Abstract:
A system for replacing a hip joint can include a first acetabular cup formed of a first material and having a first inner diameter and a first thickness. A second acetabular cup can be formed of a second material and having a second inner diameter and a second thickness. A first femoral hip prosthesis can include a first femoral head that is alternately accommodated by either of the first or second acetabular cups. A bearing can be adapted to be interposed between the first femoral head and one of the first or second acetabular cups. The first and second inner diameters can be the same. The first thickness can be less than the second thickness. The first material can be distinct from the second material.

Description:
FIELD 
     The present disclosure relates generally to a system and method for use in orthopedic surgery and, more particularly, to an acetabular cup system or kit, which includes a plurality of different sized acetabular cups formed from two different materials having different stiffnesses. 
     BACKGROUND 
     A natural hip joint may undergo degenerative changes due to a variety of etiologies. When such degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural hip joint with a prosthetic hip. If the acetabulum needs repair, all remnants of articular cartilage may be removed from the acetabulum and an acetabular prosthesis which will accommodate the head or ball of the hip prosthesis may be affixed to the acetabulum. 
     The acetabular prosthesis can include an acetabular cup and a bearing that, in combination, cooperate with the head or ball of the hip prosthesis. One suitable material for such an acetabular cup is titanium. Titanium has the benefit of being biocompatible as well as elastic. Elasticity can be an important material characteristic as most acetabular cups need to deform slightly during press-fitting into a prepared acetabulum. However, because titanium is so elastic, the material generally needs to be a predetermined minimum thickness (e.g., about 3.5 mm or larger) in order to accommodate the loads in this area. This minimum thickness either requires the head of the femoral component to be smaller or additional reaming and bone removal to accommodate an acetabular cup having a larger outer diameter. In most cases however, reducing the size of the femoral head is unfavorable as it may increase the risk of dislocation. Moreover, it is desirable to keep reaming and bone removal at a minimum in order to maximize the amount of host bone in the acetabular socket for receipt of the acetabular cup. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A system for replacing a hip joint can include a first acetabular cup formed of a first material and having a first inner diameter and a first thickness. A second acetabular cup can be formed of a second material and having a second inner diameter and a second thickness. A first femoral hip prosthesis can include a first femoral head that is alternately accommodated by either of the first or second acetabular cups. A bearing can be adapted to be interposed between the first femoral head and one of the first or second acetabular cups. The first and second inner diameters can be the same. The first thickness can be less than the second thickness. The first material can be distinct from the second material. 
     According to additional features, the first acetabular cup can have a first outer diameter. The second acetabular cup can have a second outer diameter. The first outer diameter can be less than the second outer diameter. The second material can be more flexible than the first material. In one example, the first material can be cobalt-chrome molybdenum and the second material can be titanium. The first and second acetabular cups can have substantially similar flexibility. 
     A related method can include preparing an acetabular socket of a hip joint. A size of the prepared acetabular socket can then be determined. One of the first or the second acetabular cups can be selected based on the determined size of the prepared acetabular socket. The selected first or second acetabular cup can be impacted into the acetabular socket. The first femoral hip prosthesis can be implanted, and the bearing can be positioned between the femoral head and the selected first or second acetabular cups. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a perspective view of a system or kit for replacing a hip joint and including a plurality of femoral hip prostheses, a first set or plurality of acetabular cups, a second set or plurality of acetabular cups and a first set or plurality of bearings; 
         FIG. 2  is an anterior perspective view of an acetabulum being reamed by an exemplary reamer; 
         FIG. 3  is an anterior perspective view of a reamed acetabular socket subsequent to reaming; 
         FIG. 4  is a perspective environmental view of a surgeon determining suitable components of the kit of  FIG. 1  based on measurements of the reamed acetabular socket of  FIG. 3 ; and 
         FIG. 5  is an anterior view of a femoral hip prosthesis, a bearing and an acetabular cup selected from the kit and shown in an implanted position in the acetabular socket. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The following description will be specifically directed toward a primary hip replacement procedure wherein a femoral hip prosthesis, an acetabular cup, and a bearing are implanted into the patient. It is appreciated however that the following teachings may also be applied to a surgical procedure for implanting other combinations of acetabular components. Moreover, the following teachings may also be applicable to a hip revision surgical procedure wherein a surgeon may be required to remove entirely or portions of a previously implanted hip prosthesis. 
