Abstract:
A device for connecting a bone fastener to a longitudinal rod has two bores spaced a distance apart and generally parallel axes. A holding member may be associated with one bore, the holding member configured to engage a bone fastener such as a bone screw or pedicle hook. A rod coupling member may be associated with the other bore, the coupling member configured to engage a longitudinal rod. The holding member and rod coupling member both are configured to articulate within their respective bores, thus allowing the rod and rod coupling, as well as the holding member and bone fastener, to rotate about both bore axes. The holding member and rod coupling member also separately lockable to allow independent locking of the bone fastener and the rod to the connector, thus preventing or enabling relative rotation as desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuation of co-pending U.S. application Ser. No. 10/372,345, filed Feb. 24, 2003, now U.S. Pat. No. ______, which is a continuation of International Patent Application No. PCT/CH00/00449, filed Aug. 24, 2000, the entire contents of both are expressly incorporated herein by reference thereto. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to spinal fixation systems and, in particular, to a device for adjustably connecting a bone fastener to a longitudinal rod.  
       BACKGROUND OF THE INVENTION  
       [0003]     In posterior treatment of spinal deformities, pedicle screws or hooks are used to connect vertebral bodies to a longitudinal rod. Prior to implantation, the longitudinal rod is shaped in a particular form so as to correct the deformity of the vertebral column. This technique has proved successful and has been considered state of the art.  
         [0004]     Despite the development of new connecting techniques, such as the use of jaws with polyaxial bearings to connect the screws and the longitudinal rod, the intra-operative connection of the two elements remains problematic, particularly in cases of heavy spinal deformities. The problem lies in the fixed distance between the head of the pedicle screw and the longitudinal carrier. In other words, the polyaxial bearing of the screw head within the connecting jaw allows for variable screw angles, but not for variable distances between the screw head and longitudinal rod carrier. A variable distance between the screw head or the end portion of the hook and the longitudinal rod carrier is desirable, because achieving 100 percent alignment of the vertebral column relative to the longitudinal rod is not always possible.  
         [0005]     It is accordingly an object of the invention to provide an apparatus for connecting a pedicle screw or a pedicle hook to a longitudinal rod that has a polyaxial bearing for the pedicle screw or pedicle hook and a pivotable connection between the connector and the longitudinal rod that can be locked in any desired position.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention relates to a device for connecting a bone fastener to a longitudinal rod. The device comprises a connector that includes a coupling portion having two bores. Each bore has a longitudinal axis, and the axes are separated by a predetermined distance. The connector also has a holding member associated with the first bore configured to engage the bone fastener to connect the fastener to the coupling. A rod coupler is associated with the second bore and comprises a bore engaging portion, a rod receiving portion, and preferably a locking member having a rod coupler engaging portion. The connector is configured so the rod and rod coupler may be rotated about the first bore longitudinal axis. In one embodiment, the holding member may be rotated about the second bore axis. In another embodiment, the rod coupler may be rotated about the second bore longitudinal axis. In yet another embodiment, the first and second bore axes are substantially parallel.  
         [0007]     The holding member may comprise top and bottom surfaces and a wall having at least one vertical slot, the slot intersecting either the top or bottom surface. The holding member may have a bore configured to engage a bone fastener, and may also have locked and unlocked positions. A tensioner may be provided to engage the holding member bore to lock the holding member, rendering the holding member immobilized with respect to the coupler first bore, and immobilizing the bone fastener within the holding member.  
         [0008]     The holding member and tensioner are configured so that when the tensioner engages the holding member to render it locked, the longitudinal rod and rod coupler may rotate 360 degrees within the second bore. In one embodiment, the tensioner may comprise the head of a bone fastener such as a bone screw or pedicle hook. Alternatively, the holding member may comprise the head of a bone fastener.  
