Abstract:
Provided is a spinal fixation system that includes a pedicle screw having a bone engagement thread at a first end of the pedicle screw and an intermediate shaft portion located between the bone engagement thread and a second end of the pedicle screw and having a substantially conical shaped flange. The system also includes a clamp that fits over the second end of the pedicle screw, a fixation rod that can be secured between the clamp and an external side of the pedicle screw, and a fastener that can be coupled to the second end of the pedicle screw. Coupling of the fastener to the second end of the pedicle screw provides a clamping force that presses the fixation rod against the intermediate shaft portion of the pedicle screw.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/622,174 filed on Oct. 26, 2004, entitled “Internal Fixation System.” 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an apparatus and method for performing spine surgery and more particularly to an internal fixation system for minimally invasive and open spine surgery and a method for using the internal fixation system for spine surgery. 
         [0003]    Referring to prior art  FIGS. 1A and 1B , the spine  120 , also known as the vertebral column or the spinal column, is a flexible column of vertebrae  100  (special types of bones) held together by muscles, ligaments and tendons. The spine  120  extends from the cranium (not shown) to the coccyx  126 , encasing a spinal cord  128  and forming the supporting axis of the body (not shown). The spinal cord  128  is a thick bundle of nerve tissue (nerves) that branch off to various areas of the body for the purposes of motor control, sensation, and the like. The spine  120  includes seven cervical vertebrae (not shown), twelve thoracic vertebrae (not shown), five lumbar vertebrae, L I -L V , five sacral vertebrae, S I -S V , and three coccyx vertebrae  126 . The sacral and coccyx vertebrae are each fused, thereby functioning as a single unit.  FIG. 1B  shows the lumbar region  122 , the sacral region  124  and the coccyx  126  of the spine  120  and that the vertebrae  100  are stacked one upon another. The top portion  100   a  and bottom portion  100   b  of each vertebrae  100  is slightly concave. The opposing concave vertebral surfaces form the intervertebral space  121  in which an intervertebral disk (not shown) resides. Each of the intervertebral disks has a soft core referred to as a nucleus pulposus or nucleus (not shown). 
         [0004]    In  FIG. 1A , directional arrow  101   a  is pointing in the posterior direction and directional arrow  101   b  is pointing in the anterior direction.  FIG. 1A  shows that each vertebrae  100  includes a body  106  in the innermost portion, a spinal canal  108  and a spinous process  102  at the posterior-most end of the vertebra  100 . The vertebrae  100  are substantially similar in composition, but vary in size from the larger lumbar to the smallest coccyx vertebrae  126 . Each vertebrae  100  further includes two transverse processes  104  located on either side and a protective plate-like structure referred to as a lamina  110 . Nerves from the spinal cord  128  pass through the spinal canal  108  and foramina  111  to reach their respective destinations within the body. 
         [0005]    After spine surgery, adjacent vertebrae  100  may require a fixation system to be clamped to the side where the surgeon accessed the vertebrae  100 . The typical fixation system includes installing pedicle screws in each vertebra  100  and securing a rigid plate or rod to the screws. The presently available systems are difficult to install through very small portals or working channels, e.g., a working channel less than one inch in diameter. 
         [0006]    It is desirable to provide an internal fixation system for minimally invasive spine surgery and a method for using the internal fixation system. It is desirable to provide an internal fixation system for securing adjacent vertebrae that includes a fixation rod having mounting members at each end. It is desirable to provide an internal fixation system for securing adjacent vertebrae that includes a fixation rod which deviates medially and dorsally. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    Briefly stated, the present invention comprises an internal fixation rod for spine surgery that includes an elongate body, a first rod end, a second rod end, a first mounting member and a second mounting member. The first mounting member is disposed proximate the first rod end, and the second mounting member is disposed proximate the second rod end. The first mounting member and the second mounting member are smaller in cross-section than the elongate body. 
         [0008]    The present invention further comprises an internal fixation system for spinal surgery that includes two pedicle screws, two locking nuts and a fixation rod. Each of the pedicle screws has a bone-mating thread at a first end and a mating thread at a second end. Each of the locking nuts has a mating thread configured to mate with the mating thread of each of the pedicle screws. The fixation rod includes an elongate body, a first rod end, a second rod end, a first mounting member and a second mounting member. The first mounting member is disposed proximate the first rod end, and the second mounting member is disposed proximate the second rod end. The first mounting member and the second mounting member are smaller in cross-section than the elongate body. The first mounting member is mounted over one of the pedicle screws and secured by one of the locking nuts and the second mounting member is mounted over the other one of the pedicle screws and secured by the other one of the locking nuts. 
         [0009]    The present invention further comprises a method of securing adjacent vertebrae. The method includes accessing a first vertebra and a second vertebra of a spine. An internal fixation rod is mounted to the first vertebra and the second vertebra. The internal fixation rod includes an elongate body, a first rod end, a second rod end, a first mounting member and a second mounting member. The first mounting member is disposed proximate the first rod end, and the second mounting member is disposed proximate the second rod end. The first mounting member and the second mounting member are smaller in cross-section than the elongate body. 
