Abstract:
A bone compacting device for compacting cancellous bone within a bone cavity, the bone compacting device including a body having a plurality of segments, wherein each segment is adjacent to at least one adjacent segment between a first end and a second end of the body, and wherein each of the plurality of segments is independently expandable to contact the cancellous bone.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/467,660, filed Mar. 25, 2011 and titled “Bone Compactor”, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the preparation of a bone for the implantation of a prosthesis. In particular, the devices of the invention are used in the preparation of a proximal cavity of a human femur so that it can receive a hip stem implant of a total or partial hip replacement system, although the devices can be applicable for use in other areas where bone compaction is desirable. 
       BACKGROUND 
       [0003]    Hip stems are available in different sizes such as small, medium, and the like, in order to accommodate the needs of individual patients and their unique anatomies. In many cases, different shaped hip stems are also available, such as primary stems or revisions stems. During surgery, it is desirable for the surgeon to carve out a portion of the inner cavity of the femur to closely match size and shape of an available hip stem, since different individual patients have bones with different anatomical shapes. One common practice is to shape the proximal cavity of the femur by removing part of the inner cancellous bone using a sharp broach or rasp. However, laboratory studies have shown that if cancellous bone is compacted instead of being removed from the bone cavity, it can provide a more stable bed for the implant. That is, compacting the bone can provide for a stronger interface connection between an implant and the bone, which can be true for both cemented and cementless implant applications. 
         [0004]    Certain devices are known in the art for compacting cancellous bone, such as a bone tamp of the type described in U.S. Pat. No. 5,800,437 (Gustilo et al.), which patent is incorporated herein by reference in its entirety. However, such bone tamps have certain limitations due to the forces exerted on the femur when the bone tamp is pounded into the bone. Thus, there is a need to provide alternative devices and methods for compacting cancellous bone in a controlled manner, without exerting undue force on the bone. 
       SUMMARY 
       [0005]    A bone compacting device of the invention is provided for compacting cancellous bone within a bone cavity, such as can be done to prepare a cavity of a femur prior to receiving a hip stem implant, for example. In one aspect of the invention, a bone compacting device includes an elongated member and a port at a proximal end of the elongated member, wherein the port is in communication with a supply of an inflation medium so the elongated member is expandable in response to a quantity of the inflation medium entering the elongated member through the port. In another aspect of the invention, a bone compacting device includes a body comprising a plurality of segments, wherein each segment is adjacent to at least one adjacent segment between a first end and a second end of the body and along a length of the body, wherein each of the plurality of segments is independently expandable to contact the cancellous bone. The plurality of segments can include ring segments and the device can further include a core member having an outer surface over which the plurality of segments are adjacently positioned. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present invention will be further explained with reference to the appended Figures, wherein like structure is referred to by like numerals throughout the several views, and wherein: 
           [0007]      FIG. 1  includes a perspective view and a front view of a prior art hip stem prosthesis; 
           [0008]      FIG. 2  is a perspective view of an embodiment of a bone compactor of the invention; 
           [0009]      FIG. 3  is a perspective view of another embodiment of a bone compactor of the invention; 
           [0010]      FIG. 4  is a perspective view of a centering rod that is positionable within a bone compactor of the invention; 
           [0011]      FIG. 5  is a front view of another embodiment of a bone compactor of the invention, which includes multiple expandable segments; 
           [0012]      FIG. 6  is a perspective view of an expandable segment of a bone compactor of the invention, including a pressure connector; 
           [0013]      FIG. 7  is a perspective view of the bone compactor illustrated in  FIG. 5 , as positioned relative to a centering rod; 
           [0014]      FIG. 8   a  is perspective view of another embodiment of a compactor of the invention, which is shown as partially transparent for better visibility of its internal components, along with a push rod positioned above a hole in the compactor; 
           [0015]      FIG. 8   b  is a perspective view of the compactor and push rod of  FIG. 8   a , with its components illustrated as generally opaque rather than transparent; 
           [0016]      FIG. 8   c  is a perspective view of one expandable ring segment of the type that is used in the compactors of  FIGS. 8   a  and  8   b;    
           [0017]      FIG. 9  includes a perspective view of another bone compactor of the invention, along with an enlarged view of an end portion of that bone compactor; 
           [0018]      FIG. 10  is a perspective view of a tool used for pre-cracking a bone prior to insertion of a bone compactor; 
           [0019]      FIG. 11  is a front cross-sectional view of a reamer positioned within a proximal femur; and 
           [0020]      FIG. 12  is a front cross-sectional view of a tool of the type illustrated in  FIG. 10  positioned within a femur, with the tool in an open configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Referring now to the Figures, wherein the components are labeled with like numerals throughout the several Figures, and initially to  FIG. 1 , a hip stem prosthesis  1  of the type generally known in the art is illustrated. Such a hip stem prosthesis can include an elongated portion that is positionable in the intramedullary canal of the femur of a patient, for example, along with a shoulder or collar at its proximal end. 
