Abstract:
The present invention provides an orthopaedic implant including a base device having a device surface and a fixation material attached to at least one portion of the device surface. The fixation material is configured to provide a minimally sufficient adhesive force to resist natural pull out caused by forces acting on the base device after implantation and bone growth. Also provided is a method of manufacturing an orthopaedic implant. A base device with a device surface is provided and a minimally sufficient adhesive force, that can resist natural pull out caused by forces acting on the base device after implantation and bone growth, is determined. A proper amount of fixation material sufficient to provide an adhesive force equal to the minimally sufficient adhesive force is determined and fixation material is applied to the device. When the proper amount of fixation material is applied to the device surface, application is stopped.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional application based upon U.S. provisional patent application Ser. No. 61/787,507, entitled “FIXATION OF ORTHOPAEDIC DEVICES”, filed Mar. 15, 2013, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to orthopaedic devices, and more particularly, to orthopaedic implants. 
         [0004]    2. Description of the Related Art 
         [0005]    Orthopaedic implants are known that are implanted into the body to achieve various surgical objectives. Such implants include bone pins, bone screws and bone plates. The implantation period of the implant can vary from a short period, such as a couple of days, to the end of a patient&#39;s life. During the implantation period, the implant will experience natural forces caused by surrounding anatomy structures due to static and dynamic conditions of the anatomy structures. These natural forces can cause the implant to either loosen from the implantation site or, worse, ultimately detach from the implant site. 
         [0006]    To prevent the loosening and detachment of an orthopaedic implant from its implantation site, the implant is usually fixated to the implantation site by bone screws, which must be screwed into the implantation site. The implant can also be bonded to the implantation site with an adhesive, such as bone cement, or materials can be attached to the implant that encourage natural ingrowth of tissue onto or into the implant. Natural tissue ingrowth will help to fixate the implant in place and can form a strong bond with the implant. 
         [0007]    One problem that arises with implanted devices is that there is a risk that a revision surgery, to remove the implant, may be required due to reasons such as an incorrect placement, an unforeseen event or an infection causing the implant to prematurely fail. In such cases, removing the implant can be a traumatic event for anatomy structures around the site if a lot of force is required to loosen the implant and remove it. 
         [0008]    A similar problem can occur with devices that are meant to be temporary, i.e., have a relatively short implantation period. The device can become too integrated with the body and become very difficult to remove, which can lead to trauma at the implantation site during removal. 
         [0009]    What is needed in the art is an orthopaedic implant that can resist natural pull out but does not require excessive force to remove. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an orthopaedic implant with a fixation material attached to the implant that is configured to provide a minimally sufficient adhesive force to resist natural pull out of the implant caused by forces acting on the implant during implantation and bone ingrowth. 
         [0011]    The invention in one form is directed to an orthopaedic implant including a base device with a device surface and a fixation material attached to the base device. The fixation material is attached to at least one portion of the device surface and is configured to provide a minimally sufficient adhesive force to resist natural pull out caused by forces acting on the base device after implantation and bone ingrowth 
         [0012]    The invention in another form is directed to a method of manufacturing an orthopaedic implant. The method includes providing a base device that has a surface area and determining a minimally sufficient adhesive force to resist natural pull out caused by forces acting on the base device after implantation and bone ingrowth. A proper amount of a fixation material sufficient to provide an adhesive force equal to the determined minimally sufficient adhesive force is determined and the fixation material is applied to the device surface. When the proper amount of the fixation material is applied to the device surface, application of the fixation material is stopped. 
         [0013]    The invention in yet another form is directed to a method of performing an orthopaedic surgery. The method includes providing an orthopaedic implant having a device surface and a fixation material attached to the device surface. The fixation material is configured to provide a minimally sufficient adhesive force to resist natural pull out caused by forces acting on the base device after implantation and bone ingrowth. The orthopaedic implant is implanted at an implantation site within a patient. The implantation of the orthopaedic implant is revised by applying a revisionary force to the orthopaedic implant that is slightly greater than the minimally sufficient adhesive force. 
