Background and purpose Highly cross-linked polyethylenes (PEs) all appear to reduce wear dramatically in laboratory studies, although there is substantial variation in this respect between manufacturers. Nonremelted cross-linked PE is almost as tough as unirradiated PE, but is not completely stable and can oxidize in vivo, as has been shown in recent retrievals studies.We had reported low wear and good clinical performance after 2 years for 10 non-remelted highly crosslinked PE cups compared to 16 conventional PE cups sterilized by gamma-in-air.Method Because of possible degradation by free radicals, we followed up both cohorts for 5 years (conventional PE) and 6 years (highly cross-linked PE).Result Mean (CI) proximal head penetration over the observation time was linear and measured 0.08 (0.02-0.13) mm for cross-linked PE and 0.42 (0.23-0.62) mm for conventional PE, and total penetration was 0.23 (0.1-0.35) mm and 0.75 (0.05-1.4) mm respectively. After subtracting creep, the annual wear for non-remelted highly cross-linked PE was below 6 µm. The cups had equally low migration and few radiolucencies.Interpretation The theoretical possibility of oxidation in non-remelted highly cross-linked PE may not show clinically. However, it may be that cemented cups with their thicker PE are more forgiving than metal-backed cups with thin PE moving in the locking mechanism. So far, we can conclude that the Crossfire highly crosslinked polyethylene cups performed very well clinically, with extremely low wear even after almost 6 years. This is reassuring, but care should be taken in extrapolating
A few studies have shown that cementing the stem enhances fixation of the tibial baseplate in total knee replacement (TKR). Even the horizontal technique has been shown to provide good fixation. We used radiostereometry to study migration of the tibial component in 30 knees operated with Profix TKR. The knees were randomised for either complete (both under the baseplate and around the stem) or horizontal (only under the baseplate) cementing of the tibial component. At two years the tibial baseplate rotated externally a median of 0.18°in the uncemented stem group and internally a median of 0.23°in the cemented stem group. The tibial baseplate subsided 0.14 mm in the cemented stem group, and no translation was seen in the uncemented stem group. The differences in migration were small and probably without clinical significance. The findings do not favour either of the cementing techniques in TKR.Résumé Peu d'études ont démontré que la fixation cimentée de la queue améliorait la fixation du plateau tibial dans les prothèses totales du genou. Par ailleurs, les fixations horizontales ont également montré une bonne fixation. Nous avons utilisé la radiostéréométrie pour étudier la migration du composant tibial dans 30 genoux de type Profix. Les genoux ont été randomisés cimentation sous le plateau et autour de la queue ou cimentation horizontale uniquement sous le plateau. À 2 ans le plateau tibial présente une rotation externe de 0,18°d ans les PTG avec une queue non cimentée et une rotation interne moyenne de 0,23°dans le groupe des queues cimentées. La base du plateau tibial s'enfonce de 0,14mm dans le groupe des queues cimentées et il n'y a pas de translation dans le groupe des queues non cimentées. En conclusion, la différence au niveau de la migration est minime et sans signification clinique. Cette étude ne permet pas de choisir dans les prothèses totales du genou l'une des deux techniques de cimentation.
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