Abstract:
A system and method is provided in which natural bone removed during a joint surgery is retained along with the natural attachment of the associated soft tissues. For instance, in a hip surgery, a portion of the greater trochanter is removed while retaining the soft tissue attachments. An implant and the bone portion are provided with mating features, such as a keystone configuration. The keystone configuration can include mating male and female dovetail configurations. The bone portion can be engaged to the mating feature of the implant to support the natural bone and its soft tissue attachment in an anatomically appropriate position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to orthopaedic implants and procedures in which a portion of bone is removed to which soft tissues, such as ligaments and tendons, are attached. In particular, the invention relates to systems and methods for maintaining the soft tissue attachment during an orthopaedic procedure.  
         [0002]     Certain orthopaedic surgeries, such as hip surgeries, often require osteotomies of a portion of the femur to provide full access to the hip joint. In these procedures, a portion of the greater trochanter is removed. Following the surgery, the removed bone portion is replaced and secured in a number of ways. For instance, trochanter reattachment systems can include wiring, cables or clamps that are used to hold the removed portion to the retained bone long enough to promote healing through fusion.  
         [0003]     In some orthopaedic procedures, a significant portion of a joint is replaced with a prosthesis. For instance, in some hip surgeries, the entire proximal portion of the femur is removed and replaced with the prosthesis. Since the attachment point for the soft tissue is removed with the bone, surgeons have turned to composite allograft-endoprosthesis constructs to provide a foundation for connection of the soft tissue to the implant. Usually, the soft tissue, such as tendons, are connection by sutures, so that the resulting connection is only as strong as the suture. The success of these types of reconstruction is historically low.  
         [0004]     What is needed is a system and method that preserves as much of the natural attachment point for soft tissue as possible. An optimum approach would make use of as much of the natural bone as possible so that the attachment of the soft tissue to the bone is not compromised or replaced by a less secure attachment.  
       SUMMARY OF THE INVENTION  
       [0005]     In view of these needs, the present invention contemplates a system and method in which the natural removed bone is retained, along with the natural attachment of the associated soft tissues. For instance, in a hip surgery, a portion of the greater trochanter is removed while retaining the soft tissue attachments. The present invention provides means for receiving that bone portion and connecting it to a proximal femoral implant, for instance.  
         [0006]     In one embodiment of the invention, the implant and bone portion are provided with mating features, such as a keystone configuration. The keystone configuration can include mating male and female dovetail configurations. The bone portion can be engaged to the mating feature of the implant to support the natural bone and its soft tissue attachment in an anatomically appropriate position.  
         [0007]     In a preferred embodiment, the keystone and dovetail features are angled inward so that the natural tensile forces exerted on the bone portion will tend to force the male/female features into tighter engagement. In another feature, the implant can include a bone ingrowth surface at the interface to the bone portion to enhance the fixation of the natural bone to the implant.  
         [0008]     In certain embodiments, separate fixation elements are provided to ensure a tight connection between the bone portion and the implant. In one embodiment, one or more cables can encircle the bone portion to hold the portion in position without interfering with the soft tissue and soft tissue attachments. In another embodiment, a hinged claw scaffold can be provided that can be pivoted into engagement with the bone portion. The scaffold can include claws to penetrate the bone. The scaffold can also include plate portions through which bone screws are driven into the underlying bone. The scaffold can also be configured to integrate with cables encircling the bone portion.  
         [0009]     In a method of the invention, the portion of a bone, such as the femur, is removed as necessary to accept a prosthesis or implant, such as a proximal femoral implant. Certain portions of the removed bone that include soft tissue attachment points can be removed separately, while retaining the attachment to the soft tissues. The removed portion of the bone can be engaged within a cutting jig that is configured to permit forming the mating feature in the cut surface of the removed bone. The mating feature cut into the bone is complementary to a mating feature defined in an exposed surface of the implant.  
         [0010]     In accordance with this method, the prosthesis is implanted within the remaining natural bone, with the exposed surface in proper alignment to accept the removed bone. The mating feature of the removed bone is engaged to the mating feature on the implant, while the soft tissue remains attached to the natural removed bone. Additional mechanical fixation can be provided to ensure a firm connection between the removed bone and the prosthesis as the surgical site heals.  
         [0011]     It is one important object of the invention to provide a system and method for removal of portions of a bone, while retaining other portions of the bone bearing soft tissue attachments. A further object is to provide means for conducting complex orthopaedic surgical procedures, such as joint arthroplasty, while preserving the natural soft tissue and soft tissue attachment points.  
         [0012]     Other objects and particular benefits of the present invention will become apparent upon consideration of the following written description and accompanying figures.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.  
