Abstract:
A low profile orthopedic device is used to fix and stabilize bones to correct anomalies in skeletal structure occurring naturally or by trauma. Bone screws are screwed into bones by application of torque. Connectors are attached to the anchored bone screws. Each connector includes a clamp and a compression ring. A connecting rod connects several connectors together. The clamps are tightened to hold the rod to the bone screws in a pre-selected position by linear movement of the compression ring.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to orthopedic surgery and, in particular, to a bottom loading modular head assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    Chronic back problems are caused by intervertebral disc disease and deterioration and loss of stability of the intervertebral joints. Examples of these spinal conditions include degenerative disc disease, scoliosis, spondylolithesis, spinal stenosis, etc. Stabilization and/or arthrodesis of the intervertebral joint can reduce the pain associated with movement of a diseased or deteriorated intervertebral joint. In order to allow for development of a solid intervertebral fusion, the spine has to be stabilized. Severe trauma to the back can further cause conditions wherein the spine needs to be stabilized. There are many instances in which it is necessary to stabilize and fix bones and bone fragments in a particular spatial relationship to correct the location of skeletal components due to injury or disease. One group of devices employ a number of bone screws placed across a discontinuity in adjacent vertebrae and connected by a rod to maintain a predetermined spatial location. 
         [0003]    Spinal stabilization systems have been developed to stabilize the vertebrae to allow for fusion or stabilization of diseased intervertebral joints. One type of spinal stabilization system includes connectors and rods that are used to stabilize the spine. Some examples of such spinal stabilization systems are disclosed in U.S. Pat. Nos. 6,613,050; 6,371,957; 6,050,997; 5,879,350; 5,725,527; 5,628,740; and 5,545,165, the disclosures of which are incorporated herein by reference. In these systems, connectors are anchored to the vertebral bodies desired to be stabilized by anchoring structures such as screws or hooks. One or more connecting rods are then secured to the connectors to form a connector/rod construct that stabilizes the vertebral bodies to which the connectors are secured. 
         [0004]    In many known stabilization systems, threaded nuts are used to secure the rods to the connectors. The rods can be provisionally held in position by loosely tightening the nuts on the connectors. After desired adjustments are made with respect to the relative positioning of the bones desired to be stabilized, the nuts can be further tightened to finally secure the connector/rod construct. Typically, a torque wrench or similar device is used to achieve the required torques to finally secure the connector/rod construct. To prevent torque from being transferred to the patient while tightening the nut, an anti-torque device is frequently used in combination with the torque wrench. The effective use of the torque wrench and anti-torque device can be difficult and often is dependent upon the strength and experience of the surgeon. The inventors torqueless fasteners patents include U.S. Pat. Nos. 7,105,029; 7,118,303; 7,334,961; 7,335,201; 7,438,715; 7,658,582; 7,678,138; 7,862,281; 7,981,143 and RE42,715, the entire disclosures of which are incorporated herein by reference. 
         [0005]    U.S. Pat. No. 6,626,906 issued Sep. 30, 2003 to Young teaches a spinal rod attached to a spinal anchor by a clamp. The clamp is tightened about the anchor by a collet screwed into the clamp. The rod is held in the clamp by a split ring that is reduced in size by the collet. The anchor is placed in the bone by torque and the collet is tightened by additional torque. 
         [0006]    U.S. Pat. Nos. 6,610,063; 6,610,062; 6,565,565; RE 37,665; 6,478,798; 5,584,834 teach various spinal rod coupling devices that are secured to bone screw anchors by clamps that require additional torque to be applied to the assembly after the bone screw has been seated in the bone. 
         [0007]    In normal practice, the bone screws are each anchored in the bone with a specific amount of torque that approaches the ultimate sustainable force between the screw threads and the bone. The bone screws are then connected together by a rod having sufficient stiffness to maintain the desired skeletal orientation. The connection between the rod and the bone screws must be strong enough to be immobile. Alternatively, a torqueless connector is coupled to a bone screw, wherein the bone screw is installed in combination with the connector. 
         [0008]    All these spinal fixation devices result in additional torque applied to the assembly, and thereby to the bone screw, to tighten and lock the rod to each of the bone screws. The additional load may strip the purchase between the bone and the threads of the bone screw. To prevent such a result, some tool must be used to counter the torque of locking the rod and the screws. The use of an anti-torqueing tool requires additional coordination by the surgeon or surgeons to prevent slippage. 
