Asymmetric motion distribution between components of a mobile-core lumbar disc prosthesis: an explanation of unequal wear distribution in explanted CHARITE polyethylene cores. Journal Article

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Authors: Patwardhan, A. G.; Havey, R. M.; Wharton, N. D.; Tsitsopoulos, P. P.; Newman, P.; Carandang, G; Voronov, L. I.
Article Title: Asymmetric motion distribution between components of a mobile-core lumbar disc prosthesis: an explanation of unequal wear distribution in explanted CHARITE polyethylene cores.
Abstract: BACKGROUND: The biconvex mobile core of the CHARITE lumbar disc prosthesis forms two joints (spherical bearings) with the metal end plates. We quantified the intra-prosthesis motion to test the hypothesis that the total prosthesis motion would not be equally distributed between the two bearings of implanted CHARITE discs, which might explain the unequal wear distribution reported in explanted cores. METHODS: The hypothesis was tested by studying the flexion-extension motion responses of (1) twenty-six monosegmental CHARITE III discs implanted in nineteen human cadaveric lumbar spines, and (2) twenty-one CHARITE III discs (fifteen monosegmental, six bisegmental) implanted in eighteen patients in other published clinical studies. Intra-prosthesis motions were quantified with use of a radiographic image analysis technique. RESULTS: Eighty-eight percent of the CHARITE discs implanted in cadaveric specimens exhibited larger motion at the superior bearing, with 54% demonstrating more than twice as much motion at the superior bearing as at the inferior bearing. The ratio of motion at the superior bearing to motion at the inferior bearing averaged 2.68 +/- 1.84, which was significantly larger than 1.0 (p 0.001). Ninety percent of prostheses implanted in patients showed larger motion at the superior bearing. The motion ratio averaged 2.39 +/- 2.47 for monosegmental cases and 2.55 +/- 2.66 for all cases; both ratios were significantly larger than 1.0 (p 0.05). CONCLUSIONS: We found preferentially larger motion at the superior bearing of the CHARITE discs implanted in human cadaveric lumbar spines and in patients, regardless of the implanted level.
Journal Title: Journal of Bone Joint Surgery - American Volume
Volume: 94
Issue: 9
ISSN: 1535-1386
Publisher: Unknown  
Journal Place: United States
Date Published: 2012
Start Page: 846
End Page: 854
Language: English
DOI/URL:

http://ovidsp.ovid.com/ovidweb.cgi?T=JS=Y=N=fulltext=medl=22552675

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Notes: ID: 12445; Record Owner: From MEDLINE, a database of the U.S. National Library of Medicine.; Status: MEDLINE; Publishing Model: Journal available in: Print Citation processed from: Internet; NLM Journal Code: hjr, 0014030; CAS Registry/EC Number/Name of Substance: 9002-88-4 (Polyethylene).; Entry Date: 20120719