Abstract:
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.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     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&#39;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.  
         [0002]     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.  
         [0003]     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.  
         [0004]     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.  
         [0005]     Neither of these constructions are suitable for use with a flexible acetabular cup due to the flexibility of the cup itself.  
         [0006]     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  
       [0007]     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.  
         [0008]     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.  
         [0009]     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.  
         [0010]     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.  
         [0011]     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.  
         [0012]     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.  
         [0013]     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.  
         [0014]     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.  
         [0015]     Preferably the body portion, handle and trigger are detachable from the engagement element.  
         [0016]     The invention also includes a prosthesis implantation inserter in combination with an acetabular cup with which it is to be used.  
         [0017]     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.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The invention can be performed in various ways and some embodiments will now be described by way of example and with reference to the accompanying drawings in which  
         [0019]      FIG. 1  is an isometric view of an acetabular cup inserter according to the present invention with an acetabular cup in place therein;  
         [0020]      FIG. 2  is a side view of the acetabular cup inserter and an acetabular cup as shown in  FIG. 1 ;  
         [0021]      FIG. 3  is a cross-sectional side view of the acetabular cup inserter and the acetabular cup shown in  FIGS. 1 and 2 ;  
         [0022]      FIG. 4  is an enlarged cross-sectional view of part of the acetabular cup inserter shown in  FIG. 3  with the engagement element in its operational position engaged into an opening in the rim of the cup;  
         [0023]      FIG. 5  is an enlarged view of part of the cup inserter with the engagement element in its released position;  
         [0024]      FIG. 6  shows a flexible acetabular cup  1  of the type described in U.S. Pat. No. 5,609,646 and which has a keyhole shaped opening  2  in its peripheral rim  3  for use with the inserter of the present invention;  
         [0025]      FIG. 7  is an isometric view of the cup inserter without the cup;  
         [0026]      FIG. 8  is an enlarged view of part of the inserter without the cup;  
         [0027]      FIG. 9  is an isometric view of an alternative construction of a cup inserter on which a cup with 9 slots is secured;  
         [0028]      FIG. 10  is an isometric view of a flexible cup of which the flexibility is achieved by 9 slots;  
         [0029]      FIG. 11  is an isometric view of part of the cup inserter and the appropriate engagement element for a cup with 9 slots;  
         [0030]      FIG. 12  is a diagrammatic front view of a flexible cup with an anatomic rim;  
         [0031]      FIG. 13  is a detailed side view of the cup inserter on which is secured a flexible cup with an anatomic rim; and,  
         [0032]      FIG. 14  is an isometric view of the flexible cup shown in  FIG. 12  with the engagement element engaged but removed from the remainder of the inserter. 
     
    
     DETAILED DESCRIPTION  
       [0033]     An inserter, according to the present invention and for use with an acetabular cup  1  as shown in  FIG. 6  is shown in  FIGS. 1-5  and comprises an engagement element  4  carried on a locator  5  which is mounted on a main body  6  which is in the form of a hollow tube carrying an operating rod  7 . One end of the operating rod  7  is screw threaded to locate in and engage a socket  8  in the engagement element  4 . The other end of the operating rod  7  is enlarged and indicated by reference numeral  9  and is mounted in an enlarged bore  10 . The end of the portion  9  carries a flange  11  which is engaged by a compressed coil spring  12  which is in turn held in place by an end stop  13 . The operating rod  7  is therefore biased to the left to force the engagement portion towards the position shown in  FIG. 3  and which is its operational position. The engagement element can be withdrawn from its operational position towards the right by a trigger  14  when moved in the direction of the arrow  15 .  
         [0034]     In the preferred embodiment a handle  16  is provided to facilitate handling.  
         [0035]     In  FIGS. 4 and 5  the cup  1  to be inserted is shown in position on the inserter. As will most clearly be seen from  FIG. 4  the rim  3  of the cup rests against the locator  5  which is in the form of a substantially flat disc and which bears against a flared circumferentially shaped collar  18  on the end of the main body portion  6  which has four arms  24 .  
         [0036]     The overall shape of the engagement element is most clearly shown in  FIGS. 7 and 8  and comprises a cylindrical portion  19  which extends through a circular opening  20  in the location plate  5  and extends into a cylindrical socket  21  in the collar  18  as is most clearly shown in  FIGS. 4 and 8 .  
