Abstract:
An interference fit screw driver has a polygonal driving surface to impart torque to a corresponding surface in a screw. The end of the polygonal driving surface has a frusto-conical shaped gripping member which fits into an aperture in the screw to create a friction fit between the screw and screw driver. This allows the screw to be attached to the screw driver to facilitate installation of the screw. The friction fit is tight enough to hold the screw to the driver, yet allows the driver to be easily disengaged from the screw by pulling the driver away from the screw once the screw is lodged in place. The interference fit screw driver is particularly useful in turning bone screws into the spine of a patient during orthopedic surgery.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/894,330, filed Jun. 28, 2001, entitled “INTERFERENCE FIT SCREW DRIVER,” which is hereby incorporated by reference herein in its entirety, including but not limited to those portions that specifically appear hereinafter, the incorporation by reference being made with the following exception: In the event that any portion of the above-referenced application is inconsistent with this application, this application supercedes said portion of said above-referenced application. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    1. The Field of the Invention  
           [0004]    The present invention relates generally orthopedic driving tools and fasteners, and more particularly, but not necessarily entirely, to screw drivers capable being attached to screws by an interference fit for use in orthopedic surgery, to turn bone screws into the spine of a patient.  
           [0005]    2. Description of Related Art  
           [0006]    A typical screw driver known in the art has a driving surface or bit which mates with a complementary recess on a screw to allow the screw driver to impart torque to the screw. An area of concern related to screw drivers has been retaining the screw on the bit of the driver while positioning the screw. This aspect of screw drivers is particularly important in the medical profession, for example, as bone screws are inserted into the spine of a patient during orthopedic surgery.  
           [0007]    Screw drivers known in the prior art have used various techniques to attach the screws to the bits. For example, U.S. Pat. No. 4,970,922 (granted Nov. 20, 1990 to Krivec) discloses a rotatable driving tool having a plurality of substantially circularly helical driving portions with small helix angles. The driving portions mate with lobes of the fastener recess but are slightly inclined with respect to the lobes. This provides a wedge fit to retain the fastener with the tool. However, the inclined driving portions allow the driver to efficiently apply torque only in one direction. If torque is applied to the fastener in the opposite direction, the inclined driving portions force the driver out of engagement with the lobes of the fastener. Thus, a reverse driver may be required to remove the screw.  
           [0008]    Another approach has been to use a tapered bit on the driving tool which is adapted to wedge into the recess of the screw. For example, U.S. Pat. No. 4,269,246 (granted May 26, 1981 to Larson et al.) discloses a driver bit with multiple lobes. The lobes are tapered axially, converging toward the tip end of the driver. The driver bit enters a socket of the fastener to a predetermined depth before wedging the fastener to the driver. A disadvantage of this arrangement is that the bit engages the fastener only at the outer end of the socket. This results in inefficient transfer of the torque from the driving member to the fastener. Also the concentration of force at one contact location tends to wear and deform the socket in the contact region. Furthermore, close tolerances are necessary in order to provide the proper wedge fit in a consistent manner.  
           [0009]    U.S. Pat. No. 5,277,531 (granted Jan. 11, 1994 to Krivec) discloses another technique for attaching a fastener to a tool. This patent discloses a polygonal shaped tool fitting a socket recess formed in a fastener. The recess has planar drive surfaces alternating with sloping retaining surfaces. The polygonal tool is wedged in contact with the sloping retaining surfaces to retain the fastener on the tool. This configuration also reduces the contact area between the tool and the fastener. Furthermore, if significant torque is applied to the fastener, the retaining surfaces may become tightly wedged to the tool making it difficult to release the fastener.  
           [0010]    An additional type of retention technique is the use of a magnetized bit on the driving tool. However, this type of retention is only useful in screws formed of magnetic material.  
           [0011]    The prior art is thus characterized by several disadvantages that are addressed by the present invention. The present invention minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.  
