Abstract:
A spinal implant system for use in immobilizing adjacent vertebral bodies in a minimally invasive manner, including a pair of implants having lengths {sufficient so that one of the ends extend outside of a patient&#39;s body when the implants are installed. Each implant has a pair of opposed elongated posts which in conjunction with an orthogonally arranged support surface define a transverse opening for receiving a stabilizing rod. A cap having upper and lower surfaces is associated with each implant, each cap and it&#39;s associated post has means for advancing the cap along the posts toward the support surface to lock a stabilizing rod therebetween. The rod is pivotally coupled to one of the caps so that the rod, when pivoted, will extend between the transverse openings in adjacently installed implants.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the medical field commonly referred to as Osteosynthesis, i.e., the fusion between segments of the spine and more particularly to an implant system and minimally invasive method for immobilizing the segments preceding the fusion process. 
       BACKGROUND OF THE INVENTION 
       [0002]    Osteosynthesis is achieved by immobilizing separate bone segments and in particular vertebral segments on either side of a failed or damaged disc. When trying to achieve osteosynthesis and specifically fusion between different segments of the spine, one has to provide some type of immobilization. There are various prior art systems and methods which try to achieve this purpose. The different systems involve the placement of implants which typically include pedicle screws threaded into the bone. The implants are then secured to each other by stabilizing or fixation rods. 
         [0003]    Traditionally an open large incision is made exceeding the area to receive the implants. Such a large incision involves extensive stripping and/or cutting of musculature from the posterior elements. An implant system successfully used in the traditional approach is described in U.S. Publication No. 2007/0073291 (“291 publication”) which is assigned to the assignee of this application, SeaSpine, Inc. (“SeaSpine”). The contents of the &#39;291 publication are incorporated herein by reference. 
         [0004]    Recently the trend has been moving to less invasive techniques and the use of devices accommodating such techniques. A minimally invasive approach attempts to avoid a majority of this muscle stripping and subsequent morbidity by using dilators, to hold open a smaller incision, through which the implants can be inserted. Also, the minimally invasive technique usually relies on the dilators stretching the muscles out of the surgical path rather than cutting them, and the dilators can be placed between natural muscle planes to further avoid muscle damage. As is pointed out in  An Anatomic Approach to Minimally Invasive Spine Surgery , by Perez-Cruet M J, Khoo L T, Fessler R G, Quality Medical Publishing, Inc. 2006, pg. 150-151: 
         [0005]    “Many of the procedures have steep learning curves and require additional training to master, including fellowship training, cadaveric workshops, and animal laboratory study. However, once mastered, these techniques can result in a significant reduction of complications and postoperative pain and discomfort, and allow patients to return to their activities of daily living sooner than standard open, more conventional procedures.” 
         [0006]    Various prior art minimally invasive techniques and devices for use therewith are discussed in the following U.S. patents and U.S. application publications: 
         [0007]    US2005/0131421 (“&#39;421 publication”); US2005/0085813 (“&#39;813 publication”); US2005/0154389 (“&#39;389 publication”); U.S. Pat. No. 6,530,929 (“&#39;929 patent”); US 2006/0122597 (“&#39;597 publication”); U.S. Pat. No. 7,160,300 (“&#39;300 patent”); US2005/0131408 (“&#39;408 publication”); US2006/0241600 (“&#39;600 publication”); and US2006/007445 (“&#39;445 publication”). 
         [0008]    The above patents/publications disclose different types of implant systems and methods, including the use of a variety of access tubes, to enable a surgeon to install the implants in a relatively less invasive manner. In addition to the installation of the spinal implants, a fixation element, such as a rod, must be securely connected between the installed implants to insure that the distance and orientation of the implants relative to each other remains fixed. 
         [0009]    It is the delivery of the spinal fixation rod to the installed implants in a reliable and minimally invasive manner which presents a major challenge. For example, the &#39;421 publication teaches the use of angled guide member positioned at the distal end of one of the access sleeves to transition a loose fixation rod from its lengthwise orientation as it travels down one of the access tubes to a transverse orientation necessary for entering the transverse rod receiving opening in the adjacent implant. Among other shortcomings, it would appear that only a small portion of the rod could be seated in the rod receiving opening in the implant located beneath the guide through which the rod is inserted. 
