Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-09-29
2002-12-31
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023230
Reexamination Certificate
active
06500209
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a centralizer for a prosthetic component, and more particularly to an intramedullary centralizer having fins of varying length and associated method of implanting an orthopaedic component into a patient.
BACKGROUND OF THE INVENTION
During the lifetime of a patient, it may be necessary to perform a hip replacement procedure on the patient as a result of, for example, disease or trauma. The hip replacement procedure may involve the use of a femoral component which has a head portion that is utilized to replace the natural head portion of the thigh bone or femur. The femoral component typically has an elongated intramedullary stem which is utilized to secure the femoral component to the patient's femur. In particular, the medullary canal of the patient's femur is first surgically prepared (e.g. reamed and/or broached) such that the intramedullary stem of the femoral component may be subsequently implanted therein. Bone cement may then be utilized to secure the femoral component within the medullary canal.
When bone cement is utilized to secure the femoral component within the medullary canal in such a manner, it is desirable to form a relatively even or uniform mantle around the intramedullary stem of the component. Hence, during such implantation of the femoral component into the femur, a mechanical guide or “centralizer” is typically utilized to position the intramedullary stem of the femoral component in a neutral or “centered” position within the medullary canal of the femur. By centering the intramedullary stem within the medullary canal of the femur, the centralizer may advantageously provide for the formation of a relatively uniform bone cement mantle between the intramedullary stem and the surgically prepared interior walls of the medullary canal of the femur.
Centralizers are typically secured to the intramedullary stem of the femoral component prior to implantation thereof. Centralizers have heretofore been classified based on the location along the intramedullary stem at which the centralizer is secured. For example, distal centralizers are secured to the distal end of the stem, whereas mid-shaft centralizers are typically secured to the intramedullary stem at a location between the distal end and the proximal end of the stem. Each type of heretofore designed centralizers have a number of unique drawbacks associated therewith.
For example, a thin mantle may be formed at mid-shaft regions as a result of use of certain heretofore designed distal stabilizers. In particular, even when the distal stabilizer properly centralizes the intramedullary stem at the distal end thereof, an incomplete or slightly thinner bone cement mantle may be formed around the anterior side of the mid-shaft portion of the intramedullary stem. It should be appreciated that an incomplete or thin bone cement mantle may lead to crack propagation in the bone cement or even loosening of the implanted femoral component.
As a result of these and other concerns, a number of mid-shaft centralizers were designed. While heretofore designed mid-shaft stabilizers have been relatively successful at centering the mid-shaft portion of the intramedullary stem (thereby providing a more uniform bone cement mantle around the mid-shaft portion), a number of other problems have been associated with their use. For example, heretofore designed mid-shaft centralizers may have a tendency to tip the stem in the anterior or posterior direction thereby creating a relatively thin (or even incomplete) bone cement mantle at the distal end of the stem.
Another drawback associated with heretofore designed centralizers is the configuration of the interior surfaces of the centralizers. In particular, centralizers which have heretofore been designed often have a smooth interior surface which forms substantially continuous (i.e. line-toline) contact with the outer surface of the stem when the centralizer is secured to the stem. Such centralizers, often referred to as “napkin ring” centralizers, restrict the bone cement from coming into direct contact with the outer surface of the intramedullary stem thereby potentially creating a void or non-bonded region in the cement. The formation of such a void increases the potential of crack propagation.
What is needed therefore is a centralizer which overcomes one or more of the above-mentioned drawbacks. What is particularly needed is a centralizer which centers the intramedullary stem of a femoral component while also facilitating the formation of a relatively uniform bone cement mantle along the entire length of the stem.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, there is provided a centralizer for an intramedullary stem of an orthopaedic component that is adapted to be implanted into a medullary canal of a bone. The centralizer includes an annular body having an interior surface and an exterior surface. The centralizer also includes a first exterior fin secured to the exterior surface of the annular body so as to extend outwardly therefrom. The first exterior fin possesses a first length. The centralizer also includes a second exterior fin secured to the exterior surface of the annular body so as to extend outwardly therefrom. The second exterior fin possesses a second length which is greater than the first length.
In accordance with another embodiment of the present invention, there is provided a centralizer for an intramedullary stem of a femoral component that is adapted to be implanted into a medullary canal of a femur. The intramedullary stem of the femoral component has a lateral surface, a medial surface, an anterior surface, and a posterior surface. The centralizer includes an annular body having an interior surface and an exterior surface. The interior surface is adapted to receive the intramedullary stem of the femoral component. The centralizer also includes an anterior fin secured to the exterior surface of the annular body so as to extend outwardly from the exterior surface in an anterior direction away from the anterior surface of the intramedullary stem when the centralizer is secured to the femoral component. The anterior fin possesses a first length. The centralizer also includes a lateral fin secured to the exterior surface of the annular body so as to extend outwardly from the exterior surface in a lateral direction away from the lateral surface of the intramedullary stem when the centralizer is secured to the femoral component. The lateral fin possesses a second length. The centralizer further includes a posterior fin secured to the exterior surface of the annular body so as to extend outwardly from the exterior surface in a posterior direction away from the posterior surface of the intramedullary stem when the centralizer is secured to the femoral component. The posterior fin possesses the first length. The centralizer yet further includes a medial fin secured to the exterior surface of the annular body so as to extend outwardly from the exterior surface in a medial direction away from the medial surface of the intramedullary stem when the centralizer is secured to the femoral component. The medial fin possesses the second length. The second length is greater than the first length.
In accordance with a further embodiment of the present invention, there is provided a method of implanting an orthopaedic component into a patient. The method includes the step of securing a centralizer to an intramedullary stem of the orthopaedic component. The centralizer includes an annular body having an interior surface and an exterior surface. The centralizer also includes a first exterior fin secured to the exterior surface of the annular body so as to extend outwardly therefrom. The first exterior fin possesses a first length. The centralizer also includes a second exterior fin secured to the exterior surface of the annular body so as to extend outwardly therefrom. The second exterior fin possessing a second length which is greater than the first length. Th
Barrett Thomas
DePuy Orthopaedics, Inc.
Maginot Moore & Bowman
McDermott Corrine
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