     With initial reference to  FIG. 1 , a system or kit for use during a surgical hip replacement procedure is shown and generally identified at reference numeral  10 . The kit  10  can generally include a plurality of femoral hip prostheses collectively referred to at reference numeral  12 , a first set of acetabular cups collectively referred to at reference numeral  14 , a second set of acetabular cups collectively referred to at reference numeral  16  and a set of bearings collectively referred to at reference numeral  18 . The femoral hip prostheses  12  can include a first, second, third and fourth femoral hip prosthesis  22   a ,  22   b ,  22   c  and  22   d , respectively. The first femoral hip prosthesis  22   a  can generally include a stem  24   a , a neck  26   a  and a head  28   a . The second femoral hip prosthesis  22   b  can generally include a stem  24   b , a neck  26   b  and a head  28   b . The third femoral hip prosthesis  22   c  can include a stem  24   c , a neck  26   c  and a head  28   c . The fourth femoral hip prosthesis  22   d  can include a stem  24   d , a neck  26   d  and a head  28   d . The heads  28   a - 28   d  each have a different diameter d 1 -d 4 , respectively. In one example, as will be described further below, the diameters d 1 -d 4  can increase in size sequentially from the head  28   a  to the head  28   d . The hip prostheses  12  can be modular having specific head, neck and stem configurations. The hip prosthesis  12  can also be monolithic. 
     The first set of acetabular cups  14  can generally include a first acetabular cup  34   a , a second acetabular cup  34   b , a third acetabular cup  34   c  and a fourth acetabular cup  34   d . Each of the acetabular cups  34   a - 34   d  is formed of a first material and has a common thickness T 1 . In one example, the first material can be cobalt-chrome molybdenum. According to the present teachings, and as will be described further below, the inner diameter and the outer diameter of the first set of acetabular cups  14  is sequentially increased from the first acetabular cup  34   a  through the fourth acetabular cup  34   d . The first set of acetabular cups  14  can each include a plurality of passages  35   a - 35   d  formed therethrough. 
     The second set of acetabular cups  16  can generally include a first acetabular cup  36   a , a second acetabular cup  36   b , a third acetabular cup  36   c  and a fourth acetabular cup  36   d . Each of the acetabular cups  36   a - 36   d  is formed of a second material and has a thickness T 2 . In one example, the second material can be titanium. According to the present teachings, and as will be described further below, the inner diameter and the outer diameter of the second set of acetabular cups  16  is sequentially increased from the first acetabular cup  36   a  through the fourth acetabular cup  36   d . Each of the acetabular cups of the second set of acetabular cups  16  includes a plurality of optional screw receiving passages  37   a - 37   d . Any or all of the first and second sets of acetabular cups  14  and  16  can include an outer layer of porous material to enhance bony ingrowth. 
     The first set of bearings  18  can generally include a first bearing  38   a , a second bearing  38   b , a third bearing  38   c  and a fourth bearing  38   d . Each of the bearings  38   a - 38   d  has a common thickness T 3 . The bearings  18  can have any suitable configuration, such as constrained bearings, high-wall bearings or other bearing configurations. 
     According to the teachings of the present disclosure, in the present example, each component in the kit  10  is compatible with other components of the kit  10  having a similar suffix. In other words, in the present example, the femoral hip prosthesis  22   a  can cooperate with the bearing  38   a  and either one of the acetabular cups  34   a  or  36   a . Likewise, the femoral hip prosthesis  22   b  can be used with the bearing  38   b  and either of the acetabular cups  34   b  or  36   b . The femoral hip prosthesis  22   c  can be used with the bearing  38   c  and either of the acetabular cups  34   c  or  36   c . The femoral hip prosthesis  22   d  can be used with the bearing  38   d  and either of the acetabular cups  34   d  or  36   d.    
     Exemplary dimensions of the components of the kit  10  will now be described for exemplary purposes. It is appreciated however that the dimensions may be changed without departing from the scope of the present disclosure. As used herein the phrase “the same” is used to denote an identical or substantially identical dimension within a tolerance. In one example, the dimensions can be the same within a tolerance of about 0.25 mm. All of the acetabular cups  34   a - 34   d  and  36   a - 36   d  have a hemispherical shape and include an inner bearing engaging surface and an outer bone engaging surface  40  and  42 , respectively (only identified on acetabular cup  34   a  for clarity). Various diameters can be provided for the acetabular cups  34   a - 36   d  as described below. In general, an inner diameter D 5  of the acetabular cup  34   a  is the same or substantially the same as an inner diameter D 6  of the acetabular cup  36   a . Likewise, an inner diameter D 7  of the acetabular cup  34   b  is the same or substantially the same as an inner diameter D 8  of the acetabular cup  36   b . The inner diameter D 9  of the acetabular cup  34   c  is the same or substantially the same as the inner diameter D 10  of the acetabular cup  36   c . The inner diameter D 11  of the acetabular cup  36   d  is the same or substantially the same as the inner diameter D 12  of the acetabular cup  36   d.    
