Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-03-01
2001-07-24
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S091000, C606S092000
Reexamination Certificate
active
06264698
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and instrumentation for implanting an acetabular cup which is to be held in place by polymethyl-methacrylate (PMMA) bone cement.
2. Description of the Prior Art
It is known, for example, to provide a flexible flange around the rim of an acetabular cup to pressurize the cement, but this only occurs as the cup approaches its final position in the acetabulum. The flexible flange touches the acetabular margin tending to occlude cement flow.
Another device for pressurizing cement is known as the Exeter Acetabular Pressurizer. In this arrangement a water filled seal mounted on the end of a handle is used after the acetabulum has been filled with cement, but before the cup is introduced, the seal covers the acetabulum and the surgeon pushes on the handle thereby forcing the doughy cement in the holes, ridges and trabeculae of the acetabulum. When the instrument is removed and the pressure is released, blood flow can squeeze between the cement and the bone.
It is also known to provide cup positioning instruments with long pointers (vertical, horizontal and at right angles to the patient's center line of body symmetry) to enable the surgeon to control cup orientation reasonably well provided the pelvis does not move. Linear positioning of the cup is determined by eye in a medio-lateral and anterio-posterior sense. If the natural acetabulum is well formed, an eyeball judgment can be acceptable, but many acetabulae are deformed or eroded, in which case eyeball judgment can be confused.
A further method is to use what are usually referred to as acetabular spacers. These can be lugs or PMMA spacers (see for example, U.S. Pat. Nos. 4,883,490 and 4,955,325) fixed to the outside of the acetabular cup or can be press studs pushed into the bone base of the natural acetabulum. These prevent the cup from being pushed too deeply into the acetabular socket and can control medio-lateral and anterio-posterior positioning. However, they force some degree of centralization of the cup. If the surgeon chooses to place the cup eccentrically to make use of a particular area of solid bone support, acetabular spacers may not permit such a placement.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for overcoming some of the difficulties referred to above, to allow pressurization of the cement so that good holding is obtained and to provide a method of operation which will ensure accurate location of the cup in the socket.
According to the present invention a method of implanting an acetabular cup includes preparing an acetabular socket to receive the cup, placing bone cement in the socket before or after locating a loading tube in line with the socket and inserting the acetabular cup through the tube and into the socket by pushing it down the tube with an inserter to a predetermined position therein defined by a stop element acting on the inserter or attachment thereto.
Where the cup is provided with a flanged rim, the stop element can be arranged within the bore of the tube and the flange rim and the stop element can be constructed to allow the cup to pass the stop element but engage the inserter. Another method may include using a tube and an inserter having a stop element which engage an abutment on the tube located at a position spaced away from the end of the tube which is adjacent the socket. If desired, the position of the stop element can be adjusted prior to use.
The method may also include locating a flexible skirt assembly around the rim of the socket with the tube extending from the flexible skirt, and then inserting the acetabular cup through the tube and into the socket.
With these arrangements, it is possible to either fill the acetabulum with doughy cement and then reposition the skirt and tube assembly or the tube on the bone using markers to ensure that a previously chosen position and orientation are reestablished. Alternatively, the cement can be injected, for example by a cement gun, through the tube. The surgeon can then push the cup into the cement with the inserter to create a pressure and ensure that the cement fills all the openings in the socket. If the flexible skirt assembly is used it can be secured around the rim of the socket preventing the escape of cement and allowing it to be pressurized. The flexible skirt can be held in place by means of screws, pins and/or staples, or finger pressure alone.
The method also includes allowing some of the pressurized cement to escape from the socket and through a controlled orifice in the skirt. With this arrangement, the tube can be integral with the flexible skirt or it can be removably connected. Preferably, the flexible skirt is made from a synthetic plastics material and if it is to be left in place, could be polyethylene, polypropylene, polyurethane, or even a resorbable material for example, polyglycolic acid, or polylactic acid.
In order to locate the cup, the surgeon can control the release of cement through the orifice in the skirt, and he can push the cup with the inserter thereby feeling the desired level of cement pressure. If he is not able to reach the desired predetermined position when the stop elements are activated, he can release the pressure on the cement, allowing a little more cement to escape while the cup progresses further down the inside of the tube. An expandable tube can be used with a system for adjusting its diameter.
An advantage of the invention is that no spacers are required which may cause discontinuities in the cement mantle. The arrangement also enables the surgeon to accurately locate the position and attitude of the cup. An apparatus can also be included for positioning and orienting the tube or the tube and skirt on the bone into which the cup is to be implanted.
The invention also includes apparatus for use in the method set forth above which comprises a loading tube adapted for alignment with an acetabular socket, an inserter adapted to fit into the tube and stop elements which can act on the inserter or attachment thereto to limit movement of the inserter down the tube to a predetermined position therein. The stop element can be provided on part of the bore of the tube and act on an inner end of the inserter. This construction is particularly applicable when a flanged socket is used, the socket being provided with a gap in the flange.
In an alternative construction, stop elements can be provided on the inserter which engage an abutment on said tube located at a position spaced away from the end of the tube which is intended to be adjacent the acetabular socket when in use. This construction can be used with sockets having a flange or a plain upper rim.
These and other objects and advantages of the present invention will become apparent from the following description of the accompanying drawings, which disclose several embodiments of the invention. It is to be understood that the drawings are to be used for the purposes of illustration only and not as a definition of the invention.
REFERENCES:
patent: 4463875 (1984-08-01), Tepic
patent: 4611233 (1986-09-01), Brown
patent: 4865609 (1989-09-01), Reche
patent: 5098437 (1992-03-01), Kashuba et al.
patent: 5133765 (1992-07-01), Cuilleran
patent: 5181918 (1993-01-01), Brandhurst et al.
patent: 5201779 (1993-04-01), Shiao
patent: 5527317 (1996-06-01), Asby et al.
patent: 5879402 (1999-03-01), Lawes et al.
patent: 6045555 (2000-04-01), Smith et al.
patent: 0073604 A1 (1983-03-01), None
patent: 0650707 (1994-10-01), None
patent: 0650706 (1994-10-01), None
Lawes Peter
Ling Robin S. M.
Howmedica International S. de R.L.
Lerner David Littenberg Krumholz & Mentlik LLP
Stewart Alvin
Willse David H.
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