[Metacarpophalangeal prosthesis modeling. Comparison of stress factors in a normal and a prosthetic metacarpophalangeal joint using finite element analysis].
BACKGROUND
Prosthetic replacement of the metacarpophalangeal joints of long fingers is a problematical technique for the surgeon. The aim of the present study was to examine and compare, by means of finite element analysis, stress distribution in a normal metacarpophalangeal joint and to compare this with the findings in a similar joint with a prosthesis in order to better determine the risk of aseptic loosening, and also to examine possible solutions to limit these risks.


METHODS
Finite element modelling was carried out using Abaqus software. Various criteria were taken into account including anatomical data, stress distribution, mechanical characteristics of the materials used, and different positions of the phalanx.


RESULTS
A comparison of the results showed two significant stress distribution factors, i.e., a reduction of normal stress in the cortical bone of the finger fitted with a prosthesis; and the appearance of a flexion moment which completely modified the stress distribution throughout the metacarpal and therefore also in the opposite phalanx.


CONCLUSIONS
To reduce the risk of aseptic loosening, two solutions were proposed: a) to reduce Young's module. The problem which arises, as in the case of total hip prosthesis, is that of finding a material with a Young's module which is closer to that of cortical bone, and which at the same time has a high elastic limit and breakage point and good biocompatibility; b) to reduce the inertia of the prosthesis, which seems the more likely of the two propositions, as it is based on the results of the modelling. The inertia of the prosthesis on stress distribution can be reduced by modifying two parameters, namely by producing a hollow section and shortening the structure of the prosthesis.
Gayet
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Service d'orthopédie-traumatologie du Pr Clarac, hôpital Jean Bernard, Poitiers, France.
Texereau
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Dumas
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D004548:Elasticity; D019544:Equipment Failure Analysis; D020342:Finite Element Analysis; D006801:Humans; D007595:Joint Prosthesis / Q000009:adverse effects / Q000592:standards* / Q000600:supply & distribution; D008422:Materials Testing; D008662:Metacarpophalangeal Joint / Q000503:physiopathology* / Q000601:surgery*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular; D012307:Risk Factors; D013314:Stress, Mechanical