     In one example, the inner diameters D 5  and D 6  can be 41 mm, the inner diameters D 7  and D 8  can be 45 mm, the inner diameters D 9  and D 10  can be 49 mm and the diameters D 11  and D 12  can be 53 mm. In general, the outer diameters D 13 -D 20  sequentially increase by 2 mm. Thus, the acetabular cup  34   a  can have an outer diameter D 13  of 46 mm. The acetabular cup  36   a  can have an outer diameter D 14  that is 48 mm. The acetabular cup  34   b  can have an outer diameter D 15  that is 50 mm. The acetabular cup  36   b  can have an outer diameter D 16  that is 52 mm. The acetabular cup  34   c  can have an outer diameter D 17  that is 54 mm. The acetabular cup  36   c  can have an outer diameter D 18  that is 56 mm. The acetabular cup  34   d  can have an outer diameter D 19  that is 58 mm. The acetabular cup  36   d  can have an outer diameter D 20  that is 60 mm. In one example, the thickness T 1  is 2.5 mm and the thickness T 2  is 3.5 mm. 
     In the present example, the bearing  38   a  has an inner diameter D 21  of 32 mm and an outer diameter D 22  of 41 mm. The bearing  38   b  has an inner diameter D 23  of 36 mm and an outer diameter D 24  of 45 mm. The bearing  38   c  has an inner diameter D 25  of 40 mm and an outer diameter D 26  of 49 mm. The bearing  38   d  has an inner diameter D 27  of 44 mm and an outer diameter D 28  of 53 mm. In this example, the thickness T 3  of each of the bearings  38   a - 38   d  can be 4.5 mm. 
     The diameter of the head  28   a  of the femoral hip prosthesis  22   a  can be 32 mm. The diameter of the head  28   b  of the femoral hip prosthesis  22   b  can be 36 mm. The diameter D 3  of the head  28   c  of the femoral hip prosthesis  22   c  can be 40 mm. The diameter D 4  of the head  28   d  of the femoral hip prosthesis  22   d  can be 44 mm. Again it will be appreciated that the dimensions set forth herein are merely exemplary. Furthermore, the dimensions may be approximate. Again, inner diameters of various acetabular cups  14 ,  16  that are described as being the same or substantially the same are so within specific tolerances. 
     With additional reference now to  FIGS. 2-5 , an exemplary method for using the kit  10  to replace a hip joint according to one example of the present teachings will now be described. Initially, an acetabulum  50  can be reamed, such as with a reamer  52 . The exemplary reamer  52  can comprise a reamer drive shaft  54  that is rotatably supported within a cannulated shaft  56 . A cutting member  60  can be selectively coupled at a distal end  62  of the reamer drive shaft  54 . A mating structure  64  can be provided at a proximal end of the reamer drive shaft  54 . A driver (not shown) may be operably coupled with the mating structure  64  to impart rotational force through the reamer drive shaft  54  to the cutting member  60 . The acetabulum  50  may be generally hemispherically reamed until concentric removal of all acetabular cartilage and/or bone cement and portions of host bone if necessary (e.g., such as during a revision procedure) is achieved. Once the acetabulum  50  has been appropriately reamed, trial gauges (not shown), which are well known in the art, may be used to determine the size of the reamed acetabulum  50 . A corresponding outer diameter of a suitable acetabular cup (e.g., a corresponding acetabular cup from the first and second sets of acetabular cups  14  and  16 ) is then known. 
