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Asymmetric Motion Distribution Between Components of a Mobile-Core Lumbar Disc ProsthesisAn Explanation of Unequal Wear Distribution in Explanted CHARITÉ Polyethylene Cores
Avinash G. Patwardhan, PhD1; Robert M. Havey, BS1; Nicholas D. Wharton, MS2; Parmenion P. Tsitsopoulos, MD, PhD1; Patrick Newman, MS2; Gerard Carandang, MS3; Leonard I. Voronov, MD, PhD1
1 Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153. Email address for A.G. Patwardhan: apatwar@lumc.edu
2 Medical Metrics, Inc., 2121 Sage Road, Houston, TX 77056
3 Edward Hines Jr. VA Hospital, 5000 South Fifth Avenue, Hines, IL 60141
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  • Disclosure statement for author(s): PDF

Investigation performed at the Musculoskeletal Biomechanics Laboratory, Edward Hines Jr. VA Hospital, Hines, Illinois



Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, one or more of the authors has had another relationship, or has engaged in another activity, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 May 02;94(9):846-854. doi: 10.2106/JBJS.J.00638
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Abstract

Background: 

The biconvex mobile core of the CHARITÉ 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 CHARITÉ 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 CHARITÉ III discs implanted in nineteen human cadaveric lumbar spines, and (2) twenty-one CHARITÉ 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 CHARITÉ 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 CHARITÉ discs implanted in human cadaveric lumbar spines and in patients, regardless of the implanted level.

Clinical Relevance: 

The findings regarding unequal motion distribution between the dual bearings of mobile-core disc prostheses are relevant to improving in vitro wear testing protocols to better replicate in vivo wear-producing conditions.

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    References

    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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