Abstract:
An instrument for positioning a hollow cup component of an orthopaedic joint prosthesis. The instrument includes an insertion end section, a handle end section opposite the insertion end section, and a shaft coupling the insertion end section to the handle end section. The insertion end section includes a cam wheel and a plurality of expanding pieces coupled to the cam wheel such that when the cam wheel is rotated in one direction, the expanding pieces expand out in a radial direction and frictionally engage an inner surface of the hollow cup component.

Description:
CROSS-REFERENCE INFORMATION 
     Technical Field of the Invention 
       [0001]    The present invention relates generally to the field of orthopedics, and, more particularly, to an instrument for inserting a cup into an acetabulum. 
       Background 
       [0002]    Certain orthopaedic joint prostheses include a hollow cup with an inner surface which defines a generally hemispherical hollow region, and another component which has a spherical part which can be received in the hollow region for articulation relative to the cup component. Such joint prostheses can include hip joint prostheses and shoulder joint prostheses. The exterior of the cup will contact the prepared surface of the patient&#39;s bone in which the component is to be implanted. The interior of the cup will present a smooth bearing surface to the spherical part of the other component of the joint prosthesis. The bearing surface can be provided by a single piece cup component. Alternatively, the cup component can comprise a shell part which contacts the prepared surface of the patient&#39;s bone, and a bearing part which provides the bearing surface, and which fits into the shell part. The bearing part can be made from a material which is different from the material of the shell part: for example the bearing part can be made from a polymeric material (such as polyethylene) and the shell part (and the spherical part of the other component) can be made from a metal (such as a cobalt-chromium based alloy, or a stainless steel, or a titanium based alloy). 
         [0003]    It is important that the components of an orthopaedic joint prosthesis are positioned accurately in a patient&#39;s bone. Both location and alignment are important. Accurate positioning of a component requires that the component be engaged by an appropriate instrument, allowing considerable force to be applied to the component if and as necessary. However, it can be important not to contact the external surface or the internal surface or both of the component with the instrument, especially the internal surface when it has been provided with a smooth polished bearing surface. Scratching or otherwise damaging that surface can impair the bearing properties of the prosthesis. 
         [0004]    In some prior art instruments, the insertion tool includes a flange that interacts with a groove cut into an inner surface of the cup. Other prior art instruments utilize a plurality of jaw members which extend radially from a central drive shaft. The jaw members can be made to slide radially inwardly so that they engage the outside wall of a cup component. Each of the jaw members has a pin at one end which is received in a spiral track on a drive plate. The jaw members are made to slide radially by rotating the drive plate. The jaw members engage a corresponding recess in the cup. 
         [0005]    In each of these prior art examples, the insertion tool works by interacting with special features on the cup. This limits the instrument to only be able to be used with certain cups. Therefore, there is a need for an insertion instrument that can be used on a cup 
       SUMMARY OF THE INVENTION 
       [0006]    According to one embodiment, an instrument for positioning a hollow cup component of an orthopaedic joint prosthesis is provided. The instrument includes an insertion end section, a handle end section opposite the insertion end section, and a shaft coupling the insertion end section to the handle end section. The insertion end section includes a cam wheel and a plurality of expanding pieces coupled to the cam wheel such that when the cam wheel is rotated in one direction, the expanding pieces expand out in a radial direction and frictionally engage an inner surface of the hollow cup component. 
         [0007]    According to yet another embodiment, a system including a hollow cup having a concave inner surface and an instrument for positioning the hollow cup component is provided. The instrument includes an insertion end section and a handle end section opposite the insertion end section. A shaft couples the insertion end section to the handle end section, wherein the insertion end section includes a cam wheel and a plurality of expanding pieces coupled and adjacent to the cam wheel such that when the cam wheel is rotated in one direction, the expanding pieces expand out in a radial direction and frictionally engage the concave inner surface of the hollow cup. 
         [0008]    According to yet another embodiment of the present invention, method for inserting a hollow cup into an acetabulum is provided. An instrument is used and the instrument has an insertion end section, a handle end section opposite the insertion end section, and a shaft coupling the insertion end section to the handle end section. The insertion end section includes a cam wheel and a plurality of irregular shaped expanding pieces coupled to the cam wheel. The insertion end section is inserted into the inner surface of the hollow cup. A knob extending from a portion of the shaft on the instrument is rotated in a first direction. Rotating the knob causes the plurality of irregular shaped expanding pieces to expand and frictionally engage the inner surface of the cup. The instrument is used to insert the cup into a patient&#39;s acetabulum. The knob is rotated in a direction opposite the first direction, causing the irregular shaped expanding pieces to release the inner surface of the cup. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a cross-sectional view of a cup inserting instrument according to one embodiment of the present invention. 
           [0010]      FIG. 2  is an exploded view of the instrument of  FIG. 1 . 
           [0011]      FIG. 3  is a cross-sectional view of an end of the instrument of  FIG. 1  with a cup. 
           [0012]      FIG. 4  is a cross-sectional view of the instrument of  FIG. 1 . 
