PATENT ABSTRACT
An orthopedic cup impactor for use in minimally invasive hip replacement surgical procedures is described. The impactor comprises a handle, residing at a proximal end portion, and a cup engagement sub-assembly located at a distal portion. A shaft resides therebetween. The shaft portion is designed with a large radius of curvature that provides added clearance when inserting the impactor in obese patients. The cup engagement sub-assembly features a drive train that comprises a series of “U” and “H” joints deigned to provide full rotational motion. The drive train may be designed to be removable from the cup impactor to provide more efficient and thorough cleaning.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/370,487, filed Aug. 4, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to minimally invasive surgery, and more particularly to an acetabular prosthetic cup impactor tool for use in minimally invasive hip replacement surgery. 
       PRIOR ART 
       [0003]    Approximately 200,000 hip replacements are performed each year in the United States and the number is expected to continue to grow as the population continues to age. The usual reasons for hip replacement are osteoarthritis, rheumatoid arthritis and traumatic arthritis, all of which can cause pain and stiffness that limit mobility and the ability to perform daily living activities. Hip replacement surgery is usually performed where other measures (e.g. physical therapy, medications, and walking aids) are unable to overcome the chronic pain and disability associated with these conditions. 
         [0004]    Obesity is an increasingly common health concern in the United States. According to the Center for Disease Control and Prevention (CDC), about one third of the U.S. population is obese. Studies have suggested that obesity is linked to the development of joint ailments, particularly of the hip and knee. These studies disclosed, for example, that obesity increases the risk for developing osteoarthritis in the hip and the knee, and suggest that obesity plays a role in initiating and accelerating hip and knee osteoarthritis. The development of osteoarthritis occurs either directly by the increased load on a joint or indirectly because obesity is associated with a variety of metabolic disorders. Additionally, the added weight of an obese person contributes to the stresses that are applied to a person&#39;s joints thereby increasing joint wear, and in so doing accelerating the need for replacement. Therefore, there is an increasing need to address joint ailments for obese patients as well. 
         [0005]    Various techniques are used by orthopedic surgeons to perform hip replacements. These include the following approaches: anterior, antero-lateral, lateral, postero-lateral and posterior. The posterior and postero-lateral approaches account for approximately 60%-70% of hip replacement surgeries. 
         [0006]    Traditional hip replacement surgery involves an open surgical procedure and extensive surgical dissection. However, such procedures require a longer recovery period and rehabilitation time for the patient. The average hospital stay for open hip replacement procedures is 4-5 days, followed in most cases by extensive rehabilitation. 
         [0007]    More recently, there has been considerable interest and research done in Minimally invasive Surgery (MIS), including the use of MIS procedures in connection with hip replacement surgery. In comparison with the traditional open surgical approach, MIS hip replacement surgeries involve fewer traumas to the muscles surrounding the hip joint. Specifically, fewer muscles that help to stabilize the hip joint are cut in MIS hip replacement surgeries, reducing the risk of dislocation of the hip surgery and speeding recovery. Patients spend less time in the hospital and return to normal life activities more quickly. 
         [0008]    MIS approaches use smaller surgical openings, which require specialized instruments to perform hip replacement procedures. As such, these MIS procedures are beneficial since they are less traumatic to the body. However, these MIS procedures are particularly difficult to perform with obese patients. The increased body mass and overall tissue volume of obese patients add additional complications in performing MIS procedures, particularly in accessing the surgical site. 
         [0009]    In these cases, the incision is especially deep as there are thicker and deeper masses of soft tissue. Traditional acetabular cup impactors provide some clearance of soft tissue. However, traditional impactors provide inadequate clearance particularly when performing a MIS procedure on an obese patient. Accordingly, there is a need for an improved impactor tool for use in MIS orthopedic procedures (e.g., hip replacement surgery) with obese patients that addresses some of the shortcomings in the existing surgical impactors noted above. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with one embodiment, an orthopedic cup impactor for use in minimally invasive hip replacement surgical procedures is provided. The impactor comprises a handle, residing at a proximal end portion and a cup engagement sub-assembly located at a distal portion. A shaft resides therebetween. The shaft portion is designed with a large radius of curvature that provides added clearance when inserting the impactor in obese patients. The shaft portion is further designed with a curved underside surface and a planar top surface with beveled side edges. These features aid in the insertion of the impactor and provide surfaces to aid in the leverage of the tissue. 
