Abstract:
A screw insertion/extraction device is disclosed that is useful as a tool for screw insertion and extraction procedures. The device includes a shaft sleeve that is formed to define a passage for accommodating the shaft of a wrench. In an exemplary embodiment, the shaft sleeve has a proximal portion and a distal portion interposed by an intermediate portion, where the proximal and distal portions extend along opposite sides of a central axis of the wrench shaft passage and the intermediate portion extends both along and about the central axis to connect the proximal and distal portions. A shoulder portion extends inwardly from the distal end of the shaft sleeve for engaging the base of a screw head such that the screw head can be captured between the distal end of a wrench and the shoulder portion of the shaft sleeve.

Description:
FIELD 
     This invention relates to tools used for the extraction and insertion of screws, having particular application in the medical field where screws are inserted and/or extracted as part of a medical procedure. 
     BACKGROUND 
     The use of bone screws for medical procedures, such as the repair of bone fractures, is known. For example, U.S. Pat. No. 4,463,753 describes a bone screw having distal threads and proximal threads. That bone screw is specifically intended for repair of a fracture by compressing the fractured segments of a bone while maintaining proper bone alignment. An end of the screw is provided with a hexagonal bore for engaging an Allen wrench, which can then be used for inserting the bone screw. However, for purposes of removing the bone screw, an Allen wrench cannot be used for exerting a pulling force for forcibly removing the bone screw. 
     One technique for addressing this problem is described by U.S. Pat. No. 5,375,956, which discloses a bone screw having a smooth shaft with threads near the head of the screw, as well as reverse threads extending about the head of the screw for engaging an internally-threaded extraction device. The screw can be removed by driving the extraction device onto the reverse threads to an engagement limit, at which point the extraction device can be further driven for partial extraction of the screw from the bone. Once the threads have been backed out of the bone, the screw is pulled until the remaining smooth shaft is extracted. The engagement of the internal threads of the extraction device with the external threads of the screw head allows the extraction device to be used for exerting a pulling force for extracting the smooth shaft of the screw from the bone. 
     However, the internally-threaded screw extractor still presents several drawbacks. For example, the use of the internally-threaded screw extractor requires the use of a screw having a threaded screw head, thus adding to the complexity and expense of manufacturing the bone screw. In addition, tissue growth often occurs in the threads of the screw head while it is in place, making it difficult to thread the extractor onto the screw for removal. 
     SUMMARY 
     In view of the shortcomings associated with the prior art, a device for screw insertion and extraction is presented herein that can be used for exerting a pulling force for removal of a screw without requiring that the screw head be threaded. 
     According to one aspect of the present invention, a screw extraction and insertion device comprises a shaft sleeve for engaging the shaft of a wrench. The shaft sleeve extends along a longitudinal axis, and has a proximal portion and a distal portion. The proximal and distal portions are adjacent to respective opposing sides of the wrench shaft when the shaft sleeve is engaged with the wrench shaft. The device also comprises a shoulder extending radially inward from a distal end of the shaft sleeve. 
     According to another aspect of the present invention, a screw extraction and insertion device comprises a shaft sleeve having a proximal portion and a distal portion connected by an intermediate portion. At least part of the proximal portion extends along a first longitudinal axis, and at least part the distal portion extends along a second longitudinal axis parallel to and offset from the first longitudinal axis. The device also comprises a shoulder that extends from the distal portion towards the first longitudinal axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and is not limited by the figures of the accompanying drawings, in which like reference numbers indicate similar parts: 
         FIGS. 1A and 1B  show perspective views of respective sides of a first embodiment of a screw extraction/insertion device; 
         FIG. 1C  shows an enlarged perspective view of a distal end of the screw extraction/insertion device shown in  FIGS. 1A and 1B ; 
         FIGS. 2A and 2B  show a perspective view and an enlarged perspective view, respectively, of the screw extraction/insertion device shown in  FIGS. 1A-1C  while engaging a screw; 
         FIGS. 3A-3D  show steps for engaging a screw using the screw extraction device; and 
         FIGS. 4A and 4B  show perspective views of a second embodiment of the screw extraction device. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1A-1C , a screw extractor  100  is shown that can serve as a wrench frame for assisting in maintaining a secure coupling between a wrench and a screw. As the name implies, the screw extractor  100  is particularly useful for screw extraction procedures. However, it is important to note that the extractor  100  can be equally useful for other procedures, including screw insertion procedures. In other words, the term “extractor” is merely a term of convenience and thus is not intended to limit in any way the scope of the present invention. The screw extractor  100  is preferably constructed of a rigid material, for example stainless steel. The screw extractor  100  includes a handle  110  and a shaft sleeve  120 . As shown in  FIGS. 3A-3D , which are discussed in greater detail below, the shaft sleeve  120  has a form that allows it to be engaged with a wrench shaft  310  even while the wrench  300  is engaged with a screw  200 . 