         [0010]    The present invention also comprises a method of installing an internal fixation system for securing adjacent vertebrae. The method includes making an incision between about 10 millimeters (mm) and about 100 mm in span in a posterior region of a patient proximate a first vertebra and a second vertebra of a spine of the patient. A distal end of a working channel is inserted adjacent the first vertebra and the second vertebra of the spine accessible through the incision. The first vertebra and the second vertebra of the spine are accessed through the working channel. The internal fixation system is mounted to the first vertebra and the second vertebra. The internal fixation system includes a fixation rod. The fixation rod includes an elongate body, a first rod end, a second rod end, a first mounting member and a second mounting member. The first mounting member is disposed proximate the first rod end, and the second mounting member is disposed proximate the second rod end. The first mounting member and the second mounting member are smaller in cross-section than the elongate body. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
           [0012]    In the drawings: 
           [0013]      FIG. 1A  is a top sectional view of a human vertebrae as is known in the art; 
           [0014]      FIG. 1B  is a side sectional view of the lumbar and sacral regions of a human spine as in known in the art; 
           [0015]      FIG. 2  is a perspective view of an internal fixation rod for minimally invasive and open spine surgery in accordance with a first preferred embodiment of the present invention; 
           [0016]      FIG. 3  is a perspective view of an internal fixation rod for minimally invasive and open spine surgery in accordance with a second preferred embodiment of the present invention; 
           [0017]      FIG. 4  is a front elevational view of a first internal fixation clamp in accordance with the preferred embodiments; 
           [0018]      FIG. 5  is a rear elevational view of the first internal fixation clamp of  FIG. 4 ; 
           [0019]      FIG. 6  a top view of the first internal fixation clamp of  FIG. 4 ; 
           [0020]      FIG. 7  is a partial perspective view of the fixation rod of  FIG. 2  mounted on a mating portion of a pedicle screw with the fixation clamp of  FIG. 4  mounted on top thereof; 
           [0021]      FIG. 8  is a perspective view of an internal fixation rod for minimally invasive and open spine surgery in accordance with a third preferred embodiment of the present invention; 
           [0022]      FIG. 9  is a perspective view of an internal fixation rod mounted to adjacent vertebrae of a spine using pedicle screws, fixation clamps and locking nuts, together forming an internal fixation system in accordance with the various preferred embodiments the present invention; 
           [0023]      FIG. 10  is a perspective view of a plurality of internal fixation rods mounted to a plurality of adjacent vertebrae of a spine using pedicle screws, fixation clamps and locking nuts, together forming an internal fixation system in accordance with the various preferred embodiments the present invention; 
           [0024]      FIG. 11A  is a side elevational view of a locking nut for use with the preferred embodiments of the present invention; 
           [0025]      FIG. 11B  is a bottom plan view of the locking nut of  FIG. 11A ; 
           [0026]      FIG. 12A  is a side elevational view of a first pedicle screw for use with the preferred embodiments of the present invention; 
           [0027]      FIG. 12B  is a top plan view of the first pedicle screw of  FIG. 12A ; 
           [0028]      FIG. 13A  is a side elevational view of a second pedicle screw for use with the preferred embodiments of the present invention; 
           [0029]      FIG. 13B  is a top plan view of the second pedicle screw of  FIG. 13A ; 
           [0030]      FIG. 14A  is a side elevational view of a third pedicle screw for use with the preferred embodiments of the present invention; 
           [0031]      FIG. 14B  is a top plan view of the third pedicle screw of  FIG. 14A ; 
           [0032]      FIG. 15A  is a side elevational view of a fourth pedicle screw for use with the preferred embodiments of the present invention; 
           [0033]      FIG. 15B  is a top plan view of the fourth pedicle screw of  FIG. 15A ; 
           [0034]      FIG. 16A  is a side elevational view of a fifth pedicle screw for use with the preferred embodiments of the present invention; 
           [0035]      FIG. 16B  is a top plan view of the fifth pedicle screw of  FIG. 16A ; 
           [0036]      FIG. 17A  is a side elevational view of a sixth pedicle screw for use with the preferred embodiments of the present invention; 
           [0037]      FIG. 17B  is a top plan view of the sixth pedicle screw of  FIG. 17A ; 
           [0038]      FIG. 18  is a side elevational view of a second fixation clamp mounted on a pedicle screw in accordance with the preferred embodiments of the present invention; 
           [0039]      FIG. 19  is a top perspective view of the fixation clamp of  FIG. 18 ; and 
           [0040]      FIG. 20  is a perspective view of a working channel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower”, and “upper” designate directions in the drawing to which reference is made. The words “inwardly” and “outwardly” refer direction toward and away from, respectively, the geometric center of the object described and designated parts thereof. The terminology includes the words above specifically mentioned, derivatives thereof and words of similar import. Additionally, the word “a”, as used in the claims and in the corresponding portions of the specification, means “at least one.” 