         [0011]    In accordance with another embodiment, the impactor of the present invention features an offset between the handle portion and the distal portion. The offset between the handle portion and the distal end allows for a much deeper insertion of the cup impactor into obese patients than traditional impactors with obese patients. 
         [0012]    In accordance with an additional embodiment, the impactor of the present invention features a shaft with a curved cross-section. This feature enables the impactor access into an obese patient with increased efficiency. Furthermore, the shaft&#39;s curved cross-section helps to retard tissue necrosis. 
         [0013]    In accordance with yet another embodiment, the impactor features a cup engagement subassembly comprising a drive shaft having multiple degrees of freedom. This drive shaft design feature, comprising a series of “U” and “H” joints, provides full rotation at differing bend angles when inserting an orthopedic implant. Furthermore, in yet another embodiment, the drive train may be designed to be removable from the cup impactor. Such a feature allows for efficient and thorough cleaning of the drive train after a surgical procedure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of an embodiment of a cup impactor. 
           [0015]      FIG. 2  is a side view illustrating alternate orientations of the cup impactor embodiment shown in  FIG. 1 . 
           [0016]      FIG. 3  illustrates a bottom view of the embodiment of the cup impactor shown in  FIG. 1 . 
           [0017]      FIG. 4  shows a magnified cross-sectional view of a distal end portion of the cup impactor embodiment shown in  FIG. 1 . 
           [0018]      FIG. 5  illustrates a side view of an embodiment of a drive train of the present invention. 
           [0019]      FIG. 6  shows a magnified side view of the embodiment of the drive train shown in  FIG. 5 . 
           [0020]      FIG. 7  is a perspective view of the cup impactor with an embodiment of a drive tool. 
           [0021]      FIG. 8  shows an end view of the cup impactor embodiment shown in  FIG. 1 . 
           [0022]      FIG. 8A  illustrates an alternate embodiment of the cup impactor shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Now turning to the figures,  FIGS. 1 to 8A  illustrate embodiments of a cup impactor  10  of the present invention. As illustrated in FIG. I, the cup impactor  10  comprises a handle  12  located at a proximal end portion  14  and an orthopedic cup engagement sub-assembly  16  located at a distal end portion  18  thereof. A shaft  20  resides between the respective handle portion  12  and the distal end portion  18  of the impactor  10 . 
         [0024]    The cup impactor  10  has an impactor length  22  and an impactor height  24  ( FIG. 7 ). In a preferred embodiment, the impactor length  22  ranges from about 20 cm to about 100 cm, more preferably, from about 40 cm to about 60 cm. In a further embodiment, the impactor height  24  ranges from about 5 cm to about 20 cm, more preferably, from about 10 cm to about 15 cm. 
         [0025]    In an embodiment, the shaft  20  is curved between the handle  12  residing at the proximal end  14  and the distal end  19  of the impactor  10 . Preferably, the shaft  20  is curved similarly to that of an arc  26  with an apex  28  positioned at about its maximum height. In a preferred embodiment, the arc  26  has a radius of curvature  30  that ranges from about 10 cm to about 20 cm as measured with respect to an inner surface  32  thereof. 
         [0026]    The shaft  20  preferably has a planar top surface  34 . Beveled top side edges  36 ,  38  transition from the top surface  34  to respective left and right sidewalls  40 ,  42  of the shaft  20  ( FIG. 8 ). The beveled side edges  36 ,  38  further extend longitudinally from the handle portion  12  to the distal end  19  of the impactor  10 . In a preferred embodiment, the top side edges  36 ,  38  have a radius of curvature  44 ,  46  that ranges from about 0.1 cm to about 2 cm. Furthermore, the left and right sidewalls  40 ,  42  may have a surface  48  that is planar. Alternatively, the left or right sidewall  40 ,  42  may also have a curved surface  48 . 
         [0027]    In a preferred embodiment, the inner surface  32  has curved inner surface side edges  50 ,  52 . These side edges  50 ,  52  are designed such that they fluidly transition into the left and right sidewalls  40 ,  42  of the shaft  20 , as illustrated in  FIG. 3 . In a preferred embodiment, the inner surface  32  has an inner surface radius of curvature  54  that ranges from about 1 cm to about 5 cm. 
         [0028]    Alternatively, the shaft  20  could be constructed such that it has a curved cross-section and more preferably, a round cross-section. As such, the shaft  20  may have a diameter that ranges from about 1 cm to about 10 cm. The curved cross-section of the shaft  20  is beneficial because it reduces the physical resistance of the cup impactor  10  as it is inserted within the body of a patient. Reduced resistance is especially beneficial when the impactor  10  is inserted within an obese human body of a large mass and volume. The curved surfaces of the impactor  10  allow the user to turn and rotate the instrument more efficiently. Furthermore, the arc design of the shaft  20  provides for improved access to the hip area of the patient. 
