Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Ligament or tendon
Patent
1992-11-17
1994-10-18
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Ligament or tendon
623 18, A61F 208
Patent
active
053564340
DESCRIPTION:
BRIEF SUMMARY
This invention concerns artificial ligaments and more particularly, but not exclusively, such ligaments for replacement of the cruciate ligaments of the knee.
Significant interest arose in the use of such ligaments about a decade ago, but the results have proved unreliable and many surgeons now prefer instead to use autologous grafts, mainly from muscle tendons, for ligament replacement.
The effective failure of artificial ligaments used to date may be explained by a new analysis which indicates that a satisfactory model for a cruciate ligament represented by a bundle of fibres co-extending between the femur and tibia should exhibit changes in shape and strain distribution in association with the relative rotation and translation which occur between those bones during flexion-extension movement or the knee. More particularly, this analysis shows that the changes in shape and strain distribution depend, during passive movement and under load, on the relationship between the respective distributions of ligament fibre attachments on the two bones interconnected by the ligament, i.e. on what can be termed the fibre mapping.
Further details of this analysis are given in a series of papers by O'Connor et al in Chapters 10, 11 and 12 of Knee Ligaments: Structure, Function, Injury and Repair p. 163-218 Raven Press, New York 1990, and also in Chapter 25, entitled "Kinematics and Mechanics of the Cruciate Ligaments of the Knee" by 0'Connor J. J. and Zavatsky A. in The Biomechanics of Diathrodial Joints, Vol. 2, Pages 197-252, edited by V. C. Mow, A. R. Cliffe and F. L-Y Woo, Springer Veragg, New York, 1990, the contents of which are hereby incorporated by reference. The analysis described therein was presented at the First World Congress on Biomechanics San Diego, Calif., 1990.
In any event prior artificial ligaments do not conform with this analysis. They have, tot example, commonly involved an overall woven or otherwise transversely interconnected structure and this can be seen to represent a contradiction to the generation of changes as indicated above in that there will necessarily be a counterproductive interaction between longitudinal elements of the structure which should otherwise tend to move or tense in an effectively independent and differential manner.
An object of the present invention is to improve this situation and to this end, in a general aspect, the invention provides an artificial ligament having a structure which can function n general conformity with the above analysis and so more closely simulate a natural ligament.
In a more particular aspect the invention provides an artificial ligament comprising a bundle of coextensive elongate elements that are held at their opposite ends in a mutual one-to-one relationship by respective attachment means suitable for securement in bone, with the relative disposition of the individual elements at one end of the bundle corresponding generally with that at the other end, each element otherwise extending between the points of connection to said attachment means substantially freely of other elements of the bundle.
Conveniently, each attachment means comprises a grill and a tube, the grill allowing the elements to be threaded individually through respective perforations thereof prior to being secured in the tube.
Also, it is preferable that such attachment means have cross-sectional forms which approximate the natural attachment areas of the relevant ligament. Thus, for the anterior cruciate ligament, the means are appropriately elliptic and semi-circular to approximate the attachment areas on he tibia and femur respectively.
It may also be appropriate to provide the main lengths of the elements in the bundle with a sheath, wrapping or some other additional feature, such as a distinctively coloured element, to indicate the relative rotational dispositions of the bundle ends when deployed during surgery. This will facilitate avoidance of deployment with an undesirable or additional twist relative to the natural situation which is to be simulated, and the sheath
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Goodfellow John W.
O'Connor John J.
British Technology Group Limited
Isabella David
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