Abstract:
A double-jointed bone bolt for use in an apparatus for maintaining vertebra in a desired relationship. The apparatus has a rod that extends substantially along the spine and one or more bone bolts. At least one of the bone bolts is double jointed. The double-jointed bolt has a mounting portion with a hook or coarse threads to engage a vertebra, and the mounting portion is attached to a pivot post in a manner that allows the pivot post to be rotatable about a common axis in respect to the mounting portion. The pivot post of the bone bolt is then pivotally attached to a connector portion of the bone bolt that has machine threads upon which a surgeon may attach a clamp. The clamp has a second bolt and an arm. The second bolt holds the rod and the arm to the clamp. The second bolt has a first channel to attach to the rod, while the arm has a second channel to attach the double-jointed bone bolt.

Description:
[0001]    This application is a continuation of and claims priority to U.S. patent application No. 09/526,435, filed Mar. 15, 2000, which is incorporated herein by reference. 
     
    
     
       BACKGROUND  
         [0002]    Spinal implant systems provide a rod for supporting the spine and properly positioning components of the spine for various treatment purposes. Bolts or screws are typically secured into the vertebrae for connection to a supporting rod. These bolts must frequently be positioned at various angles due to the anatomical structure of the patient, the physiological problem to be treated, and the preference of the physician. It is difficult to provide secure connection between the spinal support rod and these connecting bolts at various angles, and where there are differing distances between the rod and bolts and different heights relative to these components.  
         SUMMARY OF THE INVENTION  
         [0003]    In one aspect, this invention is a bolt for connecting a vertebra to a longitudinal member. The bolt has a mounting portion with a hook or coarse threads to engage a vertebra. The mounting portion is attached to a pivot post in a manner that allows the pivot post to be rotatable about a common axis in respect to the mounting portion of the bolt. The pivot post is then pivotally attached to a connector portion that has machine threads upon which a surgeon may attach other structures.  
           [0004]    In another aspect, this invention is an apparatus for maintaining vertebra in a desired relationship. The apparatus has a rod that extends substantially along the spine and one or more bone bolts. At least one of the bone bolt has a mounting portion with a hook or coarse threads to engage a vertebra, and the mounting portion is attached to a pivot post in a manner that allows the pivot post to be rotatable about a common axis in respect to the mounting portion of the bolt. The pivot post of the bone bolt is then pivotally attached to a connector portion of the bone bolt that has machine threads upon which a surgeon attaches a clamp. The clamp, also a part of this embodiment of the invention, has a second bolt and an arm. The second bolt holds the rod and the arm to the clamp. The second bolt has a first channel to hold the rod while the arm has a second channel to hold the bone bolt.  
           [0005]    It is an object of this invention to provide a connection assembly that will allow connection between a spinal support rod to a vertebra at a variety of angles relative to the vertical, taken when the patient is lying down.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a perspective view of one embodiment of the present invention.  
         [0007]    FIGS.  2 - 4  are respectively top, side, and cross-sectional views of a clamp that may be used in one embodiment of the present invention.  
         [0008]    FIGS.  5 - 8  are respectively, top, side, end, and cross-sectional views of a clamp bolt that may be used in one embodiment of the present invention.  
         [0009]    FIGS.  9 - 10  are respectively end and side views of a stop that may be used in one embodiment of the present invention.  
         [0010]    FIGS.  11 - 14  are respectively end cross-sectional, top, side, and side cross-sectional views of an arm that may be used in one embodiment of the present invention.  
         [0011]    FIGS.  15 - 17  are respectively end, side, and top views of a washer that may be used in one embodiment of the present invention.  
         [0012]    [0012]FIGS. 18, 19 are top views of alternative embodiments for an arm in the practice of the present invention.  
         [0013]    [0013]FIG. 20 is a side view of a nut that may be used in one embodiment of the present invention.  
         [0014]    [0014]FIG. 21 is an exploded view of a bone bolt in one embodiment of the present invention.  
         [0015]    [0015]FIG. 22 is a cross-sectional view of a mounting portion of a bone bolt according to one embodiment of the present invention.  
