like reference numerals refer to like parts throughout the following description and the accompanying drawings . referring now to fig1 , 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 . as shown in fig1 , 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 fig1 , 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 . turning now to fig2 , 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 ( fig1 ). 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 . also shown in fig2 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 ( fig3 ) of an acetabular cup 40 . fig3 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 . fig3 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 . in the embodiment illustrated in fig3 , 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 . fig4 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 ( fig3 ) of the base plate 28 . turning now to fig5 , 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 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 . 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 .
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 .