       SUMMARY OF THE PRESENT INVENTION 
       [0009]    In particular, the present invention provides a linear locking set screw system capable of rapid linear engagement of a bone screw and a rod. Bone screws are screwed into bones by application of torque, the top of each bone screw having a spherical head. A connector is attached to the head of each of the anchored bone screws. Each connector includes a clamp body having a rod slot section, a receptacle section for placement over the spherical head and a pin retention slot for stabilizing and immobilizing the assembly once it has been installed in a subject. A compression ring is placed around the clamp body. A connecting rod connects several connectors together upon placing the rod within the rod slot. The clamps are tightened to hold the rod to the bone screws in a pre-selected position by linear movement of the compression ring. 
         [0010]    It is an objective of the present invention to provide a low profile spinal stabilization system capable of precise and reproducible linear engagement and disengagement. 
         [0011]    Still another objective of the present invention is to provide a connector that provides a bottom loading low profile spinal stabilization system, the connector being attached to a bone screw after the bone screw has been anchored. 
         [0012]    Yet another objective of the present invention is to provide a low profile spinal stabilization system capable of locking a spinal connecting rod to an anchored bone screw by linear engagement so as to eliminate torque fastening. 
         [0013]    Yet a further objective of the present invention is to teach the use of a linear fastener that is adjoined to an anchored bone screw for support of ancillary devices adapted to be secured together without rotational torque forces. 
         [0014]    Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings which set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an exploded view of the bottom loading orthopedic device of the instant invention; 
           [0016]      FIG. 2  is a plane view of the device with the connector coupled to the bone screw; 
           [0017]      FIG. 3  is a plane view of the device locked to a rod providing a vertical low profile vertical stance; 
           [0018]      FIG. 4  is a plane view of the device locked to a rod providing an angular low profile stance. 
           [0019]      FIG. 5  is a perspective view of the connector; 
           [0020]      FIG. 6  is an upper perspective view of the clamp portion of the connector; 
           [0021]      FIG. 7  is a lower perspective view of  FIG. 6 ; 
           [0022]      FIG. 8  is a perspective view of a pin used to secure the clamp to the compression ring; 
           [0023]      FIG. 9  is an upper perspective view of the compressing ring portion of the connector; 
           [0024]      FIG. 10  is a lower perspective view of  FIG. 9 ; 
           [0025]      FIG. 11  is a cross sectional view of the connector before attachment to a bone screw; 
           [0026]      FIG. 12  is a cross sectional view of the connector during attachment to the bone screw; 
           [0027]      FIG. 13  is a cross sectional view of the connector after attachment to the bone screw; 
           [0028]      FIG. 14  is a cross sectional view of the connector in locked or closed position; 
           [0029]      FIG. 15  is a side view of the clamp body showing a pin retention slot; 
           [0030]      FIG. 16  is a perspective view of  FIG. 15 ; 
           [0031]      FIG. 17  is a side view of the clamp body showing a pin retention slot with a pin inserted therein; 
           [0032]      FIG. 18  is a side view of the clamp body showing the pin in the pin retention slot moving up past the lip portion; 
           [0033]      FIG. 19  is a side view of the clamp body showing the pin moving up into the pin shaft or passageway during installation of the instrument. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring now to the Figures, set forth is an orthopedic fixation device  10  for use in stabilizing and fixing the vertebra in relation to each other and the sacrum. The fixation device  10  employs a bone screw anchor  12  having an exterior helical threaded shank  14  to gain purchase in the cancellous bone through application of torque. A spherical head  16  is formed at the top of the helical threaded shank  14  which is constructed and arranged for bottom loading into a connector  19  formed from a clamp  20  positioned within compression ring  22 . A recess  24  is formed in the top of the bone screw anchor  12  to permit installation of the bone screw anchor into cancellous bone by rotation. A torque is applied to the bone screw anchor by the surgeon using a tool (not shown) that engages the recess  24  in the head  16  and rotates the screw about its longitudinal axis. The amount of torque is critical to installation and the long life of the prosthesis in that too little does not secure the screw from loosening or backing out, and too much causes the stripping of the thread path in the bone and loss of purchase. The surgeon attempts to apply the optimum torque when placing the screws in the bone and additional torque on the bone screw is to be avoided.  