         [0042]    Referring to the drawings in detail, wherein like reference numerals indicate like elements throughout,  FIG. 2  shows an internal fixation rod  22  for minimally invasive and open spine surgery in accordance with a first preferred embodiment of the present invention. The fixation rod  22  is an internally-mounted device, with respect to a patient, for fixing two or more adjacent vertebrae  100  after a surgical procedure such as installing a fusion cage (not shown) or the like. 
         [0043]    The internal fixation rod  22  has an elongate body  23 , a first rod end  22   a , a second rod end  22   b , a first mounting member  22   c  disposed proximate the first rod end  22   a  and a second mounting member  22   d  disposed proximate the second rod end  22   b . The fixation rod  22  is about 2-5 centimeters (cm) long, but the fixation rod  22  may vary in length depending on the size and shape of the patient. The elongate body  23  of the fixation rod  22  has a diameter or cross-sectional dimension RDI of about 4-7 mm, but need not have a circular cross-section. The mounting members  22   c ,  22   d  each have a diameter or cross-sectional dimension MDI of about 0.1-2 mm, but need not have a circular cross-section. Thus, the first and second mounting members  22   c ,  22   d  each have a cross-sectional dimension M D1  that is smaller than the cross-sectional dimension R D1  of the elongate body  23  of the fixation rod  22 . Preferably, the elongate body  23  and the first and second mounting members  22   c ,  22   d  are rounded or chamfered. The fixation rod  22  is preferably configured for minimally invasive spine surgery. But, the fixation rod  22  may also be used in conventional open surgery. 
         [0044]    Each rod end  22   a ,  22   b  is configured to be mounted to an exposed portion of a pedicle screw  50  as shown in  FIG. 7 . The first and second mounting members  22   c ,  22   d  are preferably smaller in cross-sectional dimension than the main elongate body  23  of the fixation rod  22  permitting the fixation rod  22  to tilt freely at nearly any angle during installation. The first and second mounting members  22   c ,  22   d  preferably connect to the elongate body  23  of the fixation rod  22  at two places in order to form a loop or eyelet  24 ,  26 , respectively. The first and second mounting members  22   c ,  22   d  may be mounted on either a concave side of the elongate body  23  of the curved rod  22  (shown in solid in  FIG. 2 ) or convex side of the curved rod  22  (shown in phantom in  FIG. 2 ). Alternately, the fixation rod  22  is generally straight and the first and second mounting members  22   c ,  22   d  may be mounted on any side of elongate body  23  of the internal fixation rod  22 . 
         [0045]    The first and second mounting members  22   c ,  22   d  are generally only structurally relied upon during installation of the internal fixation rod  22  to hold the respective first and second rod ends  22   a ,  22   b  to a pedicle screw  50  ( FIGS. 12A-12B ) before a surgeon fixes the respective first and second rod ends  22   a ,  22   b.    
         [0046]    Alternately, the first and second mounting members  22   c ,  22   d  can be a thin wire or cable because they are only structurally relied upon during installation of the internal fixation rod  22  to hold the respective first and second rod ends  22   a ,  22   b  to a pedicle screw  50  before a surgeon fixes the respective first and second rod ends  22   a ,  22   b . The surgeon sets the internal fixation rod  22  on a fixed (nonmoving) screw  50 , and the internal fixation rod  22  takes a particular tilt to accommodate the particular installation, then the surgeon fixes the respective first and second rod ends  22   a ,  22   b.    
         [0047]    Preferably, the internal fixation rod  22  deviates medially and dorsally between the first rod end  22   a  and the second rod end  22   b . The fixation rod  22  deviates medially and dorsally to ease installation or adjustment of material or devices through the foramen  104  between adjacent vertebrae  100 . Preferably, the deviation of the fixation rod  22  is generally arcuate, and a dorsal side of the fixation rod  22  is generally convex. 
         [0048]      FIG. 3  shows an internal fixation rod  32  for minimally invasive and open spine surgery in accordance with a second preferred embodiment of the present invention. The fixation rod  32  is substantially similar to the fixation rod  22  of the first preferred embodiment. The fixation rod  32  has an elongate body  33 , a first rod end  32   a , a second rod end  32   b , a first mounting member  32   c  disposed proximate the first rod end  32   a  and a second mounting member  32   d  disposed proximate the second rod end  32   b . The first and second mounting members  32   c ,  32   d  are open-ended (i.e., only connect to the fixation rod  32  at a single point each), thereby forming a generally Y-shape or U-shape defining openings  34 ,  36 , respectively, at each of the rod ends  32   a ,  32   b.    
