Oxidation and other property changes of a remelted highly crosslinked UHMWPE in retrieved tibial bearings.

This study examined retrieved UHMWPE tibial bearings made from a remelted highly crosslinked (HXL) UHMWPE to determine whether the material is chemically stable in vivo. Retrieved tibial components were measured for changes in ketone oxidation and crosslink density. Oxidation increased with in vivo duration, and a significant decrease in crosslink density with increased mean ketone oxidation index was observed.

Oxidation and other property changes of retrieved sequentially annealed UHMWPE acetabular and tibial bearings.

This investigation analyzed retrieved sequentially crosslinked and annealed (SXL) ultra-high molecular weight polyethylene bearings to determine whether the material is chemically stable in vivo. A series of retrieved tibial and acetabular components were analyzed for changes in ketone oxidation, crosslink density, and free radical concentration. Oxidation was observed to increase with in vivo duration, and the rate of oxidation in tibial inserts was significantly greater than in acetabular liners.

Knee wear measured in retrievals: a polished tray reduces insert wear.

Background: Polyethylene wear is often cited as the cause of failure of TKA. Rotating platform (RP) knees show notable surface damage on the rotating surface raising concerns about increased wear compared to fixed bearing inserts.

Questions/purposes: We therefore addressed the following questions: Is wear in RP inserts increased compared to that in fixed bearing inserts? Does the surface roughness of the tibial tray have a measurable impact on in vivo wear of modular knees? And does wear rate differ between posterior stabilized (PS) and cruciate retaining (CR) knees?

Methods: We compared wear in two series of retrieved knee devices: 94 RP mobile bearings with polished cobalt-chrome (CoCr) trays and 218 fixed bearings with both rough titanium (Ti) and polished CoCr trays.

Femoral stem fracture and in vivo corrosion of retrieved modular femoral hips.

A series of 78 retrieved modular hip devices were assessed for fretting and corrosion. Damage was common at both the head-neck junction (54% showing corrosion; 88% showing fretting) and at the stem-sleeve junction (88% corrosion; 65% fretting). Corrosion correlated to in vivo duration, patient activity, and metal (vs ceramic) femoral heads but did not correlate to head carbon content.

Gamma-irradiation sterilization in an inert environment: a partial solution.

Background: In the mid to late 1990 s, to sterilize UHMWPE bearings, manufacturers changed from gamma-irradiation-in-air (gamma-air) sterilization, which initiated oxidation leading to bearing fatigue, to gamma-irradiation sterilization in an inert environment (gamma-inert). The change to gamma-inert sterilization reportedly prevented shelf oxidation before implantation but not in vivo oxidation.

Questions/purposes: We asked: (1) Has the change to gamma-inert sterilization prevented shelf oxidation that led to early in vivo fatigue damage in gamma-air-sterilized tibial inserts? And (2) has the change to gamma-inert sterilization prevented the occurrence of fatigue secondary to in vivo oxidation?

Methods: We rated 183 retrieved gamma-air- and 175 retrieved gamma-inert-sterilized tibial inserts for clinical fatigue damage and analyzed 132 gamma-air- and 174 gamma-inert-sterilized tibial inserts for oxidation by Fourier transform infrared spectroscopy.

The effect of radiation dose on the tensile and impact toughness of highly cross-linked and remelted ultrahigh-molecular weight polyethylenes.

Several highly cross-linked and remelted ultrahigh-molecular weight polyethylenes (UHMWPE) were introduced in 1998 as bearing materials for orthopaedic implants to achieve superior wear performance. However, gamma radiation and the subsequent postirradiation thermal treatment are associated with decreased mechanical properties such as ductility, toughness, and fatigue strength compared to noncross-linked materials. The purpose of this study was (a) to characterize the toughness (tensile and impact) of highly cross-linked and remelted UHMWPE of varying doses (0-255 kGy) and (b) determine whether a correlation exists between both toughness measures.

