Abstract:
Disclosed is an implantable medical device, specifically a spinal cross-connector, for connection to approximately parallel spinal fixation rods, the spinal fixation rods being configured to attach to the vertebrae of the spine. The spinal cross-connector may be curved to facilitate installation of the cross-connector over the vertebrae of the spine and allow space for the muscles along the spinal column to heal. The spinal cross-connector may also provide three degrees of adjustment of the spinal cross-connector. The spinal cross-connector may be adjustable or telescoping to vary the width of the spinal cross-connector according to an individual&#39;s anatomy and the distance between the spinal fixation rods. The spinal cross-connector may also facilitate rotation of a longitudinal member around a vertical axis. The spinal cross-connector may also facilitate rotation of a longitudinal member around a longitudinal axis. Once installed, the spinal cross-connector protects against torsional forces acting on the spinal fixation rods which may be disruptive to fusion and/or healing of the vertebrae fixed to the spinal fixation rods.

Description:
BACKGROUND 
       [0001]    Spinal fixation systems are employed in the context of orthopedic surgery to stabilize vertebrae of the spine and to establish or correct the spatial relationship between separate vertebra. In some cases, two spinal fixation rods running in an approximately parallel manner are affixed to multiple vertebrae of the spine on opposite sides of the spinous process by fasteners such as pedicle screws. The spinal fixation rods act as anchoring devices, immobilizing the vertebrae in a desired spatial relationship in order to facilitate spinal fusion or healing. 
         [0002]    A spinal cross-connector may be used in conjunction with the spinal fixation rods to provide torsional stiffness to the spinal fixation rods and to provide additional stability to the vertebrae in order to help facilitate spinal fusion or healing. Spinal cross-connectors are preferably adjustable in some fashion to accommodate the contours of the spinal fixation rods attached to the spine. Depending on the size of the spinal fixation, one or more cross-connectors may be utilized. 
         [0003]    Linear or uncurved spinal cross-connectors have been used historically because of the ease of manufacture and adjustment, but often interfere with the spinal anatomy. Such interference may prove painful to the patient and may also prevent a secure attachment of the spinal cross-connector to the spinal fixation rods. 
         [0004]    Employment of curved cross-connectors may be beneficial in avoiding and protecting the anatomy of the spine. However, implementing the desired adjustability of the cross-connector to conform with the positioning of the spinal fixation rods has proven difficult with curved cross-connectors. Typically the attempts at implementing curved cross-connectors have been overly complex and expensive. Furthermore, because of the difficulty in adjusting the curved cross-connectors found in previous attempts, a secure attachment to the spinal fixation rods has been difficult to establish. 
       SUMMARY 
       [0005]    One embodiment of the invention comprises a spinal cross-connector for attachment to spinal fixation rods, the cross-connector comprising a coupler comprising a head portion and a threaded portion, wherein the head portion comprises a bore therethrough and the threaded portion extends from the head portion. The embodiment may further comprise a first longitudinal member comprising a spinal fixation rod coupler on a first end and a curved arm extending from the first end and through the bore of the coupler and a second longitudinal member comprising a spinal fixation rod coupler on a first end and an annular flange at a second end, wherein the threaded portion of the coupler extends through the annular flange. The embodiment may further comprise a washer positioned over the threaded portion of the coupler between the annular flange of the second longitudinal member and the head portion of the coupler and a nut engaged with the threaded portion of the coupler and located above the annular flange of the second longitudinal member. 
         [0006]    In some embodiments, the threaded portion of the coupler extends along an axis perpendicular to the bore of the coupler. In some embodiments, the bore in the head portion of the coupler is oblong in vertical cross section. In some embodiments, the curved arm of the first longitudinal member may contact the bore at only two contact locations. 
         [0007]    In some embodiments, the washer may contact portions of the curved arm at two locations opposite to the contact points between the bore and the curved arm. In some embodiments, the nut is tightened against a top surface of the annular flange and the washer is forced against the top portion of the curved arm. 