           [0012]    In view of the foregoing state of the art, it would be an advancement in the art to provide an interference fit screw driver which is simple in design and manufacture which is attached to a screw by a friction fit to facilitate positioning the screw. It would be a further advancement in the art to provide such a screw driver which is capable of applying torque in two directions and which engages the screw over a large surface area such that wear and deformation of the screw and screw driver are reduced, and which can be released from the screw even after a large torque has been applied to the screw by the screw driver. It would be an additional advancement in the art to provide a screw driver which is capable of retaining contact with screws made of nonmagnetic materials. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 is a side view of a driving tool and driven member made in accordance with the principles of the present invention, the upper portion of the driven member being illustrated in a cross-sectional view;  
         [0015]    [0015]FIG. 1A is an enlarged, cross-sectional view of the upper portion of the driven member illustrated in FIG. 1, made in accordance with the principles of the present invention;  
         [0016]    [0016]FIG. 2 is an end view of the driving tool of FIG. 1;  
         [0017]    [0017]FIG. 3 is a break-away cross-sectional view of an alternative embodiment of the driving tool and driven member of FIG. 1, made in accordance with the principles of the present invention; and  
         [0018]    [0018]FIG. 4 is an end view of the alternative embodiment of the driving member of FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    For the purposes of promoting an understanding of the principles in accordance with the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would normally occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention claimed.  
         [0020]    Referring now to FIG. 1, a side view is illustrated of an exemplary embodiment of a screw driver  10 , also referred to herein more generally as a driving tool, and a screw  20 , also referred to herein more generally as a driven member, in accordance with the principles of the present invention. The screw driver  10  is substantially cylindrical in shape having a longitudinal axis  16 , and includes a body  30  having a proximal end  32  and a distal end  34 . The body  30  includes a fitting  26  disposed on the proximal end  32 , to allow a user to attach an implement, such as a wrench or other device for applying a force to the screw driver  10 , to facilitate applying torque if necessary. The fitting  26  may be a polygonal surface or socket for example. However, as those skilled in the art will appreciate, various different configurations may be used as fittings, and such variations are intended to fall within the scope of the present invention. The body  30  may also include a handle  28  disposed on the proximal end  32  to facilitate gripping the body  30  so that torque may be applied more easily without slipping. The handle  28  may be formed of a series of grooves or knurls in the body  30  to create a frictional surface. Other varieties of handles known in the art may also be used and are intended to fall within the scope of the present invention.  
         [0021]    A driving means  12 , also referred to herein as a driving component, may be disposed on the distal end  34  of the body  30 . The driving means  12  has a first end  36 , a second end  38 , and may comprise a constant cross-sectional configuration throughout the length of the driving means  12 . The constant cross-section in that example allows efficient transfer of torque from the screw driver  10  to the screw  20  without the tendency to separate as is common with tapered driving surfaces. Also, such constant cross-sectional configuration allows the driving means  12  to impart torque efficiently when rotated in both clockwise and counter-clockwise directions. This feature is an improvement over driving surfaces with curved or angled driving surfaces, which work to transfer torque efficiently in only one direction.  
         [0022]    The driving means  12  may be polygonal in shape. For example, the polygonal shape of the driving means  12  may be a hexagonal shape as shown most clearly in FIG. 2. However, as those skilled in the art will appreciate, driving surfaces of various shapes, such as star shapes, cross shapes, blade shapes, or fluted configurations, may be used for the shape of the driving means  12  and such shapes are intended to fall within the scope of the present invention.  
         [0023]    A gripping means  14 , also referred to herein as a gripping surface  14 , may be disposed on the second end  38  of the driving means  12  such that the gripping means extends below said second end  38  for gripping the screw  20  and to removably attach the screw  20  to the screw driver  10 . It will be appreciated that the gripping means  14  may be substantially frusto-conical in shape, however other configurations of the gripping means  14  are possible, and are intended to fall within the scope of the present invention. The gripping means  14  may be located along the axis  16  such that a break  46  may be disposed radially from the longitudinal axis  16  between the driving means  12  and the gripping means  14 . The separation of the gripping means  14  from the driving means  12  allows the gripping means  14  to function independently from the driving means  12  and vice versa. The function of the gripping means  14  will be described more fully below.  
         [0024]    As illustrated in FIG. 2, the driving means  12  may have a radial dimension  48  from the longitudinal axis  16  of the tool  10  which may be larger than a radial dimension  50  of the gripping means  14 . The difference in radial dimension forms the radial break  46  to separate the drive means  12  from the gripping means  14 , and the difference in radial dimension provides a larger surface area to the driving means  12  for efficiently applying torque rather than for gripping the screw  20 . The radial dimension  48  of the driving means  12  may be sized in a range of between approximately two to four times the radial dimension  50  of the gripping means  14  from the longitudinal axis  16 .  