         [0022]    One exemplary embodiment of a bone compactor  2  of the invention is illustrated in  FIG. 2 . The compactor  2  includes an inflatable or expandable structure that is made of a flexible material (such as rubber, plastic, impermeable fabric, or combinations thereof, for example). The compactor  2  includes an elongated portion with a pressure connector or port  3  at its proximal end. Prior to positioning the compactor  2  within a bone of a patient, it can be in a deflated or semi-inflated condition so that it will fit relatively easily into the femur. The compactor  2  is then placed inside the femur and inflated or expanded using a gas or liquid medium, such as by introduction of such materials through the pressure connector  3 . The pressure at which the gas or liquid is delivered to the compactor  2  can be set or monitored and controlled so that it is sufficient to compress the cancellous bone by a desired amount, but so that it is not so high that it causes the bone to fracture. When the compactor  2  is inflated by a desired amount, it generally assumes the shape and size of the hip stem prosthesis that will be positioned within that area of the bone. For example, the compactor  2  can be inflated by a desired amount to compact the cancellous bone and create a cavity that matches the size and shape of a hip stem prosthesis that will be implanted in that bone. 
         [0023]      FIG. 3  illustrates another embodiment a compactor  4  of the invention, which has a similar outer shape to that of the compactor  2 . However, compactor  4  includes a hole or channel  5  extending through at least a portion of a length of its elongated member. With this embodiment, compactor  4  can be inflated and deflated via a pressure connector  3   a , which is located adjacent to the elongated member of the compactor. Hole or channel  5  can be designed and constructed to accommodate the insertion of a centering rod therein, such as centering rod  6  illustrated in  FIG. 4 . A portion of a proximal end of the centering rod  6  can extend beyond the proximal end of the compactor  4 , as illustrated. Centering rod  6  can be used to assist in the accurate centering and alignment of the compactor  4  inside the femur during its insertion. 
         [0024]    In yet another embodiment of the invention, a compactor  4   a  can be composed of multiple discrete segments  7  that are positioned adjacent to each other to make up a desired overall compactor size and shape, such as is illustrated in  FIG. 5 . Each of these segments  7  can be an inflatable or expandable balloon-type structure that can be used to compact the cancellous bone in a generally similar manner as other inflatable compactors described herein. Although ten of such segments  7  are illustrated relative to compactor  4  of  FIG. 5 , it is understood that more or less than ten segments can be used for this embodiment of a compactor of the invention. Each segment is an inflatable or expandable member (e.g., an expandable balloon) that is made of a relatively flexible material (such as rubber, plastic, impermeable fabric, or combination thereof, for example). The materials from which each segment is made can be the same or different from the materials from which the other segments of a particular compactor are made. For example, it may be desirable that some segment(s) are easier or harder to inflate than other segment(s) along a length of a compactor when each segment of that compactor is subjected to the same pressure. 
