Abstract:
In a screwdriver for bone screws, having a handle and rotationally fixedly held thereon a shaft, the free end of which has a non-circular cross section and is insertable in a positively locked manner in a non-circular receiving opening in the head of a bone screw, at least one expander element being mounted so as to be displaceable in the longitudinal direction in the shaft and so as to slide, when displaced in the longitudinal direction, along a slide surface in the area of the free end of the shaft in such a way that it projects laterally over the contour of the shaft, in order to simplify the actuation of the at least one expander element, it is proposed that the at least one expander element be pretensioned by an elastic spring element in the direction towards the free end of the shaft and be retractable against the action of the spring element in the shaft until it no longer projects laterally over the contour of the shaft.

Description:
[0001]    This application is a continuation of international application number PCT/EP2006/006423 filed on Jul. 1, 2006. 
         [0002]    The present disclosure relates to the subject matter disclosed in international application number PCT/EP2006/006423 of Jul. 1, 2006 and German applications number 10 2005 044 445.8 of Sep. 9, 2005 and number 10 2005 058 868.9 of Dec. 9, 2005, which are incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The invention relates to a screwdriver for bone screws, having a handle and rotationally fixedly held thereon a shaft, the free end of which has a non-circular cross section and is insertable in a positively locked manner in a non-circular receiving opening in the head of a bone screw, at least one expander element being mounted so as to be displaceable in the longitudinal direction in the shaft and so as to slide, when displaced in the longitudinal direction, along a slide surface in the area of the free end of the shaft in such a way that it projects laterally over the contour of the shaft. 
         [0004]    Such a screwdriver is described in DE 100 42 424 C2. With this screwdriver, the shaft can be releasably connected to the bone screw in a simple way by advancing the expander element, so that the bone screw is held at the free end of the shaft and can be taken to the intended point of application. 
         [0005]    In the known screwdriver, the expander element is advanced by means of a sleeve which is rotatably mounted on a thread of the shaft. The object of the invention is to so construct a generic screwdriver that the advancing and retracting of the expander element are simpler than with the known screwdriver. 
       SUMMARY OF THE INVENTION 
       [0006]    This object is accomplished in a screwdriver of the kind described at the outset, in accordance with the invention, in that the at least one expander element is pretensioned by an elastic spring element in the direction towards the free end of the shaft and is retractable against the action of the spring element in the shaft until it no longer projects laterally over the contour of the shaft. 
         [0007]    By using such a spring element, the at least one expander element, i.e., one, two or more expander elements, is automatically moved into the advanced clamping position in which the shaft is pressed in a forceful and positively locked manner by the at least one expander element against the inside wall of the receiving opening of the bone screw. A connection between screwdriver and bone screw is thereby effected automatically. To release this connection, the at least one expander element need only be retracted against the action of the elastic spring element. The operator can, therefore, release the connection in a simple way and also reestablish it in just as simple a way by releasing the elastic spring element, which then automatically displaces the at least one expander element into the advanced clamping position. 
         [0008]    It is favorable for a stop to be provided for limiting the advancing movement of the at least one expander element in the direction towards the free end of the shaft, so that the advancing movement of the at least one expander element is limited when the shaft does not engage the receiving opening of a bone screw. 
         [0009]    Provision is made in accordance with a preferred embodiment for the at least one expander element to be connected via a transmission member to an advancing device located on the handle, and for the spring element to be part of the advancing device. In this way, the operator can retract or release the expander element, i.e., release or secure the connection between bone screw and screwdriver, in the area of the handle. 
         [0010]    It is favorable for the transmission member to comprise at least one bar which is placed in at least one longitudinal groove which is laterally open and extends over the entire shaft as far as the handle. One, two or more bars may be provided, and, similarly, one, two or more longitudinal grooves. 
         [0011]    In accordance with a preferred embodiment, the advancing device comprises a sleeve which is connected to the at least one expander element and is displaceable on the shaft. The at least one expander element can thus be retracted into the release position by displacement of the sleeve on the shaft. 
         [0012]    To facilitate the retraction, it is favorable for the sleeve to carry gripping surfaces which project laterally. In particular, these may be formed by a radially projecting ring flange. 