         [0049]    The fixation rod  32  is about 2-5 cm long, but the fixation rod  32  may vary in length depending on the size and shape of the patient. The elongate body  33  of the fixation rod  32  has a diameter or cross-sectional dimension R D2  of about 4-7 mm, but need not have a circular cross-section. The mounting members  32   c ,  32   d  each have a diameter or cross-sectional dimension M D2  of about 0.1-2 mm, but need not have a circular cross-section. Thus, the first and second mounting members  32   c ,  32   d  each have a cross-sectional dimension M D2  that is smaller than the cross-sectional dimension R D2  of the elongate body  33  of the fixation rod  32 . Preferably, the elongate body  33  and the first and second mounting members  32   c ,  32   d  are rounded or chamfered. Each end  32   a ,  32   b  is mounted to an exposed portion of a pedicle screw  50 , similar to the fixation rod  22  that is shown in  FIG. 7 . The first and second mounting members  32   c ,  32   d  are preferably smaller in cross-sectional dimension than the main body of the fixation rod  32  permitting the fixation rod  32  to tilt freely at any nearly angle during installation. The first and second mounting members  32   c ,  32   d  may be mounted on either a concave side of the curved rod  32  (shown in solid in  FIG. 3 ) or a convex side of the curved rod  32  (shown in phantom in  FIG. 3 ). Alternately, the fixation rod  32  is generally straight and the first and second mounting members  32   c ,  32   d  may be mounted on any side of the elongate body  33  of the internal fixation rod  32 . 
         [0050]    The first and second mounting members  32   c ,  32   d  are generally only structurally relied upon during installation of the internal fixation rod  32  to hold the respective first and second rod ends  32   a ,  32   b  to a pedicle screw  50  ( FIGS. 12A-12B ) before a surgeon fixes the respective first and second rod ends  32   a ,  32   b.    
         [0051]    Preferably, the fixation rod  32  deviates medially and dorsally between the first rod end  32   a  and the second rod end  32   b . The fixation rod  32  deviates medially and dorsally to ease installation or adjustment of material or devices through the foramen  104  between adjacent vertebrae  100 . Preferably, the deviation of the fixation rod  32  is generally arcuate, and a dorsal side of the fixation rod  32  is generally convex. 
         [0052]      FIG. 8  shows an internal fixation rod  42  for minimally invasive and open spine surgery in accordance with a third preferred embodiment of the present invention. The fixation rod  42  is substantially similar to the fixation rod  32  of the second preferred embodiment. The fixation rod  42  has an elongate body  43 , a first rod end  42   a , a second rod end  42   b , a first mounting member  42   c  disposed proximate the first rod end  42   a  and a second mounting member  42   d  disposed proximate the second rod end  42   b . The first and second mounting members  42   c ,  42   d  are open-ended (i.e., only connect to the fixation rod  42  at a single point), thereby forming a generally Y-shape or U-shape at each end  42   a ,  42   b  defining openings  44 ,  46 , respectively, at each of the rod ends  42   a ,  42   b.    
         [0053]    The fixation rod  42  is about 2-5 cm long, but the fixation rod  42  may vary in length depending on the size and shape of the patient. The elongate body  43  of the fixation rod  42  has a diameter or cross-sectional dimension R D3  of about 4-7 mm, but need not have a circular cross-section. The mounting members  42   c ,  42   d  each have a diameter or cross-sectional dimension M D3  of about 0.1-2 mm, but need not have a circular cross-section. Thus, the first and second mounting members  42   c ,  42   d  each have a cross-sectional dimension M D3  that is smaller than the cross-sectional dimension R D3  of the elongate body  43  of the fixation rod  42 . Preferably, the elongate body  43  and the first and second mounting members  42   c ,  42   d  are rounded or chamfered. Each end  42   a ,  42   b  is mounted to an exposed portion of a pedicle screw  50  ( FIG. 9 ). The first and second mounting members  42   c ,  42   d  are preferably smaller in cross-sectional dimension M D3  than the main body of the fixation rod  42  permitting the fixation rod  42  to tilt freely at nearly any angle during installation. The first and second mounting members  42   c ,  42   d  may be mounted on either a concave side of the curved rod  42  (not shown) or a convex side of the curved rod  42  (shown in solid in  FIG. 8 ). Alternately, the fixation rod  42  is generally straight and the first and second mounting members  42   c ,  42   d  may be mounted on any side of the internal fixation rod  42 . 
         [0054]    The first and second mounting members  42   c ,  42   d  are generally only structurally relied upon during installation of the internal fixation rod  42  to hold the respective first and second rod ends  42   a ,  42   b  to a pedicle screw  50  ( FIGS. 12A-12B ) before a surgeon fixes the respective first and second rod ends  42   a ,  42   b.    
         [0055]    Preferably, the fixation rod  42  deviates medially and dorsally between the first rod end  42   a  and the second rod end  42   b . The fixation rod  42  deviates medially and dorsally to ease installation or adjustment of material or devices through the foramen  104  between adjacent vertebrae  100 . Preferably, the deviation of the fixation rod  42  is generally arcuate, and a dorsal side of the fixation rod  42  is generally convex. 