         [0008]    In some embodiments, the curved arm of the first longitudinal member includes two straight sides and a rounded top and a rounded bottom. In some embodiments, the washer may include two skirt portions, which may be configured to fit against the straight sides of the curved arm of the first longitudinal member. 
         [0009]    Some embodiments comprise a pin extending through a distal bore in the distal end of the curved arm, the distal bore running in a direction transverse to the bore in the coupler, wherein the pin is of a length greater than the smallest cross-sectional diameter of the bore in the coupler. Some embodiments may comprise two set screws, each set screw extending through a threaded bore in the first and second longitudinal members. Each of the screws engages a spinal fixation rod and secures the spinal fixation rod to the first and second longitudinal members. 
         [0010]    In some embodiments, the curved arm of the first longitudinal member is configured to move longitudinally through the bore in the coupler. The curved arm of the first longitudinal member may also be rotatable inside the bore of the coupler. The annular flange of the second longitudinal member may be configured to rotate radially around the threaded portion of the coupler. 
         [0011]    In another embodiment, a spinal cross-connector for attachment to spinal fixation rods comprises a first curved longitudinal member, a second longitudinal member, a coupler for coupling the first and second longitudinal members, wherein the coupler comprises an oblong bore configured to accommodate the curve of the first longitudinal member, wherein the first longitudinal member is rotatable around a longitudinal axis and is configured to move along the longitudinal axis through the coupler, and wherein the second longitudinal member is rotatable around a vertical axis. 
         [0012]    In another embodiment, a spinal cross-connector for attachment to spinal fixation rods comprises a first curved longitudinal member, a second longitudinal member, a coupler for coupling the first and second longitudinal members, wherein the coupler comprises an oblong bore configured to accommodate the curve of the first longitudinal member, wherein the first longitudinal member is configured to move along a longitudinal axis through the coupler, and wherein the second longitudinal member is rotatable around a longitudinal and a vertical axis. 
         [0013]    In another embodiment, a spinal cross-connector for attachment to spinal fixation rods comprises a first longitudinal member, a second longitudinal member, and means for coupling the first and second longitudinal members, wherein the coupling means allows the first longitudinal member to move laterally along the longitudinal axis through the coupling means and allows the first and second longitudinal member to rotate relative to one another around a vertical axis and to rotate relatively around a longitudinal axis. The means for coupling may be a coupler comprising a head portion and a threaded portion, wherein the head portion comprises a bore therethrough and the threaded portion extends from the head portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  provides a prospective view of the disassembled components which comprise an embodiment of the spinal cross-connector. 
           [0015]      FIG. 2  is a side view of an embodiment of the assembled spinal cross-connector. 
           [0016]      FIG. 3  is a top view of an embodiment of the assembled spinal cross-connector. 
           [0017]      FIG. 4  is a cross-sectional side view of an embodiment of the spinal cross-connector corresponding to  FIG. 2 . 
           [0018]      FIG. 5  is a perspective view of an embodiment of the coupler. 
           [0019]      FIG. 6  is another cross-sectional view of an embodiment of the spinal cross-connector. 
           [0020]      FIG. 7  is a perspective view of several assembled components of an embodiment of the spinal cross-connector. 
           [0021]      FIG. 8  provides a perspective view of the disassembled components which comprise an embodiment of the spinal cross-connector. 
           [0022]      FIG. 9  is a side view of an embodiment of the assembled spinal cross-connector. 
           [0023]      FIG. 10  is a cross-sectional view of an embodiment of the spinal cross-connector. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIGS. 1-10  depict a spinal cross-connector, embodiments of which will now be described with reference to the accompanying figures, wherein like numerals refer to like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner, simply because it is being utilized in conjunction with a detailed description of certain specific embodiments disclosed herein. Furthermore, embodiments disclosed herein may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to the embodiments herein described. 