         [0013]    In a modified embodiment, a swivel element which is mounted on the shaft for swivel movement at one end and is able to swivel about this bearing point against the shaft is provided for displacing the sleeve. The swivel element comprises a driver which displaces the sleeve against the action of the spring element when the swivel element is swiveled against the shaft. The user can thus displace the sleeve and, consequently, retract the expander element by actuating this swivel element. 
         [0014]    This swivel element can be configured as a simple swivel lever, however, a configuration is particularly advantageous, in which the swivel element is configured as a swivel sleeve surrounding the sleeve. Such a swivel sleeve surrounds the sleeve at all sides and can be swiveled in any direction against the shaft, so that the user can perform this swiveling independently of the angular position of the screwdriver. 
         [0015]    It is favorable for the swivel element to be held by an elastically deformable holder on the shaft, and for the bearing point to be formed by a supporting element of the swivel element on the shaft. The bearing point is thus formed solely by the abutment of the supporting element on the shaft or on a part fixedly connected thereto. A fixing of the swivel sleeve on the shaft or on a part connected thereto is, however, effected by means of the elastically deformable holder. 
         [0016]    This can be advantageously formed by a bellows concentrically surrounding the shaft. 
         [0017]    In a preferred embodiment, the supporting element is formed by a ring flange projecting inwardly on the inner side of the swivel sleeve. In accordance with a particularly preferred embodiment, this can also simultaneously form the driver, which displaces the sleeve and, consequently, the expander element on the shaft when the swivel sleeve is swiveled. 
         [0018]    If suitably configured, the resetting force of the bellows upon swiveling the swivel sleeve may be so strong that this bellows alone forms the elastic spring element which pretensions the expander element in the position of rest in the direction towards the free end of the shaft. 
         [0019]    It is particularly advantageous for the sleeve to surround the shaft in spaced relation thereto, and for a helical spring which surrounds the shaft and is supported on the shaft and on the at least one expander element to be arranged as spring element in a ring space between sleeve and shaft. A very space-saving and compact assembly is then obtained for retracting and automatically clamping the at least one expander element. 
         [0020]    In accordance with a particularly preferred embodiment, provision is made for the at least one longitudinal groove and the at least one bar to be of such dimensions that, at least in the area of the free end of the shaft, the at least one bar engages the at least one longitudinal groove without play. It is thereby ensured that in the area in which the shaft abuts on the inside wall of the receiving opening in the bone screw no free spaces for the shaft remain, into which the material of the shaft could flow when subjected to mechanical stress. The deformation of the shaft caused by such a flow is thereby definitely avoided. 
         [0021]    In a preferred embodiment, for example, the at least one longitudinal groove and the at least one bar have, at least in the area of the free end of the shaft, planar side surfaces having the same inclination and converging towards the bottom of the groove. The at least one bar then abuts with these inclined side surfaces on the identically inclined side surfaces of the at least one longitudinal groove with surface-to-surface contact, so that freedom from play is thereby achieved. The side surfaces of the at least one longitudinal groove may simultaneously serve as slide surface, for example, by the spacing of the side surfaces of the at least one longitudinal groove from one another decreasing in size towards the free end of the shaft or by the at least one longitudinal groove extending to a lesser depth into the shaft towards the free end. 
         [0022]    The at least one bar is preferably, at least in the area of the free end of the shaft, wider on its underside facing the bottom of the groove than the bottom of the groove, so that a spacing remains between the underside and the bottom of the groove when inserting the at least one bar into the at least one longitudinal groove. It is thereby ensured that the at least one bar will always abut via the converging side surfaces on the corresponding side surfaces of the at least one longitudinal groove. 
         [0023]    It may be provided that the side walls of the at least one longitudinal groove continue, at least in the area of the free end of the shaft, via a rounding-off into the bottom of the groove. The stability of the shaft is thereby increased, as sharp edges are avoided in the area of transition between the side surfaces and the bottom of the groove. 
         [0024]    The bottom of the groove may have, at least in the area of the free end of the shaft, an arcuate cross section. 
         [0025]    It also advantageous for the side walls of the at least one bar to also continue, at least in the area of the free end of the shaft, via a rounding-off into the underside. The underside of the at least one bar may also have, at least in the area of the free end of the shaft, an arcuate cross section. 