           [0013]      FIG. 5  is a flow chart illustrating a method of using the instrument according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Like reference numerals refer to like parts throughout the following description and the accompanying drawings. Referring now to  FIG. 1 , an insertion instrument  10  is shown. As shown, the instrument  10  includes an insertion end section  12  and a handle end section  14  opposite the insertion end section  12 . A shaft  16  couples the insertion end section  12  to the handle end section  14 . In the illustrated embodiment, the shaft  16  includes three portions: a first portion  16   a  coupled to the insertion end section  12 ; a second portion  16   b  coupled to the first portion  16   a,  and a third portion  16   c,  coupled to the second portion  16   b  and the handle end section  14 . As shown, the first portion  16   a  extends at an angle from the insertion end. The second portion is bent and extends away from the first portion. The third portion  16   c  is an angle to the second portion  16   b  and is in-line with the insertion end section  12 . The three portions  16   a,    16   b,    16   c  may be one piece or they may be modular. In other embodiments, the shaft  16  may be a single portion in a straight line. The design of the shaft will depend upon the surgical procedure and the wound site. 
         [0015]    As shown in  FIG. 1 , a knob  20  extends from the first portion  16   a.  The knob  20  is coupled to an internal rod  22  that extends through a cavity  24  in the first portion  16   a  of the shaft  16 . Also as shown in  FIG. 1 , the handle end section  14  includes a handle  25  adapted to be gripped by a user during the use of the tool. The handle  25  may be ergonomically shaped for ease of handling. At the very end of the handle end section  14  is an impaction surface  26 . The impaction surface  26  is structured to be able to be struck by a hammer, mallet or other impaction tool during use and to transfer the force through the shaft to the insertion end section  12 . 
         [0016]    Turning now to  FIG. 2 , an exploded view of the instrument  10 , especially the insertion end section  12  is shown. Coupled to the first portion  16   a  of the shaft  16  is a base plate  28 . The base plate  28  provides support to the other components located at the insertion end section  12 . The base plate  28  is coupled to a plurality of expanding pieces  30 . The expanding pieces  30  have irregular shapes such that as they are rotated, the distance between the center of the rotation and the expanding piece  30  changes. Located in the middle of the expanding pieces is a cam wheel  32 . The cam wheel  32  is coupled to the internal rod  22  ( FIG. 1 ). When the knob  20  is rotated, the internal rod  22  rotates, rotating the cam wheel  32 . The cam wheel  32  acts as a center of rotation for the expanding pieces  30 . As the cam wheel  32  is rotated, the expanding pieces expand so that an edge expands beyond the edge of the base plate  28 . In other words, as the cam wheel  32  rotates, the expanding pieces  30  expand inwardly and outwardly in a radial direction. 
         [0017]    Also shown in  FIG. 2  is an impactor cap  34 . The impactor cap  34  has a partially spherical convex outer surface  36 . The outer surface  36  is designed to engage an inner surface  38  ( FIG. 3 ) of an acetabular cup  40 . 
         [0018]      FIG. 3  illustrates a perspective cut-away view of the insertion end section  12 . As shown, the base plate  28  supports the cam wheel  32  and the expanding pieces  30 .  FIG. 3  illustrates an expanded state in which the cam wheel  32  has been rotated to cause the expanding pieces to extend beyond the base plate  28  and to engage the inner surface  38  of the acetabular cup  40 . 
         [0019]    In the embodiment illustrated in  FIG. 3 , the cup  40  is a monoblock cup. The outer surface  42  is made of a biocompatible metal, such as titanium. The outer surface  42  may also have a porous coating as is known in the art to promote bone in-growth. The inner surface  38  may be made of a polyethylene, such as antioxidant polyethylene. Other polyethylenes, such as ultra high molecular weight polyethylene (UHMWPE) may also be used. In this embodiment, the polyethylene inner surface  38  is molded into the metal outer surface  42 . 
         [0020]      FIG. 4  shows the interaction between the cam wheel  32  and the expanding pieces  30  in more detail. As shown, the expanding pieces have edges  43 . As the cam wheel  32  rotates, the edges  43  are engaged. Because the edges  43  of the expanding pieces  32  are not spherical, the expanding pieces move relative to the base plate  28 . Specifically, the expanding pieces  30  are forced to move in and out relative to an edge  44  ( FIG. 3 ) of the base plate  28 . 
         [0021]    Turning now to  FIG. 5 , the opearation of the insertion instrument  10  will be described. Beginning at step s 100 , the inner surface  38  of the cup  40  is placed in contact with the outer surface  36  of the impactor cap  34 . The user then rotates the knob  20  and locks it at step s 102 . Internally, the rotation of the knob  20  causes the internal rod  22  to rotate, which in turn causes the cam wheel  32  to rotate. As discussed above, as the cam wheel  32  rotates, expanding pieces  30  expand outward, entering into a friction fit with the inner surface  38  of the cup  40 . At step  104 , the user may then use the instrument  10  to insert the cup  40  into the prepared acetabulum. This step may involve using a hammer, mallet or other tool to strike the tool to firmly seat the shell in the acetabulum. Once the cup  40  is seated, the user then rotates the knob  20  in the opposite direction at step s 106 , causing the expanding pieces  30  to move back in toward the center and releases the friction fit between the expanding pieces  30  and the inner surface  38  of the cup  40 . This step disengages the instrument  10  from the cup  40  and the instrument can be removed at step s 108   
         [0022]    Although the instrument of the present embodiment is used to describe inserting a cup, the instrument  10  may also be used to remove a cup. For example, if after the cup  40  is inserted into the acetabulum, the user is unhappy with the position, the user may insert the insertion end section  12  into the cup  40 , turn the knob  20  in a direction to cause the expanding pieces  30  to engage the inner surface  38  of the cup  40 , and then remove the instrument  10  and the cup  40  from the acetabulum. This is best if done prior to any impaction. 
         [0023]    The foregoing description of the invention is illustrative only, and is not intended to limit the scope of the invention to the precise terms set forth. Further, although the invention has been described in detail with reference to certain illustrative embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.