     The shaft sleeve  120  includes a proximal portion  130 , an intermediate portion  140 , and a distal portion  150 . In the present embodiment, the proximal portion  130  and distal portion  150  are both generally semi-cylindrical in order to provide a secure interface with the cylindrical shaft of a wrench. However, it will be appreciated that alternate shapes the shaft sleeve  120  can be implemented without departing from the spirit and scope of the present invention, particularly where an alternate shape is desired for accommodating the shape of a wrench shaft. For example, the shaft sleeve  120  can include portion or portions having a parabolic, curved, curvilinear, semipolygonal (i.e., multi-faceted), U, V, or C-shaped cross section. In the illustrated embodiment the semi-cylindrical shape is preferable for providing a secure interface with a cylindrical wrench shaft (e.g., wrench shaft  310  shown in  FIGS. 3A-D ) and for providing a low profile for passage into soft tissue en route to a screw secured in a bone. 
     The semi-cylindrical component of the proximal portion  130  and the distal portion  150  are offset from each other by an angle of approximately 180 degrees about a longitudinal axis of the shaft sleeve  120 . The intermediate portion  140  is generally semi-cylindrical, but forms a helical shape that twists approximately 180 degrees over the length thereof according to the angular offset between the distal portion  130  and the proximal portion  150 . The proximal portion  130  can be angularly offset from the distal portion  150  by other angles about the longitudinal axis of the shaft sleeve  120 , or even aligned. However, the offset as shown in  FIGS. 1A-1C  is preferred since it allows the shaft sleeve  120  to more securely engage the wrench shaft  310  by extending longitudinally along opposing sides of the wrench shaft  310 . As best shown in  FIG. 1C , a shoulder  160  is provided at a distal end of the distal portion  150 . The shoulder  160  extends radially inward from the shaft sleeve  120 . 
     The screw extractor  100  can be used for aiding in the removal and/or implantation of surgical screws. For example, the screw extractor  100  can be used for removal and/or implantation of a peg-design (i.e., smooth shaft) locking screw  200  shown in  FIGS. 2A and 2B . The screw  200  can be used for fixing the position of an intramedullary nail (not shown). The locking screw  200  has a screw head  210  having a hexagonal recess  215  for driving engagement by an Allen-head wrench  300  (shown in  FIGS. 3A-3D ). Naturally, other types or styles of recess/wrench combinations can be used, for example slotted, Phillips, Torx, or square. The locking screw  200  also has a screw shaft  220  extending longitudinally from the screw head  210 . The screw shaft  220  is smoothly cylindrical except for a threaded portion  230 . The threaded portion  230  is preferably distanced longitudinally from the screw head  210  sufficiently enough to allow space for the shoulder  160  of the screw extractor  100  to engage the locking screw  200 . The screw head  210  preferably has an outer diameter that is greater than an outer diameter of the screw shaft  220 , or at least a portion of the screw shaft  220  adjacent to the screw head  210 , in order to allow the shoulder  160  to engage the screw  200  at the base of the screw head  210 . Also, the inner diameter of the distal portion  150  of the shaft sleeve  120  is preferably equal to or slightly greater than the outer diameter of the screw head  210  in order to allow the screw head  210  to be accommodated by the distal portion  150  of the shaft sleeve  120 . 
     A method of using the screw extractor  100  for extracting a bone screw such as bone screw  200  will now be discussed in conjunction with  FIGS. 3A-3D . Under typical circumstances, the locking screw  200  is removed by turning the screw counter-clockwise until the threaded portion  230  backs out of the bone  400 . At this point, the screw  200  must be pulled in order to extract the smooth portion of the screw shaft  220  from the bone  400 . Frictional forces between the bone  400  and the screw shaft  220  usually inhibit easy extraction. The screw extractor  100  provides a secure capture of the screw  200 , particularly when used in combination with the wrench  300 , for pulling the screw  200  from the bone  400 . It will be appreciated that the screw extractor  100  can be similarly used for inserting the screw  200  into the bone  400 . 
     In  FIG. 3A , the wrench  300  is engaged with the screw  200 , which has been turned to the point that the threaded portion  230  has been backed out of the bone  400 . That is, in  FIG. 3A  the screw head  210  and threaded portion  230  are shown external to the bone  400  while the screw shaft  220  (shown in broken lines) remains in the bone. At this point, the screw extractor  100  is employed for extracting the screw  200  by pulling on the screw  200  until the screw shaft  220  exits the bone  400 . As shown in  FIG. 3A , the screw extractor  100  is positioned for placement over the wrench shaft  310 . Specifically, the intermediate portion  140  of the shaft sleeve  120  is placed adjacent to the wrench shaft  310  with the inner side of the semi-cylindrical proximal and distal portions  130  and  150  facing the wrench shaft  310 . The screw extractor  100  is initially positioned such that the shaft sleeve  120  extends at an angle to the longitudinal axis of the wrench shaft  310 . Once the intermediate portion  140  of the shaft sleeve  120  is adjacent to the wrench shaft  310 , the screw extractor  100  is tilted relative to the wrench  300  in the direction indicated by arrow A. The tilting motion is continued until the longitudinal axis of the shaft sleeve  120  is close to parallel with the longitudinal axis of the wrench shaft  310  as shown in  FIG. 3B . 