         [0026]    The shaft with its non-circular cross section is pressed by the at least one expander element against the inside wall of the receiving opening, whereby a rotational locking is enabled by the non-circular cross sections of shaft and receiving opening and the positive locking between these surfaces. In principal, such a rotational locking could be achieved by, for example, a regular hexagonal shape for the receiving opening and the shaft. However, with such a shaping, the shaft is pressed by the at least one expander element with only one surface of the hexagonal cross section against only one surface of the hexagonal receiving opening. A better torque transmission would be achieved if the abutment occurred at several surfaces. To achieve this, provision is made, in accordance with a preferred embodiment of the invention, for the non-circular cross section of the receiving opening and the non-circular cross section of the free end of the shaft to be configured such that the shaft is pressed by the at least one expander element in two areas of the receiving opening that are separate from one another against an inside wall of the receiving opening. A contact between the shaft and the receiving opening is then obtained at three locations in the circumferential area, namely, on the one hand, in the area of the at least one expander element, and, on the other hand, in the area of the two areas of the receiving opening that are separate from one another, with the result that an enlarged transmission surface area is made available for the torque. 
         [0027]    In particular, provision may be made for the receiving opening to have the shape of a regular symmetrical hexagon or octagon, and for the shaft to be of substantially complementary shape, the side surface of the shaft that lies opposite the at least one expander element being set back radially inwardly to a slight extent. The cross section of the shaft is, therefore, not exactly symmetrical, but deviates slightly from the symmetry. It is thereby ensured that the two side surfaces adjoining the side surface of the shaft that lies opposite the at least one expander element will, in any case, abut on corresponding inner surfaces of the-receiving opening. Consequently, the torque transmission occurs not only at the surface that lies opposite the at least one expander element, but at the two surfaces adjacent to this surface and at the at least one expander element. 
         [0028]    The advantageous embodiments of the screwdriver described herein, which relate, in particular, to the mounting of the bar without play in the at least one longitudinal groove and/or to the abutment of the shaft on the inside wall of the receiving opening in areas that are separate from one another, are particularly advantageous in combination with the spring-loaded actuation of the at least one expander element. However, these features may also be employed in screwdrivers in which the at least one expander element is not displaced in the described manner by an elastic spring element into the clamping position, i.e., for example, in a screwdriver such as that described in DE 100 42 424 C2. The mounting of the bar without play in the longitudinal groove and the abutment of the shaft on separate areas of the receiving opening are particularly favorable in combination, but each of these features may also be realized on its own on a screwdriver. Such embodiments are also intended to be covered by the scope of the present invention. 
         [0029]    The following description of preferred embodiments of the invention serves in conjunction with the drawings for further explanation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0030]      FIG. 1  shows a perspective view of a screwdriver with a spring-loaded expander element and a bone screw prior to insertion of the shaft of the screwdriver into a receiving opening of the bone screw; 
           [0031]      FIG. 2  shows a longitudinal sectional view of a portion of the screwdriver of  FIG. 1  after insertion into the head of a bone screw; 
           [0032]      FIG. 3  shows a longitudinal sectional view taken along line  3 - 3  in  FIG. 2  with a shaft of asymmetrical, hexagonal cross section; 
           [0033]      FIG. 4  shows a view similar to  FIG. 3  with a longitudinal groove for the expander element having inclined, planar side walls; 
           [0034]      FIG. 5  shows a view similar to  FIG. 4  with the longitudinal groove having a rounded-off contour; 
           [0035]      FIG. 6  shows a perspective sectional view of a further embodiment of a screwdriver in the area of the advancing device with an actuating element in the form of a swivel sleeve with a relaxed spring element; and 
           [0036]      FIG. 7  shows a sectional view of the advancing device of  FIG. 6  taken along line  7 - 7  with a tensioned spring element. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]    The screwdriver  1  shown in the drawings comprises a handle  2  and rotationally fixedly held thereon a shaft  3 , which is of hexagonal cross section ( FIG. 3 ) at its free end  4 . 