         [0016]    [0016]FIGS. 23 and 24 are respectively side and top views of a connecting portion of a bone bolt according to one embodiment of the present invention.  
         [0017]    [0017]FIGS. 25 and 26 are respectively front and side views of a pivot post in a bone bolt according to one embodiment of the present invention.  
         [0018]    [0018]FIG. 27 is a top view of a snap ring for a bone bolt according to one embodiment of the present invention.  
         [0019]    [0019]FIG. 28 is a side view of a bone bolt according to one embodiment of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Specific language is used in the following description to publicly disclose the invention and to convey its principles to others. No limits on the breadth of the patent rights based simply on using specific language are intended. Also included are any alterations and modifications to the description that should normally occur to one of average skill in this technology.  
         [0021]    A bone bolt  1  according to one embodiment of the invention is shown as part of a larger spinal implant system in FIG. 1. Bone bolt  1  is shown attached to a clamp  2  with the longitudinal axis L 1 , and clamp  2  is shown attached to a spinal implant rod  3  with a longitudinal axis L 2 . Clamp  2  includes a clamp bolt  4 , an arm  5 , a rod interface washer  6 , a set screw  7 , and a nut  12 . Clamp bolt  4  has an aperture  8  for receiving rod  3 , and while the aperture is shown closed around rod  3 , it will nevertheless be understood that an open-sided aperture may also be used to permit top-loading of rod  3  into clamp  2 . Set screw  7  is inserted through a threaded opening  9  and into aperture  8  in clamp bolt  4  so as to allow set screw  7  to push against rod  3 . Arm  5  has a bore  10  for receiving bone bolt  1 . Arm  5  is simultaneously tightened to clamp  2  when set screw  7  is tightened against rod  3 . As set screw  7  pushes against rod  3 , rod  3  pushes against rod interface washer  6 , which pinches arm  5  between rod interface washer  6  and stop  11 . In this manner, set screw  7  acts as a compression member to tighten clamp  2  and achieve substantial fixation of arm  5  to rod  3 .  
         [0022]    Details of clamp bolt  4  are shown in FIGS.  2 - 8 . Clamp bolt  4  can be subdivided into bolt head portion  13 , bolt shaft portion  14 , washer seat portion  15  and washer stop portion  16 . Threaded openings  9   a  &amp;  9   b , and aperture  8  reside in bolt head portion  13 . Threaded openings  9   a  &amp;  9   b  open into aperture  8  at an oblique angle A 4  with respect to longitudinal axis L 1  to allow set screw  7  (FIG. 1) to force spinal rod  3  toward the distal end  17  of aperture  8 . Clamp bolt  4  is substantially symmetrical about longitudinal axis L 1  such that threaded openings  9   a  and  9   b  are substantially mirror images. Bolt shaft portion  14  is generally cylindrical in shape and is sized to accept the eye  18  (FIGS. 13 &amp; 14) of arm  5 . Arm  5  is then held on shaft portion  14  by attaching stop  11  (shown in isolation in FIGS. 9 &amp; 10) to the end  19  of shaft portion  14 , either by welding or some other suitable means. As an alternative, shaft portion  14  may include threads and stop  11  may be correspondingly threaded onto shaft portion  14  to hold arm  5  in position. In this alternative design, stop  11  may be the compressive member utilized to tighten clamp  2  onto rod  3  instead a set screw threaded into bolt head portion  13 .  
         [0023]    Clamp bolt  4  also preferably includes washer seat portion  15  and washer stop portion  16 . A washer seat portion  15  that is substantially rectangular in cross-section is currently preferred, but washer seat portion  15  can be of any suitable shape that may interlock with a complementary shape in rod interface washer  6  (FIGS. 1, 15,  16  &amp;  17 ) to prevent rod interface washer  6  from rotating in relation to clamp bolt  4 . As shown, a washer stop  16  is generally provided in clamp bolt  2  by placing a raised edge in bolt head portion  13 . Washer stop  16  prevents rod interface washer  6  from being inadvertently removed from clamp  2 .  
