Inserter for a flexible acetabular cup

A prosthesis implantation inserter is used with a flexible acetabular cup which has an opening or openings in its peripheral rim. The inserter has engagement elements which in an operational position frictionally engage the opening or openings in the flexible cup rim. A release is provided which can be operated to withdraw the engagement element from the opening or openings. When the cup is held §in position it can be guided and inserted into the acetabulum and impacted. Once the position of the prosthesis satisfies the surgeon the engagement element can be removed by operating the release and the cup inserter is removed without any risk of compromising the position or the stability of the implant.

BACKGROUND OF THE INVENTION

This invention relates to a prosthesis implantation inserter for use with a flexible acetabular cup. Flexible acetabular cups have shown their ability to transfer the load in a natural manner to the patient's pelvis. An acetabular cup of this kind is described in U.S. Pat. No. 5,609,646 the disclosure of which is incorporated herein by reference.

To achieve an initial stability and a long term implantation of a flexible acetabular cup prosthesis it is necessary to ensure that the position of the implant is appropriate and that the contact between the bone and the outer surface of the prosthesis is maximized. Moreover, the stability is achieved due to an interference fit between the host bone cavity and the implant. The outcome during the implantation is its inclination to deform itself. As a consequence, it is difficult to place the acetabular cup adequately and guarantee an intimate contact with the bone. The present invention is intended to provide an instrument to overcome these difficulties.

U.S. Pat. No. 5,954,727 shows a positioning tool for reversibly engaging an acetabular cup, an elongate cylindrical section of the positioning tool being insertable through a posterior opening in the cup. The outer diameter of the cylindrical portion is expandable to engage the inner wall of the cup in an interference fit to prevent movement of the cup relative to the tool and hold the cup in engagement when planting the cup at a desired position.

U.S. Pat. No. 5,098,437 also shows the use of a positioning rod which has spring elements which engage a circumferential groove on the inner surface of the implant.

Neither of these constructions are suitable for use with a flexible acetabular cup due to the flexibility of the cup itself.

In U.S Pat. No. 5,609,646 the flexibility of the cup is provided by the materials from which it is fabricated and a separation or opening in its peripheral rim and the present invention utilizes one opening or separation of this type.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a prosthesis implantation inserter for use with a flexible acetabular cup which has an opening or openings in its peripheral rim comprises engagement elements which in an operational position frictionally engage the said opening or openings, and a release which can be operated to withdraw the engagement element from the opening or openings.

It will be appreciated that although only one opening is shown in U.S. Pat. No. 5,609,646 a flexible acetabular cup could have a number of openings in its rim and wall to provide the required flexibility. Preferably the engagement element acts to deform the opening or openings when they are engaged thereby in its operational position. The engagement element which contacts the opening or openings can be slightly larger than the opening so that the flexible cup grips the engagement element by friction which acts to secure the cup to the inserter.

When the cup is in position it can be guided and inserted into the acetabulum and impacted. Once the position of the prosthesis satisfies the surgeon the engagement element can be removed by operating the release and the cup inserter is removed without any risk of compromising the position or the stability of the implant.

In a preferred construction the inserter includes a locator adapted to locate the rim of the acetabular cup and in relation to which the engagement element can be moved by the release. Thus the engagement element may comprise a sliding component positioned on the locator.

The engagement element can be resiliently biased towards the operational position and in one preferred embodiment the engagement element can include an engagement portion or portions which is or are shaped to co-operate with the shape of the opening or openings in the peripheral rim of the cup with which it is to be used.

Thus, the engagement portion can be shaped to engage a keyhole-shaped opening in the peripheral rim of the cup with which it is adapted to be used. Alternatively, the engagement portion can be shaped to engage a substantially radially extending slot in the peripheral edge of the cup with which it is to be used.

In another embodiment the engagement portion can be shaped as a series of radially extending fins adapted to engage a series of radially extending openings in the form of slots in the peripheral rim of the cup with which it is to be used.

The locator against which the peripheral rim of the acetabular cup is located can be shaped to accommodate an acetabular cup with a rim which mimics the natural shape of the acetabulum. In a convenient construction the inserter can include a body portion which carries the engagement means, a handle and a trigger which can operate the release means.

Preferably the body portion, handle and trigger are detachable from the engagement element.

The invention also includes a prosthesis implantation inserter in combination with an acetabular cup with which it is to be used.

Also included within the invention is a prosthesis implantation inserter as set forth above in combination with a flexible acetabular cup with which it is to be used and in which the engagement means, detached from the body portion, handle and trigger, and engaged in the cup are located in a sterile package.

DETAILED DESCRIPTION

An inserter, according to the present invention and for use with an acetabular cup1as shown inFIG. 6is shown inFIGS. 1-5and comprises an engagement element4carried on a locator5which is mounted on a main body6which is in the form of a hollow tube carrying an operating rod7. One end of the operating rod7is screw threaded to locate in and engage a socket8in the engagement element4. The other end of the operating rod7is enlarged and indicated by reference numeral9and is mounted in an enlarged bore10. The end of the portion9carries a flange11which is engaged by a compressed coil spring12which is in turn held in place by an end stop13. The operating rod7is therefore biased to the left to force the engagement portion towards the position shown inFIG. 3and which is its operational position. The engagement element can be withdrawn from its operational position towards the right by a trigger14when moved in the direction of the arrow15.

