Abstract:
A tapered screw or dowel made from allograft, autograft or xenograft bone is used to keep an osteotomy or fracture distracted during healing to result in proper alignment of the knee, wrist or any other skeletal site where an opening osteotomy is required to provide for improved bone alignment.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention provides a bone screw or dowel made of allograft bone, for use in an osteotomy or fracture to result in proper bone alignment.  
         BACKGROUND INFORMATION  
         [0002]    Various devices and methods have been developed to assist in the correction of a malaligned joint or in the repair of a fracture. Malaligned knees have been corrected according to methods known in the art using either an opening or closing wedge osteotomy. A closing wedge osteotomy requires the surgeon to cut a wedge out of the bone and hold the bones together with a metallic fracture plate and screws or other external fixation device. An opening wedge osteotomy requires a surgeon to create a fracture in a bone into which a wedge is inserted and held in place with metallic plates and screws or external fixators. Distal radial fractures are traditionally fixed with metallic pins, wires, and screws, which require the surgeon to “eyeball” the proper alignment.  
           [0003]    In U.S. Pat. No. 5,766,251, a wedge-shaped spacer usable for varus, valgus, flexion, extension, and derotation osteotomies is disclosed. The spacer is made of sintered hydroxyapatite and contains at least one thorn-shaped projection extending outwardly from the upper or lower surface and one hole extending from the upper surface to the lower surface. The sintered hydroxyapatite lacks the collagen fibers found in bone, therefore the hydroxyapatite is not analogous to the allograft bone used in the present invention. In addition, the wedge-shaped spacer requires the use of plates and screws to be held in place in the osteotomized site. While both the wedge-shaped spacer of the &#39;251 patent and the present invention are used for corrective osteotomies, the &#39;251 patent does not teach or suggest the novel device and method of the present invention.  
           [0004]    In U.S. Pat. No. 6,008,433, an osteotomy device, kit and methods for realigning varus angulated knees is disclosed. The device is similar to the &#39;251 patent in that it is substantially wedge-shaped. The &#39;433 patent does not disclose a device made from bone. In addition, the &#39;433 patent does not have a substantially circular cross section which is embodied in the present invention. Other than disclosing a device and method for realigning varus angulated knees, the &#39;433 patent does not teach or suggest the novel device and method of the present invention.  
           [0005]    For other devices and methods developed to assist in the correction of malaligned joints, or in the repair of a radial fracture see U.S. Pat. No.&#39;s 5,868,749; 5,968,047; 5,180,382.  
           [0006]    Accordingly, having reviewed devices and methods known in the art, it is concluded that there remains a need for an osteotomy device that potentially eliminates the need for metallic plates and screws or other external fixation devices. The present invention provides such a device.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    A tapered screw or dowel made from allograft, autograft or xenograft (cortical or cancellous or both) bone or combinations thereof is used to keep an osteotomy or fracture distracted during healing to result in proper alignment of the knee, wrist or any other skeletal site where an opening osteotomy is required to provide for improved bone alignment. In one embodiment, the implant of this invention has a smaller diameter front end which is flat, and a larger diameter back end which is provided with a notch, slot, circular, hexagonal or other shaped protrusion or indenture, cannulation or other structures known in the art enable the use of an insertion device for implantation. The larger diameter end of the implant preferably includes a cannular opening to allow for either a guide or insertion device in positioning the implant into the fracture, or for use as a means to secure the implant onto an insertion device during implantation. The implant is preferably provided with an opening to be filled with autogenic bone, allogenic bone, a demineralized bone product or other osteogenic factors, cells or the like to stimulate healing in the fracture.  
           [0008]    The implant is inserted into the fracture after the fracture is opened with a distracter to accommodate the smaller diameter front end. The distracter is later removed from the surgery site. Threads on the implant allow it to be screwed in to control the angle of distraction. In addition, threads ensure that the implant remains in place inside the fracture. The remaining portion of the implant, which is not screwed into the fracture site, can be removed using a saggital saw or similar device. A larger implant can be used for large bone osteotomies, such as tibial or femoral osteotomies. A smaller version can be used for small bone osteotomies, such as in the distal radius.  
           [0009]    Accordingly, it is one object of this invention to provide an osteotomy device made from bone, a bone-like substance, or a biocompatible synthetic material for use in an osteotomy procedure.  
           [0010]    Another object of this invention is to provide proper alignment of bones, whether after an osteotomy or trauma, without the need for plates and screws, or wires and pins to hold the implant in place.  
           [0011]    Another object of this invention is to provide an implant with at least one cavity, and preferably a plurality of microcavities (specify a size range?, and define a microcavity?) running therethrough to accept packing having osteogenic properties.  