         [0024]    Details of arm  5  are shown in FIGS.  11 - 14 . Arm  5  includes a flange portion  20 , and a collar portion  21 . Flange portion  20  has an eye  18 , and as previously presented, clamp bolt  4  attaches to arm  5  by placing the shaft portion  14  of clamp bolt  4  through eye  18  and then attaching stop  11  on end  19  of shaft portion  14 . The medial face  22  of flange portion  20  also includes a connection surface  23 . Connection surface  23  preferably includes structure for facilitating the engagement of arm  5  against rotational movement relative to rod interface washer  6 . This engagement structure is preferably a plurality of variable angle ridges that radiate from the rotational center of eye  18 . In other words, the structure is a set of interlocking teeth that can generally be characterized as male protrusions and complementary female cavities that upon interlock, prevent rod interface washer  6  from rotating in respect to arm  5 .  
         [0025]    Referring to FIGS. 12, 18 and  19 ; collar portion  21  of arm  5  has a bore  10 . Bore  10  may assume various orientations in relation to the centerline  24  of arm  5 . FIG. 12 depicts bore  10  offset from centerline  24  toward the stop (not shown) of clamp bolt  4 . Optionally, bore  10  can be offset from centerline  24  toward the clamp aperture  8  (not shown) of clamp bolt  4 , as shown in FIG. 19, or bore  10  can be placed in the same plane as centerline  24 , as shown in FIG. 18. It being understood that the alternative arm designs may permit even a smaller total width of clamp  2  by bringing bone bolt  1  closer to the rod  3 .  
         [0026]    Referring to FIG. 20, there is shown nut  12 , which is preferably used to threadably engage bone bolt  1  (not shown) to arm  5 , and prevent bone bolt  1  from moving longitudinally along longitudinal axis L 3  with respect to arm  5 . Nut  12  has as set of internal threads  32  to mate with the machine threads  60  on bone bolt  1  and a set of locking tabs  33  on the proximal face  34  of nut  12  to firmly hold nut  12  upon bone bolt  1  once nut  12  is threaded into place. The distal face  35  of nut  12  also includes an annular collar  36 . Annular collar  36  is integrally connected to nut  12 , and has a channel  70  that opens into internal threads  32 . The end  39  of collar  36  terminates in an annular rim  37  that laterally projects beyond the diameter of annular collar  36 , and forms an annular groove  71  between annular rim  37  and distal face  35  of nut  12 .  
         [0027]    Referring back to FIGS.  11 - 14 , arm  5  is preferably adapted to rotatably secure nut  12  by annular rim  37  and annular collar  36 . The proximal face  72  of collar portion  21  of arm  5  includes a semicircular cavity  38  around the entrance of bore  10  that is sized to accept annular collar  36  and annular rim  37 . By fitting collar  36  and rim  37  into cavity  38 , annular rim  37  rides against semi-circular lip  40 , on the roof of cavity  38 ; opening  70  and internal threads  32  of nut  12  are axially aligned with bore  10  of arm  5 ; and nut  12  is rotatably secured to arm  5 . In other words, nut  12  is free to rotate about axis  41  or axis L 3 , but nut  12  is substantially fixed against movement along longitudinal axis L 3  (Figs. 11 &amp; 13) relative to arm  5  because annular rim  37  rides against semi-circular lip  40  in one direction and proximal face  72  in the other. In one preferred embodiment, nut  12  is temporarily held in semicircular cavity  38  by slightly bending corners  73  &amp;  74  of lip  40  against annular rim  37 . Bending these corners will temporarily hold nut  12  in arm  5  until the surgeon threads nut  12  onto bone bolt  1 , and will not significantly hinder the surgeon&#39;s rotation of nut  12  around bone bolt  1 .  
