Longer-term studies will be necessary to establish the fate of rim cracks and thus the overall clinical fatigue performance of crosslinked liners.

Section: Discussionsupporting

confidence: 76%

Retrieved Highly Crosslinked UHMWPE Acetabular Liners Have Similar Wear Damage as Conventional UHMWPE

Schroder

Kelly

Wright

et al. 2011

“…Elevated crosslinked polyethylenes reduce wear rates in TKA simulator studies [8,19,21], but this benefit must be balanced with the mechanical changes that accompany the increased crosslinking, specifically reduced fracture toughness and reduced resistance to fatigue crack propagation [3,6,10].…”

Section: Discussionmentioning

confidence: 99%

Implant Design Influences Tibial Post Wear Damage in Posterior-stabilized Knees

Dolan

Kelly

Nguyen

et al. 2011

Background The tibial post in posterior-stabilized total knees is a potential source of polyethylene wear debris, but the relationship between the shape and location of the tibial post in relation to the tibiofemoral bearing surfaces and the subsequent wear damage patterns remains unknown. Questions/purposes We used observations made on retrieved implant components from three contemporary posterior-stabilized knee designs to examine how differences in tibial post design affected wear damage on the post. Methods We examined 113 retrieved Zimmer NexGen 1 , 103 Exactech Optetrak 1 , and 58 Smith and Nephew Genesis 1 II posterior-stabilized inserts using a subjective scale to grade post damage.Results All 274 inserts demonstrated wear damage. Total wear scores and scores for wear damage on the anterior post differed among designs: Optetrak 1 20 ± 4 and 5 ± 1, NexGen 1 13 ± 4 and 3 ± 1, and Genesis 1 II 8 ± 3 and 1 ± 1, respectively. The Optetrak 1 had predominantly anterior wear damage, the NexGen 1 had more global wear damage, and the Genesis 1 II had predominantly posterior wear damage. Tibial post wear damage and anterior post wear damage were primarily determined by implant design and to a lesser extent by length of implantation and revision diagnosis. Conclusions Although tibial post wear damage is multifactorial, the primary determinant of wear damage, and specifically anterior wear damage, is implant design. Clinical Relevance The constraint provided by the posterior-stabilized post-cam contact in modern knee arthroplasties is reflected in the wear damage patterns that occur during in vivo use. Unintended constraint such as anterior impingement should be addressed through design modifications for future posterior-stabilized knee arthroplasties.

“…More than 70% of total joint implants consist of a metal or ceramic component articulating against a UHMWPE component [21,26]. The long-term oxidation of historical UHMWPE components sterilized in the presence of oxygen is a cause of fracture [4] and wear [46] that can lead to osteolysis, aseptic loosening, and instability, which are common reasons for revision total joint arthroplasty [26,39]. Radiation-crosslinked UHMWPE has been used clinically for joint implants since the 1990s [21].…”

Section: Introductionmentioning

confidence: 99%

Natural Polyphenols Enhance Stability of Crosslinked UHMWPE for Joint Implants

Shen

Gao

Liu

2015

Background Radiation-crosslinked UHMWPE has been used for joint implants since the 1990s. Postirradiation remelting enhances oxidative stability, but with some loss in strength and toughness. Vitamin E-stabilized crosslinked UHMWPE has shown improved strength and stability as compared with irradiated and remelted UHMWPE. With more active phenolic hydroxyl groups, natural polyphenols are widely used in the food and pharmaceutical industries as potent stabilizers and could be useful for oxidative stability in crosslinked UHMWPE. Questions/purposes We asked whether UHMWPE blended with polyphenols would (1) show higher oxidation resistance after radiation crosslinking; (2) preserve the mechanical properties of UHMWPE after accelerated aging; and (3) alter the wear resistance of radiation-crosslinked UHMWPE. Methods The polyphenols, gallic acid and dodecyl gallate, were blended with medical-grade UHMWPE followed by consolidation and electron beam irradiation at 100 kGy. Radiation-crosslinked virgin and vitamin E-blended UHMWPEs were used as reference materials. The UHMWPEs were aged at 120°C in air with oxidation levels analyzed by infrared spectroscopy. Tensile (n = 5 per group) and impact (n = 3 per group) properties before and after aging as per ASTM F2003 were evaluated. The wear rates were examined by pin-on-disc testing (n = 3 per group). The data were reported as mean ± SDs. Statistical analysis was performed by using Student's t-test for a two-tailed distribution with unequal variance for tensile and impact data obtained with n C 3. A significant difference is defined with p \ 0.05. Results The oxidation induction time of 100 kGy UHMWPE was prolonged to 144 hours with 0.05 wt% dodecyl gallate and 192 hours with 0.05 wt% gallic acid compared with 48 hours for 0.05 wt% vitamin E-blended UHMWPE. Accelerated aging of these polyphenol-blended UHMWPEs resulted in ultimate tensile strength of 50.4 ± 1.4 MPa and impact strength of 53 ± 5 kJ/m 2 for 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate, for example, in comparison to 51.2 ± 0.7 MPa (p = 0.75) and 58 ± 5 kJ/m 2 (p = 0.29) before aging. The pin-on-disc wear rates of 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate and 0.05 wt% gallic acid were 2.29 ± 0.31 and 1.65 ± 0.32 mg/million cycles, comparable to 1.68 ± 0.25 and 2.05 ± 0.22 mg/million cycles for 100 kGy-irradiated virgin and 0.05 wt% vitamin E-blended UHMWPE. Conclusions Based on the sample numbers tested in this study, polyphenols appear to effectively enhance the oxidation stability without altering the mechanical properties or pin-on-disc wear rate of radiation-crosslinked UHMWPE. Clinical Relevance Crosslinked UHMWPE with natural polyphenols with improved oxidative stability and low wear may find clinical application in joint implants.