         [0029]    In a preferred embodiment, the handle  12  is positioned such that it is about coplanar with that of the distal end  19  of the impactor  10 . As illustrated in  FIG. 1 , longitudinal axis A-A extends through the center of the handle  12  and through the distal end  19  of the impactor  10 . Alternatively, as shown in  FIG. 2 , the handle  12  may be positioned such that it is offset from the plane of the distal end  19 , i.e., deviating from axis A-A. In a further embodiment, a handle offset angle  56  is established between longitudinal axis A-A and handle axis B-B. Axis B-B is herein defined as the axis that extends longitudinally through the center of the handle portion  12 . Handle axis B-B can therefore assume multiple positions depending on the particular handle offset that is desired, as shown in  FIG. 2 . The handle offset angle  56  is herein defined as the angle  56  between the intersection of longitudinal axis A-A and handle axis B-B. It is preferred that the handle offset angle  56  range from about 2° to about 40°. 
         [0030]    Furthermore, the distal end  19  of the impactor  10  may be constructed such that it is offset from longitudinal axis A-A. In an additional embodiment, a distal end offset angle  58  is established between axis C-C, an axis extending longitudinally through the center of the distal end  19  of the impactor  10 , and imaginary line D-D ( FIG. 2 ). Line D-D is an imaginary line that extends about the middle of a distal portion  57  of the shaft  20 , along sidewall  40 ,  42  as shown in  FIG. 2 . The distal end offset angle  58  is herein defined as the angle between the intersection of axis C-C and imaginary line D-D. It is further preferred that the distal end offset angle  58  may range from about 40° to about 60°. Additionally, the offset of the distal end  19  from the proximal end  14  may be defined by a distal end offset distance  59 . The distal end offset distance  59  is herein defined as the distance between longitudinal axis A-A and axis CC as shown in  FIG. 2 . In a preferred embodiment, the offset distance  59  ranges from about 1 cm to about 10 cm. 
         [0031]    It is further contemplated that the cup impactor  10  may or may not have an offset handle angle  56  or a distal end offset angle  58  or a distal end offset distance  59 . Furthermore, the respective offset angles  56 ,  58  of the impactor  10  may be offset at angles that are similar or different from each other. 
         [0032]    The cup engagement sub-assembly  16  comprises a drive train  60  that extends to a rod end  62  as shown in  FIGS. 1 ,  4 , and  7 - 8 . The cup engagement sub-assembly  16  preferably resides at the distal end portion  18  of the impactor  10 . In a preferred embodiment, the drive train  60  at least partially resides within a cavity  64  at the distal end portion  18  of the impactor  10 . 
         [0033]    The cavity preferably extends from the distal end  19  of the impactor  10  to a region proximate the distal end  19 . The cavity  64  preferably furthermore resides within the top surface  34  of the shaft  20  of the impactor  10 . In a preferred embodiment, the cavity  64  has a cavity depth  66  from about 1 cm to about 4 cm, a cavity length  68  from about 10 cm to about 20 cm and a cavity width  70  from about 1 cm to about 5 cm. Left and right cavity sidewalls  72 ,  74  extend along the length  68  of the cavity  64 . The cavity  64  is further positioned such that it extends through the distal end  19  of the impactor  10  creating an opening  76  thereof. The opening  76  is preferably dimensioned such that at least a portion of the distal end of the cup engagement sub-assembly  16 , particularly the rod  62  of the sub-assembly  16 , extends therethrough. In a preferred embodiment, the opening  76  at the distal end  19  may have a diameter that ranges from about 0.5 cm to about 2 cm. In a preferred embodiment, the cavity  64  ends at a position that is distal of the apex  28  of the middle shaft portion and provides for receiving a driver tool  78  for rotating the drive shaft with the threaded rod  62  being at an angle  80  from about 40° to about 60°, preferably at about 55° with respect to a major shaft  82  of the drive train  60 . 
         [0034]    Furthermore, the depth  66  of the cavity  64  may be designed such that it gradually increases from the proximal end  18  to the distal end  19  of the impactor  10 . The maximum cavity depth  66  is achieved at the opening  76  of the distal end  19  of the impactor  10 . This design feature of the cavity  64  allows for improved unobstructed motion of the drive train  60  within the cavity  64  and provides an improved means of accessing the drive train  60  within the body of the patient. 