         [0014]     For illustrative purposes, the preferred embodiments of the present invention will be explained in the context of an orthopaedic joint arthroplasty procedure for the hip joint involving the proximal portion of the femur, as depicted in  FIG. 1 . It is understood, of course, that the principles discussed herein can be applied to other joints and bones of the body. In the context of the present invention, one goal is to preserve the soft tissue attachments to portions of natural bone. It is further understood that features of the present invention can be utilized even where soft tissue attachments are not a concern.  
         [0015]     As shown in  FIG. 1 , a bone, such as the femur, includes a shaft S terminating in a proximal portion P that is configured to form an articulating component of a joint, such as the hip joint. To that end, the proximal portion includes a neck N supporting a head H that provides the articulating surface. In the case of a femur, the head H is a ball joint component. Various soft tissues, such as flexor tissues, are connected to the bone at the proximal portion P, particularly at the greater trochanter T. The trochanter includes various soft tissue attachment points T for tendons associated with muscles of the hip joint, such as certain gluteal muscles.  
         [0016]     In certain orthopaedic procedures, the proximal portion P of the femur is removed, as depicted by the dashed lines in  FIG. 2 . A bore B is formed in the bone shaft S to receive portions of an implant or prosthesis, such as the proximal prosthesis shown in  FIG. 3 . In a typical procedure, the trochanter T is removed with the proximal portion, and the soft tissue attachments severed. In some procedures, it is possible to integrate an allograft component with the prosthesis, and then to suture the soft tissues to the allograft component, thereby restoring the soft tissue attachment to the bone.  
         [0017]     The prosthesis  10  can be similar to known designs for use in hip joint arthroplasty procedures. For instance, the prosthesis  10  can include a body  11  that is configured to approximate the removed proximal portion P of the femur. The body defines a neck  12  onto which a prosthetic articulating component of known design can be mounted. The prosthesis also includes a stem  13  that is implanted within the bore B to fix the prosthesis to the bone.  
         [0018]     While prior hip joint prostheses include a body that emulates the shape of the trochanter, the present invention contemplates that the body  11  defines a mounting platform  15  that is arranged to coincide with the surface of the proximal portion P remaining after the trochanter T has been removed therefrom (see  FIG. 2 ). This mounting platform  15  defines surface features for mating engagement with the removed portion of the trochanter T. As shown in  FIG. 3 , the attachment point A for certain flexor tissues F is maintained even as the trochanter portion T is engaged to the mounting platform.  
         [0019]     In one aspect of the invention, the mounting platform and the bone portion T define mechanical engagement or mating features that allow the bone portion to be engaged to the prosthesis  10  when the prosthesis is in its implanted position. As shown in  FIGS. 4 and 5 , the mounting platform defines a keystone slot  17  with a dovetail undercut  19  (best seen in  FIG. 5 ). The slot includes a mating surface  21  that is in direct contact with the bone portion T.  
         [0020]     The bone portion T is cut to define a mating feature  25 , as illustrated in  FIGS. 6 and 7 . The mating feature includes a dovetail cut  27  at opposite sides of a mating surface  28 . In the illustrated embodiment, the mating feature  25  is a male feature that projects from the cut surface C of the bone portion T and that is configured for interlocking engagement with a female feature  17  defined in the mounting platform  15  of the prosthesis. Alternatively, the male and female features can be swapped between the prosthesis and the bone portion, or a combination of male and female features can be defined on each component.  
         [0021]     The dovetail elements, i.e., the undercut  19  and cut  27 , are formed at a converging angle M. This converging feature provides a natural stop for insertion of the male mating feature  25  of the bone portion T into the female feature  17  of the prosthesis. In other words, once the prosthesis has been implanted, the bone portion T can be mounted to the prosthesis by sliding the mating feature  25  into the keystone slot  17 . The bone portion is firmly engaged to the prosthesis when the angled walls of the dovetail cut  27  are flush with the complementary angled walls of the dovetail undercut  19 . The converging angle M can be a Morse angle to enhance the engagement between the bone and the prosthesis.  
         [0022]     As shown in  FIG. 4 , the keystone slot  17  can extend along the entire length of the mounting platform  15 , as depicted in  FIG. 4 . Similarly, the mating feature  25  cut into the bone portion T can extend along the entire cut surface C, as represented by the dashed lines in  FIG. 6 . It is preferable that the extended mating features  17 ,  25  be fully complementary so that the male feature resides entirely and firmly within the female feature when the bone portion T is finally mounted to the prosthesis  10 .  
         [0023]     In the present embodiment, the fixation between the prosthesis and the bone portion is accomplished by the mating features  17  and  25 . The mating surface  21  of the prosthesis contacts the mating surface  25  of the bone portion T. Preferably, the prosthesis mating surface  21  includes a bone ingrowth feature to permit bone ingrowth from the bone portion T into the prosthesis. The bone ingrowth feature can include a porous surface that can be filled with a bone growth promoting or enhancing material, such as bone morphogenic protein.  