         [0025]    The technology described herein provides an implantable medical device, specifically a spinal cross-connector, for connection to approximately parallel spinal fixation rods. The spinal fixation rods are configured to attach to the vertebrae of the spine. 
         [0026]    The spinal cross-connector disclosed herein is curved to facilitate installation of the cross-connector over the vertebrae of the spine and allow space for the muscles along the spinal column. Historically, implementing the desired adjustability to conform with the positioning of the spinal fixation rods has proven difficult with curved cross-connectors and typically the attempts have been overly complex, expensive to implement, and have had difficulty in establishing a secure connection with the spinal fixation rods. 
         [0027]    The curved spinal cross-connector disclosed herein maintains the distinct advantages of a curved spinal cross-connector, but is also extremely easy to implement and adjust, and likewise provides a secure connection to the spinal fixation rods. As seen in  FIG. 1 , some implementations of the spinal cross-connector  100  comprise eight components: a first longitudinal member  12 , a second longitudinal member  18 , a coupler  4 , a washer  26 , a pin  36 , and a nut  28 . Housed within the first and second longitudinal members  12 ,  18  are respective set screws  38 ,  40 . As will be explained further below, the washer  26  may be provided with cutouts  82 ,  84  on opposed lower portions thereof, only one of which is visible in  FIG. 1 . The components of the spinal cross-connector  100  may be made of medical-grade stainless steel, titanium, or other such material suitable for placement in the human body. 
         [0028]      FIG. 2  provides a side view of the assembled spinal cross-connector  100  as attached to spinal fixation rods  1 ,  2 .  FIG. 3  is a perspective view from above the spinal cross-connector  100 . Like  FIG. 1 ,  FIGS. 2 and 3  show the cross-connector  100  comprises eight components: the first longitudinal member  12 , the second longitudinal member  18 , the coupler  4 , the washer  26 , the pin  36 , and the nut  28 . Also visible in  FIGS. 2 and 3  are the set screws  38 ,  40 . 
         [0029]    The first longitudinal member  12  comprises a spinal fixation rod coupler  14  on a first end and a curved arm  16  on a second end. When the spinal cross-connector  100  is assembled, the curved arm  16  extends through the bore  8  in the coupler  4  from a first side  42  of the coupler  4  and exits the bore  8  from a second side  44  of the coupler  4 . The curved arm  16  has a distal end  34 , the distal end  34  comprising a bore  37  running in a direction generally transverse to the length of the first longitudinal member  12 . The bore  37  in the first longitudinal member  12  houses the pin  36  extending through it. The pin  36  is of a length greater than the smallest cross-sectional diameter of the bore  8  in the coupler  4 , such that when the curved arm  16  is positioned in the coupler  4 , the pin  36  prevents the distal end  34  of the curved arm  16  from passing back through the bore  8  in the coupler  4 . 
         [0030]    The second longitudinal member  18  comprises a spinal fixation rod coupler  20  on a first end and an annular flange  22  on a second end. The annular flange  22  comprises a bore  24  therethrough, which, when the spinal cross-connector is assembled, is positioned around a threaded portion  10  of the coupler  4 . The washer  26  is also positioned around the threaded portion  10  of the coupler  4  and is disposed between the coupler  4  and the annular flange  22  of the second longitudinal member  18 . The nut  28  can be tightened on the threaded portion  10  of the coupler  4  above the annular flange  22  of the second longitudinal member  18  to secure the component pieces of the spinal cross-connector  100  in the desired spatial arrangement. 
         [0031]    Set screw  38  extends through a bore  46  in the first longitudinal member  12  into a rod receiving space  54 . In the rod receiving space  54 , the set screw  38  contacts and engages the spinal fixation rod  1 . The set screw  40  extends through a bore  48  in the second longitudinal member  18  into a rod receiving space  56 . In the rod receiving space  56 , the set screw  40  contacts and engages the spinal fixation rod  2 . Set screws  38 ,  40  engage and hold the spinal fixation rods  1 ,  2  in place against interior surfaces  50 ,  52  of the spinal fixation rod couplers  14 ,  20 . 
