Abstract:
A spinal fixation assembly using a hinged bone screw with a tulip blob connector, a variable height, hinged bone screw with a tulip bulb connector or both. The bone screws have a post section connected to a screw section by a hinge. In the basic hinged bone screw, a bulb shaped head is formed at the end of the post section opposite the hinge and a tulip bulb connector is attached to the bulb shaped head. For the variable height hinged bone screw, a collet is used with an interior bore that slides over the post section of the bone screw. The collet has a cylindrically shaped sleeve at one end and a bulb shaped head at the other end. The tulip bulb connector is attached to the bulb shaped head of the collet. In both cases, the tulip bulb connector has a cavity for receiving a connector rod and a set screw for firmly attaching said connector rod within said tulip bulb connector cavity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/479,273, filed on Apr. 26, 2011, the disclosure of which is incorporated herein by reference in its entirety for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to orthopedics and spinal surgery and, more particularly, to a hinged bone screw with a tulip bulb connector in a spinal fixation assembly. 
         [0003]    Back pain is a commonly reported medical aliment. It is most frequently associated with degenerative changes or fractures in the spinal vertebra. Most of the 30 million U.S. patients who report back pain each year resolve their pain with conservative treatment (e.g., rest and exercise). Nonetheless, approximately 15 percent, or 4.5 million, fail conservative therapy and are left with debilitating pain. Out of these, approximately 500,000 people opt for spinal surgery. In addition to alleviating pain, spinal surgery seeks to minimize damage to adjacent supportive muscle and skeletal components. 
         [0004]    Several techniques and systems have been developed for correcting and stabilizing the spine and facilitating a common spinal surgical procedure—spinal fusion. The most widely used systems use a bendable rod that is placed longitudinally along the length of the spine. Such a rod is bent to follow the normal curvature of the spine, whether it is the normal kyphotic curvature for the thoracic region or the lordotic curvature for the lumbar region. In such a procedure, a rod is attached to various vertebrae along the length of the spinal column by a number of bone anchor assemblies. A bone anchor may be a hook that engages the vertebra laminae or a bone screw threaded into the vertebral body. When stabilized, the vertebra is decortified where the outer cortical bone is removed to provide a foundation for bone grafts. Over time, these bone grafts fuse the damaged vertebrae together. 
         [0005]    A good example of a traditional rod spinal fixation assembly is the Cotrel-Dubosset/CD Spinal System® sold my Medtronic Sofamor Danek, Inc. As shown in  FIG. 1 , the CD Spinal System® includes a bone screw with a tulip bulb connector  2  having a top cavity  4  where the spinal rod  6  is placed. The cavity includes a threaded bore into which a set screw  8  is engaged to clamp the rod  6  down. Additional details of this technology can be found in U.S. Pat. No. 5,005,562 to Cotrel. One benefit of the CD Spinal System is that the fixation element is positioned directly beneath the rod. Although the bone screw  10  rotates  12  about 30° from vertical in the lateral direction  14  in the coronal plane  16 , it lacks the ability to make spinal adjustments in the dorsal  18 , ventral  20  and medial-sagittal  22  planes. Since the CD Spinal System® can only rotate in lateral directions  14  from vertical within the coronal plane  16 , any dorsal, ventral and medial vertebral body correction or translation is limited. 
         [0006]    In degenerative and deformity cases, the spine is misaligned in either the coronal (scoliosis) and sagittal (kyphosis) planes or both (spondylolisthesis). For such degenerative and deformity cases, the concept of attaching a pre-contoured rod to a deformed spine was used by Luque and Asher (w/wires and cables) for scoliosis, and Edwards (w/threaded connectors) and Steffe (w/threaded screw posts) for spondylolisthesis. For many years, there was no single bone screw spinal fixation assembly that solved all of these problems. When vertebral correction or translation occurred in both the coronal and sagittal planes, it generated such high force loads that bone screw pullout was common. In cases when the bone is strong and healthy, the initial fixation of traditional spinal and orthopedic screws is usually excellent and pullout strength is around 150 N/mm. With degenerative cases, pullout strength falls to about 50-60 N/mm. 