         [0009]     The coupling portion first bore may comprise a substantially spherical inner surface and the holding member may comprise a correspondingly substantially spherical outer surface configured to slide within the inner surface. This configuration allows the holding member to rotate within the first bore about multiple axes, which may include axes both parallel and perpendicular to the first bore axis.  
         [0010]     The holding member bore may have a conical profile and internal threads, and the tensioner may have a corresponding conical outer profile and external threads which mate with those of the bore. The holding member may be resiliently displaceable so that upon engagement with the tensioner, the holding member outer spherical surface may expand to engage the coupling first bore inner surface, configuring the holding member in the locked position. The holding member may have at least one slot configured to render the holding member resiliently displaceable.  
         [0011]     The rod receiving portion may have at least one vertical leg configured to accept the longitudinal rod, and the rod coupler may have locked and unlocked positions. The rod coupler and holding member may, independent of each other, be configured in their respective locked or unlocked positions.  
         [0012]     The rod receiving portion may comprise a channel having a longitudinal axis, a top distal from the bore engaging portion, and a bottom end opposite the top end. The channel longitudinal axis may be coaxial with that of the rod receiving portion. The top end of the channel may be open to allow a longitudinal rod to be introduced into the receiving portion by pressing the rod into the channel top end in a direction substantially parallel to the second bore axis.  
         [0013]     The rod coupler bore engaging portion may comprise a bottom end having an increased portion having a dimension greater than that of the second bore, preventing the rod coupler from passing all the way through the coupling when the coupler is inserted into the bore. This increased portion may comprise a conical flange, and the second bore may have a corresponding conical recess adjacent the bottom surface of the coupling. The conical flange and recess may have corresponding engagement surfaces, and at least one of the engagement surfaces may have serrations to prevent relative movement of the flange and coupling bore.  
         [0014]     An alternative embodiment of the connector may be provided for connecting a bone screw to a rod, the connector having a coupling with first and second bores separated by a predetermined distance, each bore having a longitudinal axis. A holding member may be associated with the first bore, and may be capable of engaging a bone screw. A rod coupler may be associated with the second bore, and may have a bore engaging portion and a rod receiving portion. The rod coupler may be rotatable about the second bore longitudinal axis.  
         [0015]     The holding member and coupling first bore may have corresponding spherical surfaces configured to allow the holding member to rotate within the first bore about multiple axes.  
         [0016]     The connector may also have a tensioner which may engage the holding member and immobilize the bone screw with respect to the holding member. The connector may be configured so that when the holding member engages the bone screw and the tensioner engages the holding member, and the rod coupler engages the longitudinal rod, the rod and rod coupler may be rotated 360 degrees within the second bore.  
         [0017]     The rod coupler may be provided with first and second vertical legs to receive a longitudinal rod. A rod locking member may also be provided to engage a top portion of each of the first and second legs to retain the rod within the rod coupler along a direction perpendicular to a longitudinal axis of the rod. The rod locking member may have threads which engage corresponding threads in the top portion of at least one of the first and second vertical legs of the rod coupler.  
         [0018]     The first and second legs may each have a top end distal from the coupling, where the top ends are open to allow a rod to be introduced into the rod receiving portion by pressing the rod between the legs in a direction substantially parallel to the second bore axis. The rod receiving portion of the rod coupler may form a channel configured to allow a rod to be introduced into the rod receiving portion by threading the rod into the channel in a direction substantially perpendicular to the second bore axis.  
         [0019]     The connector may also have a tensioner configured to engage the holding member to immobilize the bone screw with respect to the holding member. The holding member may be radially expandable so that when engaged by the tensioner, the holding member spherical surface expands to engage the inner surface of the coupling first bore, thus locking the holding member to the coupling.  
