Abstract:
A hand held instrument is provided in one embodiment in a kit for use in positioning a constraining ring of an acetabular liner system and includes a shaft including a first coupling member, and a plurality of heads, each of the plurality of heads including (i) a base configured to couple with the first coupling member and (ii) a pair of resilient gripper arms, each of the pair of resilient gripper arms defining a constraining ring reception area having a size different from the constraining ring reception area defined by the pair of gripper arms of each of the other of the plurality of heads.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to surgical instruments, and particularly to an instrument for positioning a constraining ring for an acetabular insert. 
       BACKGROUND OF THE INVENTION 
       [0002]    Joint arthroplasty is a well known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. Joint arthroplasty is commonly performed for hips, knees, elbows, and other joints. The health and condition of the joint to be replaced dictate the type(s) of prosthesis necessary to replace the natural joint. The hip joint includes the acetabulum of the pelvis which receives the head or ball of a femoral component. Replacement of the acetabulum is necessary when there is an inadequate articulation surface for a head or ball of a femoral component, natural or prosthetic. Prosthetic components that are used in a hip arthroplasty include acetabular cups and acetabular liners. An acetabular cup is implanted in the acetabular cavity in the pelvis to replace the natural acetabulum and the liner provides the bearing surface. 
         [0003]      FIG. 1  shows an exemplary acetabular replacement system  10  including an acetabular cup  12 , an acetabular liner  14  and a constraining ring  16 . The acetabular cup  12  includes a cavity  18  which is configured to receive the acetabular liner  14 . The acetabular liner  14  includes an outer surface  20  configured to be received by the cavity  18  and a lip  22  defining an opening to a cavity  24 . 
         [0004]    The acetabular system  10  may be used with a femoral system  26  shown in  FIG. 2 . The femoral system  26  includes a stem  28 , a neck  30  and a femoral ball  32 . The cavity  24  is configured to receive the femoral ball  32 . The cavity  24  is slightly more than a hemispherical cavity and the diameter defined by the lip  22  is less than the diameter of the femoral ball  32 . Thus, once the femoral ball  32  is received into the cavity  24 , the potential for inadvertent dislocation of the hip joint is reduced. In order to allow the ball  32  to be positioned within the cavity  24 , the lip  22  is somewhat flexible. The constraining ring  16  is positioned over the lip  22  to restrict flexure of the lip  22  after the ball  32  is positioned within the cavity  24 . 
         [0005]    To implant an acetabular cup such as the acetabular cup  12 , a cavity is reamed in the pelvis of a patient. The reamed cavity generally conforms to the outer surface of the acetabular cup  12 . The acetabular cup  12  is then inserted into the formed cavity and secured to the native bone. The acetabular cup  12  is positioned in the pelvis at a fixed orientation in the acetabulum so as to emulate the patient&#39;s natural anatomy. The implanted cup  12  should remain stable to prevent erosion of the surrounding bone and to inhibit generation of excessive wear debris in the prosthetic joint. 
         [0006]    Various methods and techniques have been used to secure an acetabular cup within a formed acetabular cavity. One such method includes the use of bone cement to secure the acetabular cup to the acetabulum. Another technique utilizes an acetabular cup having holes for receiving screws, or other types of fasteners, to affix the acetabular cup to bone. A further method includes the implantation of an acetabular cup having an outer surface with various surface features to enhance fixation of the cup within the acetabular cavity. Two or more of these methods may be used in conjunction with each other to secure the acetabular cup to the acetabulum. 
         [0007]    No matter which technique(s) are used to secure the acetabular cup, proper initial positioning of the acetabular cup within the reamed cavity is critical to the proper functioning of the prosthetic component. The positioning of the cup is complicated by the fact that incisions used in hip or femoral operations may be quite deep, with the implantation site remote from the initial incision location. Moreover, it is desired to keep the incision as small as possible both for improved healing as well as aesthetic purposes. 
         [0008]    Next, the liner  14  is inserted into the acetabular cup  12 . The liner  14  acts as a bearing surface against which the ball or head of the femoral component presses. The implantation of a liner presents many of the same difficulties as the implantation of a cup. The instruments used to keep the incision site open crowd the incision area and obscure the surgeon&#39;s vision. Thus, the liner must be manipulated into position in a very confined space. Moreover, care must be taken to ensure that no tissue is trapped between the acetabular cup and the acetabular liner as the liner is being inserted. Obviously, obscuring the vision of the surgeon hinders the procedure and can result in undesired delays. 