     As illustrated in  FIG. 3 , the acetabulum  50  is shown having a reamed acetabular socket  68 . Again, it can be desirable to leave as much host bone from the acetabulum  50  in place. As explained above, the first set of acetabular cups  14  are all formed by cobalt-chrome molybdenum and have a thickness of 2.5 mm. The second set of acetabular cups  16  are all formed of titanium and have a thickness of 3.5 mm. As is known, the stiffness of cobalt-chrome molybdenum per unit thickness is higher than titanium. Moreover, titanium has a higher flexibility per unit thickness than cobalt-chrome molybdenum. Because each acetabular cup  34   a - 34   d  of the first set of acetabular cups  14  is thinner than each acetabular cup  36   a - 36   d  of the second set of acetabular cups  16  (2.5 mm vs. 3.5 mm), the stiffness of an acetabular cup  34   a - 34   d  of the first set of acetabular cups  14  relative to a corresponding acetabular cup  36   a - 36   d  of the second set of acetabular cups  16  is the same or substantially the same. In this way, a surgeon  70  ( FIG. 4 ) is able to achieve a desired stiffness utilizing any of the acetabular cups from the first or second sets of acetabular cups  14  and  16  to attain a desired press-fit relationship into the reamed acetabular socket  68  of patient  72 . 
     With continued reference now to  FIG. 4 , by initially starting with cobalt-chrome molybdenum, a thinner 2.5 mm thickness acetabular cup (such as acetabular cup  34   a ) can be used to accommodate a first femoral head size (i.e., D 1  of femoral head  28   a ). When the surgeon  70  may require the next larger size outer diameter acetabular cup (such as the acetabular cup  36   a ), the same femoral head  28   a  can be used since the inner diameter (i.e., D 5  vs. D 6 ) stays the same and the material of the acetabular cup changes to titanium having a thickness of 3.5 mm (and consequently the acetabular cup outer diameter increases by 2 mm). If the surgeon  70  determines that the next larger size femoral head (i.e., femoral head  28   b ) should be used, the surgeon  70  can select the cobalt-chrome molybdenum acetabular cup  34   b  having the thickness of 2.5 mm. If it is determined that the next size larger outer diameter acetabular cup is required, the surgeon  70  can select the titanium acetabular cup  36   b  having a thickness of 3.5 mm. Again, it is appreciated that the femoral hip prosthesis  22   b  having the head  28   b  can be used for either of the acetabular cups  34   b  or  36   b  because the inner diameters D 7  vs. D 8  are the same or substantially the same. As can be appreciated, the surgeon  70  can make similar decisions as to whether other acetabular cups, such as  34   c - 36   d  or others may be particularly suited for a given patient  72 . Nevertheless, the kit  10  can be used by the surgeon  70  to minimize host bone loss without having to compromise head size of the femoral hip prosthesis while at the same time providing the surgeon  70  with the desired acetabular cup flexibility during implantation. Furthermore, with the kit  10 , a larger diameter head can be used 50% of the time as a cobalt-chrome molybdenum cup can be used having the same outer diameter as a comparable titanium cup while offering a larger inner diameter that accommodates the larger diameter head. As used herein, the term “kit” or “system” is used to denote a collection of readily available components (i.e., acetabular cups, bearings and/or femoral hip prostheses) available for a surgeons easy selection. The collection of readily available components can be grouped or arranged in any manner that provides the surgeon with comprehensive access and ease of identification. In this way, each of the components may be prepackaged individually in sterile containers while still being offered as a collective kit or set of components. 
     Turning now to  FIG. 5 , an acetabular cup  36   a  is shown implanted into the reamed acetabular socket  68 . The cup  36   a  can be implanted by any suitable method. According to one such method, an impacting instrument (not shown) may be used to properly position the acetabular cup  36   a . In one example, the impacting instrument may be threadably secured to an apical hole (not specifically shown) of the acetabular cup  36   a . Once the orientation of the acetabular cup  36   a  is acceptable, the inserting instrument may be solidly impacted to fully seat (or press-fit) the acetabular cup  36   a  into the acetabular socket  68 , such that firm rim fixation is achieved. Once the acetabular cup  36   a  has been solidly impacted, the inserting instrument may be carefully removed from the acetabular cup  36   a.    
     A plurality of bone screw holes (not specifically shown) may be bored into the acetabulum  50  while aligning with existing holes  37   a  already formed in the acetabular cup  36   a . Once the bone screw holes have been formed in the acetabulum  50 , as is also known in the art, a depth gauge (not shown) may be used to determine the length of the fixation screws. With the length of the screws determined, a fixation screw or multiple fixation screws  76  may be advanced through the respective holes  37   a  in the acetabular cup  36   a  and driven into the screw holes in the acetabulum  50 . In other examples, the acetabular cup  36   a  additionally or alternatively may be cemented into the acetabulum  50 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.