         [0014]    An advantage of the present invention is that it provides an orthopaedic implant that can withstand natural pull out forces when implanted within a patient while not requiring excessive force to remove, if necessary. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0016]      FIG. 1  is a perspective view of an embodiment of an orthopaedic implant of the present invention; 
           [0017]      FIG. 2  is another perspective view of the orthopaedic implant shown in  FIG. 1 ; 
           [0018]      FIG. 3  is a cross-sectional view of the orthopaedic implant shown in  FIG. 2  along line A-A; 
           [0019]      FIG. 4  is a perspective view of another embodiment of an orthopaedic implant of the present invention; 
           [0020]      FIG. 5  is a cross-sectional view of the orthopaedic implant shown in  FIG. 4  along line A-A; 
           [0021]      FIG. 6  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0022]      FIG. 7  is a sectional view of the orthopaedic implant shown in  FIG. 6 ; 
           [0023]      FIG. 8  is a sectional view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0024]      FIG. 9  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0025]      FIG. 10  is a sectional view of the orthopaedic implant shown in  FIG. 9 ; 
           [0026]      FIG. 11  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0027]      FIG. 12  is a sectional view of the orthopaedic implant shown in  FIG. 11 ; 
           [0028]      FIG. 13  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0029]      FIG. 14  is a sectional view of the orthopaedic implant shown in  FIG. 13 ; 
           [0030]      FIG. 15  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0031]      FIG. 16  is a sectional view of the orthopaedic implant shown in  FIG. 15 ; 
           [0032]      FIG. 17  is a before and after exploded view of forming yet another embodiment of an orthopaedic implant of the present invention; 
           [0033]      FIG. 18  is another before and after exploded view of forming yet another embodiment of an orthopaedic implant of the present invention; 
           [0034]      FIG. 19  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0035]      FIG. 20  is another perspective view of the orthopaedic implant shown in  FIG. 19 ; 
           [0036]      FIG. 21  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; 
           [0037]      FIG. 22  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention; and 
           [0038]      FIG. 23  is a perspective view of yet another embodiment of an orthopaedic implant of the present invention. 
       
    
    
       [0039]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplification are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown an orthopaedic implant  30  which generally includes a base device  32  and a fixation material  34  attached to the base device  32 . The base device  32  shown is a bone pin that can reside within a patient for a short period of time. The base device  32  can be constructed of metals commonly used in orthopaedic implants such as titanium, cobalt chrome and stainless steel. Alternatively, the base device can be constructed of biocompatible polymers such as polyether ether ketone (PEEK), polylactic acid (PLA), polyglycolic acid (PGA), polyethylene (PE) and blends thereof. 
         [0041]    The fixation material  34  attached to the base device  32  is shaped as a thin band wrapped around the circumference of the base device  32 . The fixation material  34  can be a porous polymer or metal that has a roughened surface  36  to provide immediate fixation of the device  30  due to frictional forces and to encourage quick tissue ingrowth into the fixation material  34 . The roughened surface  36  can have customized surface properties for a specific tissue type and desired tissue ingrowth amount or rate. Such surface properties can include a surface energy density, wettability and electrostatic charge. Polymers and metals that can act as the fixation material  34  include PEEK, PLA, PGA, PE, titanium, cobalt chrome and stainless steel. Pores  38  of the fixation material  34  can be sized to allow or prevent ingrowth of tissue into the fixation material  34 . Additionally, biologically active substances can be included in the pores  38  to encourage or limit tissue ingrowth into the fixation material  34 , as well as provide other useful properties such as antimicrobial activity to reduce the risk of infection. 
         [0042]    As the orthopaedic implant  30  is a small diameter bone pin that will likely be removed within a few weeks of implantation, a strong interface between surrounding tissue and the orthopaedic implant  30  is undesirable as it will cause removal of the orthopaedic implant  30  to be unnecessarily difficult. As can be seen in  FIGS. 2 and 3 , only a relatively small band of fixation material  34  is necessary to provide a minimally sufficient adhesive force that will resist pull out of the orthopaedic implant  30  while it is implanted in a patient while not causing excessive adhesive force that could make the device  30  difficult to remove. As shown in  FIG. 3 , the fixation material  34  has a relatively low thickness T (0.010″) and a width W (“0.050”) significantly greater than the thickness T. For the orthopaedic device  30  shown, a thickness T range of about 0.005″ to 0.015″ and a width W range of about 0.020″ to 0.125″ can be appropriate dimensions for the fixation material  34  shaped as a band to provide the minimally sufficient adhesive force. It is also contemplated that there can be multiple fixation materials attached to the base device  32 , which would alter the dimensions of each fixation material region. An additional design consideration when shaping and placing the fixation material  34  on a small diameter pin is that the pin won&#39;t provide much leverage to apply torque and overcome the adhesive force provided by the fixation material  34 . 