         [0007]    To address these shortcomings, a hinged bone screw shown in  FIG. 2  was disclosed in U.S. Pat. Nos. 6,309,391 and 7,322,979 to Crandall. Whereas a short screw post enhances bone screw assembly in passive fixation, the long post screw  24  shown in  FIG. 2  facilitates simultaneous correction in both the coronal  16  and sagittal  22  planes in active fixation cases. When the long post screw  24  is screwed into the pedicle  26 , it offers vertebral body movement  28  in both the coronal  16  and sagittal  22  planes through its hinge  30 . In combination with the vertical  32  and rotational ability of Simonson&#39;s TSRH® 3D connectors  34 , pulling the vertebrae  36  and the spine to the pre-contoured rod  38  via this pivoting post system facilitates simultaneous correction in both the coronal  16  and sagittal  22  planes. By adjusting the vertical height  32  of the TSRH® 3D connectors  34  shown in  FIG. 3 , the vertebrae  36  can now move in the lateral-sagittal  40 , medial-sagittal  42 , dorsal-coronal  44  and ventral-coronal  46  directions ( FIG. 3 ). Together, the hinged bone screw of Crandall and TSRH® 3D connectors  34  by Simonson provide a planar rotation of more than 180° from vertical and allows for vertebral body correction or translation  48  in all planes. With such a bone screw fixation assembly, the force load on a bone screw can be reduced by as much as 60%. A commercial example of such a vertebral translation system is the TSRH-3Dx® Multi-Planar Adjusting (MPA™) Screw  50  sold by Medtronic Sofamor Danek Inc. Shown in  FIG. 3 , the MPA™ Screw  50  repositions the vertebrae  36  in medial-sagittal plane  22  while also placing the vertebrae  36  into a more dorsal-coronal plane  18  toward the rod  38 . If necessary, it can also move the spine downward toward the ventral-coronal plane  20 . With such vertebral translation  48 , the force load on a MPA™ Screw  50  averages between 20-40 N/mm—well below the bone screw pullout strength in degenerative bone. 
         [0008]    This principle of direct vertebral translation in multiple planes with respect to the rod is now a powerful tool for deformity and degenerative correction, especially for scoliosis, kyphosis and spondylolisthesis. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a spinal fixation assembly that facilitates the simultaneous active and passive correction or translation of fractured, degenerative or deformed vertebrae not only in the coronal plane but also in the dorsal-coronal, ventral-coronal, lateral-sagittal and medial-sagittal planes as well. 
         [0010]    In one embodiment, the present invention is a hinged bone screw with tulip bulb connector in a spinal fixation assembly. The first component is a bone screw with a hinge. A shaft or post extends from the hinge. The post can be either short or long in length. With its hinge, the bone screw provides vertebral body movement in both the coronal and sagittal planes. 
         [0011]    For the basic hinged bone screw with a tulip bulb connector, there is a bulb-shaped head at the end of the post. In turn, this bulb-shaped head fits into the tulip bulb connector. This tulip bulb connector possesses a top cavity where a spinal rod is placed. The cavity includes a threaded bore into which a set screw is engaged to clamp the rod down. This tulip bulb connector, however, only provides rotational vertebral body movement of about 30 degrees in the coronal plane. By combining the hinged bone screw with the tulip bulb connector, the vertebral body can not only move in the coronal and sagittal plane but also laterally and medially. As a result, the present invention in its basic form increases the rotational ability of the bone screw to about 130° from its original 30° from vertical. 