         [0056]    The internal fixation rod  22 ,  32 ,  42  can be formed of a rigid material such as a metal, composite or polymeric material. The internal fixation rod  22 ,  32 ,  42  can also be formed of a flexible or resilient material such as a flexible metal, a flexible metal composite, a flexible carbon-fiber composite or a flexible or resilient polymeric material. The internal fixation rod  22 ,  32 ,  42  can also be formed of combinations thereof. 
         [0057]    Optionally, a central portion of the elongate body  23 ,  33 ,  43  of the fixation rod  22 ,  32 ,  42  may be substituted with a flexible material, a resilient material or any other structure allowing motion such as a spring, a cord, a dynamic stabilization device, an artificial facet or the like, without departing from the invention. 
         [0058]      FIGS. 12A-12B  show a first pedicle screw  50  for use with the preferred embodiments of the present invention. The first pedicle screw  50  has a bone-mating thread  50   b  at a first end  50   c , a first mating thread  50   a  at a second end  50   d  and a longitudinal axis L defined between the first end  50   c  and the second end  50   d . Generally, the pedicle screw  50  is one solid piece with the bone thread or bone-mating thread  50   b  machined, cast or tapped at the distal portion, and a machine or other mating thread  50   a  machined, cast or tapped at a proximal portion. But, the pedicle screw  50  may include multiple pieces that are assembled or welded together. The first mating thread  50   a  is configured to receive a locking nut  55  ( FIGS. 11A-11B ). The length of the pedicle screw  50  varies depending on the size and shape of the patient, but typically, the pedicle screw is about 5-8 cm in overall length. Likewise, the mating thread portion  50   a  varies in length depending on how many vertebrae  100  are being fused (i.e., permitting stacking as shown in  FIG. 10 ) and/or if there is need to correct alignment of adjacent vertebrae  100  (e.g., anterolistheis or retrolisthesis). For example, the degree of ventral-dorsal displacement of adjacent vertebrae  100  and/or misalignment of adjacent vertebrae  100  with respect to one another may require a longer mating thread portion  50   a . The pedicle screw  50  includes a domed or spherical intermediate-portion  52  which functions both as a mechanical stop when screwing the pedicle screw  50  into a patient&#39;s vertebra  100  and as a mounting base for receiving the ends  22   a ,  22   b  of the fixation rod  22  (see  FIG. 9  for example). The expanded diameter at, for example, domed portion  54  allows the rod  22 ,  32 ,  42  to tilt as necessary during installation. The tilting is to minimize or eliminate metal-metal, material-material, metal-bone, material-bone interface stress that would otherwise be caused during the fastening/securing. Optionally, the intermediate shaft  52  includes a smooth portion  53  of about the same or slightly larger diameter as the first mating thread  50   a.    
         [0059]      FIGS. 13A-13B  show a second pedicle screw  250  for use with the preferred embodiments of the present invention. The second pedicle screw  250  is similar in size, shape and material of construction as the first pedicle screw  50 . The second pedicle screw  250  has a bone-mating thread  250   b  at a first end  250   c , a first mating thread  250   a  at a second end  250   d  and a longitudinal axis L defined between the first end  250   c  and the second end  250   d . The pedicle screw  250  has an intermediate shaft  252  disposed between the bone-mating thread  250   b  and the first mating thread  250   a . The intermediate shaft  252  includes an upper surface  254  that is generally sloped downwardly and outwardly from the first mating thread and a lower surface  256  that extends generally radially outwardly from the longitudinal axis L of the pedicle screw  250 . The expanded diameter at, for example, sloped upper surface  254  allows the rod  22 ,  32 ,  42  to tilt as necessary during installation, and the generally flat lower surface  256  provides a stopping function during installation with less chance of bone fracture than a rounded lower surface such as the intermediate section  52  of the first pedicle screw  50 . The tilting is to minimize or eliminate metal-metal, material-material, metal-bone, material-bone interface stress that would otherwise be caused during the fastening/securing. Optionally, the intermediate shaft  252  includes a smooth portion  253  of about the same or slightly larger diameter as the first mating thread  250   a.    
         [0060]      FIGS. 14A-14B  depict a third pedicle screw  350  for use with the preferred embodiments of the present invention. The third pedicle screw  350  is similar in size, shape and material of construction as the first pedicle screw  50 . The third pedicle screw  350  has a bone-mating thread  350   b  at a first end  350   c , a first mating thread  350   a  at a second end  350   d  and a longitudinal axis L defined between the first end  350   c  and the second end  350   d . The third pedicle screw  350  has an intermediate shaft  352  disposed between the bone-mating thread  350   b  and the first mating thread  350   a . The intermediate shaft  352  includes an upper surface  354  that extends generally radially outwardly from the longitudinal axis L of the pedicle screw  350  and a lower surface  356  that extends generally radially outwardly from the longitudinal axis L of the pedicle screw  350 . The generally flat lower surface  356  provides a stopping function during installation with less chance of bone fracture than a rounded lower surface such as the intermediate section  52  of the first pedicle screw  50 . Optionally, the upper surface  354  may be slightly chamfered or rounded to allow the rod  22 ,  32 ,  42  to tilt as necessary during installation. Optionally, the intermediate shaft  352  includes a smooth portion  353  of about the same or slightly larger diameter as the first mating thread  350   a.    