         [0025]    As illustrated in FIGS. 1 and 1A, the screw  20  may include a first aperture  24  and a second aperture  22 . The first aperture  24  may be aligned coaxially with the second aperture  22  and may be smaller than the second aperture  22 , such that the second aperture  22  circumscribes the first aperture  24 . The first aperture  24  may be defined by a circumferential edge  40 , which circumferential edge  40  may be engaged by a portion of an outer surface of the gripping means  14  to attach the screw  20  to the screw driver  10 . The first aperture  24  and the circumferential edge  40  are illustrated as being circular in shape, however, various shapes may be used for the first aperture  24  and the circumferential edge  40 , and each of the various shapes are intended to fall within the scope of the present invention. As further illustrated in FIGS. 1 and 1A, the circumferential edge  40  defines a diameter  140  of the first aperture  24  that may be less than twenty percent of a length of a diameter  141  of the second aperture  22 . More specifically, the diameter of the first aperture  24  may be less than three millimeters in length.  
         [0026]    The second aperture  22  may be defined by a socket  42 , sometimes referred to herein as a receiving cavity, which comprises a surface  42   a  that engages the driving means  12  of the screw driver  10  to form an interference fit. The socket  42  may have a shape which corresponds to the shape of the driving means  12 , such as a hexagonal shape for example. However, it will be appreciated that the socket  42  may have various corresponding shapes of polygons, stars, crosses, blades, or fluted configurations for example, that are intended to fall within the scope of the present invention.  
         [0027]    The screw  20  may also have an engaging means for advancing the driven member into the patient&#39;s bone, said engaging means comprising a shank  49  with threads  44  of any variety known in the art located thereon. However, the principles of the present invention may be applied to any such driven member  20  which may employ other engaging means for advancing the driven member into the patient&#39;s bone such as flanges or pins for example, in addition to threads  44 .  
         [0028]    In use, the screw  20  may be attached to the screw driver  10  by inserting the gripping means  14  into the first aperture  24  to the point where the edge  40  engages the gripping means  14  to wedge the gripping means  14  against the edge  40  with a friction fit. The area of contact between the gripping means  14  and the edge  40  may be large enough to supply sufficient force to attach the screw  20  to the screw driver  10 , yet small enough such that the screw  20  may be released when desired without undue effort. As the gripping means  14  enters the first aperture  24 , the driving means  12  may be aligned against the socket  42 . The surface area of the contact between the driving means  12  and the socket  42  may be large as compared to the contact between the gripping means  14  and the edge  40 . This relationship allows efficient transfer of torque from the screw driver  10  to the screw  20  without imposing concentrated loads on a single point. Furthermore, since the contact between the driving means  12  and the socket  42  may be separate from the contact between the gripping means  14  and the edge  40 , the screw  20  can be easily released from the screw driver  10 , regardless of how much torque is applied. In other words, a high torque placed on the socket  42  by the driving means  12 , may have no effect on the frictional connection between the gripping means  14  and the edge  40 . Once it is desired to release the screw  20  from the screw driver  10 , the screw driver  10  may be simply pulled from the screw  20  with a force sufficient to overcome the frictional fit between the gripping means  14  and the edge  40 .  
         [0029]    It will be appreciated that the friction fit of the present invention occurs between a fractional portion of the outer surface of the gripping means  14  and the circumferential edge  40 , which friction fit occurs along a portion of the gripping means  14  and the circumferential edge  40  that is substantially less than a majority. Therefore, it will be appreciated that the phrase “fractional engagement” shall refer to the concept that a gripping piece  41  engages with a some fractional portion of the surface of another member in which said fractional portion is substantially less than a majority of its surface. One embodiment of this concept of “fractional engagement” is illustrated and characterized by the absence of full contact along a majority of the surface of the gripping means  14  and the circumferential edge  40  of the driven member  20 . Additionally, the friction fit of the present invention is not a press-fit, and the gripping means  14  does not bite into, or otherwise deform, the circumferential edge or any other portion of the driven member  20 . As used herein, the term “bite” refers to the slight deformation that occurs in the driven member as an end of the screw driver is located within said driven member.  