In the preferred embodiment a handle16is provided to facilitate handling.

InFIGS. 4 and 5the cup1to be inserted is shown in position on the inserter. As will most clearly be seen fromFIG. 4the rim3of the cup rests against the locator5which is in the form of a substantially flat disc and which bears against a flared circumferentially shaped collar18on the end of the main body portion6which has four arms24.

The overall shape of the engagement element is most clearly shown inFIGS. 7 and 8and comprises a cylindrical portion19which extends through a circular opening20in the location plate5and extends into a cylindrical socket21in the collar18as is most clearly shown inFIGS. 4 and 8.

The engagement element4also includes a shaped engagement portion22whose cross-sectional shape is similar to the cross-sectional shape of the horse shoe shaped opening2in the cup to be fitted. The edges of the engagement portion22are chamfered, as indicated by reference numeral23. The dimensions of the engagement portion22are slightly larger than the dimensions of the opening2with which it is intended to be used. The lower part of the engagement portion22also has an extension25which acts as a guide between two of the arms24and passes through an opening26in the location plate5.

When engagement element4is in the operational position, as shown inFIG. 4, the cup to be implanted is pushed over the engagement portion22so that, due to its flexible nature, it distorts slightly so that the edges of the opening2are gripped by friction on the surface of the engagement portion22adjacent its edge. In this position the locator plate5is held in position by the shaped collar.

The locator plate5can be replaced by smaller or larger plates depending on the outer diameter of the cup1. Preferably the diameter of the locator plate5is smaller than the outer dimensions of the cup1, as shown inFIGS. 3 and 4, so that the rim3of the cup is visible when the cup is secured to the inserter. This is desirable in order to help the surgeon to control the position of the cup in relation with other anatomical landmarks.

The engagement element4can be interchangeable with other engagement elements in order to match the specific shape or size of the cup to be implanted.

In order to remove the inserter once the cup has been placed in the acetabulum by the surgeon the trigger14is operated in the direction indicated by the arrow15. This action acts to withdraw the engagement element4to the position shown inFIG. 5thus moving the engagement portion22out of the opening2and thus releasing the inserter from the cup. The chamfer23on the engagement portion22assists release.

The position of the “pinch” of the engagement element4can be adjusted by changing the shape and the oversize of the engagement portion22.

The inserter can also be used with flexible cups of alternative constructions, for example the cup29shown inFIG. 10. In this construction the flexibility is achieved by replacing the opening2of the cup shown inFIG. 6by a number of slots30, disposed regularly or not, around the peripheral rim31of the cup. In order to operate with this type of cup the engagement element4of the construction shown inFIGS. 1 to 8is replaced by the engagement element32shown inFIG. 11. With this arrangement the part of the cylindrical portion19which passes through the location plate5and enters the socket21is retained as is a guide extension25which passes between the arms24, but the outer shaped portion22is replaced by a dome35and a series of shaped fins36which are shaped to engage the slots30in the rims31of the cup29. The thickness of the fins is slightly larger than the width of the slots30so that there is slight deformation of the cup as it is pushed onto the fins. In the position shown inFIG. 11the engagement means are in their withdrawn position, that is after the inserter has been removed from the cup. In the operational engagement position the fins will project further outwards and there is allowance at the rear of the fins for the withdrawal action.

Once again the dimensions of the location plate can be adjusted as required with regard to the visible rim31of the cup.

The engagement element32is held on the operating rod7in a similar manner to that described with regard to the earlier construction.

In a further alternative construction (not shown) the number of openings30can be reduced in number and the flexibility could even rely on a single slot. To operate with this type of construction the number of fins36would be adjusted appropriately.

The material employed to produce the cup1or29can be composite material such as PEEK, alternatively metal alloys are commonly employed for orthopaedic prostheses such as titanium alloys, cobalt, chromium or molybdenum alloys can be used. They all provide the desired flexibility and the inserter can be used with any of these material cups.

The engagement element4and/or the locator plate5can be stainless steel alloys commonly employed for producing orthopaedic instruments or other metallic alloys. Alternatively plastics or composite material can be used and in such a case the parts can be made by machining, injection molding or any process suitable with the material concerned.

FIGS. 12 and 13show how the cup inserter, according to the present invention, can also be used with a cup which has a rim40which is shaped with peaks and valleys that mimic the natural shape of the acetabulum, for example of the type shown in U.S. Patent Publication 2005/0060040. The cup41shown inFIGS. 12 to 14has a shaped opening42in its rim40which is of a keyhole shape similar to the opening2in the rim of the cup shown inFIG. 6. In order to accommodate the shaped rim the facing surface44of the location plate5is shaped appropriately.

FIG. 14shows a cup41of the kind shown inFIGS. 12 and 13located on the shaped engagement portion22and the engagement means and locator plate5removed from the main body portion, trigger and handle. The removal is achieved by unscrewing the operating rod7from the socket8in the cylindrical portion19of the engagement means4.

The cup41which is to be used can be delivered pre-positioned on the engagement means4as shown inFIG. 14in a sterile packaging in order to simplify attaching the cup to the cup inserter. To secure the cup to the inserter, the cylindrical portion19is threaded onto the operating rod7in the cylindrical socket21and tightened by rotating the end stop13. In such an arrangement the engagement means and/or the location plate5can be disposable. Preferably both of these are made of a plastic material and injection molded.