         [0061]      FIGS. 15A-15B  show a fourth pedicle screw  450  for use with the preferred embodiments of the present invention. The fourth pedicle screw  450  is similar in size, shape and material of construction as the first pedicle screw  50 . The fourth pedicle screw  450  has a bone-mating thread  450   b  at a first end  450   c , a first mating thread  450   a  at a second end  450   d  and a longitudinal axis L defined between the first end  450   c  and the second end  450   d . The fourth pedicle screw  450  has an intermediate shaft  452  disposed between the bone-mating thread  450   b  and the first mating thread  450   a . The intermediate shaft  452  includes a plurality of protuberances  454  disposed around a circumference of the intermediate shaft  452 . The protuberances  454  may be hemi-spherical, sloped, partially rounded or the like. The expanded diameter at, for example, the protuberances  454  allows the rod  22 ,  32 ,  42  to tilt as necessary during installation. The tilting is to minimize or eliminate metal-metal, material-material, metal-bone, material-bone interface stress that would otherwise be caused during the fastening/securing. Optionally, the intermediate shaft  452  includes a smooth portion  453  of about the same or slightly larger diameter as the first mating thread  450   a.    
         [0062]      FIGS. 16A-16B  depict a fifth pedicle screw  550  for use with the preferred embodiments of the present invention. The fifth pedicle screw  550  is similar in size, shape and material of construction as the first pedicle screw  50 . The fifth pedicle screw  550  has a bone-mating thread  550   b  at a first end  550   c , a first mating thread  550   a  at a second end  550   d  and a longitudinal axis L defined between the first end  550   c  and the second end  550   d . The fifth pedicle screw  550  has an intermediate shaft  552  disposed between the bone-mating thread  550   b  and the first mating thread  550   a . The intermediate shaft  552  includes an upper surface  554  that extends generally radially outwardly from the longitudinal axis L of the pedicle screw  550  and a lower surface  556  that extends generally radially outwardly from the longitudinal axis L of each pedicle screw  550 . The expanded diameter at, for example, rounded hemi-spherical like surface  554  allows the rod  22 ,  32 ,  42  to tilt as necessary during installation, and the generally flat lower surface  556  provides a stopping function during installation with less chance of bone fracture than a rounded lower surface such as the intermediate section  52  of the first pedicle screw  50 . The tilting is to minimize or eliminate metal-metal, material-material, metal-bone, material-bone interface stress that would otherwise be caused during the fastening/securing. Optionally, the intermediate shaft  552  includes a smooth portion  553  of about the same or slightly larger diameter as the first mating thread  550   a.    
         [0063]      FIGS. 17A-17B  show a sixth pedicle screw  650  for use with the preferred embodiments of the present invention. The sixth pedicle screw  650  is similar in size, shape and material of construction as the first pedicle screw  50 . The sixth pedicle screw  650  has a bone-mating thread  650   b  at a first end  650   c , a first mating thread  650   a  at a second end  650   d  and a longitudinal axis L defined between the first end  650   c  and the second end  650   d . The sixth pedicle screw  650  has an intermediate shaft  652  disposed between the bone-mating thread  650   b  and the first mating thread  650   a . The intermediate shaft  652  includes a protuberance  654 . The protuberance  654  has a width P W  that is at least half the diameter or cross-sectional dimension R D1 , R D2 , R D3  of the fixation rod  22 ,  32 ,  42 . The protuberance  654  may be hemi-spherical, sloped, partially rounded or the like. The expanded diameter at, for example, the protuberance  654  allows the rod  22 ,  32 ,  42  to tilt as necessary during installation. The tilting is to minimize or eliminate metal-metal, material-material, metal-bone, material-bone interface stress that would otherwise be caused during the fastening/securing. Optionally, there may be two to four protuberances  654  (phantom in  FIG. 17B ). By using one to four protuberances  654 , the field of view beyond the protuberances  654  is improved over a solid circumferential structure such as intermediate portion  54 . Optionally, the intermediate shaft  652  includes a smooth portion  653  of about the same or slightly larger diameter as the first mating thread  650   a.    
         [0064]    Optionally, each of the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  may include a grip portion such as a hexagonal or dihexagonal grip for tightening using a nut driver (not shown) or wrench (not shown). Optionally, each of the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  may include a slot(s) (not shown) at the proximal end  50   d ,  250   d ,  350   d ,  450   d ,  550   d ,  650   d  for installing using a screw driver (not shown), hex-wrench (not shown) Torx-wrench (not shown) or the like. Torx is a Registered Trademark of Camcar Div. of Textron Inc., Providence, Road Island. 