         [0028]    Details of rod interface washer  6  are shown in FIGS. 15, 16 &amp;  17 . Rod interface washer  6  can be any of several suitable shapes, including the circle that is depicted. The medial face  25  of the rod interface washer  6  has an engagement surface, which preferably includes an engagement groove  26  that accepts a cylindrical spinal implant rod (such as rod  3  in FIG. 1). Engagement groove  26  preferably runs across the entire face of medial face  25 . Rod interface washer  6  also has a central opening  27  that corresponds to the cross-sectional shape of previously presented washer seat portion  15  in clamp bolt  4 . In the currently preferred embodiment, both washer seat portion  15  and opening  27  are substantially square. Although, this shape could vary from many possible shapes that would similarly prevent rod interface washer  6  from rotating in respect to clamp bolt  4 . To assist in this regard, it is also preferable that rod interface washer have a guide groove  28  to accept bolt head portion  13  of clamp bolt  4  to further lock clamp bolt  4  and rod interface washer  6  together. It should be noted that guide groove  28  and engagement groove  26  are preferably placed in such a manner that orients aperture  8  substantially parallel to groove  26 . This placement helps insure that spinal rod  3  will be held in the connector assembly in a direction that is substantially perpendicular to clamp bolt  4 , and in turn, also substantially perpendicular to set screw  7 .  
         [0029]    Rod interface washer  4  also includes connection surface  29  on the lateral face  30  of rod interface washer  6 . Connection surface  29  preferably includes structure for facilitating the engagement of rod interface washer  6  against rotational movement relative to arm  5 . This engagement structure is preferably a plurality of variable angle ridges  31  that radiate from the rotational center of rod engagement washer  6 , similar to those previously described on the medial face  22  on flange  20  of arm  5 . Variable angle ridges  31  are sized to mate with the similar variable angle ridges  23  on arm  5 . Referring to FIGS. 13 and 15, both sets of ridges consist of alternating male protrusions and female cavities. Hence, once placed together, these interlocking ridges prevent rod engagement washer  6  from rotating in respect to arm  5 . And although radiating ridges are shown to facilitate the fixation of these two parts, it is also contemplated that other structures could serve this function. For example, it is also contemplated that one could use any number of interlocking male and female structures such as rounded bumps or knurling and mating cavities. The locking engagement of connection surface  23  with connection surface  29  may occur at any of a plurality of angles. More specifically, the angle between longitudinal axis L 3  of bone bolt  1  and the longitudinal axis L 2  of rod  3  may be adjusted to meet the requirements of the patient&#39;s anatomy.  
         [0030]    Details of bone bolt  1  can be seen in FIGS.  21 - 28 . Bone bolt  1  includes a mounting portion  42 , a pivot post  43 , and a connector portion  44 . The distal end of mounting portion  21  has a set of coarse threads  45 . Coarse threads  45  have a thread convolution for engaging cancellous bone and terminate in a tapered tip  46 . Tapered tip  46  helps align bone bolt  1  into a predrilled opening in a vertebra and also helps coarse threads  45  to gradually engage and advance into the vertebra upon rotation of mounting portion  21 . In this regard, although coarse threads are shown as a means for engaging a vertebra, it is also contemplated that a hook, mounted on the end of mounting portion  42 , could also be used as an alternative means to engage a vertebra. The proximal end  47  of mounting portion  42  terminates in hex-headed drive portion  49 . The inside of hex-headed drive portion  49  includes an annular receptacle  48 , and the inner wall of receptacle  48  has an annular groove  50 . (FIG. 22) Annular receptacle  48  is sized to accept hub  51  of pivot post  43  (FIGS. 25 &amp; 26), and annular groove  50  is sized to accept snap ring  52 . (FIG. 27) Pivot post  43  is shown in isolation in FIGS. 25 &amp; 26. Pivot post  43  has a hub  51  and an ear  53  with a channel  55 . Hub  51  preferably has a circular cross-section and is circumscribed by an annular groove  54 . Hub  51  is sized to freely rotate about longitudinal axis L 4  inside receptacle  48  of the mounting portion  42  of bone bolt  1 . During assembly in one preferred embodiment, snap ring  52  (FIG. 27) is placed partly inside annular groove  54  before hub  51  is inserted into receptacle  48 . Then, upon insertion into receptacle  48 , snap ring  52  partially expands into annular groove  50 , and thereby rotatably connects pivot post  53  to the proximal end  47  of mounting portion  42 .  