         [0012]    A more advanced form of hinged bone screw of the present invention includes a collet—a cylindrically shaped sleeve with a bulb shaped head. The bulb shaped head of the collet is placed into the tulip bulb connector. Both the collet bulb and cylindrical shaft have an interior bore that slides over the bone screw post like a sleeve or collet. By changing the amount of the post covered by this collet, the height of the bone screw vis-à-vis the tulip shaped connector can be varied. In other words, the collet allows for variable height positions along the post. By combining the collet with the hinged bone screw and tulip bulb connector, simultaneous correction in both the coronal and sagittal planes is now possible. If one adjusts the vertical height of the tulip bulb connector with this configuration, the hinged bone screw fixation assembly can now move the vertebrae in the lateral-sagittal, medial-sagittal, dorsal-coronal and ventral-coronal directions, thereby vastly increasing the vertebral body translation abilities. 
         [0013]    With such a system, the force load on the hinged bone screw falls between 20-40 N/mm—well below the bone screw pullout strength in degenerative bone. With this hinged bone screw fixation assembly, direct vertebral translation in multiple planes is now possible in deformity and degenerative cases, especially for scoliosis, kyphosis and spondylolisthesis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows the planar movements of a prior art bone screw with a tulip bulb connector. 
           [0015]      FIG. 2  shows a view of the prior art TSRH-3D® Multi-Planar Adjusting (MPA™) Bone Screw. 
           [0016]      FIG. 3  shows the planar movements of the prior art TSRH-3Dx® Multi-Planar Adjusting (MPA™) Bone Screw. 
           [0017]      FIG. 4  shows a side view of a hinged bone screw of the present invention attached to a tulip bulb connector. 
           [0018]      FIG. 5  shows a side view of a hinged bone screw of the present invention without the tulip bulb connector. 
           [0019]      FIG. 6  shows a front view of a hinged bone screw of the present invention without the tulip bulb connector. 
           [0020]      FIG. 7  shows the lateral and medial movement of a hinged bone screw of the present invention with a tulip bulb connector. 
           [0021]      FIG. 8  shows the coronal rotation movement of the tulip bulb connector along with the lateral and medial movement of a hinged bone screw. 
           [0022]      FIG. 9  shows the planar movements of a hinged bone screw with a tulip bulb connector of the present invention. 
           [0023]      FIG. 10  shows the variable height, hinged bone screw with a tulip bulb connector of the present invention. 
           [0024]      FIG. 11  shows the planar movements of the variable height, hinged bone screw of  FIG. 10 . 
           [0025]      FIG. 12  shows a spondylolisthesis reduction using a variable height, hinged bone screw with a tulip bulb connector along with the CD Horizon® Sextant® II System. 
           [0026]      FIG. 13  shows a variable height, hinged bone screw with a tulip bulb connector actively moving the vertebral body in the coronal, sagittal and dorsal planes in conjunction with CD Horizon® Sextant® II System 
           [0027]      FIG. 14  shows variable height, hinged bone screws in a spinal fixation assembly moving the vertebral body passively in conjunction with CD Horizon® Longitude® System. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I. Definitions 
       [0028]    “Active Fixation” means moving, fixing and stabilizing the spine, generally used in degenerative and deformity cases. 
         [0029]    “Coronal” means a vertical plane that divides the body into a ventral and dorsal section (belly and back) sections. It is also known as the frontal plane. 
         [0030]    “Dorsal” refers to a plane that is parallel to or in a direction toward the back. 
         [0031]    “Kyphosis” means a curvature of the upper back, also known as hunchback. 
         [0032]    “Lateral” means to the side, either left or right. 
         [0033]    “Median or Medial” defines a point in the center of the organism that bisects the body vertically through the navel, dividing the body in a left and right side. 
         [0034]    “Mid-sagittal” is the mid-line that passes through the navel or spine and all other sagittal planes are parallel to it. 
         [0035]    “Passive Fixation” means fixing and stabilizing the spine in, generally, fractured or degenerative cases. 
         [0036]    “Pullout Strength” means the force or stress necessary to dislodge an embedded bone screw from a bone. 
         [0037]    “Sagittal” refers to a plane that divides the body into right or left parts. 
         [0038]    “Scoliosis” means the spine is curved from side to side creating a “S” or “C” shape. 
         [0039]    “Spinal Fixation Assembly” means a complete spinal system including bone screws, connectors and rods. 
