Shepherd-New-Designs-Spec-Issue-2009

Shepherd-New-Designs-Spec-Issue-2009 - SPECIAL ISSUE PAPER...

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Investigating the potential advantages of a new design metacarpophalangeal joint M Yeoman 1 , A Johnstone 2,3 * , S V Karuppiah 2,3 , J Targell 4 , and D E Shepherd 5 1 Continuum Blue Ltd, East Sussex, UK 2 Department of Orthopaedic Surgery, Aberdeen Royal Infirmary, Aberdeen, UK 3 School of Engineering, The Robert Gordon University, Schoolhill, Aberdeen, UK 4 The Medical Device Company Ltd, Ayrshire, UK 5 School of Mechanical Engineering, University of Birmingham, UK The manuscript was received on 1 January 2009 and was accepted after revision for publication on 29 June 2009. DOI: 10.1243/09544119JEIM569 Abstract: This paper investigates a new metacarpophalangeal joint design aimed at treating patients with moderate to severe forms of arthritis affecting the index, long, ring, and little fingers. Current small joint arthroplasty designs, including those for the metacarpophalangeal joint of the hand, have had limited success owing to mechanical failures and can be divided into two main families: single-piece elastomer implants and surface articulating implants. The design proposed in this study involves combining the principles of a surface weight-bearing articulating implant with those of a spanning elastomeric implant. The design consists of metacarpal and proximal phalangeal articulating housings and a central flexible spanning elastomer rod that maintains the alignment of the metacarpal and proximal phalangeal components. A preliminary finite element analysis was used to investigate the stresses in the design, the wear of the articulating bearing surfaces for different material combinations, and the stresses between the central elastomer rod and the articulating housings. This preliminary analysis shows that the design should withstand the probable loading conditions experienced within the human body and that the wear rates of the articulating surfaces and the central elastomer are acceptable. Keywords: arthroplasty, design, finger, finite element analysis, stress, small joint, wear 1 INTRODUCTION Finger joint replacements (finger joint arthroplas- ties) are most commonly used to treat advanced arthritis affecting the metacarpophalangeal (MCP) joints of the hand. Despite their limited durability, finger joint replacements are good at relieving pain and restoring some elements of hand function, especially in patients who have severely deformed and cripplingly painful hands [ 1 , 2 ]. For some patients, successful fingers joint replacements help them to continue self-care and can make all the difference between independence and being institu- tionalized. Essentially, finger joint replacements can be placed in two main families: single-piece elasto- mer implants and surface articulating implants. Of these, the single-piece elastomer implants such as the Swanson implant (Wright Medical Technology, Arlington, Tennessee, USA) and modifications of this design such as the Neuflex implant (DePuy International Ltd, Leeds, UK) remain the most popu- lar [
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Shepherd-New-Designs-Spec-Issue-2009 - SPECIAL ISSUE PAPER...

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