Prosthetic implant and surgical tool

Details Prosthetic implant and surgical tool Prosthetic implant and surgical tool

1999-06-29

2002-09-17

Robert, Eduardo C. (Department: 3732)

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

Implantable prosthesis

Bone

Reexamination Certificate

active

06451058

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a prosthetic implant and to a surgical tool for gripping the prosthetic implant during a surgical procedure.
BACKGROUND OF THE INVENTION
The replacement of all or a part of the bone surface of an articulation with a prosthetic implant has become a common surgical procedure. The procedure requires the surgeon to exercise both precision and delicacy in the placement of the prosthetic implant. However, it is frequently necessary for the surgeon also to exercise a degree of force, sometimes a vigorous force, in order to situate the prosthetic implant in a desired location on the bone surface.
For example, in an operation to insert a prosthetic acetabulum in a patient's pelvis the surgeon first uses a reamer to grind a cavity of appropriate size in the patient's pelvis. The surgeon then inserts an acetabular cup into the cavity. By “appropriate size” is meant a size which is selected by the surgeon as being the most appropriate for that particular patient. Normally, it is desirable to retain as much of the original healthy bone surface as possible.
Commercially available acetabular cups are sold in a range of sizes to suit the needs of individual patients. Generally, acetabular cups are available in sizes of from 42 mm to 62 mm diameter, with 2 mm increments between neighbouring sizes.
Prosthetic acetabular cups generally require the use of an insertion tool to achieve correct positioning of the prosthesis in the patient's pelvic cavity. A typical insertion tool is described in U.S. Pat. No. 4,305,394 (Bertuck).
There are a number of different types of prosthetic acetabular cups. Firstly, cups made from polyethylene are available. Polyethylene cups are cemented into the acetabulum and require only light pressure to seat them in the cement. Secondly, there are cups which comprise a metal shell for insertion into the pelvic cavity and a polyethylene liner for articulation with the femur. Some polyethylene cups with metal shells are implanted without cement and rely on a jam fit between the metal shell and the patient's acetabulum. Often these metal shells have surfaces or coatings which encourage bone to grow into them over time. A typical coating material is hydroxyapatite. With this type of prosthesis, the polyethylene liner is snapped or screwed into the metal shell after the metal shell has been seated in the acetabulum to form the socket part of the patient's joint.
Cups which rely on a jam fit require a greater force to be applied via the insertion tool than is the case with cemented polyethylene cups. This force is usually applied as a direct impact into the acetabulum, for example by use of a mallet on the free end of the insertion tool. However, it may also be necessary to adjust the angular position of the cup in the bone or to take it out if positioned incorrectly. Therefore the insertion tool must positively grip the cup by some mechanical feature. This feature cannot impinge upon the outside of the metal shell because the insertion tool may then become trapped between the shell and the bone. Also there is little room around the rim of the shell because the wall thickness of the shell is generally kept to a minimum. Therefore the insertion tool usually grips on a mechanical feature on the inner hemisphere of the metal shell. An insertion tool of this type is described in International Patent Publication No. WO 94/21199 (Howmedica Limited). The mechanical feature is usually designed so as to cause minimum compromise to the function of the prosthetic hip joint. As a result it is often not strong enough for the impaction forces applied. This often results in damage to the insertion tool, or metal shell or both.
A third category of prosthetic hip joint exists which is manufactured entirely from metal so that the prosthetic articulation comprises a metal on metal joint. These are nearly always implanted without cement, relying on a jam fit in the acetabulum. With this type of cup the inner hemisphere is not a convenient place to locate a mechanical feature for the insertion tool to grip on. First, it would reduce the surface area of the prosthetic articulation. Secondly, it could cause damage to the highly polished concave metal against which the ball of the patient's femur or the ball head of a femoral prosthesis is to bear.
Therefore, the provision of means for attaching an insertion tool to a prosthetic implant so that the attachment is sufficiently robust to withstand the impaction and other forces to which it may be subject during insertion of the prosthesis and yet which does not compromise the structural strength or the articulating properties of the prosthesis itself remains a problem in the art.
Another disadvantage of conventional tools is that they must be manufactured in a range of different sizes to receive acetabular cups or sheaths of the different sizes referred to above.
The difficulty of gripping and positioning prosthetic implants applies not only to acetabular implants but more generally to implants such as the tibial and femoral components of a prosthetic knee.
U.S. Pat. No. 5,376,126 (Lin) discloses use of cords to assist in fastening a femoral implant to the upper end of a resected femur.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a prosthetic implant which does not suffer from one or more of the disadvantages of the prior art devices. It is further an object of the present invention to provide a surgical tool for use with such an implant.
Accordingly, the present invention provides a prosthetic implant comprising a main body portion, having a first surface for presentation to a receptive bone surface or to a surgically prepared bone cavity and a second surface for receipt of an articulating joint, and filamentary member attachment means adapted for attachment of a filamentary member to the implant.
The filamentary member can be a monofilamentary member, such as a Kevlar™ monofilament, or a multifilament member such as a Kevlar™ polyfilamentary thread or a metallic cable made, for example, from stainless steel. Such a cable may be, for example, from about 0.5 mm thick to about 2 mm thick. If desired, the cable can be coated with an inert material, such as polypropylene. Preferably the filamentary member is formed into a closed loop.
In one form of prosthetic implant according to the invention the filamentary member attachment means comprises a lug on the main body portion around which a filamentary member can be looped. Alternatively the filamentary member attachment means can comprise a bore in the main body portion through which a filamentary member can be threaded. In such a case it will normally be preferred to provide plurality of such bores, for example, three such bores.
The invention further provides such a prosthetic implant further comprising a cable attached to the main body portion of the implant by the filamentary member attachment means. Thus in a preferred embodiment of the invention the filamentary member attachment means comprises a plurality of bores in the main body portion and a filamentary member is threaded through each of the plurality of bores in turn, the free ends of the filamentary member being secured one to another so as to form a closed loop of filamentary member. The free ends of the filamentary member can be secured to one another by means of a sleeve having first and second ends, the sleeve snugly receiving a first looped portion of filamentary member located near a first end portion of the filamentary member and inserted from the first end of the sleeve so as to project as a first loop from the second end of the sleeve with the first end portion being passed through the first loop, and the sleeve further snugly receiving a second looped portion of filamentary member located near a second end portion of the filamentary member and inserted from the second end of the sleeve so as to project as a second loop from the first end of the sleeve with the second end portion being passed through the second loop,

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