         [0010]    The &#39;455 publication discloses the use of several different tools for positioning a fixation rod into the rod receiving openings in the installed implants. The insertion tools are either designed to penetrate the tissue surrounding the implants to deliver a separate fixed length rod or one positioned outside of the patient&#39;s body to deliver an elongated rod through the tissue to the implants with any excess rod being cut off in the surgical area. 
         [0011]    The &#39;589 publication, like the &#39;455 publication, discloses the use of an angled guide member positioned at the distal end of an access sleeve to reorient a fixation rod in a transverse direction as it leaves the access sleeve and a rather complicated instrument for seating the reoriented rod in the implants. Such an instrument would not appear to be particularly compatible with a minimally invasive procedure. 
         [0012]    The &#39;813 publication discloses the insertion of a fixation rod pivotally mounted on the top of an implant through an access tube. The rotation of the rod serving to screw the pedicle screw of the implant into the underlying bone. The rod is then pivoted out through a slot in the tube and into the rod receiving opening in an adjacent implant with wires extending through the access tube and connected to the proximal end of the rod. The wires are controlled by a manually operated tool arrangement. 
         [0013]    The &#39;600 publication discloses a percutaneous pedicle screw assembly in which each pedicle screw is inserted through an access tube and then threaded into the underlying pedicle. Then a housing with a fixation rod pivotally mounted thereto, is assembled over the head of the screw on site via a split ring where the housing is open at the bottom or through a side opening in the housing. The assembly of the housing over the head of an installed pedicle screw deep inside a patient&#39;s body would be challenging to a surgeon to say the least. In addition, the method of deployment of the fixation rod from an orientation aligned with the access tube axis to a perpendicular alignment with minimal disturbance to the surrounding tissue is not disclosed. 
         [0014]    The &#39;408 publication discloses inner and outer coaxial access tubes designed to install fixed (versus polyaxial) bone anchors with the outer tube arranged to releasably engage the anchor. The placement of a fixation rod within the anchor is not addressed. 
         [0015]    The &#39;300 publication discloses several tools for installing a fixation rod into the rod accommodating opening in installed implants. The tools include a tubular guide extending from each implant to a location outside of the particular body with each guide having internal threads at the proximal end thereof to guide a set screw into the upper threaded portion of the implant. Each guide has a longitudinally extending slot therein for receiving the rod. A tool is disclosed for advancing the rod along each tubular guide. This arrangement would not appear to be particularly conducive to a minimally invasive procedure. 
         [0016]    The &#39;597 publication discloses the use of longitudinally slotted tubular extenders in which the distal ends thereof are arranged to mate with the collar of an implant. Several forms of adjuster tools are disclosed for adjusting the distance between implanted vertebrae. While installed fixation rods are disclosed the manner of inserting the rods to their final resting place within the implants is not addressed. 
         [0017]    The &#39;929 publication discloses a complicated tool for inserting a curved fixation rod within two or more installed implants. The tool does not appear to be particularly conducive to minimizing the disturbance of tissue around the surgical site. 
         [0018]    It is believed that the steep learning curve required for mastering a minimally invasive approach discussed earlier is, in large part, due to the difficulties in inserting and securing the implants and fixation rods through the smaller incisions. Visualization is limited and most of the manipulation of the implants and fixation rods must occur deep within the incision. This invention addresses these difficulties by creating an improved method for the surgeon to insert the implants and deploy a fixation rod in a minimally invasive fashion, through the use of specially designed approach instrumentation and implants. 
