Aiguo Wang

Tribological Assessment of UHMWPE in the Hip

Publisher Summary The need for and role of hip simulation is well established in orthopedics. There is, however, a healthy skepticism that exists regarding hip simulator data. Most surgeons believe that the data typically presented to them are in fact real and a precise representation of in vitro outcomes. But the question of reliability, that is, clinical correlation or validity, is a basic litmus test that hip simulation deservedly must face. A basic fact that cannot be overlooked is that not all hip simulator data are equivalent. There are many variables that play a role in hip simulation, and the precise way these variables are addressed can affect the clinical relevance of the data. The details of the particular test methodology employed are of critical importance. There are numerous variables that can influence the tribological performance of hip bearing devices in vivo. It is impossible to simulate all of these known variables in vitro, let alone the unknown ones.

The effect of neutron radiation on conventional and highly cross-linked ultrahigh-molecular-weight polyethylene wear.

The effects of a sarcoma therapy dose level neutron radiation on oxidation and wear were compared between conventional (N2\Vac, Stryker Orthopedics, Mahwah, NJ) and highly cross-linked (Crossfire, Stryker Orthopedics) ultrahigh-molecular-weight polyethylene acetabular liners. Liners were exposed to 15 Gy, a typical sarcoma treatment dose. Wear testing was conducted on a hip simulator. Transvinylene and oxidation indices were measured to determine if significant radiolytic reactions and oxidation occurred after the neutron beam exposure. The neutron bombardment produced further oxidation in both N2\Vac and Crossfire liners. Surprisingly, neutron radiation caused 62% increase in wear for N2\Vac but 0% change for the Crossfire acetabular liners. This study suggested that when joint implants are exposed to neutron beam radiation therapy, the conventional polyethylene liner is at risk for rapid wear.

Chapter 14 – Highly Crosslinked and Annealed UHMWPE

Publisher Summary This chapter explores the sequential irradiation and annealing process that is shown to eliminate free radicals more effectively and form crosslinks than a single cumulative radiation dose of the same magnitude followed by annealing. The sequential and annealing process produces a microstructure that is not significantly different from that of ultra-high molecular weight polyethylene (UHMWPE) gamma sterilized in nitrogen (N2/Vac). The use of sequential irradiation and annealing provides the same level of crosslinking at a lower radiation dose with a consequent improvement in mechanical properties that allows X3 to be used for total knee replacement (TKR). The experience with highly crosslinked UHMWPEs over the last decade shows a progressive development in understanding the relationship between UHMWPE structure (crosslink density and crystallinity) and properties (strength, ductility, and wear). Highly crosslinked UHMWPEs were introduced clinically in the 1970s by Oonishi and coworkers and by Grobbelaar and associates, and reintroduced by Wroblewski and colleagues in the 1980s. The crosslinking methods used were not based directly on knowledge of UHMWPE structure–property relationships, and clinical use was limited. There was no commercial introduction, but these materials are of historical interest.