     Next, as shown in  FIG. 3B , the screw extractor  100  is slid along the wrench shaft  310  towards the screw  200  in the direction indicated by arrow B. The wrench shaft  310  guides the shaft sleeve  120  directly to the screw  200  so long as the shaft sleeve  120  remains in contact with the wrench  300 , and the wrench  300  remains engaged with the screw  200 . The screw extractor  100  is slid relative to the wrench  300  in the direction B until the handle  110  of the screw extractor  100  arrives at the handle  320  of the wrench  300 . 
     Next, as shown in  FIG. 3C , the extractor handle  110  is moved under the wrench handle  320  to the position shown in  FIG. 3D  in a motion as generally indicated by the arrow C in  FIG. 3C . The motion of the extractor handle  110  over the wrench handle  320  simultaneously moves the distal end of the shaft sleeve  120 , moving the shoulder  160  of the shaft sleeve  120  behind the screw head  210 . This movement captures the screw head  160 , locking the screw head  210  between the wrench shaft  310  and the shoulder  160  of the shaft sleeve  120 . Once the screw  200  is secured in this manner, both the screw extractor  100  and wrench  300  can be pulled as shown in  FIG. 3D  in the direction indicated by arrow D to extract the screw  200  from the bone  400 . 
     As previously mentioned, the extractor  100  can also be used for screw insertion procedures. For example, the extractor  100  can be assembled with the screw  200  and the wrench  300  in order to securely capture the screw head  210  and maintain engagement between the screw  200  and the wrench  300 . Once assembled, the screw shaft  220  can be pushed into a pre-drilled hole in the bone  400  to the position shown in  FIG. 3D . The extractor  100  can then be removed from the wrench  300  by following the steps outlined above in connection with  FIGS. 3A-3D  in reverse order. The form of the extractor  100  advantageously allows the extractor  100  to be disengaged from the wrench  300  while the wrench  300  remains engaged with the screw  200 . Thus, upon removal of the extractor  100  from the wrench  300 , the wrench  300  can readily be used for driving the threaded portion  230  of the screw  200  into the bone  400 . 
     Having now described an exemplary embodiment of the screw extraction/insertion device and uses therefore, it will be appreciated, particularly by those skilled in related arts, that there are numerous modifications that can be made to the screw extraction/insertion device without departing from the spirit and scope of the present invention. 
     Examples of modifications that are contemplated for the screw extraction/insertion device are exemplified in an alternate embodiment—screw extractor  500 —shown in  FIGS. 4A and 4B . The screw extractor  500  includes modified forms of features included in the screw extractor  100 , such as an alternate handle  510 , shaft sleeve  520 , and shoulder  560 , as well as an optional collar  570 . Any one or more of these modified features can be incorporated into the screw extractor  100 . As shown in  FIG. 4A , the shaft sleeve  520  forms a semi-circular channel that extends in a longitudinal direction between distal and proximal ends thereof. The handle  510  extends from the proximal end of the shaft sleeve  520  and the shoulder  560  extends from the distal end, the handle  510  and shoulder  560  extending in opposite directions. The shoulder  560  is a crescent-shaped member for engaging the base of the screw head as shown in  FIG. 4B . The collar  570  extends from the shaft sleeve  520  longitudinally offset from the shoulder  560  by a distance sufficient to accommodate the screw head  210 , allowing for the screw extractor  500  to engage the screw  200  as shown in  FIG. 4B . The collar  570  assists in providing a secure coupling with the screw  200 . In addition, for screw insertion procedures, the collar  570  serves as a surface for applying pressure against the screw head  210 . In the embodiment shown in  FIGS. 4A and 4B  the collar  570  defines an aperture that allows the wrench  300  to engage and drive the screw  200 . However, since the collar  570  would completely circumscribe the shaft of the wrench  300 , it will be appreciated that this configuration does not allow for the screw extractor  500  to be engaged/disengaged from the wrench  300  while the wrench  300  is engaged with the screw  200 . Thus, the collar  570  can instead have crescent shape similar to that of the shoulder  560 , which would allow for the screw extractor  500  to be engaged/disengaged from the wrench  300  while the wrench  300  is engaged with the screw  200 . 
     Although the present invention has been fully described by way of preferred embodiments, one skilled in the art will appreciate that other embodiments and methods are possible without departing from the spirit and scope of the present invention.