         [0020]     The rod locking member and rod coupler of this embodiment may be configured to engage the rod so that the rod may not move with respect to the rod coupler or rod locking member. The rod locking member and rod coupler may also be configured so that the rod is held between the rod locking member and a top surface of the connector. The rod coupler bore engaging portion may comprise a bottom end having an increased portion having a dimension greater than that of the second bore, wherein when the rod coupler is inserted into the second bore, the increased portion prevents the rod coupler from passing through the coupling. The increased portion may comprise a conical flange, and the second bore may have a corresponding conical recess adjacent to a bottom surface of the coupling. The conical flange and conical recess may have corresponding engaging surfaces, at least one of which may have serrations to prevent relative movement between the flange and bore.  
         [0021]     The rod coupler bore engaging portion may further comprise a top end opposite the bottom end, the bore engaging portion further may comprise a second increased portion located between the bore engaging portion top and bottom ends, the second increased portion having a dimension greater than that of the second bore, wherein when the rod coupler is inserted into the second bore, the first and second increased portions couple the rod coupler to the second bore. The rod coupler bore engaging portion may have at least one slot between the first and second increased portions, the at least one slot making at least part of the bore engaging portion resiliently displaceable to allow the second increase portion to be accepted within the second bore.  
         [0022]     In yet another embodiment of the invention, a connector for connecting a bone screw to a rod has a coupling portion with first and second bores, each bore having a longitudinal axis, the axes separated by a predetermined distance. The first bore is associated with the bone screw, and the second bore is associated with a rod coupler. The rod coupler has an articulating portion and a rod receiving portion. The articulating portion is configured to be rotatably and axially slidably receivable within the second bore. The rod receiving portion has at least one vertical leg configured to receive the rod in a direction substantially perpendicular to the second bore longitudinal axis. When the rod engages the rod coupler, the rod may be selectively rotated about the first bore longitudinal axis. The rod coupler may comprise a cap configured to engage the top end of the at least one vertical leg to retain the longitudinal rod in at least one direction perpendicular to the rod longitudinal axis.  
         [0023]     The connector of this embodiment may further comprise a holding member associated with the first bore and configured to receive the bone screw. The holding member may have a bore configured to accept the bone screw, the holding member further having an unlocked position in which it is free to rotate within the first bore, and a locked position in which it is immobilized within the first bore. A tensioner may be provided to engage the holding member and configure the holding member in the locked position whereby the holding member is immobilized within the first bore. The tensioner may comprise external threads configured to engage internal threads of the holding member bore.  
         [0024]     The connector is configured such that when the holding member engages the bone fastener, and the tensioner engages the holding member, and the rod coupler engages the rod, the rod and rod coupler may be rotated 360 degrees about both the first and second bore longitudinal axes.  
         [0025]     The first bore of the connector may have a substantially spherical inner surface and the holding member may have a substantially spherical outer surface configured to be slidably received within the first bore. The holding member may further be radially expandable such that when the tensioner engages the holding member bore, the holding member spherical outer surface expands to engage the inner spherical surface of the coupling first bore, thus locking the holding member to the coupling.  
         [0026]     The holding member bore may have a conical profile and internal threads, and the tensioner may have a conical outer profile and external threads corresponding to the holding member bore.  
         [0027]     The rod coupler may comprise a channel having a top end distal from the coupling portion and a bottom end proximal to the coupling portion, the channel top end being open to allow a rod having an axis substantially parallel to the channel axis to be introduced into the rod engaging portion by pressing the rod through the channel top end in a direction substantially parallel to the second bore axis.  
         [0028]     The connector articulating portion may comprise an increased portion having a dimension greater than that of the second bore, such that when the rod coupler is inserted into the second bore, the increased portion prevents the rod coupler from passing through the coupling. The increased portion may comprise a conical flange, and the second bore may have a corresponding conical recess adjacent to the coupling portion bottom surface. The conical flange and bore may have corresponding engagement surfaces, and at least one engagement surface comprises serrations to prevent relative rotation between the flange and bore.  
