Ex vivo stability loss of irradiated and melted ultra-high molecular weight polyethylene.
BACKGROUND
Radiation crosslinking reduces wear of ultra-high molecular weight polyethylene (UHMWPE), and subsequent annealing or melting increases oxidative stability. Little is known about the oxidative stability of polyethylene total joint components after in vivo service and subsequent shelf storage in air.


METHODS
We analyzed thirty-four surgically retrieved, radiation crosslinked acetabular liners to determine their oxidative stability after in vivo service (range, 0.5 to 84.0 months). Oxidation was determined at the time of explantation. After shelf storage in air (range, 7.0 to 72.0 months), oxidation, crosslink density, and thermal properties were determined. Oxidation of one control liner that was shelf-aged in air (for eighty-four months) was also determined.


RESULTS
At the time of explantation, all components showed minimal oxidation; however, oxidation levels increased during shelf storage, with a concomitant decrease in crosslink density and increase in crystallinity. Increasing oxidation, increasing crystallinity, and decreasing crosslink density correlated with the duration of ex vivo storage. The shelf-aged control liner showed no detectable oxidation.


CONCLUSIONS
The oxidation and loss of crosslink density of the irradiated and melted UHMWPE was surprising. Two potential mechanisms that might alter the oxidative stability of UHMWPE in vivo are cyclic loading and absorption of lipids. Both of these mechanisms can generate new free radicals in UHMWPE and can initiate and propagate its oxidation.
Harris Orthopaedic Laboratory, Massachusetts General Hospital, 55 Fruit Street, GRJ-1206, Boston, MA 02114, USA. omuratoglu@partners.org
Orhun K
OK
Muratoglu
Keith K
KK
Wannomae
Shannon L
SL
Rowell
Brad R
BR
Micheli
Henrik
H
Malchau
D000077:Acetabulum; D001672:Biocompatible Materials; D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D010084:Oxidation-Reduction; D011095:Polyethylenes; D017550:Spectroscopy, Fourier Transform Infrared
D001672:Biocompatible Materials; D011095:Polyethylenes