Evaluating the suitability of highly cross-linked and remelted materials for use in posterior stabilized knees.

Posterior stabilized (PS) knee designs are a popular choice for cruciate sacrificing knee arthroplasty procedures. The introduction of PS inserts fabricated from highly cross-linked and remelted Ultra High Molecular Weight Polyethylene (UHMWPE) has recently generated concern as these materials have been shown to possess reduced mechanical properties. This study investigated whether highly cross-linked and remelted UHMWPE material (referred to as XRP) can be expected to perform similarly to historical gamma-air polyethylene, which has suffered few reported incidences of tibial post failure.

Clinical wear measurement on low contact stress rotating platform knee bearings.

Whereas fixed-bearing total knee arthroplasty (TKA) designs secure the polyethylene bearing to the tibial tray, mobile-bearing TKAs allow the bearing to move relative to the tray. This study evaluated wear performance of the rotational articulation of the Low Contact Stress Rotating Platform mobile-bearing TKA (DePuy, Warsaw, Ind) by analyzing 100 retrievals. All retrieved bearings showed rotation surface damage, but severity of the damage did not correlate with duration.

Evaluation of oxidation and fatigue damage of retrieved crossfire polyethylene acetabular cups.

Background: Crossfire cross-linked polyethylene is produced differently from other cross-linked polyethylene materials; a below-melt-temperature annealing process is used with the goal of avoiding compromised mechanical properties. The present study was performed to evaluate retrieved Crossfire acetabular cups to determine whether they had oxidized and to what extent oxidation might have influenced their clinical performance.

Methods: Eleven acetabular cups were received at retrieval and a twelfth acetabular cup was received two years post-retrieval over a period of four years.

Unilateral tibial polyethylene liner failure in bilateral total knee arthroplasty--bilateral retrieval analysis at 8 years.

This is a report of a unique case of bilateral simultaneous total knee arthroplasties in which one tibial liner failed dramatically, whereas the other liner showed minimal evidence of wear. This unique case allows isolation of component factors as the primary contributing etiology to failure. The differentiating characteristic was the method of sterilization and the shelf life of the polyethylene liner.

In vivo oxidation of gamma-barrier-sterilized ultra-high-molecular-weight polyethylene bearings.

gamma-Barrier packaging is shown to be effective in preventing oxidation of polyethylene during shelf storage and in addressing the problem of early fatigue failure seen in gamma-air-sterilized bearings with long shelf-storage before implantation. The series of gamma-barrier retrievals studied suggests that oxidation occurs in the body via the same mechanism as seen in gamma-air-sterilized bearings. A critical oxidation level is identified above which polyethylene bearings are susceptible to fatigue damage after sufficient cycles of use.

Differences in articular track area of posterior-stabilized and cruciate-retaining retrieved total knee implants.

Press-fit condylar total knee arthroplasties removed at revision surgery from 27 knees were examined. Fourteen of the implants were posterior-stabilized press-fit condylar systems and 13 were cruciate-retaining press-fit condylar systems. The articular track areas were examined using a digital camera and manual measurements.

Comparison of cross-linked polyethylene materials for orthopaedic applications.

Cross-linked polyethylenes are being marketed by orthopaedic manufacturers to address the problem of osteolysis caused by polyethylene particulate wear debris. Wear testing of these cross-linked polyethylenes in hip simulators has shown dramatic reduction in wear rate compared with standard ultrahigh molecular weight polyethylene, either gamma irradiated in air or nitrogen - or ethylene oxide-sterilized. However, this reduction in wear rate is not without cost.

Rapid polyethylene failure of unicondylar tibial components sterilized with gamma irradiation in air and implanted after a long shelf life.

Background: The mechanical toughness of polyethylene that has been sterilized by gamma irradiation in air decreases after a long shelf life. The purpose of the present study is to report the high failure rate after unicondylar knee replacements performed with polyethylene bearings that had been sterilized with gamma irradiation in air and implanted after a shelf life of < or = 4.4 years.