         [0029]     The holding member may have top and bottom surfaces and a wall. The wall may have at least one vertical slot intersecting at least the jaw top surface so that when the tensioner engages the holding member, the holding member expands along the at least one slot. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The features and advantages of the invention will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:  
         [0031]      FIG. 1  is an exploded view of a first embodiment of the invention;  
         [0032]      FIG. 2  is a sectional view of a second embodiment of the invention of  FIG. 1 , showing a fastener holding member formed integrally with a bone fastener, a tensioner, a holding member expansion feature, and a rod coupler;  
         [0033]      FIG. 3  is a sectional view of a third embodiment of the invention, showing the fastener holding member formed integrally with a pedicle hook; and  
         [0034]      FIG. 4  is a sectional view of a fourth embodiment of the invention, showing an alternative arrangement of the longitudinal rod coupler.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]      FIGS. 1 and 2  show a coupling  3 , a fastener holding member  10 , a tensioner  12  for releasably fixing a bone fastener  2 , a rod coupler  13 , and a rod locking element  33  configured for releasably fixing a longitudinal rod  1  to coupling  3 . Coupling  3  has a longitudinal axis  30 , a top surface  5  configured to contact longitudinal rod  1 , a bottom surface  6 , and a fastener coupling bore  7  which connects top and bottom surfaces  5 ,  6 . Fastener coupling bore  7  further has an axis  11  that is substantially perpendicular to the coupling longitudinal axis  30 . In addition, coupling  3  has a rod coupling bore  19  which connects top and bottom surfaces  5 ,  6  and has an axis  14  which is substantially parallel to fastener coupling bore axis  11 . The fastener and rod coupling bores  7 ,  19  are separated by a distance  31  measured along the coupling longitudinal axis  30 .  
         [0036]     The rod coupling bore  19  is configured to slidingly receive a cylindrical articulating portion  130  of longitudinal rod coupler  13  such that coupler  13  may rotate within the bore  19  about the rod coupling bore axis  14 . The bottom end portion  16  of rod coupler  13  comprises an increased-diameter flange portion  35 , configured to mate with a corresponding recess  27  in the rod coupling bore  19 , so that when articulating portion  130  is inserted into the rod coupling bore  19 , the coupler flange portion  35  axially engages the rod coupler recess  27 , preventing further axial movement in the insertion direction of rod coupler  13  with respect to coupling  3 .  
         [0037]     The fastener coupling bore  7  may comprise a partial spherical profile, the top and bottom portions of the sphere being intersected and cut by coupling  3  top and bottom surfaces  5 , 6 . The fastener holding member  10  may have a partial spherical outer surface profile designed to correspond to the fastener coupling bore  7  inner surface. The corresponding spherical surfaces allow the fastener holding member  10  to be received in the fastener coupling bore  7  so that the holding member  10  is fully pivotable within the bore (i.e., it may rotate about any one of, or combination of, three orthogonal axes).  
         [0038]     The fastener holding member  10  may further comprise top and bottom surfaces  20 ,  21  positioned adjacent top and bottom surfaces  5 ,  6  respectively. Holding member  10  may further comprise a conical bore  23  having a conical internal screw thread  24  and an axis  230  that when installed is concentric to fastener coupling bore axis  11 .  
         [0039]     The fastener holding member  10  further may be configured so that its angular position within the fastener coupling bore  7  is lockable. Such a configuration may allow the user to lock the position of the associated fastener  2  in the desired pivot position, immobilizing it with respect to coupling  3 . This locking feature may be effected by providing a radial expansion feature within holding member  10 , so that when the desired holding member/fastener position is obtained at least a portion of the holding member  10  spherical surface may be expanded to contact or interfere with fastener coupling bore  7 , the frictional contact between surfaces preventing further relative movement. This radial expansion feature may be provided in the form of at least one vertical slot  101  located in holding member  10  between the holding member outer spherical surface and conical bore surface  23 . The at least one slot  101  may extend along a portion of the height of holding member  10 , and may be parallel to holding member bore axis  230 . The slot or slots  101  may intersect the top end surface  20  of holding member  10 , but not the bottom end surface  21 . Alternatively, the slot or slots  101  may intersect the bottom end surface  20 , but not the top end surface  21 . In one embodiment, the fastener holding member  10  comprises a series of parallel vertical slots evenly spaced about the circumference of the holding member  10 , each slot intersecting one of the top or bottom end surfaces  20 ,  21  of holding member  10 .  