         [0032]    In addition to being curved, the first longitudinal member  12  can slide and rotate or twist within the bore  8  and the second longitudinal member  18  can rotate on the threaded portion  10  of the coupler  4 . Each of these adjustments may be utilized individually or in conjunction with one another depending on the positioning of the spinal fixation rods to which the spinal cross-connector is to be attached and depending on the anatomy of the patient. 
         [0033]    The rotation/twisting of the first longitudinal member  12  within the bore  8  of the coupler  4  is possible, despite the curvature of the curved arm  16 , because the bore  8  is oblong shaped. The bore  8  has a sufficiently large vertical diameter such that the curvature of the curved arm  16  is accommodated in the oblong-shaped bore  8 . 
         [0034]    The first longitudinal member  12  can slide longitudinally back and forth through the bore  8  in the coupler  4  to adjust the width of the spinal cross-connector  100 . The spinal cross-connector  100  is longitudinally adjustable to vary the width of the spinal cross-connector  100  according to an individual&#39;s anatomy and the distance between the spinal fixation rods. 
         [0035]    The spinal cross-connector  100  also facilitates rotation of the second longitudinal member  18  around a vertical axis. When the second longitudinal member  18  is placed over the threaded portion  10  of the coupler  4 , the second longitudinal member is rotatable around the vertical axis of the threaded portion  10  of the coupler  4  until the nut  28  is securely tightened down. 
         [0036]      FIG. 4  shows a cross-sectional view of the spinal cross-connector  100  in an assembled state. Seen in  FIG. 4  is the coupler  4  which comprises a head portion  6  and a threaded portion  10 . The head portion  6  has a bore  8  and the threaded portion  10  extends from the head portion  6 . Also visible in  FIG. 4  are the bores  46 ,  48  through which the set screws  38 ,  40  extend through the first and second longitudinal members  12 ,  18  into the rod receiving spaces  54 ,  56 . Also visible in  FIG. 4  is the bore  24  of the annular flange  22  of the second longitudinal member  18 . The bores  46 ,  48  are threaded for enabling the set screws  38 ,  40  to be tightened within the bores  46 ,  48  in applying pressure against and securing the spinal fixation rods  1 ,  2 . The bores  46 ,  48  may be slanted outwards towards the rod receiving spaces  54 ,  56  in order to better allow the set screws  38 ,  40  to engage the spinal fixation rods  1 ,  2  against the interior surfaces  50 ,  52  of the spinal fixation rod couplers  14 ,  20 . 
         [0037]    The curved arm  16  of the first longitudinal member  12  extends through the bore  8  in the coupler. Because of the curvature of the curved arm  16 , the curved arm  16  touches the bottom of the bore  8  of the coupler  4  at two contact points  68 ,  70 , creating a lower gap  66  between the curved arm  16  and the bottom of the bore  8 . The bore  8  in the coupler  4  has a sufficiently large vertical diameter that as the curved arm  16  contacts the coupler  4  at contact points  68 ,  70  on the bottom of the bore  8 , an upper gap  72  is created in the bore  8  between the top of the curved arm  16  and the top of the bore  8 . Thus, when the curved arm  16  is in place in the bore  8 , the curved arm  16  does not contact the upper side of the bore  8 . As described further below, the existence of the upper gap  70  and lower gap  66  allows for the rotation/twisting of the curved arm  16  within the bore  8 . 
         [0038]    Also seen in the cross-sectional view of  FIG. 4  is the nut  28  located above the annular flange  22  of the second longitudinal member  18 . The nut may contact the top surface  30  of the annular flange  22 . A washer  26  is also disposed around the threaded portion  10  of the coupler  4 . As the nut  28  is tightened on the threaded portion  10  of the coupler  4 , the nut  28  applies a pressure against the top surface  30  of the annular flange  22 ; the annular flange  22  in turn applies pressure to the washer  26  at the point where the bottom surface  32  of the annular flange  22  contacts the washer  26 ; the washer  26  then exerts pressure on the curved arm  16  at locations  62 ,  64  defined by cutouts  82 ,  84  on the bottom portion of the washer  26 . 
