Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1990-11-19
1991-08-06
Frinks, Ronald
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, A61F 238, A61F 230
Patent
active
050374397
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a knee-joint prosthesis for unicompartmental joint surface replacement by permanent anchoring of the prosthesis in the bone tissue of a knee-joint in the human body, on the one hand consisting of a femur part, which comprises an articulation element with a convex joint surface, an elongate intermediate element with a first side, intended to bear against a surface of the bone tissue, and a second, opposite side intended to bear against an inner surface of the articulation element, in which respect the intermediate element is designed to be anchored in the bone tissue by means of at least one anchoring element intended to be introduced into a recessed channel in the bone tissue and to be connected to this, and in which respect the articulation element for the femur is designed to be locked on the intermediate element by means of a positive lock, and, on the other hand, a tibia part with a concave joint surface for cooperation with the convex joint surface of the femur part, and at least one anchoring element intended to be introduced into a recessed channel in the bone tissue for anchoring the tibia part in the tibia.
On the market and in clinical use there are at present a large number of knee-joint prostheses intended for permanent anchoring in the bone tissue. These prostheses are intended as replacement material in cases of morbid defects which have developed as a result of joint-destructive disorders, either degenerative disorders or rheumatism. The joint replacement material, which can replace parts of or all of the knee-joint, generally consists of a metal and polyethylene component, but there are also other material combinations such as, for example, a ceramic articulating with polyethylene. The metal component in artificial joints consists almost exclusively of one of three alloy types, so-called super alloys. These three alloys are stainless steel, which is now generally nitrogen-based with a high chromium content, cobalt chromium alloys or the titanium alloy Ti 6Al 4V. All these alloys contain metals which are potentially toxic. For example, aluminium has been shown to be neurotoxic. Chromium, which is included in steel and cobalt-based alloys, is considered to be carcinogenic. Nickel, which is also included in the same two alloys, is a powerful allergen In spite of the potential risks and despite the fact that certain of these alloys have been used for as long a period as 30 years or more, there have been surprisingly few reports which have given convincing evidence of material complications. However, in this context it should be added that it is only in the last 20 years that joint replacements of the said material have been available on a large scale.
In general it may be said that the knee-joint replacements available on the market today give reasonable results over a ten-year period, but the experiences with this type of material are largely limited to older patients with relatively low levels of activity. Complications have been reported to a fairly large extent. It is scarcely by chance that there is an abundance of different knee-prosthesis designs of different materials and with different biomechanical solutions. As regards previously known knee-joint replacements, none can be said to represent a definitive solution with respect to anchoring in the bone tissue, wear-resistance, joint stabilization or material strength. The central problem would appear to be the anchoring stability of the prosthesis components.
It is nowadays agreed that an as exact as possible contact fitting should be created between prosthesis component and bone tissue, regardless of whether the contact is established via a filling material or not. Filling material in the form of polymethyl methacrylate (PMMA) permits a more or less exact initial contact fitting between foreign material and bone tissue in the wider sense. Bone cement (PMMA) in the low-viscous form can, under pressure, be made to penetrate into the bone tissue and create a positive lock on the microplane.
REFERENCES:
patent: 4309778 (1982-01-01), Buechel et al.
patent: 4673407 (1987-06-01), Martin
patent: 4673408 (1987-06-01), Grobbelaar
patent: 4838891 (1989-06-01), Branemark et al.
Albrektsson Bjorn
Wennberg Stig
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