       SUMMARY OF THE INVENTION 
       [0019]    A minimally invasive implant system for immobilizing adjacent vertebral bodies, in accordance with the present invention, includes a pair of spinal implants, a fixation rod, a pair of caps for connecting the fixation rod to the implants and a pair of percutaneous tubes to enable a surgeon to secure the caps and rod to the installed implants. Each implant has a pair of elongated opposed posts extending upwardly along a longitudinal axis from a bottom support surface so that the proximal end of the posts are initially positioned outside the patient&#39;s body during the surgical procedure. The elongated posts may be formed as part of a housing which encloses the head of a pedicle screw and preferably are formed with weakened demarcation lines to enable the portions of the posts above the lines to be removed after the surgical procedure is completed. A similar housing with short posts, not designed for a minimally invasive procedure, is illustrated and described in the &#39;291 publication. The bottom support surface may be in the form of a saddle formed in the top surface of a pressure washer arranged to lock the screw head to the housing as is shown in the &#39;291 publication. The implants are adapted or arranged to be secured to the underlying vertebral bodies via the pedicle screws or similar devices. The posts and support surface of each implant define a transverse opening or channel for receiving a fixation or stabilizing rod. The lower portion of the posts is internally threaded to accept a locking set screw. 
         [0020]    Each cap has a top and a bottom and opposed side wall openings adapted to extend around the posts. A locking set screw is associated with each cap so that the set screw, when rotated, will engage the internal threads on the implant posts to advance the cap along the posts toward the support surface forcing a fixation rod disposed within the transverse opening against the support surface to lock the rod and implant together. See the &#39;291 publication. 
         [0021]    The present invention comprises not only a pair of implants with elongated posts to allow the distal ends of the posts of each implant to be located outside of the patient&#39;s body during the surgical procedure and a cap associated with each implant as pointed out above, but a fixation rod that is pivotally mounted at one end to the bottom of one of the caps. In addition, percutaneous access tubes allow the surgeon to install the implants, caps and fixation rod in a minimally invasive manner. 
         [0022]    The pivotally mounted cap and rod are sometimes hereinafter referred to as a cap/rod construct. This pivotal mounting arrangement eliminates the need to position a separate fixation rod into the transverse openings of the installed implants. Preferably the rod is mounted to the associated cap so that the distal or free end of the rod is maintained a given distance from the longitudinal axis of the cap as the cap and rod move down the implant posts within an access tube. This distance allows the free end of the rod to be pivoted from a position generally aligned with the longitudinal axis of one of the tube to a generally perpendicular orientation suitable for entering the transverse opening in an adjacent implant at the surgical site as will be explained. 
         [0023]    The construction of the percutaneous access tubes and their use may be best understood in the description of the method which follows. As an initial step K wires or targeting needles may be used to locate the pedicles selected to be immobilized. Next, conventional dilators may be used to expand the incision sufficiently to receive the implants. The implants are then inserted through the respective (remaining) dilator tubes and the pedicle screws thereof are threaded into the underlying bones so that the transverse rod receiving openings or channels between the posts of the implants are aligned. Next, the pair of percutaneous access tubes are inserted over the remaining dilator tubes and the installed implants. The proximal ends of the installed implants are positioned outside of the patient&#39;s body. Alternatively, the implants may be installed through the access tubes after the dilator tubes are removed. 
         [0024]    Both of the access tubes have rod accommodating openings extending upwardly from the distal ends thereof in at least one side. One of the tubes, designed to accommodate the cap/rod construct, is often referred to hereinafter as the first or the deployment tube. The other access tube is often referred to as the second or mating tube. The mating tube is preferably circular in cross-section and includes two aligned slots to allow the fixation rod to extend through the tube to accommodate an anticipated range of distances between adjacent vertebral bodies to be immobilized. 
         [0025]    In one embodiment the deployment tube may have a lower circular section and an upper section with a tear drop shape in cross-section to accommodate the cap/rod construct as it moves downwardly through the implant posts. The rod accommodating opening in the deployment tube may be in the form of a vertical oriented window extending from a point in the upper section to a horizontally oriented ledge formed in the lower section and then diagonally downwardly through the lower section. The ledge serves to contact the free end of the rod and move it out of the deployment tube in a direction toward the mating tube. Rotation of the deployment tube (e.g., through say 90°) lowers the rod to the level of the bottom support surface in the transverse opening in the adjacent implant. 