         [0040]     A tensioner  12  may be provided to radially expand holding member  10  to its aforementioned locked position. The tensioner  12  may comprise a frustoconical outer surface  120  corresponding to the holding member conical bore  23  and further may be provided with a conical external screw thread  25  corresponding to the holding member bore threads  24 . The tensioner  12  may have an adjustment end  121  and a leading end  122 , the adjustment end  121  comprising a connection  123  suitable for engagement with a standard driving tool. Because the conical shape of tensioner  12 , adjustment end  121  has a larger outer diameter than leading end  122 . Under this arrangement, holding member  10  may be expanded by threadably driving the tensioner  12  into the bore so that the larger diameter adjustment end  121  enters a relatively smaller diameter portion of the holding member conical bore  23 , forcing open the at least one vertical slot  101  in the holding member  10 . Such expansion of the at least one slot  101  may be sufficient to press the holding member  10  outer surface against the fastener coupling bore  7 , fixing holding member  10  to coupling bore  7  and coupling  3 , as previously described.  
         [0041]     In one embodiment, tensioner  12  itself comprises head portion  8  of bone fastener  2 . In an alternative embodiment, holding member  10  comprises head portion  8  of bone fastener  2 . Bone fastener  2  may be a bone screw  9  or a pedicle hook  90 . Where tensioner  12  is integral to head portion  8  of bone fastener  2 , bone fastener  2  may be releasably fixed to coupling  3  by threadably driving head portion  8  into holding member  10 , the corresponding conical surfaces  23 ,  120 , threads  24 ,  25 , and at least one slot  101  serving to expand holding member  10  and fix fastener  2  to the fastener coupling bore  7 .  
         [0042]     A longitudinal rod coupler  13  is used to receive and engage the longitudinal rod  1 . The rod coupler  13  may have an articulating portion  130  that is configured to be rotatable and axially slidable within rod coupling bore  19 , and which has an axis  131  that, when coupler  13  is engaged with coupling  3 , is substantially coaxial to the rod coupling bore axis  14 . Rod coupler  13  may also have a rod receiving portion  132  which, in one embodiment, comprises a channel  17  having a channel axis  32  oriented substantially perpendicular to the rod coupling bore axis  14 . Channel  17  may have at least one vertical leg  137  configured to retain the longitudinal rod in at least a direction substantially perpendicular to the rod longitudinal axis  4 .  
         [0043]     The longitudinal rod coupler  13  may have a top end  15 , adjacent to which channel  17  is open. The longitudinal rod coupler  13  may also have a bottom end  16  opposite the top end  15 , and adjacent to the coupling bottom surface  6 . The bottom end  16  may comprise an increased portion  35  having a diameter greater than the diameter of the rod coupling bore  19 , so that when the rod coupler  13  is inserted into the rod coupling bore  19 , the increased portion  35  prevents the rod coupler  13  from passing through the coupling bore  19  completely. Where the bottom end  16  comprises an increased portion  35 , the bottom surface  6  of the coupling  3  may comprise a corresponding recess  27  configured to engage the increased portion  35 . In one embodiment, the increased portion may comprise a conical flange  26 , and coupling  3  may comprise a correspondingly conical recess  27 . To prevent post-installation rotation between coupling  3  and rod coupler  13 , at least one of the conical flange  26  or coupling recess  27 , or both, may comprise serrations  28 .  