FIG. 1  illustrates an exploded view with the bone screw anchor  12  of head  16  exposed and available for receipt of the clamp  20  and compression ring  20 .  FIG. 2  illustrates the bone screw anchor  12  upon receipt of the clamp  20  and compression ring  22 , a rod slot  30  is available for receipt of a rod. As illustrated, a first position is formed wherein the clamp  20  is placed over the spherical ball  16  and is available for receipt of a rod into the rod slot  30 . The spherical ball  16  is frictionally engaged by a lower end of the clamp  20 , to be further explained later in this specification, providing a sufficient interference fit to maintain the rod slot  30  in a position that can be directed by the surgeon awaiting receipt of the rod.  FIG. 3  illustrates the bone screw anchor  12  in a vertical stance with a rod  32  placed within the rod slot  30  and the clamp  20  drawn into the compression ring  22 , locking the rod  32  in fixed position in relation to the bone screw anchor  12 .  FIG. 4  illustrates the bone screw anchor  12  in an angular stance with a rod  32  placed within the rod slot  30  and the clamp  20  drawn into the compression ring  22 , locking the rod  32  in fixed angular position in relation to the bone screw anchor  12 . The spherical head  16  of the bone screw anchor  12  provides polyaxial movement of the clamp  20  and compression ring  22 . During the spinal fixation, several bone screw anchors are threaded into the different vertebrae according to the anatomy of each vertebra. This results in a series of bone screw anchors without uniformity in angle or alignment. To compensate for these anomalies, the connection between the head of the screw anchors and the clamp bodies pivots or swivels to capture a connector rod.  FIGS. 3 and 4  illustrate how the screw anchors can be positioned in relation to the clamp bodies. Further, the low profile stance is illustrated wherein the upper edge  34  of the rod  32  is locked in a position wherein the clamp top or proximal surface  36  is in a similar plane as the compression ring top or proximal surface  38 . 
         [0035]    The clamp body  20 , illustrated in greater detail in  FIGS. 6 and 7 , is generally tubular comprising a proximal end  200  and a distal end  201 , the proximal end  200  defined by a U-shaped opening or rod slot  30  for receipt of a rod and the distal end  201  defining an annulus. The generally tubular arrangement of the clamp body  20  forms a receptacle section  42  at the distal end  201  and a rod slot  30  at the proximal end  200 . The receptacle is of a size to accommodate the head  16  of the bone screw anchor with a wall  40  formed by an outer wall surface  44  having a cylindrical shape and an inner wall surface  46  of a conical shape for capturing the head  16  upon insertion. A series of circumferential slots and relief slits are constructed and arranged to increase the radial flexibility of the wall  40  along the receptacle section  42  in response to the curvature of the compression ring  22 . The slot  30  has an upper longitudinal ridge  60  and a lower longitudinal ridge  62  to grip the connector rod  32 . In some embodiments the clamp  20  comprises a lip is formed along the lower edge of the receptacle section  42  outer wall surface  44 . The outer wall surface  44  of clamp  20  may be tapered or otherwise shaped to provide a change in external diameter along the length. 
         [0036]    The clamp body  20  further comprises a pin receiving slot  100  constructed and arranged to receive a pin  52 . During installation, the clamp  20  captures the head  16  of the shank and the pin  52  prevents movement of the installed bone screw. 
         [0037]    The compression ring  22  is force fit on the wall  40  of the clamp  20  by flexing the tubular walls. The compression ring  22  is movable along the outer surface wall  44  from an open position to a closed position. The open position, as shown in  FIG. 2 , allows swiveling movement of the bone screw anchor head  16  and sliding movement of the connector rod  32  within the clamp  20 . In the closed position, shown in  FIGS. 3 and 4 , the compression ring  22  applies compressive forces between the clamp  20  and the rod  32 , and between the clamp  20  and the bone screw anchor  12 . The compression ring  22  has a shaped inner surface  68  with a lower annular ridge  72  and an upper annular ridge which engages the annular bulge  76 , on the outer wall surface  44  of the clamp  20  in the closed position. In addition, the compression ring  22  includes an annular surface  78  formed along compression fingers  80  for engaging the upper bulge  82  formed along the outer side surface of the clamp in the closed position. The clamp  20  is preinstalled in the compression ring  22  and a pin  52  is placed within receptacle  56  of the compression ring  22  to maintain the clamp within the compression ring. The pin operates as an interference fit to prevent the clamp  20  from disengaging the compression ring  22  while the head  16  of the bone screw anchor is installed. 