         [0035]    The cavity  64  further has a series of slots  84  that extend through each of the cavity sidewalls  72 ,  74  and bottom surface  32  of the shaft  20 . These slots  84  are designed to allow for efficient and thorough cleaning of the cavity  64 . Furthermore, the cavity  64  has an additional opening  86  extending through the inner surface  32  of the shaft  20  distal of the slot openings  84 . This additional opening  86  is preferably positioned along a bend  88  where the distal end  19  transitions into the arc  28  of the shaft  20 . The opening  86  provides for easy access to the cup engagement sub-assembly  16  to allow for efficient and through cleaning thereof. 
         [0036]    As particularly shown in  FIGS. 4-6 , the drive train  60  comprises a major shaft  82  as a cylindrically-shaped member having a proximal portion  90  and a distal end  92  with a length therebetween. Furthermore, the major shaft  82  comprises a bar bell portion  94  at both the proximal  90  and distal ends  92  thereof. The bar bell portion  94  is designed such that a portion of the major shaft  82  is removed to create a recessed region  96  along the shaft  82 . This recessed shaft region  96  is characterized with a shaft diameter that is smaller than that of the major shaft  82 . The recessed shaft region  96  is designed such that it enables a pin or pins  98  to be positioned across the region  96  between the cavity sidewalls  72 ,  74  thereby permitting rotational movement of the shaft while preventing the drive shaft  82  from being removed from the cavity  64  of the impactor  10 , as shown in  FIGS. 1 and 4 . 
         [0037]    The proximal shaft end  90  preferably has a socket  100  therewithin designed to engage the drive tool  78  ( FIG. 6 ). The drive tool  78  is designed to be inserted into the socket  100  of the proximal end  90  of the drive train  60 . The drive tool  78  comprises a hexagonal end or similar type structure that provides flats for detachable connection of the socket  100  at the proximal end  90 . In a preferred embodiment, the drive shaft  60  may be rotated clockwise or counterclockwise when the tool  78  is engaged in the socket  100 . Rotation of the drive shaft  82  in turn rotates the threaded rod  62  at the distal end  19  of the impactor  10 . Alternately, a rotary drive power source (not shown) could also engage the socket  100  of the drive shaft  82  to provide rotation. 
         [0038]    As particularly shown in  FIGS. 5 and 6 , a first or proximal U-joint  102  is supported at the distal end  92  of the major shaft  82 . The proximal U-joint  102  is comprised of a proximal cylindrical sidewall  104  supporting a pair of yoke plates  106  and  108  having respective openings  110 ,  112 . Connection of the U-joint  102  to the shaft  82  may be made by a screw and the like. The screw is received in an opening  114  in the sidewall  104  and seats against a flat  116  at the distal shaft end  92 . In the alternative, the proximal U-joint could be welded or otherwise secured in place or, the U-joint and shaft could be machined from a single piece of material. 
         [0039]    The drive train  60  further includes an H-shaped joint  118  comprising a cylindrical intermediate section  120  supporting opposed first and second pairs of yoke plates  122 ,  124  and  126 ,  128 . Respective openings  130 ,  132  and  134 ,  136  are provided in the yoke plates. A proximal pivot block  138  ( FIG. 6 ) resides between the yoke plates  106 ,  108  of the proximal U-joint  102  and the first pair of yoke plates  122 ,  124  of the H-joint  118 . The proximal pivot block  138  comprises two pairs of perpendicularly opposed openings  142  and  144 . 
         [0040]    Pin  146  is received in the openings  110 ,  112  in the yoke plates  106  and  108  of the U-joint  102  and the opening  142  in the pivot block  138 , and a pin  148  is received in the opening  142  of the pivot block  138  and the openings  110 ,  112  of the yoke plates  122 ,  124  of the H-plate  118  to thereby pivotably secure the proximal U-joint  102  to the first end of the H-joint  118 . It is noted that only one of the pins  146  or  148  extends completely from one face of the pivot block  138  to the other face. As passage from one face to the other is blocked by the first pin, the other of the two pins  146  or  148  is two “half pins”. 
         [0041]    As shown in  FIGS. 5 and 6 , the drive train  60  also includes a distal U-joint  150  that comprises a distal cylindrical side wall  152  supporting a pair of yoke plates  154  and  156  having respective openings  158 ,  160 . Opposite the yoke plates, the cylindrical sidewall  152  meets a base plate  162  having an enlarged diameter. A cylinder  164  extends outwardly from the base plate  162 . The threaded rod  62  preferably extends outwardly from the cylinder  164  of the distal U-joint  150 . Each of the components of the drive train  60  have their respective axes aligned parallel to each other and co-axial with, but spaced from, a longitudinal axis E-E of the distal U-joint  150 . 