         [0039]    The spinal cross-connector  100  described herein provides varying spatial arrangements to accommodate the needs of physicians in attaching the spinal fixation rods  1 ,  2  to the vertebrae of the spine and connecting the spinal fixation rods  1 ,  2  to each other via the spinal cross-connector  100 . The spinal cross-connector  100  provides for three degrees of adjustment which can be used singularly or in combination. When the nut  28  is loosened, the spinal cross-connector provides, first, rotation/twisting of the longitudinal member  12  relative to longitudinal member  18  around a longitudinal axis  76 ; second, it provides width adjustment along the longitudinal axis  76 ; and third, it provides rotation of longitudinal member  18  relative to longitudinal member  12  around a vertical axis  78 . 
         [0040]    Referring again to  FIG. 4 , the spinal cross-connector  100  allows rotation of the first longitudinal member  12  around the longitudinal axis  76 . When the first longitudinal member  12  is rotated around this longitudinal axis  76 , the curved arm  16  rotates within the bore  8  of the coupler  4 . This rotation around the longitudinal axis  76  allows the spinal cross-connector to accommodate the spatial arrangement of the spinal fixation rods  1 ,  2  in which, when attached to the vertebrae of the spine, the spinal fixation rods  1 ,  2  have slightly different orientations with respect to the coronal plane. To accommodate the differences in coronal orientation, the first longitudinal member  12  may be rotated around the longitudinal axis  76  and attached to the spinal fixation rod  1 . 
         [0041]    The spinal cross-connector  100  further provides adjustment of the longitudinal width of the connector  100 , thus accommodating varying distances between the spinal fixation rods  1 ,  2  when they are attached to the vertebrae of the spine. When the nut  28  is loosened, the pressure exerted by the washer  26  on the curved arm  16  is reduced or eliminated and the curved arm  16  of the first longitudinal member  12  can slide back and forth within the bore  8  of the coupler  4 . The spinal cross-connector  100  can be lengthened to the point where the pin  36  near the distal end  34  of the curved arm  16  abuts, and is blocked by, the second side  44  of the head portion  6  of the coupler  4 . Similarly, the width of the spinal cross-connector  100  can be reduced by sliding the curved arm  16  of the first longitudinal member  12  through the bore  8  of the coupler  4 , to the point that the inside edge  17  of the first longitudinal member  12  abuts the washer  26  or the first side  42  of the head portion  6  of the coupler  4 . 
         [0042]    The spinal cross-connector  100  also provides rotation of the second longitudinal member  18  longitudinally around the vertical axis  78 . This longitudinal rotation of the second longitudinal member  18  around the vertical axis  78  is accomplished by the positioning of the bore  24  of the annular flange  22  of the second longitudinal member  18  over the threaded portion  10  of the coupler  4 , thus making the second longitudinal member radially rotatable around the threaded portion  10  of the coupler  4 . This longitudinal rotation around the vertical axis  78  allows the spinal cross-connector to accommodate a spatial arrangement of the spinal fixation rods  1 ,  2  in which, when attached to the vertebrae of the spine, the spinal fixation rods  1 ,  2  have different orientations with respect to the sagittal plane. For example, in looking at  FIG. 4 , when the spinal fixation rods  1 ,  2  are attached to the spine, the far ends (into the page in  FIG. 4 ) of the spinal fixation rods  1 ,  2  may be closer to each other than the near ends (out of the page). 