         [0038]      FIGS. 11 to 14  illustrate the shank capture sequence.  FIG. 11  depicts the clamp body  20  assembled to the compression ring  22 . The clamp body  20  is shown making the initial contact with the spherical head  16 , the receptacle section  42  is available for receipt of the head  16 . The receptacle section  42  includes the wall  40  having a cylindrical shaped outer wall surface  44  that is enlarged along a length and expandable into an inner wall surface  90  of the compression ring  22 .  FIG. 12  depicts the clamp body capturing the head  16  at the maximum diameter of the head  16 , the clamp body being at its most expanded position. The series of circumferential slots and relief slits  48  increase the radial flexibility of the wall  40  along the receptacle section  42  in response to the curvature of the head  16  as it pushes apart the circumferential slots and relief slits  48  of the clamp body  20  into the inner wall surface  90  of the compression ring  22 .  FIG. 13  depicts the fully captured spherical head  16  by the clamp body  20 . The head  16  is shown within the receptacle section  42 , the wall  40  now encompasses the head  16  with the outer wall surface  44  restored to a biased position around the head  16 . The rod slot  30  is now available for positioning by the surgeon, the head  16  is in frictional contact with the clamp  20  wherein the clamp  20  can be placed in any angular position and held in position for receipt of a rod. Once a rod is inserted into the rod slot, the compression ring  22  is lifted up while the clamp  20  is pushed down to provide a low profile locked rod as illustrated in  FIGS. 3 and 4 . The pins  52  have moved into the pin shaft or passageway and prevent any further movement of the clamp. 
         [0039]      FIGS. 15 and 16  depict the clamp body  20  showing the pin retention slots  100 . The pin retention slots  100  comprise a pin receiving portion  101  constructed and arranged to receive a pin  52 . The pin receiving portion  101  is generally an open circle having an expansion slot  102  at the distal end of the pin receiving portion  101  and an opening  103  at the opposing end or apex of the pin receiving portion  101  to form a lip  104 . The lip  104  allows the uni-directional movement of the pin  52  past the lip  104  and into the shaft or passageway  105 . The shaft  105  comprises an expansion slot  106  at apex of the shaft or passageway, directly opposite and linearly disposed from the expansion slot  102  defined at the distal end  107  of the clamp  20 . The shaft or passageway can be of various lengths to allow variable positioning of the pin  52  during installation. These features and the movement of the pin  52  during installation of the assembly are shown in greater detail in  FIGS. 17, 18 and 19 .  FIG. 17  shows the pin  52  inserted into the pin receiving portion  101  of the pin retention slot  100 . In this position, the pin  52  has been inserted through the pin aperture  56  of the compression ring  22  and the pin receiving portion  101  of the clamp body  20 . In this position the head  16  is at the first or open position allowing for the insertion of the shank  12 , and the capturing of the head  16 . This position corresponds to a first or open position depicted in  FIG. 11 . As the clamp body  20  is pushed downwards to capture the head  16 , the clamp body  20  expands over the head  16  and the pin  52  moves upwards through the lip  104  as depicted in  FIG. 18 . Sufficient force is applied as the clamp  20  passes over the head  16  and the expansion slot  102  allows for flex of motion so that the pin  52  can pass through the lip  104 . As the head  16  is captured, the compression ring  22  applies compressive forces between the clamp  20  and the bone screw anchor  12 . Since the diameter of the lip portion  104  is now constricted in size, this prevents the pin  52  from re-entering the pin receiving portion  101  of the pin retention slot  100   m  as shown in  FIG. 19 . 
         [0040]    The application of the compressive force that immobilizes the components of the orthopedic device is generated by a linear movement of the compression ring relative to the exterior walls of the clamp. This movement to the closed position is accomplished using a simple telescoping instrument engaging the clamp  20  and the compression ring  22  so that equal and opposite forces move the ring without imparting stress to the anchored screw. The instrument includes an inwardly facing lip for engaging an outwardly projecting tab to pull up on the compression ring at the same time an insertion tap places an equal and opposite force onto the rod, forcing the clamp  20  into the compression ring  22  for locking the rod and bone screw anchor in position. In the event of remedial surgery, the clamp may be moved to the open position in the same manner. 