         [0040]    “Spondylolisthesis” means the vertebrae are misaligned by slipping over one another either forwards (anterolisthesis) or backwards (retrolisthesis). 
         [0041]    “Ventral” means a plane or direction toward the abdomen or belly. 
       I. Hinged Bone Screw with a Tulip Bulb Connector 
       [0042]    A hinged bone screw with a tulip bulb connector  52  is shown in  FIG. 4 . It consists of a bone screw  54 , a hinge  56 , a post  58 , a bulb shaped head  60 , a tulip bulb connector  62 , a set-screw  64  and a rod  66 . 
         [0043]      FIG. 5  shows the same hinged bone screw  51  as in  FIG. 4 , but without the tulip bulb connector  62  assembly. In this view, the bulb shaped head  60  of the hinged bone screw  51  can be more clearly seen.  FIG. 6  shows a side view of the hinged bone screw  51  where the details of the hinge  56  can be more clearly seen. For this hinge  56 , a pin  70  goes through a hole in the post  58  and attaches to both sides of the screw flanges  68 . The pin  70  is preferably flared or stamped  72  at both ends to secure it to the hinge. It may also be secured with a screw. The length of the post  58  can be varied. Now referring back to  FIG. 4 , a tulip bulb connector  62  with a threaded bore is shown into which a set screw  64  is engaged to clamp a connector rod  66  down. While a tulip bulb connector  62  is illustrated, one of skill in the art will recognize that other types of connectors can be used to connect the hinged bone screw  51  to the connector rod  66 . 
         [0044]    The hinged bone screw with a tulip bulb connector  52  provides additional planar movements as compared with prior art bone screws. Whereas the bone screw with tulip bulb connector  2  shown in  FIG. 1  only provides about a 30° lateral  14  movement on either side of vertical in the coronal plane, the hinged bone screw with a tulip bulb connector  52  shown in  FIG. 7  now allows the bone screw  54  to move almost 180° from its vertical line  74  in either the lateral  76  and medial  78  directions or both. In either case, it is more rotation than necessary for any normal vertebral body translation. 
         [0045]    In  FIG. 8 , the post  58  can also rotate  80  another 180° from its horizontal  82  line allowing both the bone screw  54  and post  58  to rotate simultaneously with respect to one another. As shown earlier in  FIG. 1 , the prior art bone screw with tulip bulb connector  2  can also rotate  12  in the coronal plane  16 . This ability to either tilt  84  the tulip bulb connector  2  of the entire hinged bone screw with tulip bulb connector  52  shown in  FIG. 8  further enhances the present invention. When tilted  84 , the hinged bone screw with a tulip bulb connector  52  can be positioned directly beneath or closer to the rod  66 . 
         [0046]    By combining the tulip bulb connector  2  and hinge  56  shown in  FIG. 9 , the hinged bone screw with tulip bulb connector  52  of the present invention can now move a vertebrae  36  in both the coronal  16  and sagittal  22  planes in either the lateral  40  and medial  42  directions or both. Similar to the prior art TSRH-3Dx® Multi-Planar Adjusting (MPA™) Screw  50  shown in  FIG. 3 , the hinged bone screw with tulip bulb connector  52  can now add vertebral translation  48  to the spine in the sagittal plane  22  and, most important, medially  42  toward the spinal rod  38 . With the present invention, it is estimated that the vertebral translation of a hinged bone screw with a tulip bulb connector  52  has increased from 30° to 130° giving the original tulip bulb connector  2  a new flexibility it never possessed. With the present hinged bone screw with tulip bulb connector  52  invention, the force load on the bone screw  54  also falls during translation. 
         [0047]    The present invention, therefore, also helps reduce bone screw pullout. 