         [0038]    This free end  4  can be inserted, in a manner known per se, into a receiving opening  5  of substantially complementary construction of a bone screw  6 , so that a rotationally fixed, positively locked connection is made in this area between shaft  3  and bone screw  6 . Arranged in the shaft  3  and extending over the major part of its length is a longitudinal groove  7  which is open towards the side surface. The width of the longitudinal groove  7  is less than the spacing between two adjacent edges  8  of the hexagonal cross section at the free end  4  of the shaft  3 , the longitudinal groove  7  being located exactly in the middle between two adjacent edges  8 . The depth of the longitudinal groove  7  is somewhat less than half of the diameter of the shaft  3 . In the area of the free end  4 , the bottom  9  of the longitudinal groove  7  continues into a slide surface  10  having the shape of an arc of a circle in longitudinal section, which tangentially adjoins the planar bottom  9  and rises up to the outer side of the shaft  3 , so that the depth of the longitudinal groove  7  drops to zero ( FIG. 2 ) at the free end  4  of the shaft  3 . 
         [0039]    On the side of the shaft  3  that is adjacent to the handle  2 , the longitudinal groove  7  extends into the interior of the handle  2  ( FIG. 2 ). 
         [0040]    Mounted inside the longitudinal groove  7  is a bar  11 , which is adapted to the contour of the longitudinal groove  7  and is guided in the longitudinal groove  7  so as to be freely displaceable in the longitudinal direction thereof. At its end  12  adjacent to the free end  4  of the shaft  3 , the bar  11  is rounded-off in arcuate configuration, and this arcuate contour corresponds substantially to the arcuate contour of the slide surface  10 . Aside from that, the bar  11  fills out the longitudinal groove substantially and extends in the longitudinal direction as far as almost the handle  2 . 
         [0041]    At the handle end of the longitudinal groove  7 , the shaft  3  is surrounded by a grip sleeve  13 , which is freely displaceable in the longitudinal direction on the shaft  3 . At its end facing the handle  2 , the grip sleeve has a radially projecting ring flange  14 , which forms a ring-shaped gripping surface. 
         [0042]    The grip sleeve  13  surrounds the shaft  3  in spaced relation thereto, thereby forming between the grip sleeve  13  and the shaft  3  a ring space  15 , in which a helical spring  16  surrounding the shaft  3  is arranged. The helical spring  16  is supported, on the one hand, on a ring flange  17 , fixedly connected to the shaft  3 , and, on the other hand, via a ring  18 , surrounding the shaft  3 , to a ring-shaped widening  19  of the bar  11 , similarly surrounding the shaft  3 . At its handle end, the bar  11  is fixedly connected to this widening  19 , so that the bar  11  is displaced by the helical spring  16  in the direction towards the free end  4  of the shaft  3 . 
         [0043]    The grip sleeve  13  engages around the widening  19  at the side thereof that faces away from the handle  2 , so that upon displacing the grip sleeve  13  in the direction towards the handle  2  (i. e. in the direction of arrow C in  FIG. 2 ), the bar  11  is displaced in the longitudinal groove  7  in the direction towards the handle  2 , and the helical spring  16  is thereby elastically compressed. When the grip sleeve  13  is released again, the helical spring  16  relaxes and displaces the bar  11  in the direction towards the free end  4  of the shaft again. The dimensions are selected such that when the helical spring  16  is relaxed, the bar  11  is raised laterally out of the longitudinal groove  7  at the free end  4  and projects laterally over the contour of the shaft, whereas the bar  11  enters the longitudinal groove  7  fully at the free end  4  of the shaft  13  when the grip sleeve  13  is retracted in the direction towards the handle  2  and the helical spring  16  is thereby tensioned. 
         [0044]    To insert the free end  4  of the shaft  3  into the receiving opening  5  of a bone screw  6 , it is sufficient for the operator to displace the grip sleeve  13  in the direction of arrow C and thereby tension the helical spring  16 . It is then readily possible to insert the free end of the shaft  3  into the receiving opening  5  as the bar  11  is fully accommodated in the longitudinal groove  7 . Once the shaft  3  is inserted in the receiving opening  5 , the operator can release the grip sleeve  13 , as a result of which, under the action of the relaxing helical spring  16 , the bar  11  is advanced in the direction towards the free end  4 , so that the end of the bar  11  is pressed by the slide surface  10  radially outwardly against the inside wall of the receiving opening  5 , and the free end of the shaft  3  is thereby clamped in the receiving opening  5 . 