           [0012]    Another object of this invention is to provide an implant with improved osteogenic and bone fusion-promoting capacity.  
           [0013]    Another object of this invention is to provide a method for using the novel osteotomy implant of this invention.  
           [0014]    Another object of this invention is to provide a method for making the novel osteotomy implant of this invention.  
           [0015]    Additional objects and advantages of the osteotomy implant of this invention will become apparent from a review of the full disclosure which follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 depicts the structure of one embodiment of the osteotomy implant.  
         [0017]    [0017]FIG. 2A is a top view of the osteotomy implant depicted in FIG. 1 showing a slot opening running therethrough.  
         [0018]    [0018]FIG. 2B is a back view of the osteotomy implant depicted in FIG. 1 showing a cannulation and notch used for insertion of the device.  
         [0019]    [0019]FIG. 3 is a top view of one embodiment of the implant depicted in FIG. 1 showing holes radiating from the canal opening.  
         [0020]    [0020]FIG. 4A is a side view of the osteotomy implant depicted in FIG. 1 showing a side view of the notch used for insertion of the implant.  
         [0021]    [0021]FIG. 4B is a magnified view of the element shown as “A” in FIG. 4A. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    The implant of this invention is useful in the elongation or realignment of bones by means of creating an intentional fracture, such as in an osteotomy, or in the event of a trauma. Elongation or realignment of bones is necessary to prevent and correct such problems as osteoarthritis or varus and valgus angulated knees. A varus angulated knee condition is commonly referred to as “bowleg”, and a valgus angulated knee condition is commonly referred to as “knock-knee”.  
         [0023]    In an osteotomy, a surgeon intentionally creates a fracture, or transverse incision in a bone, distracts the bone incision, and inserts an implant, wires or pins, which allow the bones to be distracted during healing. Common areas for use of the present invention include the proximal tibia, distal femur and distal radius, but the implant can be used in other bones where realignment is necessary. Unlike other implants and devices known in the art, the present invention does not require, or reduces the need for, plates and screws or other external fixation devices to keep the implant in place.  
         [0024]    In order to make the implant of the present invention, bone banks recover allograft bone from donor bone, whether autologous, allograft (e.g. from a human cadaver) or xenograft, (e.g. from an animal cadaver). The donor must be screened for communicable diseases, cancer, and at-risk behavior prior to bone donation. The bone pieces obtained from a donor can then be divided into blanks using an oscillating bone saw. The surfaces of the bone blanks are preferably planed smooth, for example, using a diamond plane under cool water. The bone blanks are then machined into the form of cylinders. One skilled in the art may refer, for example, to methods disclosed in U.S. Pat. No. 5,814,084, hereby incorporated by reference for this purpose. The bone blank cylinder is then machined in a lathe or equivalent device to produce, for example, a conical shape with a smaller diameter front end and a larger diameter back end. A lathe can also be used to inscribe threads, grooves or other external features into the circumference of the bone blank. At least one slot or cavity is optionally machined into the body of the cylinder to allow for biocompatible packing material to be inserted therein prior to implantation. Holes radiating from the at least one slot to the exterior of the implant may also optionally be drilled or formed by means of laser or other means, to permit diffusion of osteogenic materials from the central portions of the implant toward the external portions of the implant, and to permit recipient cells to migrate into the implant to effect expedited remodeling of the implant into host bone. An instrument attachment cannulation may optionally be machined into the back end of the implant by such methods as drilling and/or tapping. The implant is further, optionally, provided with a notch on the back end of the implant for use as a means to drive the implant into the fracture site during implantation and as an orientation marker. The implant may be autoclaved for thermal disinfection, or other disinfection means known in the art. One preferred method hereby incorporated by reference, is the method disclosed in publication number WO  00 / 29037 , hereby incorporated herein by reference. According to that methodology, various cleaning solutions are used to achieve deep interpenetration, cleaning and decellularization of the implant by enclosing the implant in a sealed chamber in the presence of the cleaning solution, and rapidly cycling the pressure within the chamber. The same methodology may be employed to infuse desired biologically active substances into the interior and interstices of the implant, such as growth factors, bone morphogenetic proteins, nucleic acids, antibiotics, anti-inflammatory substances, and the like.  
         [0025]    Specific dimensions of the implant are provided below, but those skilled in the art will recognize that these specifics may be appropriately scaled, depending on the size implant required for a given application.  