         [0043]    Referring now to  FIGS. 4 and 5 , an orthopaedic implant  40  is shown which includes a base device  42 , shown here as a large diameter pin, with a fixation material  44  attached to the pin  42 . The fixation material  44  can be the same as the fixation material  34  described previously. When utilizing a large diameter pin  42 , the amount and geometry of the fixation material  44  will need to be changed to provide a minimally sufficient adhesive force that will resist natural pull out of the pin  42 , due to increased size of the pin  42 . As shown in  FIGS. 4 and 5 , the fixation material  44  can be shaped as a band around the circumference of the pin  42 , similar to the previously described small diameter pin  32 . The band of fixation material  44  can have a thickness T ranging from about 0.015″ to 0.050″ and a width W ranging from about 0.020″ to 0.125″. As can be seen in  FIG. 5 , the pin  42  can also have a groove  46  formed on the outer surface  48  of the pin  42  where the fixation material  44  attaches to the pin  42 . The groove  46  can have a varying depth that changes how proud an outer surface  50  of the fixation material  44  is relative to the outer surface  48  of the pin  42 . As seen in  FIG. 5 , the fixation material  44  has a thickness T of 0.020″, but the outer surface  50  only elevates 0.010″ relative to the outer surface  48  of the pin  42 . Having the groove  46  in the pin  42  allows for a thicker fixation material  44 , which will increase the potential bone ingrowth and adhesive force, with a smaller increase in the overall diameter of the device  40 . The groove  46  also provides more surface area of the pin  42  to utilize for attachment to the fixation material  44 . As opposed to a small diameter pin, a large diameter pin can have a larger minimally sufficient adhesive force but still be easily removed because the large diameter pin  42  provides more leverage to apply torque and overcome the adhesive force provided by the fixation material  44 . 
         [0044]    Referring now to  FIGS. 6 and 7 , an orthopaedic implant  60  is shown which includes a base device  62 , shown as a bone screw, and a fixation material  64  attached to the bone screw  62 . The bone screw  62  can be constructed of biocompatible metals and polymers, similar to previously described base devices, and the fixation material  64  can be made of a material similar to that of previously described fixation materials. The bone screw  62  has a head end  66 , a distal end  68  and a plurality of threads  70  formed on a surface  72  of the bone screw  62 . The fixation material  64  forms a small patch on the distal end  68  of the bone screw  62 . The threads  70  of the bone screw  62  will provide some adhesive force to keep the bone screw  62  in place during implantation, so the fixation material patch  64  acts to provide additional adhesive force at the distal end  68 , if necessary, to resist natural pull out of the bone screw  62 . 
         [0045]    Referring now to  FIG. 8 , an orthopaedic implant  80  is shown which includes a bone screw  62  similar to that shown in  FIGS. 6 and 7  having a fixation material  82  attached to the distal end  68  of the bone screw  62 . The fixation material  82  can be formed from any fixation material previously described. In this embodiment, the fixation material  82  is formed as a “dot” of material on the distal end  68  of the bone screw  62  to provide additional adhesive force to the bone screw  62 . 
         [0046]    Referring now to  FIGS. 9 and 10 , an orthopaedic implant  90  is shown which includes a bone screw  92  similar to that shown in  FIGS. 6 ,  7  and  8  having a fixation material  94  attached to a surface  96  of the bone screw  92  between threads  98  formed on the surface  96  of the bone screw  92 . The fixation material  94  can be formed from any fixation material previously described. As can be seen, the fixation material  94  has a helical shape that wraps around the circumference of the bone screw  92  between the threads  98 . In this configuration, the fixation material  94  provides a substantial amount of adhesive force to resist natural pull out of the device  90 . Such a configuration may be desirable for bone screws that are intended to have a longer implantation period, where additional fixation of the bone screw is desirable. 
         [0047]    Referring now to  FIGS. 11 and 12 , an orthopaedic implant  100  is shown which includes a bone screw  101  similar to that shown in  FIGS. 6 ,  7 ,  8  and  9  having a fixation material  102  attached near a distal end  103  of the bone screw  101  between the distal end  103  and threads  104  and  106 . The fixation material  102  can be formed from any fixation material previously described. This configuration allows for the fixation material  102  to provide less fixation force than orthopaedic implant  90 , previously described. Such a configuration is better suited for bone screws that are intended to have shorter implantation periods, where too much additional fixation of the bone screw would make removal unnecessarily difficult. 
         [0048]    Referring now to  FIGS. 13 and 14 , an orthopaedic implant  110  is shown which includes a base device  112 , shown as a bone screw, with holes  114  formed through a surface  116  of the bone screw  112  between threads  118 . The holes  114  are located axially in valleys  120  between the threads  118  and go through to the centerline of the screw  112 . The holes  114  can be placed along the full length of the screw  112 . The screw  112  is a cannulated screw having an inner chamber  120  that has a fixation material  122  bonded inside the inner chamber  120 . By having holes  114  and the fixation material  122  inside the inner chamber  120 , tissue will be chemoattracted to the fixation material  122  and fill in the holes  114 , forming a strong interface with the orthopaedic implant  110 . A wall thickness (not shown) between the minor diameter of the bone screw  112  and the inner wall of the inner chamber  120  should be in a range of approximately 1 mm to 1.5 mm. Studies have shown that bone will bridge a gap of approximately 1 mm to 1.5 mm to grow into a porous material, such as the fixation material  122 .  FIGS. 15 and 16  show a similar embodiment, with fewer holes  114  formed through the bone screw  112  and the holes  114  being concentrated near a distal end  126  of the bone screw  112 . 