         [0045]    In this way, a clamped connection between screwdriver  1  and bone screw  6 , with the shaft  3  abutting substantially with positive locking on the inside wall of the receiving opening  5 , is obtained. 
         [0046]    If the hexagonal cross section of the shaft  3  and the hexagonal cross section of the receiving opening  5  were exactly identical, an abutment with exact positive locking over the entire circumference between shaft and receiving opening would be obtained. However, this is not possible in practice, as manufacturing tolerances have to be taken into account. It is, therefore, necessary for the dimensions of the shaft  3  to be slightly less than the dimensions of the receiving opening. The necessary consequence of this is, however, that under the action of the outwardly tensioned end of the bar  11 , the opposite surface of the shaft  3  is pressed against only one side surface of the receiving opening  5 , and, an abutment is, therefore, only obtained on opposite sides of the receiving opening. 
         [0047]    In order to also improve the abutment between shaft  3  and receiving opening  5  when slight play must be provided for compensation of manufacturing tolerances, it is advantageous to allow the cross section of the shaft  3  to deviate slightly from the shape of a regular hexagon. This is effected by the surface  20  of the shaft  3  that lies opposite the longitudinal groove  7  being slightly set back radially inwardly in relation to the surface of a regular hexagon. As a result, there is a slight spacing between this surface  20  and the directly opposite surface  21  of the receiving opening  5 , and this results in the inclined surfaces  22  and  23  adjoining the surface  20  of the shaft  3  on either side thereof abutting with surface-to-surface contact on the identically inclined surfaces  24  and  25  of the receiving opening  5  that directly adjoin the surface  21  of the receiving opening  5 . An abutment over a larger surface area between shaft  3  and receiving opening  5  is thereby obtained, the abutment occurring in three separate areas, namely in the area of the outwardly tensioned bar  11  and in the area of the lateral surfaces  22  and  23 . 
         [0048]    Accordingly, in the embodiment shown in  FIG. 3 , the regular hexagonal cross section of the shaft  3  is modified such that the height A of the shaft on the side that lies opposite the longitudinal groove  7  is slightly less than the height B of the shaft on the side of the longitudinal groove  7 . This difference may be very slight, for example, in the order of magnitude of a few tenths of a millimeter. For the purpose of clarification, this difference is shown exaggeratedly in  FIG. 3 . 
         [0049]    A similar configuration is also possible when, for example, a regular octagon is chosen instead of a cross section of a regular hexagon. 
         [0050]    In the embodiment of  FIG. 3 , the longitudinal groove  7  is rectangular in cross section, and the bar  11  also has a rectangular cross section. In order to also compensate manufacturing tolerances here, it is necessary for the bar  11  to be guided with play in the longitudinal groove  7 . This play is shown exaggeratedly in  FIG. 3 . However, the consequence of this play is that during the transmission of large torques, the material of the shaft  3  can undergo a deformation into the space between the shaft  3  and the bar  11 , i. e., the stability of the shaft  3  can suffer. 
         [0051]    With a view to avoiding this, a modified embodiment is shown in  FIG. 4 . In contrast to the configuration according to  FIG. 3 , the cross section of the longitudinal groove  7  and the bar  11  is altered in the embodiment according to  FIG. 4 . In this embodiment, the longitudinal groove  7  has a planar bottom  9  and two planar side surfaces  26  and  27  converging towards the bottom  9 . The angle can be, for example,  300  in relation to the vertical. The bar  11  is also of planar configuration on its underside  28 , and this planar underside  28  is adjoined on either side by planar side surfaces  29 ,  30  converging towards the underside  28 . The width of the underside  28  is slightly larger than the width of the bottom  9  of the longitudinal groove  7 , so that a small spacing remains between the underside  28  and the bottom  9 . The side surfaces  29  and  30  abut with surface-to-surface contact on the side surfaces  26  and  27 , so that the bar  11  is mounted without play in the longitudinal groove  7 . A deformation of the shaft  3  is thereby prevented. 
