Patent Publication Number: US-2006009772-A1

Title: Device for postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation

Description:
This application is a continuation of U.S. patent application Ser. No. 10/793,814, filed Mar. 8, 2004, which is a continuation of prior U.S. patent application Ser. No. 10/011,379, filed Oct. 22, 2001, now U.S. Pat. No. 6,726,688, which is a continuation of prior U.S. patent application Ser. No. 09/827,861, filed Apr. 6, 2001, now U.S. Pat. No. 6,328,743 B2, which is a continuation of prior U.S. patent application Ser. No. 09/494,599, filed Jan. 31, 2000, now U.S. Pat. No. 6,270,500 B1, which is a continuation of U.S. patent application Ser. No. 09/088,175, filed Jun. 1, 1998, now U.S. Pat. No. 6,068,631, which is a continuation of U.S. patent application Ser. No. 08/790,071, filed Jan. 28, 1997, now U.S. Pat. No. 5,800,436. 
    
    
     BACKGROUND OF THE INVENTION  
      The present background of the invention concerns a device for postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation.  
      It is often necessary during brain surgery to remove a plug of bone from the cranium to provide the surgeon with access to the field of operation. The plug is sawed out and must be replaced in the cranium after the operation and fixed thereto. Such plugs have long been fixed back into the rest of the cranium by suturing with loops of steel wire that extend through both and then twisting together the projecting ends of the emplaced loops. The contact between the plug and the rest of the cranium is relatively unstable, however. The two halves do not fuse together very well. The scalp can also become inflamed. Another drawback to such an approach is that the wire considerably distorts the images obtained in postoperative computerized tomography and accordingly impedes definitive interpretation of the soft structures of the brain. Although using nonresorbable and physiologically compatible thread instead of wire does eliminate the last-mentioned drawback, the fixation of the plug to the rest of the skull is still unstable. The two parts can also be fixed with thin plates of compatible metal, titanium for instance (EP A 0 510 390). Such plates bridge the abutment between the parts and are screwed to both, also closing off bores introduced into the cranium prior to section. This approach, however, is also not very satisfactory. It is both complicated and time-consuming and hence not inexpensive.  
     SUMMARY OF THE INVENTION  
      With the aforesaid state of the art as a point of departure, the object of the present invention is a simpler and more rapid device for accurate and permanent postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation.  
      This object is attained in accordance with the present invention in a device of the aforesaid genus comprising a pin and two concavoconvex disks of a physiologically compatible metal or metal compound. The pin has a flat head at one end and one of the disks comes to rest against the head. Each disk has row of teeth extending along the edge of the concave side and a bore through the center. The shaft of the pin fits into the bore. The disks can be mounted on the shaft with the teeth on each one facing the teeth on the other. The second disk can be fastened to the shaft.  
      The inner disks in the aforesaid fixation device in accordance with the present invention are secured to the pins in the vicinity of the head. The disks are then inserted through a slightly larger recess in the circumference of the plug, below the parts of the joint, with the shaft of the pin projecting out of the kerf between the plug and the rest of the cranium. The outer disk is then mounted over the section of pin projecting out of the kerf. The two disks are then approached until their teeth bite into the edges of both the plug and of the rest of the cranium. The second disk is then secured to the shaft.  
      Titanium is particularly appropriate for the physiologically compatible metal. Such titanium alloys as Ti 6 A 6 Va are also appropriate. A device made of titanium is of advantage because it will not distort postoperative computerized-tomography images. The inner disk can be mounted more stable on the shaft of the pin if the transition between the head of the pin and the shaft is conical and dimensioned to ensure that a disk resting against the head will be forced tight around the shaft. Slits can also extend radially outward from the bore through the first disk to be mounted on the shaft. The center of the disk can be depressed. Areas can be removed from the disks at regular intervals between the bore and the edge to conserve material. The device can be applied to the two halves of bone by a procedure similar in principle to blind riveting. Notches can accordingly be introduced into each shaft to prevent the second disk mounted thereon from sliding away from the head of the pin. If the second disk on the shaft is deformed in a direction opposite that of its concavoconvexity, the deformation alone will secure it to the shaft by compression. The shaft can also be threaded and accommodate a nut. The nut can be tightened against the second disk. The second disk will in every case be displaced until its teeth engage the two halves of the joint, creating the desired fixation of the plug back into the rest of the cranium at the adjacent edges.  