         [0009]    Once the acetabular line  14  is positioned within the acetabular cup  12 , the surgeon performs a range of motion procedure to verify that the acetabular cup  12  and liner  14  are properly positioned. The range of motion procedure involves insertion of the femoral ball  32  into the cavity  24  and manipulation of the patient&#39;s leg through various positions. When the range of motion procedure is satisfactorily completed, the surgeon inserts the constraining ring  16  onto the acetabular lip  22 , thereby inhibiting the ability of the lip  22  to flex. Accordingly, the femoral head  32  is constrained within the acetabular liner  14 . 
         [0010]    Manipulation of the constraining ring  16  implicates many difficulties which are similar to the difficulties in placing an acetabular cup or an acetabular liner. Additional difficulties, however, are presented due to the manner in which the constraining liner must be positioned. In order to position the constraining ring  16  on the lip  22 , the constraining ring  16  must be pre-positioned on the neck  30  as shown in  FIG. 3  prior to positioning the femoral ball  32  into the cavity  24 . Accordingly, the constraining ring must be located within the surgical site while the femoral component  26  and the acetabular system  10  are manipulated. Thus, any device used to install the constraining ring could further encumber the manipulation of the femoral component and the acetabular component thereby delaying the procedure. 
         [0011]    Additionally, the actual insertion of the constraining ring is difficult and awkward. Thus, the polyethylene liner may be inadvertently damaged, further delaying the procedure. 
         [0012]    What is needed therefore is an apparatus and method for positioning a constraining ring on an acetabular liner which overcomes one or more of the above-mentioned disadvantages. 
       SUMMARY OF THE INVENTION 
       [0013]    In one embodiment of the invention, a hand held instrument kit for use in positioning a constraining ring of an acetabular liner system includes a shaft including a first coupling member, and a plurality of heads, each of the plurality of heads including (i) a base configured to couple with the first coupling member and (ii) a pair of resilient gripper arms, each of the pair of resilient gripper arms defining a constraining ring reception area having a size different from the constraining ring reception area defined by the pair of gripper arms of each of the other of the plurality of heads. 
         [0014]    In a further embodiment, a hand held instrument system for insertion of a constraining ring onto an acetabular liner includes a shaft including a first coupling member, and at least one base member including a second coupling member for coupling with the first coupling member and a third coupling member configured to couple with a constraining ring. 
         [0015]    In another embodiment, a kit for a hand held instrument used in positioning a constraining ring of an acetabular liner system includes a shaft, a first base at an end portion of the shaft, a first seating portion defined by a portion of the perimeter of a first cylinder having a diameter similar to the diameter of the constraining ring, and a first pair of arms extending outwardly from the first base, each of the first pair of arms including a portion of the first seating portion and including a gripper portion configured to extend within the perimeter of the first cylinder in an un-flexed condition and to be resiliently positioned outwardly of the perimeter of the first cylinder in a flexed condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  depicts a perspective view of an exemplary acetabular cup, an acetabular liner and a constraining ring of the prior art; 
           [0017]      FIG. 2  depicts an side elevational view of a femoral component of the prior art; 
           [0018]      FIG. 3  depicts a perspective view of the constraining ring of  FIG. 1  positioned on the neck of the femoral component of  FIG. 2 ; 
           [0019]      FIG. 4  depicts a perspective view of a constraining ring inserter system in accordance with principles of the invention; 
           [0020]      FIG. 5  depicts a side plan view of the shaft of the constraining ring inserter system of  FIG. 4 ; 
           [0021]      FIG. 6  depicts a front plan view of the shaft of the constraining ring inserter system of  FIG. 4  showing the indent of the coupler of the shaft; 
           [0022]      FIG. 7  depicts a cross sectional view of shaft of the constraining ring inserter system of  FIG. 4  taken through the indent; 
           [0023]      FIG. 8  depicts a side perspective exploded view of the head of the constraining ring inserter system of  FIG. 4  showing a base, a retaining pin, a spring and a shuttle incorporating principles of the invention; 
           [0024]      FIG. 9  depicts a top plan view of the head of  FIG. 8  with the spring and restraining pin installed and the shuttle partially positioned within one of the bores of the base; 
           [0025]      FIG. 10  depicts a top plan view of the shuttle of  FIG. 8  showing a coupling bore, a lip and a plunger; 
           [0026]      FIG. 11  depicts a side plan view of the shuttle of  FIG. 8  showing a retaining pin slot, the flange and the plunger; 
           [0027]      FIG. 12  depicts a cross sectional view of the head of  FIG. 8  with the spring and restraining pin installed and the shuttle partially positioned within one of the bores of the base; 