         [0065]    Preferably, the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  are formed of a biocompatible material such as stainless steel, titanium, nickel plated metal, any biocompatible metal or alloy, a biocompatible ceramic, a biocompatible polymeric material or the like. 
         [0066]      FIGS. 11A-11B  show a locking nut  55  for use with the preferred embodiments of the present invention. The locking nut has a grip portion  55   a  such as a hexagonal or dihexagonal grip for tightening using a nut driver or wrench. The locking nut  55  further includes a shaped upper surface  55   c  and a stem portion  55   b  which protects the first mating threads  50   a  of a first pedicle screw  50  when a second or additional fixation rod  22  is mounted on top of the locking nut  55 . The shaped upper surface  55   c  of locking nut  55  preferably has a shape similar to the intermediate shaft  52 ,  252 ,  352 ,  452 ,  552 ,  652  of the respective pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  to provide a similar installation surface for the next level during multi-level/multi-rod installations (see e.g.,  FIG. 10 ). Two adjacent vertebrae  100  would require a single level of fixation (see e.g.,  FIG. 9 ), while three adjacent vertebrae  100  would require two levels of fixation with a common screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  shared between two-levels (see e.g.,  FIG. 10 ) and so on. Such a shaped locking nut  55  allows for one or more additional fixation rods  22  to be mounted on the mating thread portion  50   a  of the same pedicle screw  50 . 
         [0067]      FIGS. 4-6  are views of a first internal fixation clamp  58 . The first internal fixation clamp  58  is placed over the mating thread portion  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of the pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  after the fixation rod ends  22   a ,  32   a ,  42   a ,  22   b ,  32   b ,  42   b  are placed over the mating thread portion  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a . The first internal fixation clamp  58  has two angled projections  58   a  on the side which will face the rod  22 ,  32 ,  42  during installation to function as a clamp forcing the fixation rod  22 ,  32 ,  42  against the dome  54  of the first pedicle screw  50 ; the upper surface  254 ,  354 ,  554  of the second, third or fourth pedicle screws  250 ,  350 ,  550 ; against the protuberances  454 ,  654  of the fourth or sixth pedicle screws  450 ,  650 ; or against the shaped upper surface  55   c  of a locking nut  55  (in a multi-rod installation). The top of the clamp  58  has a dome shape with an ovoid or slotted opening  58   b  for receiving the mating thread portion  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of the pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650 . The length of the slotted opening  58   b  permits the internal fixation rod  22 ,  32 ,  42  to tilt on the intermediate shaft  52 ,  252 ,  352 ,  452 ,  552 ,  652  of the pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  during installation in order to accommodate variable angles for differing configurations and body types. 
         [0068]    Optionally, the first internal fixation clamp  58  may simply be a washer, a lock washer or a washer with a protuberance on its lower surface. Additional mounting hardware may also be utilized with or without the first internal fixation clamp  58  such as washers, lock washers or the like. 
         [0069]      FIGS. 18-19  show a second internal fixation clamp  59 . The second internal fixation clamp  59  is placed over the mating thread portion  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of the pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  after the fixation rod ends  22   a ,  32   a ,  42   a ,  22   b ,  32   b ,  42   b  are placed over the mating thread portion  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a . The second internal fixation clamp  59  has an angled projection  59   a  on the side which will face the rod  22 ,  32 ,  42  during installation to function as a clamp forcing the fixation rod  22 ,  32 ,  42  against the dome  54  of the first pedicle screw  50 ; the upper surface  254 ,  354 ,  554  of the second, third or fourth pedicle screws  250 ,  350 ,  550 ; against the protuberances  454 ,  654  of the fourth or sixth pedicle screws  450 ,  650 ; or against the shaped upper surface  55   c  of a locking nut  55  (in a multi-rod installation). The top of the second internal fixation clamp  59  has a relatively flat shape with an opening  59   b  for receiving the mating thread portion  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of the pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650 . The single projection  59   a  permits the internal fixation rod  22 ,  32 ,  42  to tilt on the intermediate shaft  52 ,  252 ,  352 ,  452 ,  552 ,  652  of the pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  during installation in order to accommodate variable angles for differing configurations and body types. 
         [0070]    Optionally, the second internal fixation clamp  59  may simply be a washer, a lock washer or a washer with a protuberance on its lower surface. Additional mounting hardware may also be utilized with or without the second internal fixation clamp  59  such as washers, lock washers or the like. 
         [0071]    The open ended U-shape or Y-shape of the rods  32 ,  42  or the closed-loop shape of rod  22  may be applied to any small plate or rod to ease installation on a pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  without departing from the present invention. 
