Effect of fabrication method and resin type on performance of tibial bearings

Abstract

Polyethylene has been used successfully for more than 30 years as an orthopedic bearing material. During this time, several polyethylene resins and fabrication methods have been used to produce bearings. Some bearings fail prematurely due to fatigue, which has been linked to oxidation and degradation of mechanical properties resulting from gamma sterilization in air. Fabrication method and/or resin have been hypothesized to govern whether oxidative degradation occurs in gamma-sterilized bearings. This study evaluates the effect of fabrication (machining/direct compression molding) and resin type on oxidation and the resulting mechanical properties for a large series of never-implanted bearings. While many molded bearings studied exhibit lower oxidation than machined bearings, fabrication method is not a significant predictor of oxidation. Resin type and shelf-age are found to be significant predictors of oxidation. Bearings fabricated from Himont 1900 exhibit lower oxidation than those from GUR 415/412 at comparable times after gamma in air. However, Himont 1900 bearings lose strength and elongation at lower oxidation levels than GUR 415/412 bearings. But since Himont 1900 oxidizes more slowly, Himont 1900 bearings retain mechanical properties for longer shelf times than comparable GUR 415/412 bearings. These effects are seen in retrievals as well.

In Vivo Oxidation Contributes to Delamination but not Pitting in Polyethylene Components for Total Knee Arthroplasty

“…Previous studies have thus reported both lower oxidation levels and superior damage resistance of polyethylene components molded from 1900H resins as compared with those machined from GUR 415 extruded bars [37–40]. 1900H polyethylene, however, was demonstrated to lose mechanical strength at lower oxidation levels than GUR 415 polyethylene, so the apparent advantage of the former material might be lost as it oxidizes [38]. Recently, no significant difference in the in vitro wear performance was observed between conventional polyethylene components and unirradiated specimens manufactured from various resins and conversion techniques, including 1900H and direct compression molding [41–42].…”

Polyethylene Wear Is Influenced by Manufacturing Technique in Modular TKA

“…From our results, DCM inserts demonstrated less backside wear than non-DCM inserts independent of time in vivo. In several studies, compression-molded polyethylene components have exhibited better articular-sided wear characteristics than machined components, indicating compression-molded polyethylene is better suited for clinical applications [2,12,24,35,38]. The sterilization process has also improved since Bohl et al demonstrated gamma irradiation in an oxygen environment resulted in poor wear characteristics [3].…”

“…Compression-molded inserts are fabricated by directly conforming polyethylene resin to molds of predetermined geometry. Although earlier reports indicated compression-molded inserts had better articularsided wear characteristics than machined components, limited data are available characterizing the impact of manufacturing technique on backside polyethylene wear [12,35,38]. An improved understanding of the relationship between polyethylene manufacturing and backside wear may facilitate improvements in polyethylene bearing design and development, which would improve implant survival and functional outcomes for patients with TKAs.…”

All-polyethylene and Metal-backed Tibial Components Are Equivalent With BMI of Less Than 37.5

“…However, in the late 1990s, the benefits of modular MBT components were questioned by reports of backside wear of the polyethylene modular insert, poorly functioning tibial base plate locking mechanisms, and osteolysis associated with these problems [4,8,24,27]. Alternatives to MBT components were therefore developed.…”