         [0025]    In one embodiment of compactor  4   a , each segment  7  is inflated or expanded individually in a pattern or sequence, such as from a distal to proximal direction, from a proximal to a distal direction, or in some other sequence of pattern. In an inflation sequence that involves sequential inflation of adjacent segments  7 , a first segment at one end of the compactor  4   a  is inflated, and after this segment is inflated, an adjacent segment or more than one adjacent segment is inflated while the first segment can be deflated or partially deflated. By using this method of dividing the length of the compactor  4   a  into multiple segments  7  that are individually inflatable or expandable, the expansion force acting on the entire femur or other bone at any given time will be minimized. In other words, the sequential expansion of the segments  7  will concentrate the expansion forces to one area of the bone at a time, rather than exerting the force over the entire length of the compactor at once. Such a force distribution can be advantageous for certain patients and bone conditions, for example. 
         [0026]      FIG. 6  shows an individual expandable segment  7  with a pressure connector  8  through which a gas or liquid inflating medium can be passed to inflate and deflate the segment. Each of the balloon segments  7  can be attached to a centering rod, such as centering rod  6  (illustrated in  FIG. 7 ). As with other embodiments described herein, the multiple segments are sized, shaped, and arranged in such a way that the outer surface of the compactor  4   a  will take on the general shape of the hip stem prosthesis (e.g., hip stem prosthesis  1  described above) when all segments are inflated by a desired amount, as is shown in  FIG. 7 . 
         [0027]    In another embodiment of the invention, segmental compression of cancellous bone is achieved using mechanical means.  FIGS. 8   a  and  8   b  illustrate a mechanical compactor  8  composed of one or more expandable ring sections  9  assembled over a core member  10 .  FIG. 8   c  illustrates two of the exemplary ring sections  9  of  FIGS. 8   a  and  8   b , each of which is illustrated as having four subsections around its perimeter, wherein each subsection includes an outer frame that can conform to the final shape of the femoral cavity in which it will be positioned along with one or more pushpins  13 . It is understood that the ring sections may alternatively include more or less than four subsections. It is further understood that each subsection can include more than one pushpin  13  or that one or more of the subsections do not have any pushpins  13 . In an alternative embodiment, there is no structure provided over the pushpins  13 , such that the ends of the pushpins themselves will be outwardly expandable relative to the bone, as described below. 
         [0028]      FIG. 8   a  shows the compactor  8  as partially transparent for better visibility of its internal components and structure, while  FIG. 8   b  illustrates the same compactor  8  without any of the components being shown as transparent. Each expandable ring section  9  can be expanded through mechanical means for example, by a push rod  11  being inserted into a hole  12  in core  10 , as shown in  FIGS. 8   a  and  8   b . In particular, when the expandable ring section  9  is in its unexpanded state, the pushpins  13  are protruding at least slightly into the inner opening of hole  12 . As a push rod  11  is pushed and/or twisted into the hole  12 , the pushpin or pushpins  13  of each subsection of expandable ring section  9  can engage a series of spiral grooves  14  of push rod  11 , which will thereby push each subsection of expandable ring section  9  outwardly relative to the hole  12 . In one embodiment, the spiral grooves  14  of the push rod  11  are relatively deep at the distal end of the push rod  11 , and gradually become more shallow when moving upward (i.e., in a proximal direction) until the depth essentially goes to zero (i.e., this portion of the push rod is relatively smooth), in order to be at the same level as the outside diameter of push rod  11 . Alternatively, the push rod  11  can also be designed to have a reduced outside diameter slightly above the spiral grooves  14  so that there is no pushing force exerted on push pins  13  when the push pins  13  are adjacent to this reduced diameter portion. This configuration will cause one or more ring sections  9  to expand and retract one after another in sequence. In this way, the force acting on the femur will be minimized, as is discussed above. Other expandable ring configurations and means of expanding the rings are also contemplated and are considered to be within the scope of the present invention. 