         [0024]     In some instances, additional mechanical fixation may be desirable. In these cases, one embodiment of the invention contemplates the use of one or more cables that encircle the bone portion, in the nature of a cerclage device. Thus, as shown in  FIG. 8 , a prosthesis body  31  can be provided with a keystone slot  33 , configured as described above. The body can define angled surfaces  36  on opposite sides of the keystone slot  33 . A bore  35  passes through the body beneath the slot  33 , as depicted in  FIG. 8 , opening at each of the angled surfaces  36 . The bore is sized to receive a cable or wire  37  passing therethrough. One end of the cable  37  can carry a crimp  39  that can be crimped onto the opposite free end of the cable when it encircles the bone portion T. The cable can be tightened in a conventional manner, such as the manner in which a cerclage wire is tightened. The crimp  39  can also be of known design to firmly and permanently connect the ends of the cable. The cable  37  thus adds an additional mechanical fixation to hold the bone portion T to the prosthesis body  31 .  
         [0025]     An alternative mechanical fastener is depicted in  FIGS. 9-10 . In this embodiment, a prosthesis body  41  defines a mounting platform  43  on which the bone portion T is mounted. The platform  43  can define a mating feature, such as the keystone slot  17  described above, to engage a corresponding mating feature on the bone portion, such as the dovetail feature  25 . A scaffold  45  is mounted to the platform  43 . In a specific embodiment, the platform defines a slot  47  for receiving an axle  50  of the scaffold. The slot and axle can be configured to permit pivoting of the scaffold from a position clear of the mounting platform  43 , to permit mounting of the bone portion T thereon, to a position engaging the bone portion, as shown in  FIG. 9 .  
         [0026]     The scaffold  45  includes at least two arms  55  that are configured to generally conform to the profile of the bone portion T. The arms  55  can include several claws  49  configured to penetrate at least the cortical layer of the bone portion T. The claws  49  are shown at the tip of the arms  55  in  FIG. 9 , but could be situated at different locations along the scaffold. The claws  49  provide means for engaging the scaffold to the bone portion to hold the portion in position on the prosthesis.  
         [0027]     In an alternative embodiment, the scaffold  45  can include cross bars  57  spanning between the arms  55 , as can be seen best in  FIG. 10 . The cross bars  57  provide a support surface for bone screws  52  passing through the cross bars into the underlying bone, as shown in  FIG. 9 . The bone screws  52  can be used in addition to or in lieu of the claws  49  described above. While only two bone screws are illustrated in the  FIGS. 9-10 , fewer or greater numbers of screws can be utilized. In addition, as shown in  FIG. 9 , the screws are sized to penetrate only part way into the bone portion T. Alternatively, the screws can be sized to pass entirely through the bone portion and engage a corresponding screw bore (not shown) formed in the mounting platform  43  of the prosthesis body  41 .  
         [0028]     As a further alternative, the cable system shown in  FIG. 8  can be integrated with the scaffold  45  of  FIGS. 9-10 . In this alternative, the cable crimps  39  can be configured to include a bore (not shown) through which the bone screws  52  can pass. With this feature, the cable crimps can be connected to the scaffold to solidly hold the bone portion T to the prosthesis.  
         [0029]     The present invention also contemplates a system for preparing the removed bone portion T to add the mating feature  25 . Thus, a cutting jig  70  can be provided as shown in  FIG. 11 . The jig includes two arms  82 ,  83  to clamp the bone portion therebetween. Both arms can be provided with spikes  74  to penetrate and grip the bone portion. The arm  82  defines a support base  72  to hold the proximal portion of the bone with the cut surface C ( FIG. 6 ) facing a guide plate  76  carried by the opposite arm  83 . The support base  72  can be shaped to conform to the profile of the bone portion.  
         [0030]     The guide plate  76  defines a number of slots  78  that act as guides for saw blades, such as the blades  85  shown in  FIG. 12 . The slots are arranged as necessary to create the dovetail cuts  27  in the cut surface C of the bone. In the even that the dovetail cuts extend along the entire length of the bone portion, the slots  79  can be extended accordingly, as indicated by the dashed lines in  FIG. 11 .  
         [0031]     In one embodiment, the cutting jig  70  is in the form of a manual scissors-type tool. Thus, the two arms can be connected at a pivot  87 , as shown in  FIG. 12 , and can include grippable handles  89 ,  90 . The cutting jig can thus be manipulated by the surgeon with one hand, while the cutting blades  85  are manipulated with the other hand. Of course, it is understood that the cutting jig  70  is not the only way that the bone portion can be fashioned with the mating feature  25 . Any other technique for making the necessary cuts are contemplated, provided these cuts can be in situ made with the bone portion T attached to the soft tissues F.  
         [0032]     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 specification. 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.