Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1997-04-14
1999-05-25
Yu, Mickey
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
059066431
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a total knee replacement prosthesis. Total knee replacement prostheses involve the surgical removal of the entire natural knee-bearing surfaces and their replacement with artificial femoral and tibial components. The femoral component includes condylar bearing surfaces which, to some extend, mimic the shape of the natural condyles.
2. Discussion of Related Art
The present invention relates to total knee replacement (TKR) prostheses of the three component type in which a floating meniscal component is interposed between the femoral and tibial components. The use of a meniscal component extends the range of movements that can be accommodated, including providing for a greater range of laxity of both sliding and rotational movement.
There are, however, several problems in designing a fully satisfactory TKR. One of these is to provide a high degree of flexion since, otherwise, the pre-operative range of flexion is not achieved and mobility is reduced. A high degree of flexion can be achieved by providing for roll back at maximum flexion. However, this is often achieved by providing for roll back at maximum flexion. However, this is often achieved at the risk of reduced stability. It is also important to achieve stability in extension, e.g. when the patient is standing. These requirements are difficult to achieve in a three component TKR.
SUMMARY
According to one aspect of the present invention there is provided a prosthesis for total knee replacement which comprises: located between the condylar-bearing surfaces, and and the tibial platform for sliding movement in the anterior-posterior direction, said femoral component having an intercondylar projecting surface adapted to contact the upstanding abutment at high degrees of flexion so as to influence the sliding movement of the meniscal component in a posterior direction.
In one embodiment, the abutment may be a post extending upwardly through an aperture in the meniscal component and having a surface adapted to engage the intercondylar projecting surface at some point in its flexion.
The upstanding post or abutment may also serve to guide the plastic meniscal component in the A-P direction.
In one embodiment, the post may extend through an aperture or space between the condylar surfaces and engage the intercondylar projection only at high degrees of flexion, e.g. at degrees of flexion of at least 60 or 70.degree.. The post or abutment may also engage with surfaces on the femoral component in extension so as to increase stability in extension but not engage with surfaces on the femoral component or intercondylar projection at degrees of flexion between extension and high degrees of flexion.
In another embodiment, the femoral component may have a substantially continuous surface constituting the intercondylar surface, e.g. in the form of a housing. Such a continuous surface may be in the form of a recess dividing the condylar bearing surfaces and the upstanding post may be accommodated in such recess. Again, however, the post and the intercondylar surface are preferably shaped and juxtaposed so that the post contacts the intercondylar surface only at high degrees of flexion and optionally also in extension. The reason for this is to avoid a situation where the joint is in danger of `locking up` because of continuous contact between several surfaces. The Applicant has determined that additional stability is required essentially only where the joint is at high flexion, particularly where the prosthesis incorporates a highly conforming, congruent condylar component and meniscal component.
The intercondylar projection or surface may extend between the condyles and have a surface which, together with the surface of the post, has a camming action influencing the posterior movement of the meniscal component in high degrees of flexion.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 s
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Snow Bruce E.
Yu Mickey
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