         [0042]    A distal pivot block  166 , similar in structure to the proximal pivot block  138 , comprises two pairs of perpendicularly opposed openings  168  and  170 . Pin  174  is received in the openings  158 ,  160  in the respective yoke plates  154 ,  156  of the distal U-joint  150  and the opening  168  in the pivot block  166 , and a pin  172  is received in the openings  134 ,  136  of the respective yoke plates  126 ,  128  of the H-joint  118  and opening  168  of the pivot block  166  to thereby pivotably secure the distal U-joint  150  to the second or distal end of the H-joint  118 . As with the pivotable connection between the H-joint  118  and the proximal U-joint  102 , only one of the pins  172 ,  174  extends the full width of the pivot block  166  from one face to an opposite face thereof. The other pin is provided as two partial length pins. 
         [0043]    In this manner, the drive train  60  comprising the drive shaft  82 , the proximal U-joint  102 , the first pivot block  138 , the H-joint  118 , the second pivot block  166  and the distal U-joint  150  provides for transmission of rotational motion imparted to the proximal end of the shaft  82  to the base plate  162  and its supported rod  62 . 
         [0044]    Although the H-joint  118  is preferred, it is contemplated that the drive train  60  may be constructed without the H-joint  118 . In this embodiment, the drive train  60  would comprise the drive shaft  82 , the proximal U-joint  102 , the first pivot block  138  and the distal U-joint  150 . It is further contemplated that the drive train  60  may comprise a flexible shaft design such as wire wound shaft or a shaft that is laser cut. 
         [0045]    The threaded rod  62  extends through the distal end  19  of the impactor  10 . The threaded rod  62  preferably engages with an orthopedic implant  176 . Prior to the surgical procedure, a connection between the threaded rod  62  and the orthopedic implant  176  is established. In a preferred embodiment, the threaded rod  62  is mated with corresponding grooves (not shown) of the implant  176 . Once the implant is secured to the distal end  19  of the impactor  10 , the implant  176  is inserted into a patient. Once the implant  176  is correctly positioned within the body, the drive shaft  82  is rotated in a reverse direction with respect to the threads of the rod  62 . Typically, the rod  62  is provided with right hand threads so that counterclockwise rotation disengages the implant  176  from the impactor  10 . 
         [0046]    Additionally, a series of slots  178 , as shown in  FIG. 7 , may extend around the perimeter of the base plate  162  of the threaded rod  62 . These slots  178  are designed such that they fit with corresponding implant slot grooves (not shown) providing additional support between the threaded rod  62  of the impactor  10  and the implant  176 . 
         [0047]    The drive train  60  may be designed without pins  98  such that it is removable from the cavity  64  of the impactor  10 . A removable drive shaft  82  is beneficial in that it provides for more efficient and thorough cleaning of the cup engagement sub-assembly  16 . As shown in an alternate embodiment of  FIG. 8A , a sleeve  180  may be positioned over the proximal end portion  90  of the drive shaft  82 . This sleeve  180  provides for a wider perimeter diameter that creates a snug or interference fit when positioned within the cavity  64 . Alternatively the proximal end  90  of the drive shaft  82  may be constructed with an increased diameter that creates an interference fit when positioned between the sidewalls  72 ,  74  of the cavity  64 . 
         [0048]    Furthermore, it is contemplated that a plurality of pads may be positioned around the perimeter of the major shaft  82  of the drive train  60  and/or positioned along the inside surface of the cavity sidewalls  72 ,  74 . These pads are designed to provide an additional interference fit within the cavity  64  such that the drive train  60  remains within the cavity  64  during the surgical procedure. 
         [0049]    Of course, the forgoing description is that of certain features, aspects and advantages of the present invention, to which various changes and modifications can be made without departing from the spirit and scope of the present invention. Moreover, the cup impactors need not feature all of the objects, advantages, features and aspects discussed above. Thus, for example, those of skill in the art will recognize that the invention can be embodied or carried out in a manner that achieves or optimizes one advantage or a group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. In addition, while a number of variations of the invention have been shown and described in detail, other modifications and methods of use, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is contemplated that various combinations or sub-combinations of these specific features and aspects of embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the discussed cup impactor embodiments.