The natural history of polyethylene oxidation in total disc replacement.
METHODS
This study is an evaluation of wear and oxidation in retrieved total disc replacements (TDRs). Forty-eight CHARITE TDRs were retrieved from 41 patients after 7.8 years of average implantation. All implants were removed because of intractable back pain and/or facet degeneration. Three unimplanted implants served as controls.


OBJECTIVE
Our aim was to determine whether gamma-sterilized polyethylene components implanted in the spine oxidize in vivo, and if so, whether polyethylene oxidation has clinical relevance for the long-term performance of TDRs.


BACKGROUND
The natural history of polyethylene oxidation following gamma sterilization and long-term implantation in the spine has not yet been investigated.


METHODS
Oxidation and oxidation potential were measured at the rim and dome of 47 components using Fourier transform infrared spectroscopy. The wear patterns of each retrieved polyethylene core were analyzed at the rim and dome.


RESULTS
Oxidation was significantly higher at the rim, as compared with the dome of the cores. Hydroperoxide index was also significantly higher at the rim, as compared with the dome. Dome penetration rate was negatively correlated to implantation time (P < 0.0001) but not correlated to oxidation or hydroperoxide index (P > 0.05). Implants with evidence of chronic rim loading had higher rim oxidation.


CONCLUSIONS
The data support our hypothesis that, for the historical packaging methods employed by the manufacturer, polyethylene oxidation and oxidation potential were significantly higher at the rim as opposed to the dome. The mechanism is governed by access to oxygen in vivo and may be accelerated under certain combined modes of repeated rim loading. Our findings have clinical significance in cases of chronic impingement, when the rim has to support repeated loading for the lifetime of the implant.
Drexel University, Philadelphia, PA 19104, USA. skurtz@drexel.edu
Steven M
SM
Kurtz
Daniel
D
MacDonald
Allyson
A
Ianuzzi
Andre
A
van Ooij
Jorge
J
Isaza
Edward R
ER
Ross
John
J
Regan
D000328:Adult; D000368:Aged; D019643:Arthroplasty, Replacement / Q000295:instrumentation / Q000379:methods; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D020878:Device Removal; D017586:Diskectomy / Q000009:adverse effects* / Q000295:instrumentation*; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000601:surgery*; D007593:Joint Instability / Q000601:surgery; D007595:Joint Prosthesis / Q000009:adverse effects; D017116:Low Back Pain / Q000209:etiology / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000601:surgery; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D010084:Oxidation-Reduction; D020959:Polyethylene / Q000009:adverse effects* / Q000737:chemistry; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology; D019736:Prostheses and Implants / Q000009:adverse effects*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D019919:Prosthesis Implantation; D016059:Range of Motion, Articular; D012008:Recurrence; D013499:Surface Properties; D016474:Weight-Bearing
D001672:Biocompatible Materials; D020959:Polyethylene