       II. Variable Height, Hinged Bone Screw with Tulip Bulb Connector 
       [0048]    The hinged bone screw with tulip bulb connector  52  shown in  FIG. 9  can be limited in its ability to move the vertebrae  36  in either the dorsal or ventral directions, thereby, restricting the movement in the dorsal  18  or ventral  20  planes. To overcome this limitation, a further preferred embodiment of the present invention is shown in  FIG. 10 . The variable height, hinged bone screw with tulip bulb connector  86  shown in  FIG. 10  includes a bone screw  54 , a hinge  56 , a post  58  and a collet  88 . The collet  88  consists of a cylindrically shaped sleeve  90  at its lower end and a bulb shaped head  92  at its upper end. The bulb shaped head  92  is, in turn, placed into a tulip bulb connector  62 . Both the bulb shaped head  92  and cylindrically shaped sleeve  90  have an interior bore that slides over the post  58 . A more full description of the configuration and interaction of the collet  88  with the tulip shaped connector  62  is provided in Applicant&#39;s pending U.S. patent application Ser. No. 12/731,116, which is hereby incorporated by reference. The hinge  56  of the variable height, hinged bone screw with tulip bulb connector  86  has the same construction as the hinge  56  of the previous hinged bone screw with tulip bulb connector  52  (see,  FIG. 4-6 ). More specifically, a pin  70  goes through a hole in the post  58  and attaches to both sides of flanges at the upper end of the bone screw  54 . The pin  70  is preferably flared or stamped  72  at both ends to secure it to the hinge  56 . It may also be secured with a screw. Although the length of the post  58  may be varied, the collet  88  now provides the ability to vary the height of the tulip shaped connector  62  vis-a-vis the hinge  56  without having to switch out or change the post  58 . Like the tulip bulb connector  62  in the earlier hinged bone screw with tulip bulb connector  52  embodiment (see,  FIGS. 4-6 ), the tulip bulb connector  62  in the variable height, bone screw with tulip bulb connector  86  embodiment also has a threaded bore into which a set screw  64  is engaged to clamp a connector rod  66  down. 
         [0049]    By changing the amount of the bone screw post  58  covered by the collet  88  in  FIG. 10 , one can vary the vertical height  94  ( FIG. 11 ) of the tulip shaped connector  62  vis-a-vis the hinge  56  to adjust its position in either the dorsal  18  or ventral  20  planes. The variable height, hinged bone screw with tulip bulb connector  86  of the present invention allows the bone screws  54  to be set at different axes vis-à-vis the connecting rods  66 . It can also be set at different vertebral body heights  48  vis-à-vis such rods to engage a fixed cylindrical rod in any degree of angular orientation or direction. Similar to the prior art TSRH-3Dx® Multi-Planar Adjusting (MPA™) Screw  50  referred to in  FIG. 3 , the variable height, hinged bone screw with tulip bulb connector  86  now provides direct vertebral height  48  translation in multiple planes for deformity and degenerative cases and, especially, for scoliosis, kyphosis and spondylolisthesis. It also does so at reasonable and safe bone screw stress loads. 
         [0050]    The components of both the hinged bone screw with tulip bulb connector and the variable height, hinged bone screw with tulip bulb connector are preferably made from metals such as stainless steel, titanium, cobalt chromium, nickel-titanium alloys or other suitable high strength materials. Such components may also be made of polymer materials such as PEEK (polyether ether ketone) or carbon fiber-reinforced polymers where a high strength-to-weight ratio allows reduced size. 