         [0044]     Channel  17  may be configured so that it is open at the top end  15  of the longitudinal rod coupler  13 . To capture the longitudinal rod  1  within the rod coupler channel  17 , a rod locking element  33  may be provided. In one embodiment, rod locking element  33  comprises a locking cap  133 . Cap  133  may comprise internal threads  134  configured to engage corresponding external threads  34  formed in the top end  15  of the rod coupler  13 . Upon insertion of the longitudinal rod  1  in the channel  17 , locking cap  133  may be threaded onto the coupler top end  15  and rotated until a bottom surface  135  of the cap engages the longitudinal rod  1 , thereby sandwiching longitudinal rod  1  between cap  133  and top surface  5  of coupling  3 . To release longitudinal rod  1 , locking cap  133  may be unscrewed and disengaged from the rod coupler top end  15 .  
         [0045]     In one embodiment, the portion of coupling  3  comprising fastener coupling bore  7  is recessed so that when a longitudinal rod  1  is engaged with coupling  3 , and a bone fastener  2  and tensioner  12  are fully engaged in holding member  10 , the fastener, tensioner and holding member are sufficiently recessed within coupling  3  that coupling  3  and rod  1  may be rotated without interference 360 degrees about the rod coupling bore axis  14 .  
         [0046]      FIG. 2  shows an alternative embodiment in which the fastener holding member  10  comprises the head portion  8  of bone fastener  2 , which, in this embodiment, is a bone screw  9 . In this embodiment, the bottom end  16  of longitudinal rod coupler  13  comprises a conical flange  26 , configured to be received in a complementary inner cone  27  formed in the rod coupling bore  19  of coupling  3 . Additionally, an at least partially circumferential tab segment  29  is provided on the rod coupler articulating portion adjacent the channel. This tab segment is adapted to engage the top surface  5  of coupling  3  when the rod coupler is inserted into the rod coupling bore  14 . When the tab segment  29  engages the top surface  5  of coupling  3 , it fixes rod coupler  13  axially with respect to coupling  3  and prevents rod coupler  13  from backing out of the rod coupling bore  19 . The inner diameter of the rod coupling bore  19  may be only slightly larger than the outer diameter of the articulating portion  130 . The articulation portion  130  may, therefore, comprise at least one vertical slot  36  to allow the articulating portion  130  to be compressed so that tab segment  29  can pass through the bottom surface  6  of the coupler and though the bore  19 .  
         [0047]      FIG. 3  shows an alternative embodiment of the rod coupler  13  in which the holding member  10  comprises the head portion  8  of the bone fastener  2 , which, in this embodiment, is a pedicle hook  90 . In this embodiment the head portion of the pedicle hook  90  comprises the spherically-shaped holding member  10 .  
         [0048]      FIG. 4  shows a further embodiment of the coupling  3  in which channel  17  is open at the top end  15  to permit a longitudinal rod  1  to be inserted laterally into the longitudinal rod coupler  13  (i.e. in a direction perpendicular to the rod longitudinal axis  4 ). A sleeve  360 , including a rod engaging surface  361 , and two side walls  37  extending parallel to the rod coupling bore axis  14 , is placed over the rod receiving portion  132  (in this case channel  17 ) at the top end  15  to fix the longitudinal rod  1  relative to the longitudinal rod coupler  13 . The sleeve  360  is then held in place by a nut  38  which may be screwed onto an external screw thread  34  on the channel top end  15 . Thus the longitudinal rod  1  is retained between the top surface  5  of coupling  3  and rod engaging surface  361  of the sleeve  360 . The side walls  37  provide lateral fixation. In this embodiment, conical flange  26  comprises radially aligned teeth (e.g., serrations  28 ), which secure rod coupler  13  and coupling  3  against relative rotational movement.  
         [0049]     Accordingly, it should be understood that the embodiments disclosed herein are merely illustrative of the principles of the invention. Various other modifications may be made by those skilled in the art that will embody the principles of the invention and fall within the spirit and the scope thereof.