Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1998-07-06
2000-10-24
Isabella, David J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 232
Patent
active
061360333
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an artificial cotyloid socket having a domal outer shell and a domal inner shell subtending between them a cavity and, more particularly, to such an artificial cotyloid socket wherein the inner and outer shells are non-detachably secured to each other at their rims.
2. Description of Related Art
Spherical cotyloid sockets having inner and outer shells that are non-detachably secured to each other at their rims are especially well suited for cement-free implantation into the acetabulum.
The state of the art is represented by European patent document A 444,382. This publication discloses such a cotyloid socket in the form of a "monobloc" structure. Unfortunately, this design has the drawback that its outer shell is of constant wall thickness and is in a sandwich form. These features restrict elasticity. Suspension between the outer and inner shells must be controlled by an additionally installed spring system and, consequently, is not self-supporting.
SUMMARY OF THE INVENTION
An object of the invention is to remove or minimize the aforementioned drawbacks in the state of the art. The artificial cotyloid socket according to the present invention is increasingly elastic in a direction toward the (geographic) pole while nevertheless being simple and economical to manufacture.
In accordance with the present invention, the artificial cotyloid socket has a domal outer shell and a domal inner shell subtending between them a cavity. The inner and outer shells are joined to one another at their rims. The outer shell merges into a reinforced rim underneath a circle of merging, which is the intersection of the outer shell domal wall and the outer shell rim. The outer shell continuously increases in thickness as one moves from a pole of the outer shell toward the circle of merging.
The arrangement of the present invention offers the advantage of adequate mechanical stability in the direction of the resulting axis of stress while optimal elasticity and adaptability are provided in the region of the artificial cotyloid socket's pole. Accordingly, with the present invention, improved elasticity and adaptability are provided in the region where the implant attains its lowest point in the milled-out acetabulum.
The outer shell's wall thickness is less at its pole than at its latitude of 20 to 40 degrees (preferably 25 to 35 degrees), that is the approximate site where the elastic range of the invention begins and appropriately is less than 0.30 mm, preferably less than 0.25 mm at the pole. The wall thickness at 30 degree latitude is appropriately about 0.5 mm. Preferably, the outer shell's wall thickness is 30 to 60% of its wall thickness at its latitude of 30 degrees.
The rim of the outer shell is fitted with a specific shape and outside surface for anchoring in the bone. The conical rim shape allows primary clamping, technically called a "press fit", to prevent tipping. Non-rotatability is secured by axial rim grooves. The rim surface is salient in three dimensions. Such a structure is from 0.3 to 0.8 mm, preferably, 0.4 to 0.6 mm, to facilitate bone growth onto or into the prosthesis.
The outer shell may be made of pure titanium or a titanium alloy. The inner shell advantageously is made of one of the following materials: a cobalt-chromium-molybdenum alloy, a ceramic, polyethylene or carbon-fiber reinforced carbons.
In manufacture, a complete assortment with several cotyloid sockets of different sizes can be produced, identical inner shells being used for all cotyloid sockets and the different sizes being achieved by means of outer shells of different sizes.
Essentially the advantages of the invention may be considered being that the cotyloid socket of the invention allows: the acetabulum, hence
BRIEF DESCRIPTION OF THE DRAWINGS
These and further features of the present invention will be apparent with reference to the following description and drawings, wherein:
FIG. 1 is an enlarged cross-section through the axis of ro
REFERENCES:
patent: 3584318 (1971-06-01), Scales et al.
patent: 3863273 (1975-02-01), Averill
patent: 5458649 (1995-10-01), Spotorno et al.
patent: 5549697 (1996-08-01), Caldarise
patent: 5645601 (1997-07-01), Pope et al.
Isabella David J.
Stratec Medical AG
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