         [0049]    Referring now to  FIG. 17 , a base device  130  is shown before and after being prepared into an orthopaedic implant  132  of the present invention. As can be seen, the base device  130  is a screw blank that has had elongated pockets  134  machined within. These elongated pockets  134  are filled with a fixation material  136 , which can be any fixation material previously described. Following filling of the elongated pockets  134  with the fixation material  136 , threads  138  can be cut into the base device  130  and fixation material  136  to form the completed orthopaedic implant  132 . In this configuration, the threads  138  will be composed of approximately half fixation material  136  and half material of the base device  130 , giving the orthopaedic implant  132  a substantial amount of fixation material  136  to provide adhesive force during implantation and also placing the fixation material  136  into intimate contact with surrounding anatomy structures during implantation. Such a configuration can be particularly useful when the orthopaedic implant  132  is intended to be a long-term implant. 
         [0050]    Referring now to  FIG. 18 , a base device  140  is shown before and after being prepared into an orthopaedic implant  142 . The base device  140  is a screw blank with a minor diameter d1 between a head end  144  and a distal end  146 . A fixation material  148 , which can be any fixation material previously described, is bonded to a section of the base device  140  having minor diameter d1 to create a diameter d2 similar to that of the head end  146  and distal end  148 . Threads  150  are then formed into the fixation material  148  to create the completed orthopaedic implant  142 . 
         [0051]    Referring now to  FIGS. 19 and 20 , an orthopaedic implant  160  is shown that includes a base device  162 , shown as a bone plate, and a fixation material  164  attached to the bone plate  162 . The bone plate  162  has a bare surface  166  and multiple openings  168  that are sized to allow bone screws (not shown) to be passed through. The openings  168  are shaped so that when the bone screws are driven into a bone, they will hold the bone plate  162  in place. The bone plate  162  can be made of biocompatible metals such as titanium, cobalt chrome and stainless steel, but can also be made of a biocompatible polymer such as PEEK. A polymer bone plate  162  could offer advantages over more common metal bone plates, such as higher compression and adjustable stiffening. The fixation material  164  is attached to a bottom surface (not shown) that is opposed to the bare surface  166  and will be in contact with the bone during implantation. The fixation material  164  can be any fixation material previously described. In this embodiment, the fixation material  164  forms a layer on the bottom surface of the bone plate  162 . Since bone screws will be going through the openings  168 , the fixation material  164  does not cover the openings  168 . If the bone plate  162  had a bare bottom surface, the only fixation that the bone plate  162  would have when implanted would be provided by friction from the bone screws implanted in the bone. By attaching the fixation material  164  to the bottom surface of the bone plate  162 , the bone plate  162  is provided with adhesive force of its own: initially from the roughness of the fixation material and later from bone ingrowth into the fixation material  164 . Although the fixation material  164  is shown covering the entire bottom surface of the bone plate  162 , the amount of fixation material  164  could be altered to provide a desired amount of adhesive force to the bone plate. 
         [0052]    Referring now to  FIG. 21 , an orthopaedic implant  170  is shown that includes the bone plate  162  of  FIGS. 19 and 20  with a fixation material  172  attached at one end  174  of the bone plate  162 . The fixation material  172  is shaped as a patch and can be any fixation material previously described. By attaching the fixation material  172  to only one end  174  of the bone plate  162 , bone ingrowth and fixation will only occur at the end  174  of the plate with the fixation material  172 , allowing an opposite end  176  to float to whatever degree the attached bone screws allow. Such a configuration allows for a dynamic bone plate  170 . 
         [0053]    Referring now to  FIG. 22 , an orthopaedic implant  180  is shown that includes the bone plate  162  of  FIGS. 19 ,  20  and  21  with two regions of a fixation material  182  attached at both ends  184 ,  186  of the bone plate  162 . The regions of fixation material  182  are shaped as dots of material and can be any fixation material previously described. Attaching the fixation material  182  to both ends  184 ,  186  of the bone plate  162  provides bone ingrowth, and therefore fixation, at both ends  184 ,  186  of the bone plate  162 . 
         [0054]    Referring now to  FIG. 23 , an orthopaedic implant  190  is shown that includes the bone plate  162  of  FIGS. 19 ,  20 ,  21  and  22  with three regions of a fixation material  192  surrounding the openings  168  of the bone plate  162 . The fixation material  192  can be any fixation material previously described. Bone ingrowth into the fixation material  192  around the openings  168  provide additional fixation to the bone plate  162  in those regions. Such a configuration could be desirable if the bone screws are to be removed after implantation or do not provide enough fixation of the bone plate  162  on their own. 
         [0055]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.