         [0037]     The engagement element  4  also includes a shaped engagement portion  22  whose cross-sectional shape is similar to the cross-sectional shape of the horse shoe shaped opening  2  in the cup to be fitted. The edges of the engagement portion  22  are chamfered, as indicated by reference numeral  23 . The dimensions of the engagement portion  22  are slightly larger than the dimensions of the opening  2  with which it is intended to be used. The lower part of the engagement portion  22  also has an extension  25  which acts as a guide between two of the arms  24  and passes through an opening  26  in the location plate  5 .  
         [0038]     When engagement element  4  is in the operational position, as shown in  FIG. 4 , the cup to be implanted is pushed over the engagement portion  22  so that, due to its flexible nature, it distorts slightly so that the edges of the opening  2  are gripped by friction on the surface of the engagement portion  22  adjacent its edge. In this position the locator plate  5  is held in position by the shaped collar.  
         [0039]     The locator plate  5  can be replaced by smaller or larger plates depending on the outer diameter of the cup  1 . Preferably the diameter of the locator plate  5  is smaller than the outer dimensions of the cup  1 , as shown in  FIGS. 3 and 4 , so that the rim  3  of 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.  
         [0040]     The engagement element  4  can be interchangeable with other engagement elements in order to match the specific shape or size of the cup to be implanted.  
         [0041]     In order to remove the inserter once the cup has been placed in the acetabulum by the surgeon the trigger  14  is operated in the direction indicated by the arrow  15 . This action acts to withdraw the engagement element  4  to the position shown in  FIG. 5  thus moving the engagement portion  22  out of the opening  2  and thus releasing the inserter from the cup. The chamfer  23  on the engagement portion  22  assists release.  
         [0042]     The position of the “pinch” of the engagement element  4  can be adjusted by changing the shape and the oversize of the engagement portion  22 .  
         [0043]     The inserter can also be used with flexible cups of alternative constructions, for example the cup  29  shown in  FIG. 10 . In this construction the flexibility is achieved by replacing the opening  2  of the cup shown in  FIG. 6  by a number of slots  30 , disposed regularly or not, around the peripheral rim  31  of the cup. In order to operate with this type of cup the engagement element  4  of the construction shown in FIGS.  1  to  8  is replaced by the engagement element  32  shown in  FIG. 11 . With this arrangement the part of the cylindrical portion  19  which passes through the location plate  5  and enters the socket  21  is retained as is a guide extension  25  which passes between the arms  24 , but the outer shaped portion  22  is replaced by a dome  35  and a series of shaped fins  36  which are shaped to engage the slots  30  in the rims  31  of the cup  29 . The thickness of the fins is slightly larger than the width of the slots  30  so that there is slight deformation of the cup as it is pushed onto the fins. In the position shown in  FIG. 11  the 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.  
         [0044]     Once again the dimensions of the location plate can be adjusted as required with regard to the visible rim  31  of the cup.  
         [0045]     The engagement element  32  is held on the operating rod  7  in a similar manner to that described with regard to the earlier construction.  
         [0046]     In a further alternative construction (not shown) the number of openings  30  can be reduced in number and the flexibility could even rely on a single slot. To operate with this type of construction the number of fins  36  would be adjusted appropriately.  
         [0047]     The material employed to produce the cup  1  or  29  can 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.  
         [0048]     The engagement element  4  and/or the locator plate  5  can 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.  
         [0049]      FIGS. 12 and 13  show how the cup inserter, according to the present invention, can also be used with a cup which has a rim  40  which 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 cup  41  shown in FIGS.  12  to  14  has a shaped opening  42  in its rim  40  which is of a keyhole shape similar to the opening  2  in the rim of the cup shown in  FIG. 6 . In order to accommodate the shaped rim the facing surface  44  of the location plate  5  is shaped appropriately.  
         [0050]      FIG. 14  shows a cup  41  of the kind shown in  FIGS. 12 and 13  located on the shaped engagement portion  22  and the engagement means and locator plate  5  removed from the main body portion, trigger and handle. The removal is achieved by unscrewing the operating rod  7  from the socket  8  in the cylindrical portion  19  of the engagement means  4 .  
         [0051]     The cup  41  which is to be used can be delivered pre-positioned on the engagement means  4  as shown in  FIG. 14  in a sterile packaging in order to simplify attaching the cup to the cup inserter. To secure the cup to the inserter, the cylindrical portion  19  is threaded onto the operating rod  7  in the cylindrical socket  21  and tightened by rotating the end stop  13 . In such an arrangement the engagement means and/or the location plate  5  can be disposable. Preferably both of these are made of a plastic material and injection molded.  
         [0052]     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.