           [0028]      FIG. 13  depicts a cross sectional view of the head of  FIG. 8  with the spring and restraining pin installed and the shuttle partially positioned within one of the bores of the base and the beveled portion of the shaft of  FIG. 4  abutting the lip of the shuttle; 
           [0029]      FIG. 14  depicts a cross sectional view of the head of  FIG. 8  with the spring compressed and the restraining pin installed and the shuttle positioned more fully within one of the bores of the base as compared with  FIG. 13  such that the coupling bore is aligned with one of the bores of the base allowing the beveled portion of the shaft of  FIG. 4  to pass through the coupling bore; 
           [0030]      FIG. 15  depicts a cross sectional view of the head of  FIG. 8  with the flange of the shuttle coupling with the indent of the shaft thereby coupling the shaft with the head; 
           [0031]      FIG. 16  depicts a perspective view of the constraining ring inserter system of  FIG. 4  positioned above a constraining ring of  FIG. 1 ; 
           [0032]      FIG. 17  depicts a bottom plan view of the constraining ring inserter system of  FIG. 4  showing flexure of the gripper portions of the arms in an outwardly direction to receive a constraining ring; 
           [0033]      FIG. 18  depicts a bottom plan view of the constraining ring inserter system of  FIG. 4  coupled with the constraining ring of  FIG. 1   
           [0034]      FIG. 19  depicts a perspective view of the constraining ring inserter system of  FIG. 4  coupled with the constraining ring of  FIG. 1 ; 
           [0035]      FIG. 20  depicts a perspective view of the constraining ring inserter system of  FIG. 4  coupled with the constraining ring of  FIG. 1  with the constraining ring positioned on the neck of the femoral component of  FIG. 1 ; and 
           [0036]      FIG. 21  depicts a perspective view of a kit including a shaft that can be used with each of a plurality of heads, each of the heads configured to be used with constraining rings provided with acetabular systems of different sizes in accordance with principles of the invention. 
       
    
    
     DESCRIPTION 
       [0037]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written description. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0038]    Referring generally to  FIG. 4 , a perspective view of a constraining ring inserter system  100  for positioning a constraining ring onto an acetabular liner is shown. The inserter system  100  includes a shaped shaft  102  and a head  104 . The shaft  102 , also shown in plan view in  FIGS. 5 and 6 , is connected at one end to a handle  106 . A coupling member  108  is located at the opposite end of the shaft  102 . The coupling member  108  includes an indent  110  and a lip  112 . A guide portion  114  located above the coupling member  108  includes a flat portion  116  as shown in  FIG. 7  which is a cross sectional view of the shaft  102  taken through the indent  110 . 
         [0039]    The shaft  102  further includes an upper portion  118  that extends outwardly from the handle  106  and a lower portion  120  that is substantially parallel to but offset from the axis of the upper portion  118 . A middle portion  122  of the shaft  102  extends between the upper portion  118  and the lower portion  120 . The axis of the middle portion  122  in this embodiment forms an angle with both the axis of the upper portion  118  and the axis of the lower portion  120 . In the embodiment of  FIGS. 4-7 , the angle is selected to be in the range of about 15 degrees to about 30 degrees. In one embodiment, an angle of 22.5 degrees is selected. A beveled portion  124  is located at the end of the shaft  102  opposite to the handle  106  and an enlarged portion  126  is located between the coupling member  108  and the lower portion  120  of the shaft. 
         [0040]    In the embodiment of  FIGS. 4-6 , the handle  106  is formed separately from the shaft  102  while the beveled portion  124 , the enlarged portion  126  and the coupling member  108  are integrally formed with the shaft  102 . Any or all of these components may alternatively be formed integrally or separately. 
         [0041]    Referring to  FIGS. 8-9 , the head  104  includes a base  130 , a spring  132 , a retaining pin  134 , a shuttle  136  and a pair of arms  138  and  140 . The proximal portions  142  and  144  of the arms  138  and  140  are joined to the base  130  while the distal portions  146  and  148  of the arms  138  and  140  are spaced apart from each other. 
         [0042]    Gripper portions  150  and  152  are separated from a seating portion  154  by notches  156  and  158 , respectively. A ledge  159  extends above both of the gripper portions  150  and  152  and the seating portion  154 . The opposing faces of the gripper portions  150  and  152  along with the seating portion  154  thus define a constraining ring reception area between the arms  138  and  140 . 
         [0043]    The base  130  includes a bore  160  and a bore  162  which intersect within the base  130 . The bore  160  includes a flat portion  164  located above the intersection with the bore  162 . A retaining pin bore  166  also intersects the bore  162 . As shown in  FIG. 12 , the bores  160  and  162  are generally perpendicular. In alternative embodiments, the bores may intersect in a non-perpendicular manner. In those embodiments, the cooperative shapes of the shuttle and the coupling portion of the shaft provide a keying function such that the heads and shaft are coupled in a predetermined orientation. 
