Zimmer | Longevity Highly Crosslinked Polyethylene | Which Medical Device

Description

From Which Medical Device

Zimmer Longevity Highly Crosslinked Polyethylene The Longevity is Zimmer’s highly crosslinked polyethylene insert designed for total hip arthroplasty, launched in 1999. It is available as standard, 10° elevation, 20° elevation and 7 mm offset. (Zimmer.com, accessed 13/4/11) The design rationale, much like its competitors is to reduce free radical content in order to prevent aging and to maximise cross-linking to improve wear characteristics.

The manufacturing process uses GUR 1050 as the raw polyethylene. This is machined and treated with 10 MRad of e-beam radiation in order to promote maximal cross-linking. Following this, the polyethylene undergoes melt annealing to 150°C and a slow cooling period in order to minimise free radicals. Zimmer uses gas plasma sterilization in order not to compromise the molecular structure or create free radicals.

In vitro testing using 5 million cycles of a hip simulator has demonstrated an 89% reduction in wear in comparison to standard polyethylene. The testing indicates that the rate is less dependent on the head size than normal polyethylene. Early clinical studies using radiostereometric analysis have demonstrated a steady-state wear rate reduction of around 95% in comparison to standard polyethylene. (Digas et al, 2007) Due to the relatively recent introduction of these products to the market, long term clinical follow-up data is not available.

Mr Alex Sims, CT2 Trauma & Orthopaedics, Newcastle upon Tyne.

References:

1. Georgios Digas, Johan Kärrholm, Jonas Thanner and Peter Herberts. 5-year experience of highly cross-linked polyethylene in cemented and uncemented sockets. Two randomized studies using radiostereometric analysis. Acta Orthopaedica 2007; 78 (6): 746–754

2. Zimmer Longevity Polyethylene Brochure. Accessed 13/4/11 Alex Sims. CT2 Trauma and Orthopaedic Surgery, Royal Victoria Infirmary.