         [0043]    After the longitudinal members  12 ,  18  are adjusted to fit the spatial arrangement of the spinal fixation rods  1 ,  2 , the set screws  38 ,  40  are tightened to secure the spinal cross connector  100  to the spinal fixation rods  1 ,  2 . Then, tightening the nut  28  onto the threaded portion  10  of the coupler  4  acts to secure the spatial arrangement of the longitudinal members  12 ,  18 . Upon securely tightening the nut  28 , the first longitudinal member  12  is no longer able to slide longitudinally through the bore  8  or rotate around the longitudinal axis  76 , nor is the second longitudinal member  18  able to rotate around the vertical axis  78 . 
         [0044]      FIG. 5  shows a view of the coupler  4  alone, including the threaded portion  10  and the head portion  6 , as well as the top of the head portion  60  and the oblong bore  8  through the head portion  6 . 
         [0045]      FIG. 6  provides a cross-sectional view of several components of the spinal cross-connector  100 , the view being cut along the vertical axis  78 , showing the curved arm  16  passing through the middle of the bore  8  of the coupler  4 . The rotation of the first longitudinal member  12  within the bore  8  of the coupler  4  is possible, despite the curvature of the curved arm  16 , because the bore  8  is oblong shaped. The bore  8  has a sufficiently large vertical diameter such that the curvature of the curved arm  16  is accommodated in the oblong-shaped bore. Because the curved arm  16  is curved, when the curved arm  16  is inserted in the oblong bore  8 , the curved arm  16  and the bore  8  make contact at two contact locations  68 ,  70  (seen in  FIG. 4 ) along the bottom of the bore  8  on both sides of the bore  8 . Also as a consequence of the curved arm  16  being curved, a lower gap  66  exists beneath the curved arm  16  between the contact points  68 ,  70  on the bottom of the bore  8 . The curved arm  16  does not make contact with the bore  8  in the lower gap  66 . 
         [0046]    Furthermore, the curved arm  16  also does not contact the bore  8  at all along the top of the bore  8 , which allows for the rotational freedom of the curved arm  16  around the longitudinal axis  76 . The space between the curved arm  16  and the upper part of the bore  8  is defined by an upper gap  72 . There also exist gaps  74  on both sides of the curved arm  16  between the bore  8  and the curved arm  16 . The existence of the gaps  74  on the sides provides additional space for the curved arm  16  to rotate within the bore  8  around the longitudinal axis  76 . The curved arm  16  can be a circular diameter, while the bore  8  is oblong shaped, thus the lower and upper gaps  66 ,  72  can be larger than the side gaps  74 . 
         [0047]    In one suitable implementation, for example, the vertical diameter of the bore  8  can be 4.51 mm and the horizontal diameter can be 4 mm. The circular cross-sectional diameter of the curved arm  16  can be 3.9 mm. Thus, the lower and upper gaps  66 ,  72 , in this example, are each roughly 0.3 mm and the side gaps  74  are each 0.05 mm wide. The radius of curvature of the curved arm  16  can be, for example, 38.1 mm. The adjustability features of the cross connector are facilitated by a bore  8  that is larger than the curved arm  16 , but the bore  8  can be only slightly larger, as the rotation around axis  76  does not need to be large to accommodate the variations is spinal rod coronal orientation encountered in spinal surgeries. A rotation of ±10 degrees is typically sufficient. If desired, more rotational freedom can be provided by increasing the size of the bore  8  relative to the size of the arm  16 . 
         [0048]      FIG. 7  provides a view of multiple components of the spinal cross-connector  100 , including the coupler  4 , the washer  26 , first longitudinal member  12 , and the set screw  38 . Visible from this view is the cut out  84  on the washer  26  (an identical cut out  82  is on the other side of the washer  26 , visible in  FIG. 1 ). The cut out  84  comprises an arced portion of the washer  26  where the washer  26  makes contact with the curved arm  16  at contact location  64  (similarly, the cut out  82  makes contact with a the curved arm at a contact location  62  on the other side of the washer  26 , not visible in  FIG. 7 ). When the nut  28  is tightened on the threaded portion  10  of the coupler  4 , the washer  26  applies pressure to the curved arm  16  through cut outs  82 ,  84  at the contact locations  62 ,  64 , in order to hold the first longitudinal member  12  in place. 