         [0031]    A top and side view of the connector portion  44  of bone bolt  1  is shown in FIGS. 23 &amp; 24. Most of the longitudinal length of connector portion  44  is circumscribed with machine threads  60 . The lower end  57  of connector portion  44  terminates with a pair of ears  56  that are diametrically opposite of each other at the radial perimeter of end  57 . Each of the ears  56  includes an aperture or channel  58  for insertion of pin  59  (FIG. 21). During assembly, pin  59  is inserted through aperture  58  in one ear, then through channel  55  in pivot post  43 , and then through aperture  58  in the other ear. Thusly joined to mounting portion  42  and pivot post  43 , the connector portion  44  of bolt  1  may be pivoted around pin  59  as depicted by arc A 5 , and may also be rotated around longitudinal axis  1 A of the mounting portion  42 , as depicted by arc A 6 . (FIG. 28)  
         [0032]    Referring back to FIG. 1, a typical construct in the use of this invention typically has two or more largely identical rods,  1  and  61 , and at least two or more bone bolts  1 ,  62 - 64  attached to each rod by clamps  2 ,  65 - 67 . And optionally, the rods may be joined by one or more cross-linking members  68  &amp;  69 . An example of a suitable cross-linking member is described in U.S. Pat. No. 5,947,966 to Drewry et al, the disclosure of which is specifically incorporated into this specification by reference. And although each of the clamps and bone bolts shown in this figure are identical, it is further contemplated that other clamps and bone bolts could be incorporated in a common construct in the use of this invention. For example, one could also use the clamps and bone bolts described in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson, the disclosures of which are specifically incorporated into this specification by reference with one or more of the bone bolts described herein.  
         [0033]    Clamp  2  is depicted in FIGS.  2 - 4 , less set screw  7 , which has been removed for clarity along with rod  3  and bone bolt  1 . The clamp is used by placing spinal rod  3  through aperture  8 . The connector portion  44  of bone bolt  1  is then threaded through bore  10  and nut  12  of clamp  2  as the surgeon desires. Arm  5  and the variable angle ridges  31  on the rod interface washer  6  are then interlocked with the variable angle ridges  23  on arm  5 , and the assembly is tightened by threading set screw  7  into either of the threaded openings  9 , (or by optionally turning stop  11  around connector portion  44  as described in an alternative embodiment). Upon entering aperture  8 , set screw  7  contacts the spinal rod and forces the spinal rod toward interface washer  6 . The spinal rod then contacts rod interface washer  6 , and engages groove  26 . As one continues turning set screw  7 , rod interface washer  6  presses flange portion  20  of arm  5  against stop  11 . The variable angle surfaces, item  23  on arm  5  and item  31  on rod interface washer  6 , firmly engage each other and prevent rod interface washer  6  from rotating in relation to arm  5 , which further locks arm  5  in relation to clamp bolt  4  because rod interface washer  6  cannot rotate in relation to clamp bolt  4 . Adjustments can be made by loosening set screw  5  then re-tightening the set screw when the preferred position has been located. The surgeon can adjust the longitudinal position of bone bolt  1  by rotating nut  12  as the surgeon desires. The set screws  7  shown in FIG. 1 are of a type that shear at 75 when the appropriate amount of torque has been placed on set screw  7 . Such set screws are now well-known in this art.  
         [0034]    Referring to FIGS. 1 &amp; 2, one may note some additional features of this invention by noting the locations of various longitudinal axes. L 1  is the longitudinal axis of a portion of clamp  2 . L 2  is the longitudinal axis of rod  3 , and L 3  is the longitudinal axis of both connector portion  44  of bolt  1  and bore  10  in arm  5 . In this regard, one may not that L 3  is offset from L 1  a distance D 1 . In other words, clamp  2  will contact rod  3  at  76 , and L 3  or bore  10  is spaced from  76  a distance D 1  along rod  3 . In many circumstances involving patient anatomy, distance D 1  may help the surgeon place clamp  2  and/or bone bolt  1  in a manner that avoids interfering with the patient&#39;s anatomy, such as the facet joints of the spine.  
         [0035]    While the invention has been illustrated and described in detail, this is to be considered as illustrative and not restrictive of the patent rights. The reader should understand that only the preferred embodiments have been presented and all changes and modifications that come within the spirit of the invention are included if the following claims or the legal equivalent of these claims describes them.