         [0044]    The shuttle  136 , also shown in  FIGS. 10 and 11 , includes a coupling bore  170  and a travel limiting slot  172 . One end of the shuttle  136  includes a plunger  174  and a flange  176 . A lip  178  is located adjacent to the flange  176  and the coupling bore  170 . The opposite end of the shuttle  136  is formed as a button  180 . 
         [0045]    When the head  104  is assembled as shown in  FIG. 12 , the spring  132  is positioned within the bore  162 . The button  180  of the shuttle  136  extends outwardly from the base  130 . The remainder of the shuttle  136  is positioned within the bore  162  with the plunger  174  located within the spring  132  and the flange  176  abutting the spring  132 . The spring  132  is somewhat compressed, providing a bias to the shuttle  136  in a direction outwardly from the bore  162 . The shuttle  136  is maintained partially within the bore  162  by the retaining pin  134  which extends through retaining pin bore  166  and the travel limiting slot  172 . 
         [0046]    The length of the travel limiting slot  172  is selected such that when the spring  132  biases the shuttle  136  such that the retaining pin  134  contacts the end portion of the travel limiting slot  172  closest to the spring  132 , the lip  178  is positioned partially within the bore  160  as seen in  FIGS. 9 and 12 . 
         [0047]    The base  130  is coupled to the shaft  102  by insertion of the beveled portion  124  into the bore  160  as shown in  FIG. 13 . As the beveled portion  124  approaches the intersection of the bores  160  and  162 , the beveled portion  124  contacts the lip  178  thereby applying a compressive force on the spring  132 . As the spring  132  is compressed, the shuttle  136  moves farther into the bore  162  (to the right as depicted in  FIG. 13 ), bringing the coupling bore  170  into alignment with the bore  160 . 
         [0048]    Once the coupling bore  170  and the bore  160  are substantially aligned, the beveled portion  124  is allowed to move farther into the coupling bore  170  which is located at the intersection of the bores  160  and  162  as shown in  FIG. 14 . As shown in  FIG. 14 , the guide portion  114  of the shaft  102  begins to be received into the bore  160  before the beveled portion  124  is inserted into the portion of the bore  160  below the bore  162 . The radius of the cylindrical portion of the perimeter of the guide portion  114  is selected to be slightly less than the radius of the cylindrical portion of the perimeter of the bore  160 . 
         [0049]    As shown in  FIG. 9 , the bore  160  includes a flat portion  164  that has an effective radius that is less than the radius of the cylindrical portion of the perimeter of the bore  160 . Accordingly, the guide portion  114  can only be inserted into the bore  160  when the flat portion  116  of the guide portion  114  (see  FIG. 7 ) is radially aligned with the flat portion  164  of the bore  160 . This causes the coupling member  108  to be oriented in the coupling bore  170  as shown in  FIG. 14 . 
         [0050]    Consequently, as the guide portion  114  is inserted into the bore  160 , the indent  110  is oriented with the bore  162 . Continued insertion of the shaft  102  into the base  130  causes the indent  110  to align with the bore  162  and the flange  176  as the beveled portion  124  moves into the portion of the bore  160  below the intersection with the bore  162 . Since the beveled portion  124  is no longer contacting the shuttle  136  as shown in  FIG. 15 , the force of the spring  132  moves the shuttle  136  in a direction outwardly from the bore  162  causing the flange  176  to couple with the indent  110 . The flange  176  thus axially locks the shaft  102  while the flat portion  164  of the bore  160  radially locks the shaft  102 . 
         [0051]    With the head  104  firmly coupled with the shaft  102 , the constraining ring inserter system can be used to position a constraining ring. Referring to  FIG. 16 , the head  104  is aligned with the constraining ring  16  with the arms  138  and  140  over the constraining ring  16 . The seating portion  154  is then placed against the constraining ring  16  and the head  104  is pressed and pivoted against the constraining ring  16  by movement of the head  104  in the direction of the arrows  182  and  184 , respectively. 
         [0052]    The constraining ring  16  has a diameter that is slightly less than the diameter of a cylinder shown as circle  186  in  FIG. 17 . A portion of the perimeter of the cylinder (depicted as circle  186 ) defines the seating portion  154 . Accordingly, the constraining ring  16  initially fits within the constraining ring reception area defined by the arms  138  and  140  and against the ledge  159  as the head  104  is maneuvered in the direction of the arrows  182  and  184 . The arms  138  and  140 , however, are configured such that the gripper portions  150  and  152  lie within the perimeter of the circle  186 . Thus, as the head  104  is pressed and rotated, the gripper portions  150  and  152  contact the constraining ring  16 . 