         [0029]    In another embodiment of the invention illustrated in  FIG. 9 , a bone compactor  16  is illustrated, which includes multiple longitudinal sections  15 . With this bone compactor  16 , bone compaction is achieved in a sequential manner by inserting the longitudinal sections  15  of sectional compactor  16  one at a time into the bone cavity. The longitudinal sections  15  can be coupled to each other through dovetail connections  17 , for example, or can be coupled to each other in another manner. It is also contemplated that the sections  15  are not coupled to each other, although the coupling aspect of the sections helps to keep the longitudinal sections  15  properly oriented relative to each other, thereby maintaining the desired shape of the sectional compactor  16  when all the longitudinal sections  15  have been fully inserted into the bone. Inserting the each longitudinal section  15  into the bone sequentially can minimize the expansion force acting on the femur at any single time. Although the compactor  16  is shown as having five individual segments or sections  15 , it is understood that the compactor  16  can instead include more or less than five of such segments or sections. 
         [0030]    In accordance with any or all of the embodiments of the invention, it is contemplated that the bone in which the compactor is to be inserted is “pre-cracked” prior to insertion of that compactor in order to better prepare the bone for compaction. One advantage that can be provided by such a pre-cracking process is that the force required to compact the bone with a compactor can be reduced. The amount of advantage gained can depend on the compaction amount required, the bone size, and the bone quality. An embodiment of a tool that can be used for such a process can be a device comprising a plurality of teeth that can open up before implanting the compactor, such as an expanding tool  18  illustrated in the exemplary embodiment of  FIG. 10 . As shown, expanding tool  18  includes a lateral member  19  and a medial member  20 , which can be pivoted relative to each other about a pivot point  21 . Lateral member  19  can remain generally fixed or stationary, while medial member  20  can open or move in the direction of arrow  24 . Alternatively, lateral member  19  can also open or move laterally. 
         [0031]    Medial member  20  is shown with a plurality of teeth  22  spaced from each other along the height of tool  18 . The illustrated teeth  22  of this Figure provide just one exemplary arrangement of teeth; however, it is understood that the tool may instead include more or less teeth that each have shapes and sizes that are similar or different from the illustrated teeth. Each of the teeth  22  can be relatively shallow and may be generally wedge or triangular shaped such that a point is inserted into the bone and pushed into the bone to increase the size of the bone crack or opening. The teeth of such a device can be symmetric or asymmetric, depending on the desired shape of the cracks that will be created. In addition, although teeth  22  are only shown on medial member  20 , teeth can alternatively or additionally be provided on lateral member  19 . AS a further alternative, expanding tool  18  can be configured without any teeth and can instead be used as a bone compactor by expanding or opening lateral member  19  and medial member  20  relative to each other about pivot  21 . 
         [0032]      FIG. 11  is a front cross-sectional view of a reamer  30  positioned within a proximal femur, and  FIG. 12  is a front cross-sectional view of a tool  32  of the type illustrated in  FIG. 10  positioned within a femur, with the tool  32  in an open configuration. Insertion of the tool  32  and/or any compactors of the invention can be accomplished using vibratory force in certain cases where insertion via hammer blows would not be desirable. Further, compaction of the bone is directed primarily in a medial direction, due to the lateral location of a straight intramedullary alignment rod relative to the bone in which it is inserted. In one exemplary insertion method, a reamer is used to ream at least a portion of a proximal bone, and then a correspond size of alignment rod can be inserted. After the rod is inserted, a cannulated pre-cracking tool can then optionally be slid over the alignment rod, and can be gently tapped or pressed to initiate cracks in a desired compaction zone of the bone. A compactor, which may be hinged, can then be slid over the alignment rod, where the rod and compactor are positioned to ensure that the compaction will occur in a medial direction. Controlled compaction can then be achieved by actuating the compaction hinge, for example, and monitoring force feedback. If desired, the compaction hinge can be locked in its deployed condition, which can then be used as a trial prosthesis. 
         [0033]    The present invention has now been described with reference to several embodiments thereof. The entire disclosure of any patent or patent application identified herein is hereby incorporated by reference. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the structures described herein, but only by the structures described and claimed herein and the equivalents of those structures.