         [0041]    The instant invention provides an orthopedic kit for stabilizing bones. The kit comprises at least one bone screw having a first end constructed and arranged as a shank portion  13  for penetrating securement to a bone and a second end constructed and arranged as a head portion  16 . The connector  19  is used for securing a rod to a plurality of anchored bone screws, the connector  19  is formed from a clamp universally connected to the head portion  16  of each anchored bone screw  12  for securing the anchored bone screw to a rod  32 . The clamp  20  has an elongated body with an exterior wall  40  with a first annular bulge  76 , a pin retention slot  100 , and a rod slot  30  extending across the exterior wall constructed and arranged to slidably accept the rod  32 . A compression ring  22  surrounding the exterior wall of the clamp  20 , the compression ring linearly traversable along the exterior wall  40  between a first position and a second position by a force consisting of a linear force along a longitudinal axis of the clamp  20 ; the first position permitting adjustment of the rod as depicted in  FIGS. 2 and 13 , and the second position compressing the clamp  20  to immobilize the rod  32  with respect to the bone screw  12  as illustrated in  FIGS. 3, 4 and 14 . Traversal of the compression ring  22  from the first position to the second position causes the compression ring  22  to cooperate with the annular bulge  76  to apply compressive forces to the clamp  20  to immobilize the connections between the clamp  20  and the rod  32 , and the clamp  20  and the anchored bone screw  12 . The annular bulge  76  is positioned along a length of the exterior wall  40  of the clamp thereof to provide a change in the external diameter of the clamp; the annular bulge  76  constructed and arranged to cooperate with the compression ring  22  to apply compressive forces to the clamp  20  for immobilizing the connections between the clamp and the anchored bone screw head  16 . 
         [0042]    The exterior wall  40  of the clamp  20  includes a second bulge  82  to provide a change in the external diameter along the upper edge of the exterior wall. The annular bulge is constructed and arranged to cooperate with the compression ring  33  to apply compressive forces to the clamp  20  for immobilizing the connections between the clamp and the rod using ridges  60  and  62  for additional compressive force. 
         [0043]    The first bulge  76  is constructed and arranged to cooperate with a lower annular ridge  72  while the compression ring  22  is in the second position to immobilize the connection between the clamp  20  and the anchored bone screw head  16 . 
         [0044]    The clamp  20  further comprises at least one pin retention slot  100 . The pin retention slots  100  comprise a pin receiving portion  101  constructed and arranged to receive a pin  52 . The pin receiving portion  101  is generally an open circle having an expansion slot  102  at the distal end of the pin receiving portion  101  and an opening  103  at the opposing end or apex of the pin receiving portion  101  to form a lip  104 . The lip  104  allows the uni-directional movement of the pin  52  past the lip  104  and into the shaft or passageway  105 . The shaft  105  comprises an expansion slot  106  at apex of the shaft or passageway, directly opposite and linearly disposed from the expansion slot  102  defined at the distal end  107  of the clamp  20 . The shaft or passageway having varying lengths to allow variable positioning of the pin  52  during installation. 
         [0045]    A method is further disclosed of using the orthopedic device to stabilize bones across a discontinuity. The method comprises providing at least two bone screws  12  having a threaded shaft  14  and a spherical head  16 ; anchoring the bone screws  12  into a bone by rotation of each screw  12  into the bone; providing a connector having a clamp body  20  and a compression ring  22 . The clamp body  20  has a spherical head receptacle  42  at one end and a rod slot  30  at an opposing end, the receptacle sized to accommodate the head of the bone screw  16 . The compression ring  22  has an interior wall  68  movable along an exterior wall  44  of the clamp body  20  between an open position and a closed position. The compression ring also includes an annular flange  84  at the upper edge thereof and an aperture  56  for receipt of a pin, the pin aperture  56  situated in alignment with the pin receiving slot  101  of the clamp  20 . The open position is defined when the compression ring  22  is adjacent to the receptacle  42  such that the bone screw  12  is pivotable relative to the clamp body  20 . A rod member slot  30  is placed whereby the rod member extends across a discontinuity; and repositioning the compression ring from its open position to its closed position by applying a linear force along the longitudinal centerline of the clamp  20  for traversing the compression ring  22  to a closed position along the exterior wall  44  of the clamp member  20  to compress the clamp member and prevent the pin  56  from moving. This motion substantially fixes the clamp member  20  and the rod member in a predetermined orientation with respect to the anchored bone screw  12  whereby the bones in a subject are stabilized across the discontinuity. 
         [0046]    The method also includes providing bone screws  12  with an external helical thread  13 , applying torque to the threaded bone screws for anchoring into bone, and moving the compression ring linearly by application of equal and opposite forces. 
         [0047]    Detailed embodiments of the instant invention are disclosed herein, however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific functional and structural details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representation basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
         [0048]    All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein. 
         [0049]    One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims. 
         [0050]    As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. 
         [0051]    As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0052]    For purposes of this disclosure, “proximal” refers to the end closer to the device operator during use, and “distal” refers to the end farther from the device operator during use.