Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2002-03-04
2004-03-30
Lewis, Ralph A. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S022390
Reexamination Certificate
active
06712857
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for use in surgical procedures involving arthroplasty. More specifically, it relates to a prosthetic socket portion of a joint replacement assembly, and a method for its insertion during arthroplasty. Particular reference is drawn to the apparatus in the form of an acetabular portion of a total hip replacement assembly.
BACKGROUND ART
The inclusion of the following description of the prior art is not an admission that the prior art is part of the common general knowledge in Australia.
It is well known to use prosthetic joint replacements in patients with various kinds of disorders affecting the joints, including degenerative disorders, such as severe osteoarthritis.
Over the years, a vast array of materials have been developed and utilised in the construction and manufacture of such prostheses. This is partly because the knowledge base regarding materials, and relevantly biocompatible materials, has been growing. It is also because, despite technological advances, there are a continuing number of complications associated with joint replacement prostheses with which surgeons and patients must grapple. As a result, surgeons and other inventors in the field have had, and are still challenged with, an ongoing quest to improve on the ease of insertion of the prostheses, to reduce the incidence of long and short term complications associated with using them, and to improve on the longevity of both the bio-prosthetic interface, and the prostheses themselves.
Since the present invention refers specifically to a socket portion of a joint replacement assembly, and particularly refers to an acetabular component of a total hip replacement assembly, it is the latter which the following discussion briefly addresses.
The hip joint is comprised of the head of the femur articulating with the acetabulum. The acetabulum is generally cotyloidal in shape, and is often referred to as a “cup”.
One of the first designs for the acetabular component of the hip joint, which was developed around 1960, was a hemisphere of metal internally lined with a plastics hemisphere, with the latter acting as the articulation surface. The metal was cemented into the bone and the liner was either pressed into the metal cup during the arthroplasty procedure, or was incorporated into the prosthesis during manufacture. In some later designs, the preferred method of securing the prosthesis was to screw it to the bone. However, while providing good fixation, screws have been found to lead to serious complications in the hip and are now not well regarded. Consequently, some of the more recent developments in acetabular prostheses have focused oil new designs for their bone contacting surfaces. For example, some acetabular prostheses have been manufactured with a self-cutting thread on their bone contacting surface, while others have relied on press fitting along with cement, or a combination of surface roughening and hydroxyapatite.
In addition to considerable variation in the designs of the outer, or bone contacting, surfaces of acetabular prostheses, however, much research has been done in order to provide improved means of engaging the head of the femur (or prosthesis thereof). Forte (U.S. Pat. No. 5,062,853), for example, describes a particular construction for the inner aspect of the acetabular prosthesis which is particularly well adapted to receive and engage a corresponding prosthetic head of a femur.
Nevertheless, while prosthetic hip joint replacements have been shown to be incredibly beneficial for patients who require them, there are still a number of problems associated with their insertion for which further developments in the method and apparatus would be advantageous. The present invention is, most specifically, aimed at improving the bone contacting surface of acetabular prostheses, and therefore addresses many of the problems raised above.
DESCRIPTION OF THE INVENTION
In a first aspect, the present invention consists in a device for use in surgical procedures involving arthroplasty, the device including a socket member having a first surface and a second bone engaging surface, the first surface including at least a bearing surface adapted to receive a counter-component of a joint, and the bone engaging surface including a first portion having a shape, and at least a second portion having a different shape to that of the first portion.
In a second aspect, the present invention consists in a method of inserting a device according to the first aspect during an arthroplasty procedure, the method including the steps of:
a) bringing a surface of an appropriate joint orientation determining means into apposition with the exposed surface of the socket portion of a joint;
b) manipulating the joint orientation determining means so that the correct angular orientation for a socket portion of a joint replacement assembly is determined;
c) forming a hole into the bone adjacent the joint orientation determining means with a hole forming means, using said joint orientation determining means as a guide;
d) removing the joint orientation determining means from apposition with said exposed surface:
e) using the hole formed in step (c) as a guide, reaming an appropriately shaped and sized portion of bone from the bone forming the socket portion of the joint to a desired depth, thereby creating a reamed surface of bone;
f) bringing the bone engaging surface of a device according to the first aspect of the invention into contact with the reamed surface of bone; and
g) securing the device to the bone.
The device according to this invention may be used in a range of arthroplasty procedures, but is of particular applicability when used as a replacement for the acetabular component of a hip joint. By virtue of the nature of its function, preferred embodiments disclose that the socket member, as a whole, has a cotyloidal configuration with a longitudinal axis. The first surface of the socket member includes a bearing surface having a radius of curvature which is adapted to receive the counter-component of a joint, such as the head of the femur (or prosthesis thereof) in a hip joint. The socket member is, according to this invention, defined by a bone engaging surface. In accordance with its name, the bone engaging surface is adapted to engage a bony surface comprising a portion of the joint which the device is intended to replace, such as the acetabulum in a hip joint.
Preferred embodiments of the invention disclose that the bone engaging surface of the socket member comprises at least a first and a second portion. In such embodiments, the first portion extends away from a circumferential join with the first surface of the socket member, and the second portion extends away from a circumferential join with the first portion to an extremity.
In further preferred embodiments, as the first portion extends away from its join with the first surface of the socket member, its cross-sectional diameter may decrease at a first rate. In such embodiments, the rate of change in cross-sectional diameter may be linear such that the first portion has a frusto-conical shape. In alternative embodiments, the rate of change may be logarithmic, exponential or may follow any other mathematical expression. In yet further alternative embodiments, the rate of change may itself change from one to another of these mathematical expressions as the first portion extends away from its join with the first surface.
Similarly, as the second portion extends away from its join with the first portion, its cross-sectional diameter may decrease at a second different rate to that of the cross-sectional diameter of the first portion. In preferred embodiments, the rate of change will comply with a mathematical expression which will cause the second portion to form a spherical section, and preferably, a hemi-section or a smaller section still. In alternative embodiments, the discussion of the mathematical expressions according to which the rate of change may comply from the paragraph ab
Australian Surgical Design and Manufacture Pty Limited
Jacobson & Holman PLLC
Lewis Ralph A.
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