         [0052]    Provision may be made in this embodiment for the side surfaces  26  and  27  to form the slide surfaces that drive the bar radially outwardly when it is advanced. It is, therefore, not absolutely necessary for the bottom  9  to be shaped outwards, as shown in the embodiment of  FIG. 2 . If the spacing between the two side surfaces  26  and  27  becomes smaller towards the free end  4  of the shaft  3 , the bar  11  is automatically pushed outwards when it is advanced in the longitudinal groove. The same applies when overall the longitudinal groove  7  has a lesser depth towards the free end  4 . 
         [0053]    The embodiment of  FIG. 5  corresponds substantially to that of  FIG. 4  and differs from it only in that the side surfaces  26  and  27  do not continue along a sharp edge into the planar bottom  9  of the longitudinal groove  7  but along a rounding-off  31 . In addition, the bottom  9  is not of planar configuration, but is arcuate in cross section. Similarly, provision is made in the bar  11  for the side surfaces  29  and  30  to continue via a rounding-off  32  into the underside  28 , and the underside  28  is likewise not of planar, but of arcuate cross section. Sharp edges are avoided by this configuration, and, as a result, the stability of the shaft  3  is further optimized in this area. In this case, too, a mounting of the bar  11  without play in the longitudinal groove  7  is ensured. 
         [0054]    Whereas in the embodiment of  FIGS. 1 and 2 , the bar  11  can be displaced by grip sleeve  13  against the action of the helical spring  16 , in the modified embodiment of  FIGS. 6 and 7  a sleeve  33  corresponding to the grip sleeve  13  is provided, but this cannot be directly displaced by the user via gripping surfaces against the action of the helical spring  16 , but by a swivel sleeve  34  that surrounds the sleeve  33 . The swivel sleeve  34  surrounds the sleeve  33  in spaced relation thereto, and at its distal end, it is connected via an elastically deformable bellows  35 , concentrically surrounding the shaft  3 , to a supporting ring  36 , which concentrically surrounds the shaft  3  and is fixedly connected thereto. 
         [0055]    The swivel sleeve  34  carries at the proximal end of the bellows  35  and hence at its distal end a radially inwardly projecting ring flange  37  whose inner edge  38  is supported on a ring shoulder  39  of the supporting ring  36 . This supporting of the ring flange  37  on the ring shoulder  39  forms a pivot bearing point for the swivel sleeve  34 . When the swivel sleeve  34  is pressed at a point on its circumference against the shaft  3 , this results in a swiveling of the swivel sleeve  34  about such a bearing point, which then lies on the opposite side of the user&#39;s point of engagement, as shown in  FIG. 7 . A pressure on the outer rim of the swivel sleeve  34  in the direction of arrow A in  FIG. 7  thus causes a swiveling about a swivel point B ( FIG. 7 ) which is fixed on the shaft. The ring flange  37  is thereby moved on a circular path on the side opposite the swivel point B and is lifted off the ring shoulder  39 . The circular path is indicated by the radius C in  FIG. 7 . On the side opposite the swivel point B, this also results in an axial displacement of the ring flange  37 , and the ring flange  37  transmits this axial displacement to the sleeve  33  abutting directly thereon. The sleeve  33  is thereby displaced in proximal direction against the action of the helical spring  16 , i. e., the ring flange  37  also acts as driver to displace the sleeve  33  and hence to displace the bar  11 . 
         [0056]    The user can press the swivel sleeve  34  at any point along its circumference against the shaft. A swivel point B is then always formed on the opposite side, and it displaces the ring flange  37  axially and, as a result, the sleeve  33  on the same side as that on which the swivel sleeve  34  is pressed. 
         [0057]    In the embodiment shown in  FIGS. 6 and 7 , the sleeve  33  is pushed back into the initial position again by the helical screw  16 , and the swivel sleeve  34  is thereby also swiveled into the initial position again in which it is arranged concentrically with the sleeve  33 . 
         [0058]    This return movement can be reinforced by the elastic resetting forces of the bellows  35 . If the bellows is of suitable configuration, the elastic resetting force of the bellows  35  can also be used on its own to displace the sleeve  33  into the distal end position, but it is then necessary to provide between the sleeve  33  and the ring flange  37  an additional connection, which takes the sleeve  33  along with it when the ring flange is displaced in distal direction. Such a connection is not provided in the embodiment of  FIGS. 6 and 7 , where the ring flange  37  merely abuts on the sleeve  33  and can displace it upon axial displacement in proximal direction.