         [0026]    [0026]FIG. 1 depicts a perspective view of one embodiment of the novel osteotomy implant  10 . The implant is substantially conical in shape and made substantially of bone, a bone-like substance, or a biocompatible synthetic material. The implant has a front end  20  and a back end  30 , with the back end  30  having a larger diameter than the front end  20 . The back end  30  comprises a notch  31  for receiving a means to drive said implant into the fracture site. Back end  30  also contains a center cannulation  32  set inside notch  31  for use either for a guide wire to position the implant into the fracture site or for use as a means to secure the implant in or onto an insertion device during implantation The cannulation  32  can run from the back end  30  to the front end  20  in order to be used for a guide wire or run partially through the back end  30  for means to attach the implant to an insertion device. An appropriate insertion device as is known in the art for implantation of this type of implant can be used. The body  40  of the osteotomy implant  10  can either be threaded, contain grooves or contain barbs. FIG. 1 depicts the osteotomy implant  10  with threads. The threads  41  permit the osteotomy implant  10  to be screwed into a fracture site that has been distracted during surgery. The ability to screw in the implant allows the surgeon to achieve the appropriate angle for correction. The threads  41 , also ensure that the implant stays inside the fracture site by itself, which reduces the need to use plates and screws, wires or pins, although use of such retention means in combination with the present implant is not excluded. The remaining end of the implant, which is not inserted into the fracture site, is then cut off by the surgeon using a saggital saw or similar device.  
         [0027]    [0027]FIG. 2A depicts a top view of the implant  10 . The length of the implant  10  from front end  20  to back end  30  can range from about 1 mm to about 60 mm, but is preferably about 15-20 mm in length. The ratio of the back end diameter to the front end diameter ranges from about 5:1 to about 1:1, but preferably has the ratio of about 8:1 wherein the back end  30  diameter is about 19.2 mm and front end  20  diameter is about 6 mm. Slot  50  of implant  10  is formed transversely through the implant. Slot  50  can be filled with autogenous bone, allogenic bone, xenograft bone, demineralized bone, bone paste, cellular material, growth factors, and the like to stimulate healing and remodeling of the implant within the fracture site. The length of the slot  50  can range between about 0.25 mm to about 15 mm, but is preferably about 8-10 mm in length. The width of the slot  50  can range between about 0.1 mm to about 8 mm, but about 3-7 mm is preferred to avoid the walls of the implant  10  from being too thin. It will be apparent to those skilled in the art that the slot  50  may be a plurality of slots. It will also be apparent to those skilled in the art that the size ranges provided here are not limiting but are merely a guide. For example, in radial fractures, very small implants are required.  
         [0028]    [0028]FIG. 2B depicts the back end  30  view of the implant. The width of the notch  31  can range between about 0.1 mm and about 8 mm, but is preferably about 3-5 mm wide. The depth of notch  31  is depicted in FIG. 4A and can range between about 0.1 mm to about 6 mm, but is preferably about 2 mm deep.  
         [0029]    The cannulation  32  is depicted in FIG. 2B. The cannulation  32  diameter can vary between about 2 mm to about 4 mm, but is preferably about 2 mm. The length of the cannulation can extend either partially or completely through the length of the implant.  
         [0030]    [0030]FIG. 3 depicts a top view of one embodiment of the implant containing holes  42  in the implant  10  which further stimulate healing in the fracture by allowing the autogenous bone, allogenic bone, xenograft bone, demineralized bone, bone paste, cellular material, growth factors, and the like, which is placed in the slot opening  50  to pass through the body  40  of the implant  10 . The holes  42  can range in size, but are preferably about 200 μm in size to permit the autogenic bone, allogenic bone, xenograft bone, demineralized bone, bone paste, cellular material, growth factors, and the like, to pass through without compromising the strength of the implant  10 . Such holes  42  or canals also permit rapid invasion of recipient cells into the implant, and diffusion out of the implant of, for example, mesenchymal stem cells infused or packed into the implant. As a result, the implant is more rapidly remodeled into recipient bone. Further, the implants may be assembled by combining portions of bone from different or the same donor, from allograft bone, autograft bone, xenograft bone, cortical bone, cancellous bone and synthetic materials may also be combined to form an appropriate implant according to this invention. The assembled pieces may be held together by adhesive, by pins (metal cortical bone, synthetic) or other fixation means. Due to the different properties of cortical bone and cancellous bone, a composite assembled implant according to this invention may be made with a wide range of physical, chemical and biological properties.  
         [0031]    [0031]FIG. 4A provides a side view of the implant shown in FIG. 1. FIG. 4B is a magnified view of the screw threads  41  depicted on the body  40  of the implant in FIG. 4A. The threads extend from the front end  20 , to the back end  30  of the implant  10 . Pitch can vary between about 0.5 mm to about 3 mm, but is preferably about 1.5 mm from point to point. The threads are relatively perpendicular to the implant body  40 .