Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1996-02-28
2000-02-01
Willse, David H.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
060197943
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a total knee replacement prosthesis (hereinafter called TKR) and, in particular, to a TKR which is constructed in a modular system so that additional components can be added to deal with particular problems of the natural knee.
TKR is called for in cases where the natural knee exhibits severe instability, where failure of a previously inserted TKR has resulted in further loss of bone, or where a large amount of bone is to be removed and replaced, perhaps because of cancer.
According to one aspect of the present invention there is provided a total knee replacement prosthesis (TKR) which comprises a femoral component which is pivotably connected to a tibial component at a hinge for pivoting movement, about a lateral-medial axis, at least one of the components being received within a bearing component adapted to be inserted in an intramedullary canal, so that the component is rotatable within the bearing component to provide a degree of rotational freedom of movement for the prosthesis, the femoral component comprising a stem portion fixedly attached by attachment means to said hinge, said attachment means being standardised so that a stem of desired size can be selected for a particular patient.
In general, the tibial and femoral components are constructed from a metal which is biomedically inert, e.g. a stainless steel, cobalt-chromium-molybdenum alloy or titanium alloy. The bearing components should preferably exhibit low friction with respect to the component which rotates within them and typically materials which meet this requirement are polyolefines or nylons. Particularly preferred materials for this purpose are ultra-high molecular weight polyethylenes. Preferably, the rotational movement takes place by rotation of a tibial stem within a tubular or hollow bearing component which is fixed relatively to the tibia. Thus, for example, the tibial component may comprise a spigot which is secured at one end to a part of the hinge and at the other is received by a bearing component. The bearing component may have an internal canal dimensioned to receive the tibial spigot and an external surface suitably sized to fit the bone canal. Lugs may be formed on the outer surface of the tibial bearing component in order to prevent rotation of the plastic bearing component in the bone canal.
In a preferred construction, the tibial and femoral components are pivotably connected by a pintle hinge. Such a hinge has a pin which passes through aligned bores in the two components. Conveniently, the femoral component includes a body portion which has a bore to receive the hinge pin and the tibial component includes a pair of ears or lugs which extend on each side of the body portion of the femoral component. The pin is preferably removably fixed by suitable locking means, such as circlips in apertures in the ears, and includes plastics bushes to facilitate pivoting of the hinge pin in the bore of the body portion and to avoid metal to metal contact. Thus, the femoral and tibial components can be installed in their relevant intramedullary canals and the joint made by introducing the pin and the locking means.
In order to provide further control over the movement of the joint, a plastic bearing plate or bumper component may be introduced in the area of the hinge between the tibial component and the femoral component to provide a stop at the limits of extension of the joint. This plate or bumper is preferably formed with a concave upper surface so as to provide an additional bearing surface to the hinge joint, i.e. additional to the plastics bushes. The plastic bumper may be a snap fit into a recess in the upper part of the tibial plate so as to be replaceable if worn or for adjustment of the hinging movement of the prosthesis.
In cases where it is desired to provide a tibial component which is longer or shorter than a standard size or a stem of special profile or thickness is required, the plastic bearing component is made shorter and can be fitted within a metal shell component. The metal shell compo
REFERENCES:
patent: 4136403 (1979-01-01), Walther et al.
patent: 4136405 (1979-01-01), Pastrick et al.
patent: 4262368 (1981-04-01), Lacey
patent: 4301553 (1981-11-01), Noiles
patent: 4822366 (1989-04-01), Boleksy
patent: 5370701 (1994-12-01), Finn
University College London
Willse David H.
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