         [0030]    Referring specifically to FIG. 1A, which is an enlarged view of the screw  20  of FIG. 1, socket  42  may be defined by a sidewall  43 , which extends upwardly from a base  21   a  of a head portion  21  of the screw  20 . An annular gripping piece  41  may extend radially inward from sidewall  43  of the socket  42  of the screw  20  and further provides the circumferential edge  40 , which frictionally engages a portion of gripping means  14 . It will be appreciated that the gripping piece  41  essentially separates the socket  42 , or receiving cavity, into a first chamber  45  and a second chamber  47 . Also illustrated in FIG. 1A is the first aperture  24  and the second aperture  22 , wherein the second aperture  22  may be circumscribed by sidewall  43  and may have the gripping piece  41  located within the socket  42  as illustrated. The gripping piece  41  comprises an upper surface  41   a  and a lower surface  41   b,  wherein the upper surface  41   a  faces the first chamber  45  and the lower surface  41   b  faces the second chamber  47 . It will be appreciated that the two chambers  45  and  47  may not be completely enclosed chambers, although such a configuration is contemplated by the present invention, but the chambers  45  and  47  may both be essentially part of the socket  42 , and may be separated by the gripping piece  41 .  
         [0031]    Manufacturing of the present invention may be facilitated since the gripping means  14  and edge  40  need not be constructed to exact dimensions to allow proper attachment of the screw  20  to the screw driver  10 . The gripping means  14  comprises a tapered surface  15  that allows the friction fit to occur between the tapered surface  15  and the edge  40  at various longitudinal locations along the gripping means  14  depending upon the size of the first aperture  24  in relation to the taper of the gripping means  14 . Furthermore, since the screw  20  may be attached to the screw driver  10  by the friction fit, the use of magnetic materials is not necessary. The screw driver  10  and screw  20  may be constructed of various biocompatible materials known to those skilled in the art.  
         [0032]    Reference will now to made to FIG. 3 to describe a second embodiment of the present invention. As previously discussed, the present embodiments of the invention illustrated herein are merely exemplary of the possible embodiments of the invention, including that illustrated in FIG. 3.  
         [0033]    It will be appreciated that the second embodiment of the invention illustrated in FIG. 3 contains many of the same structures represented in FIGS.  1 - 2  and only the new or different structures will be explained to most succinctly explain the additional advantages which come with the embodiments of the invention illustrated in FIG. 3. The second embodiment of the invention includes a tapered member  14   a  disposed on the screw  20 , and a gripping means including a first aperture  24   a  and edge  40   a  disposed on the screw driver  10 . The function of the second embodiment of the invention is similar to that of the first embodiment. An advantage of the second embodiment is that the tapered member  14   a  is protected within the socket  42 . Therefore, damage to the tapered member  14   a  is less likely so that a proper fit between the screw  20  and the screw driver  10  may be allowed.  
         [0034]    In accordance with the features and combinations described above, a useful method of driving a driven member  20  with a tool  10  includes the steps of:  
         [0035]    A) inserting a gripping means  14  into a first aperture  24  to attach the driven member  20  to the tool  10 ; and  
         [0036]    B) inserting a driving means  12  into a second aperture  22  to transfer a driving force from the tool  10  to the driven member  20 .  
         [0037]    In view of the foregoing, it will be appreciated that the present invention provides an interference fit screw driver which is simple in design and manufacture which is attached to a screw by a friction fit to facilitate positioning the screw. The present invention also provides such a screw driver which is capable of applying torque in two directions and which engages the screw over a large surface area such that wear and deformation of the screw and screw driver are reduced. The present invention also provides a screw driver which can be released from the screw even after a large torque has been applied to the screw by the screw driver. The present invention also provides a screw driver which is capable of retaining contact with screws made of nonmagnetic materials.  
         [0038]    Those having ordinary skill in the relevant art will appreciate the advantages provided by the potential features of the present invention. For example, it is a potential feature of the present invention to provide an interference fit screw driver which is simple in design and manufacture. It is another potential feature of the present invention to provide a screw driver which is capable of driving a screw by way of an interference fit. It is a further potential feature of the present invention to provide an interference fit screw driver which is attached to a screw by a friction fit to facilitate positioning the screw during a surgical procedure. It is another potential feature of the present invention to provide such a screw driver which is capable of applying torque in two directions. It is a further potential feature of the present invention, in accordance with one aspect thereof, to provide a screw driver which engages the screw over a large surface area such that wear and deformation of the screw and screw driver are reduced.  
         [0039]    It is an additional potential feature of the invention, in accordance with one aspect thereof, to provide an interference fit screw driver which can be released from the screw even after a large torque has been applied to the screw by the screw driver. It is another potential feature of the present invention to provide a screw driver which is capable of retaining contact with screws made of nonmagnetic materials.  
         [0040]    It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements. Thus, while the present invention has been shown in the drawings and described above with particularity and detail, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made without departing from the principles and concepts set forth herein.