Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1999-07-19
2000-12-26
Philogene, Pedro
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
061652210
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an implant for placing on a plateau or resection surface of a joint bone.
BACKGROUND OF THE INVENTION
An implant of the aforementioned type is described in the DE 42 30 118 C2. This implant can replace at least a portion of the condyle surface of a femur bone. For this purpose, it comprises a femur cap which is mounted on the bone by means of a pin. The femur cup is seated on a prepared plateau surface of the bone.
In order to guarantee a secure hold of the implant on the bone, it must be ensured that the bone cement used for fixing the implant produces an as large as possible joining surface and enters into all cavities. To ensure this whilst only lightly pressing on the implant and to prevent bone cement or a flowing bone material from laterally oozing out over the cup, the latter is at its edge provided with a continuous circularly peripheral, archlike concave shape.
Other similar implants are described in EP 0 709 075 A1, EP 0 611 559 A1 and WO 95/24874.
However, all of the aforementioned implants do not solve the following problem. When a joint is stretched, the loaded joint seating surface between the implant and the associated joint base should be as large as possible, thus ensuring small surface pressure and good stability. Small surface pressure prevents, amongst other things, rapid wear of the artificial joint section.
A large seating surface is obtained in that a large curvature radius of the joint surface, or a small curvature, is selected in this area.
However, the desired large surface seating with a stretched joint offers the following disadvantage. If the implant is inserted transversely in such a manner that its longitudinal alignment does not coincide with the pivotal plane of the joint, then edge pressure may develop when bending the joint. This edge pressure makes excessive demands on both the joint base and the implant itself and causes rapid wear.
SUMMARY OF THE INVENTION
It is an object of the invention to further develop an implant of the aforementioned type in that surface pressure on the joint seating surface of the implant is kept low when the joint is stretched, whilst preventing edge pressure or incorrect loading of a joint during bending even with not exactly aligned implantation.
An aspect of the invention includes an implant for placing on a plateau or resection surface of a joint bone. The implant includes at least one skidshaped cup having a joint seating surface, a ventral and a dorsal end. The joint seating surface extends in a longitudinal direction and has first and second curvature radii. The first curvature radius is transverse to the longitudinal direction and, at least in a coronal area, larger than the second curvature radius transverse to the longitudinal direction and in an area, which is loaded when the joint is fully bent. The first curvature radius continuously merges into the second curvature radius within a transitional area which extends over an angular range between about 30.degree. and about 70.degree..
Accordingly, the skidshaped cup comprises a joint seating surface the curvature radius of which transversely to its longitudinal extent is at least in the coronal area larger than its curvature radius transversely to its longitudinal extent in an area which is loaded when the joint is bent, and in a transitional area thereinbetween the larger curvature radius continuously merges into the smaller curvature radius.
A large seating surface of the implant in the joint base with the joint being stretched is ensured by the large curvature radius of the joint seating surface in the coronal area. Excessive wear is prevented and good stability of the joint is guaranteed.
If the joint is bent, then the curvature radius of the joint seating surface changes continuously at a point seated in the joint base, i.e. the large curvature radius merges into the smaller curvature radius. This allows prevention of edge pressure when bending the joint, even if an implant is not exactly inserted. Furthermore, freedom of move
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Philogene Pedro
Plus Endoprothetik AG
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