       III. Active Fixation Example 
       [0051]    A spinal fixation assembly incorporating the hinged bone screw with tulip bulb connector of the present invention is illustrated in  FIG. 12  involving a spondylolisthesis reduction. During active fixation in this example, the fixation assembly can be used to realign a misaligned or deformed spine to a more natural curvature. As shown in  FIG. 12 , a vertebrae  96  is misaligned in both coronal and sagittal planes. A spinal fixation assembly  86  having a variable height, hinged bone screw with a tulip bulb connector of the present invention is attached to the vertebrae  96 . In this case, the CD Horizon® Sextant® II System  98  sold by Medtronic Sofamor Danek, Inc. is connected to the variable height, hinged bone screw with a tulip bulb connector and used to perform the correction of the misaligned vertebrae  96 . The CD Horizon® Sextant® II System  98  uses an arc arm  100  for leverage to minimize the stress on the bone-screw interface during reduction. Such an instrument facilitates spondylolisthesis correction by using top-loading screws to reduce the deformity. The CD Horizon® Sextant® II System  98  locks onto the tulip bulb connector of the variable height, hinged screw. It then engages the driver  102  of the CD Horizon® Sextant® II System  98 . With the new pivoting and variable height ability of the variable height, hinged bone screw with tulip bulb connector spinal fixation assembly  86  shown in  FIG. 13 , the coronal and sagittal misalignment can be properly corrected without undue load stress on the bone screw  54 . Since, in this example, coronal and sagittal misalignment occurs at a single vertebrae  96 , the variable height, hinged bone screw with tulip bulb connector spinal fixation assembly  86  can reduce or move this vertebrae  96  either dorsally  104  in the coronal plane, medially  106  in the sagittal plane or both. This coronal and sagittal plane reduction process can be performed simultaneously to evenly spread the stress of the reduction throughout the spinal fixation assembly  86 . With only a few turns of the driver  102 , the present invention provides more accurate and precise force load during vertebral translation, thereby, avoiding possible vertebral fracture and bone screw  54  pullout. With the variable height, hinged bone screw with tulip bulb connector spinal fixation assembly  86 , both coronal and sagittal plane reduction can proceed slowly and accurately to align the vertebrae  96  into a natural and neutral spinal position. In this example, the CD Horizon® Sextant® II System  98  slides a pre-contoured rod  66  through the tulip bulb connectors  62  to secure the realigned vertebrae  108  in their proper and natural position. If properly performed, such vertebral translations may alleviate nerve compression and pain caused by such deformities as scoliosis, kyphosis, and spondylolisthesis. 
       III. Passive Fixation Example 
       [0052]    A good example of passive spinal fixation is illustrated in  FIG. 14 . During passive fixation, a fixation assembly such as the variable height, hinged bone screw with tulip bulb connector spinal fixation assembly  86  is used to stabilize the spine  110 . When stabilized, the vertebra is then decortified (i.e., the outer cortical bone is removed) to provide a foundation for bone grafts. Over time, these bone grafts fuse the damaged vertebrae together while the passive fixation assembly continues to support and stabilize the spine. 
         [0053]    In this example, the CD Horizon® Longitude®  112  sold by Medtronic Sofamor Danek, Inc. is used to place percutaneous screws and rods at multiple levels of vertebrae. As shown in  FIG. 14 , a key element of this instrument set are a free-hand or steerable rod inserter  114  and reduction screw extenders  116  that allow for tactile, freehand rod passage through the large holes at the base of screw extenders  116 . 
         [0054]    As shown in  FIG. 14 , a set of extenders  116  is placed on several variable height, hinged bone screw with tulip bulb connector spinal fixation assemblies  86 . When only using tulip bulb connectors  62 , these extenders  116  are moved by a driver  102  in stages because the complete reduction of one extender  116  without reducing the others will cause the rod  66  to put a strong force on the other extenders  116 . It is important not to over-rotate the extenders  116  when using the tulip bulb connector  62 . When the extender  116  is in the RD position  118 , advancing any further will place unneeded pressure on the tulip bulb connector  62 . With the variable height, hinged bone screw with tulip bulb connector spinal fixation assemblies  86 , this pressure is distributed throughout the assembly. As a result, reduction in any plane can be performed simultaneously with a lower probability of bone screw  54  pullout. 
         [0055]    In the foregoing specification, the invention has been described with reference to specific preferred embodiments and methods. It will, however, be evident to those of skill in the art that various modifications and changes may be made without departing from the broader spirit and scope of the invention. For example, while the hinged bone screw with tulip bulb connector spinal fixation assembly and the variable height, hinged bone screw with tulip bulb connector spinal fixation assembly has been described for vertebral translation, those of skill in the art will recognize that alternative uses in orthopedics and spinal surgery are possible. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than restrictive, sense; the invention being limited only by the appended claims.