         [0049]    When the nut  28  is loosened, the washer  26  applies less pressure (e.g., no pressure) through the cut outs  82 ,  84  to the curved arm  16 , allowing the orientation of the longitudinal members  12 ,  18  to be adjusted. When a new orientation is established, the nut  28  may be tightened, thus again applying pressure to the washer  26  to hold the longitudinal members  12 ,  18  in place. Consequently, while the spinal cross-connector can rotate around the longitudinal and vertical axes  76 ,  78  and move laterally along the longitudinal axis  76  through the coupler  4 , the spatial arrangement of the component parts of the spinal cross-connector  100  in relation to each other can be maintained by tightening the nut  28  on the coupler  4 . 
         [0050]    As shown in  FIG. 8 , another implementation of the spinal cross-connector  110  comprises eight components: a first longitudinal member  112 , a second longitudinal member  118 , a coupler  4 , a washer  126 , a pin  36 , and a nut  28 . Housed within the first and second longitudinal members  112 ,  118  are respective set screws  38 ,  40 . The washer  126  may be provided with skirt portions  186  on one side of the washer  126 . The components of the spinal cross-connector  110  may be made of medical-grade stainless steel, titanium, or other such material suitable for placement in the human body. 
         [0051]      FIG. 9  is a side view of an embodiment of the assembled spinal cross-connector  110 . The first longitudinal member  112  comprises a spinal fixation rod coupler  14  on a first end and a curved arm  116  on a second end. When the spinal cross-connector  110  is assembled, the curved arm  116  extends through the bore  8  in the coupler  4  from a first side  42  of the coupler  4  and exits the bore  8  from a second side  44  of the coupler  4 . The curved arm  116  has a rounded top  188 , a rounded bottom  189 , and flat sides  190 . The first longitudinal member  112  can slide longitudinally through the bore  8  in the coupler  4  to adjust the width of the spinal cross-connector  110 . The spinal cross-connector  110  is longitudinally adjustable to vary the width of the spinal cross-connector  110  according to an individual&#39;s anatomy and the distance between the spinal fixation rods. 
         [0052]    The washer  126  can include two skirt portions  186  forming a cut out  182  on one side of the washer  126 . The washer can include a cut out  184  on the opposite side of the washer  126 . In the embodiment shown, when the washer  126  is placed over the coupler  4 , the washer  126  is positioned such that the skirt portions  186  of the washer  126  are placed on the side closest to the inside edge  17  of the first longitudinal member  112  and the cut out  184  is placed on the side closest to the distal end  34  of the curved arm  116 . In other embodiments, it is contemplated that the skirt portions  186  are placed on the side closest to distal end  34  of the curved arm  116  and the cut out  184  of the washer  126  is placed on the side closest to the inside edge  17  of the first longitudinal member  112 . 
         [0053]    The top of cut out  182  and the cut out  184  of the washer  126  are shaped to accommodate the rounded top  188  of the curved arm  116 . The skirt portions  186  of the washer  126  are shaped to accommodate the flat sides  190  of the curved arm  116 . When the nut  28  is tightened on the threaded portion  10  of the coupler  4 , pressure is applied through the second longitudinal member  118  to the washer  126 . The washer  126  can then exert pressure on the curved arm  116  of the first longitudinal member  112  through the cut outs  182  and  184  and through the skirt portions along the flat sides  190  when the nut  28  is tightened. 
         [0054]    The second longitudinal member  118  comprises a spinal fixation rod coupler  20  on a first end and an annular flange  122  on a second end. The annular flange  122  comprises a bore  124  therethrough, which, when the spinal cross-connector  110  is assembled, is positioned around the threaded portion  10  of the coupler  4 . The second longitudinal member  118  can rotate on the threaded portion  10  of the coupler  4  around a vertical axis. In the embodiment shown, the bore  124  through the annular flange  122  has an oblong shape. Because of the oblong shape of the bore  124 , in addition to rotation around the vertical axis, the second longitudinal member  118  can also slide back and forth relative to the threaded portion  10  of the coupler  4 . In other embodiments, it is contemplated that the bore  124  can instead have an enlarged circular bore (substantially larger than the diameter of the threaded portion  10  of the coupler  4 ) to allow for sliding of the second longitudinal member  118  in more than one direction. 