         [0053]    The arms  138  and  140 , however, are somewhat flexible. The flexibility may be achieved by selection of the material used to fashion the arms  138  and  140 , which may be any acceptable biocompatible material such as surgical grade stainless steel. Flexibility in the embodiment of  FIG. 16  is further provided because the arms  138  and  140  are not joined at the distal portions  146  and  148 . 
         [0054]    In the embodiment of  FIG. 16 , the notches  156  and  158  provide even more flexibility. Accordingly, as the head  104  is pressed and rotated against the constraining ring  16 , the gripper portions  150  and  152  are flexed outwardly from the positions shown in  FIG. 17  to the position shown in shadow in  FIG. 17 , allowing the constraining ring  16  to slide into the constraining ring reception area as shown in  FIGS. 18 and 19  and against the ledge  159 . The resiliency of the arms  138  and  140  provide a gripping force on the constraining ring  16 , keeping the constraining ring  16  within the constraining ring reception area. 
         [0055]    The constraining ring  16  may now be positioned on the neck  30  in preparation for placement on the lip  22  as shown in  FIG. 20 . The shape of the shaft  102  is selected such that the shaft extends outwardly from the surgical site in a manner which does not overly interfere with the surgeon&#39;s access to the acetabular cup  12 , the acetabular liner  14 , or the femoral head  32 . Once the surgeon is ready to lock the femoral head  32  within the cavity  24 , the handle  106  is used to maneuver the constraining ring  16  into position and the ledge  159  transfers force uniformly about the constraining ring  16  to slide the constraining ring  16  onto the lip  22 . 
         [0056]    As the constraining ring  16  seats about the lip  22 , sufficient force is exerted by the lip  22  on the constraining ring  16  to overcome the frictional grip of the arms  138  and  140  on the constraining ring  16 . Accordingly, the surgeon can decouple the constraining ring inserter system  100  from the constraining ring  16 . 
         [0057]    Once the constraining ring inserter system  100  is decoupled from the head  104 , the shaft  102  may be removed from the head  104  by depressing the button  180 . This forces the shuttle  136  against the spring  132  thereby compressing the spring  132  and allowing the shuttle  136  to move more fully into the bore  162 . The process described above for coupling the shaft  102  and the head  104  is then reversed and the shaft  102  is decoupled from the head  104 . Decoupling of the head  104  and the shaft  102  facilitates decontamination and sterilization of the components. 
         [0058]    Typically, acetabular systems incorporating constraining rings are used with femoral heads of different sizes. Thus, kits for use with femoral components may include constraining rings of different sizes. By way of example, a kit  200  shown in  FIG. 21  includes a shaft  202  and five heads  204 ,  206 ,  208 ,  210  and  212 . Each of the heads  204 ,  206 ,  208 ,  210  and  212  include a base  214 ,  216 ,  218 ,  220  and  222 , respectively, which include bores and a shuttle that are identical to the bores and shuttles of the other bases. The bases  214 ,  216 ,  218 ,  220  and  222  couple with the handle  202  in the same manner as described above with respect to the shaft  102  and the base  130 . 
         [0059]    The heads  204 ,  206 ,  208 ,  210  and  212 , however, are each configured to operate with a constraining ring of a size different than the size of the constraining ring with which the other heads are configured to operate. In this embodiment, the arms  224  and  226  of the head  204  are spaced apart so as to couple with a constraining ring of a 28 millimeter acetabular cup system, the arms  228  and  230  of the head  206  are spaced apart so as to couple with a constraining ring of a 32 millimeter acetabular cup system, the arms  232  and  234  of the head  208  are spaced apart so as to couple with a constraining ring of a 36 millimeter acetabular cup system, the arms  236  and  238  of the head  210  are spaced apart so as to couple with a constraining ring of a 40 millimeter acetabular cup system and the arms  240  and  242  of the head  212  are spaced apart so as to couple with a constraining ring of a 44 millimeter acetabular cup system. 
         [0060]    As discussed above, the flexibility of the arms for a particular head may be achieved in various ways. As the heads become smaller, however, the arms tend to become stiffer. For example, even when using the same materials, arms used for larger constraining rings are longer and thus provide more flexibility than the arms used with smaller constraining rings. In the embodiment of  FIG. 21 , the relative stiffness of the shorter arms such as the arms  224  and  226  is mitigated by increasing the size of the notch in the arms. Accordingly, the size of the notches in the arms of each of the heads  204 ,  206 ,  208 , and  210  are larger than the notches in the next larger head. 
         [0061]    Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.