         [0072]      FIG. 9  shows an internal fixation system  20 ,  30 ,  40  in accordance with the various preferred embodiments the present invention. The an internal fixation system  20 ,  30 ,  40  includes an internal fixation rod  22 ,  32 ,  42  mounted to adjacent vertebrae  100  of a spine  120  using pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650 , fixation clamps  58 ,  59  and locking nuts  55 .  FIG. 10  shows the internal fixation system  20 ,  30 ,  40  in accordance with the various preferred embodiments the present invention with a plurality of internal fixation rods  22 ,  32 ,  42  mounted to a plurality of adjacent vertebrae  100  of a spine  120 . 
         [0073]    The internal fixation systems  20 ,  30 ,  40  are mounted completely within the human body, and therefore, all of the various components of the internal fixation systems  20 ,  30 ,  40  are formed of or coated with a biologically compatible material such as stainless steel, titanium, nickel plated metal, any biocompatible metal or alloy, a biocompatible ceramic, a biocompatible polymeric material or the like. 
         [0074]    The fixation system  20 ,  30 ,  40  is preferably used in outpatient spine surgery. For example, a surgeon makes an incision between about 10 mm and about 100 mm in span in a posterior region of a patient proximate a first vertebra  100  and a second vertebra  100  of a spine  120  of the patient. The incision is preferably off-center with respect to the posterior-side of the spine  120  of the patient and proximate to the foraminae  104  of the first and second vertebrae  100 . The surgeon inserts a distal end  80   a  of the working tube or channel  80  ( FIG. 20 ) proximate the first vertebra  100  and the second vertebra  100  of the spine  120  accessible through the incision. The working channel  80  permits the surgeon to access the first vertebra  100  and the second vertebra  100  of the spine  120  from a proximal end  80   b  of the working channel  80 . The surgeon then mounts the internal fixation system  20 ,  30 ,  40  for securing adjacent vertebrae  100  that includes the rod  22 ,  32 ,  42 . 
         [0075]    Mounting of the internal fixation system  20 ,  30 ,  40  is performed by installing pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  into each of the adjacent vertebrae  100 . The surgeon may pre-drill the bone of the vertebrae  100 . Optionally, but less preferably, the bone-mating thread  50   b ,  250   b ,  350   b ,  450   b ,  550   b ,  650   b  of the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  may be configured to be self-tapping. A first end  22   a ,  32   a ,  42   a  of the rod  22 ,  32 ,  42  is mounted to the mating thread  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of one of the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650 , and a second end  22   b ,  32   b ,  42   b  of the rod  22 ,  32 ,  42  is mounted to the mating thread  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of the other pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650 . The internal fixation rod  22 ,  32 ,  42  takes a particular tilt to accommodate the particular installation. An internal fixation clamp  58 ,  59  is mounted over the mating thread  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of each pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  to thereby secure each of the first and second rod ends  22   a ,  32   a ,  42   a ,  22   b ,  32   b ,  42   b , respectively. A locking nut  55  is mounted to the mating thread  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of each pedicle screw  50  over each internal fixation clamp  58 ,  59 . Then the surgeon fixes the respective first and second rod ends  22   a ,  32   a ,  42   a ,  22   b ,  32   b ,  42   b  by tightening each locking nut  55  as necessary. Additional fixation rods  22 ,  32 ,  42 , fixation clamps  58 ,  59  and locking nuts  55  may be repeatedly stacked and mounted, as necessary, on top of the mating thread  50   a ,  250   a ,  350   a ,  450   a ,  550   a ,  650   a  of each pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650  for joining a plurality of adjacent vertebrae  100  (see  FIG. 10 ). 
         [0076]    Preferably, the procedure is performed with working channels or tubes  80  that include a slot  80   c  or slots  80   c  at the distal-most portion of the working channels or tubes  80  for facilitating the complex dexterous work to be performed such as screwing in pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650 , attaching rods  22 ,  32 ,  42 , tightening mounting hardware such as nuts  55  or the like. The slots  80   c  permit sliding longer components such as the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  and rods  22 ,  32 ,  42  into the area of interest, and the slots  80   a  permit the surgeon to slide the working channel or tube  80  past the pedicle screws  50 ,  250 ,  350 ,  450 ,  550 ,  650  without lifting up the working channel or tube  80  to perform installation of the rods  22 ,  32 ,  42 , clamps  58  and/or nuts  55 . 
         [0077]    While described herein as being used with a pedicle screw  50 ,  250 ,  350 ,  450 ,  550 ,  650 , the internal fixation system  20 ,  30 ,  40  may also be used with a rod, stud, bolt or other similar mounting hardware. The bone of the vertebrae  100  may be drilled and tapped or drilled and filled with a biocompatible epoxy, acrylic or other biocompatible material that can cure and harden as an alternate to a threaded screw in order to retain a mounting rod, stud, bolt or the like. 
         [0078]    From the foregoing, it can be seen that the present invention is directed to an internal fixation system for spine surgery and a method for using the same. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.