         [0055]    The oblong shape of the bore  124  allows the second longitudinal member  118  to move from side to side relative to the threaded portion  10  of the coupler  4  and also relative to the first longitudinal member  112 . The top of the washer  126  is dome shaped. The bottom surface  132  of the annular flange  126  is shaped in a concave manner to fit over the dome of the washer  126 . Thus, when the second longitudinal member  118  is adjusted side-to-side relative to the coupler  4 , the bottom surface  132  of the annular flange  126  slides over the domed portion of the washer  126 . The second longitudinal member  118 , in effect, rotates around the longitudinal axis. 
         [0056]    In one suitable implementation, the width of the bore  124  in the annular flange  122  can be 4.5 mm and the length of the bore  124  in the annular flange can be 13.7 mm. The circular diameter of the threaded portion  10  of the coupler  4  can be 4.0 mm. In this implementation, the second longitudinal member  118  can experience rotation of ±15 degrees from the nominal center position. 
         [0057]    The top surface  130  of the annular flange  122  is spherically contoured, the slope leading downwards away from the bore  124 . The sloped nature of the top surface  130  of the annular flange  122  allows for the nut  28  to still fit above the annular flange and be tightened on the annular flange  122  at various angles of the annular flange  122  relative to the threaded portion  10  of the coupler  4 .  FIG. 10  provides a cross-sectional view of several components of the spinal cross-connector  110 , the view being cut along the vertical axis  78 , showing the curved arm  16  passing through the middle of the bore  8  of the coupler  4 . As a consequence of the curved arm  116  being curved, a lower gap  66  exists beneath the curved arm  116  on the bottom of the bore  8 . The curved arm  116  does not make contact with the bore  8  in the lower gap  66 . The space between the curved arm  116  and the upper part of the bore  8  is defined by an upper gap  72 . There also exist gaps  74  on both sides of the curved aim  116  between the bore  8  and the curved arm  116 . The flat sides  190  along with the rounded top  188  and rounded bottom  189  give the curved arm  116  an oblong shape. In this embodiment, the curved arm  116 , being oblong shaped, with the flat sides  190  adjacent to the flat sides of the bore  8 , exhibits very limited rotational motion when positioned in the oblong bore  8  of the coupler  4 . 
         [0058]    In one suitable implementation, the vertical diameter of the bore  8  can be 4.51 mm and the horizontal diameter can be 3.65 mm. The vertical diameter of the curved arm  116  can be 3.9 mm and the horizontal diameter of the curved arm  116  can be 3.45 mm. Thus, the lower and upper gaps  66 ,  72 , in this example, are each roughly 0.3 mm and the side gaps  74  are each 0.1 mm wide. The radius of curvature of the curved arm  16  can be, for example, 38.1 mm. 
         [0059]    In one implementation, the threaded portion  10  of the coupler  4  may include a cavity  192  in the top. The cavity  192  may be conical in shape. The existence of the cavity  192  in the threaded portion  10  of the coupler  4  allows an upper section (e.g., the first thread) of the threaded portion  10  to be physically deformed with a punch or press after the nut  28  is threaded on, but before the nut  28  is tightened during installation. During manufacture, the upper section of the threaded portion would be purposely deformed after first placing the nut  28  over the threaded portion  10  of the coupler. Deforming the upper section of the threaded portion  10  in this manner prevents the surgeon from accidentally removing and potentially dropping and losing the nut  28  while adjusting and tightening the nut  28 . 
         [0060]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention, which is defined by the following claims and their equivalents.