      The novel device can be easily and rapidly manipulated and accomplishes the desired accurate and permanent postoperative fixation back into the cranium of a plug of bone removed therefrom during a surgical operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will now be specified with reference to the accompanying drawing wherein  
       FIG. 1  is an exploded view of the device in accordance with the present invention,  
       FIG. 2  is a view in the direction indicated by arrow II in  FIG. 1  of one embodiment of the first disk mounted over the shaft of the pin,  
       FIG. 3  is a view in the direction indicated by arrow III in  FIG. 1  of one embodiment of the second disk mounted over the shaft of the pin,  
       FIG. 4  is a longitudinal section of the components of the device assembled,  
       FIG. 5  illustrates how the device in accordance with the present invention can be employed,  
       FIG. 6  is a section along the line VI-VI in  FIG. 5 ,  
       FIG. 7  is a schematic view and shows another embodiment of the present invention,  
       FIG. 8  is a schematic view of a still further embodiment according to the present invention; and  
       FIG. 9  is a longitudinal section of another embodiment of a device in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      A device for postoperatively fixing back into the cranium a plug of bone removed therefrom during a surgical operation comprises a pin  11  and two concavoconvex disks  21  and  22 . The pin comprises a shaft  112  and a head  111 , Disk  21 , the inner disk, is mounted on the shaft first and comes to rest against the inner surface of the plug and of the rest of the cranium that are to be united. Disk  22 , the outer disk, is mounted on the shaft next and comes to rest against the outer surface of the plug and the rest of the cranium. There is a hole  211  through the center of each disk  21  and a hole  221  through the center of each disk  22 . The shaft  112  of pin  11  extends through the holes  211  and  221  of the disks in the assembled device. A row of teeth  213  extends along the edge  212  of the concave side of disk  21 , and a row of teeth  223  extends along the edge  222  of the concave side of disk  22 . As will be evident from  FIGS. 1 and 4 , disks  21  and  22  are mounted on the shaft  112  of pin  11  with their teeth facing each other.  
      Shaft  112  fits tightly in the hole  211  through disk  21 . Any disk can be provided as illustrated in  FIG. 2  with slits  214  extending radially outward from the hole  211  through its center. If the transition between the head  111  and the shaft  112  of pin  11  is conical, slits  214  will as is desirable accurately position the disk in relation to the pin, both of which will accordingly support both the plug and the rest of the cranium once the device has been emplaced. The area between the hole through the center of any disk and its circumference can also be provided as illustrated in  FIG. 3  with perforations  226  to conserve material and decrease weight. Each disk can have both slits  214  and perforations  226 .  
       FIGS. 5 and 6  illustrate how the device is employed.  FIG. 5  illustrates part of an adult cranium  31  from which a plug  32  of bone has been sawn to provide access to the brain, which is available to the surgeon through aperture  33 . A recess  321  slightly larger than the disks has been removed from plug  32  at its circumference. once the operation is over, the plug is returned to the aperture  33 . Inner disks  22  are mounted on the shafts  112  of pins  11 . The inner disks are inserted one by one through recess  321  with the shafts projecting out and slid along the inner surface of the plug and residual cranium with the shafts extending out of kerf  331  in the directions indicated by arrows A in  FIG. 5  until they arrive at the point where they are to be positioned. outer disks  22  are now mounted on the shafts of the pins in situ. The outer disks are finally secured to the shafts with a tool of the type employed to fasten blind rivets. The tool forces outer disks  22  and inner disks  21  together in the direction indicated by arrow B in  FIG. 6  until the teeth on each disk bite into the tissue of the plug and of the residual cranium, securing the two together. The section of each shaft extending out beyond the outer disk is now trimmed off. The shaft can alternatively be threaded, and the disks forced together over the threads until the teeth bite into the tissue.  
      Thus, in another embodiment shown in  FIG. 7 , as well as in  FIG. 9 , the shaft  112  of the pin  11  has notches  112   c  engaging the outer surface of the second disc  22  and forcing it towards the head  111  of the pin.  
      In the embodiment of  FIG. 8 , the shaft of the pin  11  has a thread  112   a  and accommodates a nut  112   b  that can be screwed against the second disk  22 .  
      In the embodiment shown in  FIG. 9 , the first disk  21   a  and the second disk  22   a  are each formed in a generally concavoconvex shape with a center portion  218 ,  228  of the disk being depressed in a direction opposite that of its concavoconvexity.