Centralizer

Details Centralizer Centralizer

1999-10-07

2001-06-12

Philogene, Pedro (Department: 3732)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

C623S023480, C623S023190

Reexamination Certificate

active

06245113

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a centraliser for a prosthetic implant, in particular a prosthetic femoral stem for implantation in a patient's femur for hip replacement surgery.
Centralisers or spacers are provided for fitting to the distal end of a femoral hip replacement stem in order to keep the implant stem away from the internal surface of the cavity of the bone in which the stem is to be inserted. In the case of stems which are cemented in the bone cavity, there is a space between the stem and the internal surface of the cavity of the bone in which bone cement is placed. Controlling the position of the stem within the surrounding bone cement mantle is vital to the long-term survivability of the replacement joint. Cement can be deposited in the bone cavity and the stem with the attached centraliser is then inserted. It is important to try to obtain an even and intact cement mantle around the stem.
Known centralisers are in the form of caps which fit over the distal end of the stem and centralisers which are fixed inside the drilled end of a stem. Centralisers are also known, for example as described in U.S. Pat. No. 4,658,351, which are of ring form which can have a tapered inner surface corresponding to the tapered surface of the distal end of the femoral stem on which the centraliser is located.
U.S. Pat. No. 3,793,650 describes a centraliser or spacer which has spring members which extend from the stem for contact with the wall of the bone cavity.
European patent No. EP0427444B describes a centraliser or spacer in the form of a cap for insertion on the end of a hip stem with fins or wings extending outwardly from the cap which are adapted to fold circumferentially and inwardly towards the body portion of the cap.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, there is provided a centraliser for use on a prosthetic component to be inserted in a bone cavity, the centraliser comprising a hollow body with a plurality of spacer means projecting from the body, wherein the spacer means are in the form of arms extending outwardly from the hollow body and having a variable cross-section along the length of the arms.
The hollow body may have one open end and be in the form of a cap. Alternatively, the hollow body may have two open ends and be in the form of an elongated ring. The hollow body may be in the form of a truncated cylinder.
Preferably, each arm has a first end attached to the hollow body. A second end of each arm may also be attached to the hollow body.
Preferably, the arms have a cross-section which varies from a circle becoming increasingly ovoid along the length of the arms.
Preferably, the plurality of arms are equally spaced circumferentially around the hollow body. There may be three equally spaced arms.
Preferably, the arms are attached to the hollow body such that they extend parallel to the central axis running through the hollow body.


REFERENCES:
patent: 4064567 (1977-12-01), Burstein et al.
patent: 5080680 (1992-01-01), Mikhail et al.
patent: 5163963 (1992-11-01), Hewka et al.
patent: 5197990 (1993-03-01), Lawes et al.
patent: 5425768 (1995-06-01), Carpenter et al.
patent: 5443523 (1995-08-01), Mikhail
patent: 5658351 (1997-08-01), Dudasik et al.
patent: 5755793 (1998-05-01), Smith et al.
patent: 5997581 (1999-12-01), Khalili

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