         [0026]    In another embodiment the deployment tube may comprise concentric tubes with the outer tube having a rod accommodating opening in the form of a longitudinal slot along one side thereof. The inner tube has a spiral slot extending from the distal end to about the proximal end. By rotating the slotted inner tube relative to the outer tube as the cap/rod construct moves down the implant posts, the surgeon can set the level at which the free end of the rod moves out of the concentric deployment tube and ultimately into the rod accommodating opening in the mating tube. This arrangement allows the surgeon to minimize the disturbance of the soft tissues between the installed implants. 
         [0027]    It is to be noted that while the above summary provides an overview of the invention, it is the appended claims which define the scope thereof. The construction of the system and method for immobilizing adjacent vertebral bodies may best be understood by reference to the following description taken in conjunction with the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIGS. 1   a ,  1   b ,  1   c , and  1   d  are a perspective, front and side elevational and a side elevational view partially in cross-section, respectively, of an implant for use in a minimally invasive spinal implant system in accordance with the present invention; 
           [0029]      FIG. 2  is a top plan view of the implant of  FIG. 1   b;    
           [0030]      FIG. 3  is an enlarged view of the lower portion of the implant with the posts in cross-section showing the internal threads, the inwardly extending shelf which engages the bottom portion of the spherical head of the pedicle screw and the pressure washer which abuts the top of the screw and forms a saddle-shaped support surface for receiving a fixation rod; 
           [0031]      FIGS. 4   a  and  4   b  are top perspective and side cross-sectional views, respectively, of a conventional cap for use with the invention; 
           [0032]      FIGS. 5   a  is a bottom perspective view of a modified cap with a fixation rod pivotally mounted thereto; 
           [0033]      FIG. 5   b  is an end view of the cap/rod construct of  FIG. 5   a;    
           [0034]      FIGS. 5   c  and  5   d  are cross-sectional views of the cap/rod construct taken along lines  5   c  and  5   d  of  FIG. 5   b , respectively, showing the proximal or mounting end of the rod engaging the bottom of the cap to limit the clockwise movement of the rod as it moves downwardly along an access tube; 
           [0035]      FIG. 5   e  is a side elevational view (partially in corss-section) of the cap/rod construct showing the rod fully extended in a counterclockwise direction; 
           [0036]      FIGS. 6   a ,  6   b  and  6   c  are front, side elevational and top plan views, respectively, of an access deployment tube for use in securing a cap/rod subassembly to an implant; 
           [0037]      FIGS. 7   a ,  7   b  and  7   c  are front, side elevational and top plan views, respectively, of an access mating tube for use in securing a cap (without an attached rod) to an implant; 
           [0038]      FIG. 8  is a simplified perspective view illustrating the use of a conventional dilator to expand the incision with the last dilator tube (left hand view) in place; 
           [0039]      FIG. 9  is a simplified perspective view showing a portion of a tool, extending into one of the dilator tubes of  FIG. 8 , in the process of installing one of the implants of  FIG. 1  into a vertebral body; 
           [0040]      FIG. 10  is a simplified perspective view of the exposed portions (outside of a patient&#39;s body) of the access and dilator tubes and implants located therein; 
           [0041]      FIG. 11  is a side cross-sectional view of two implants secured to adjacent vertebral bodies within the respective access tubes, the dilator tubes having been removed; 
           [0042]      FIG. 12  is a simplified perspective view of a conventional tool grasping the end walls of a cap, with a fixation rod pivotally mounted thereon, prior to the insertion of the cap/rod assembly onto the posts of an installed implant; 
           [0043]      FIG. 13  is a simplified perspective view of the tool of  FIG. 12  beginning to insert the cap/rod assembly of  FIG. 12  in an implant; 
           [0044]      FIG. 14  is a side view, partially in cross-section, of the access tubes and implants of  FIG. 10  with the cap/rod construct beginning to move down the implant posts in the access deployment tube; 
           [0045]      FIG. 15   a  is another side view of the implants and access tubes of  FIG. 14  showing the cap/rod construct moved downwardly until the free end of the rod engages a lateral edge of slot formed in the lower section of the access deployment tube forcing the rod outwardly; 
           [0046]      FIG. 15   b  is a side elevational view (partially in cross-section) of the tubes of  FIG. 15   a  showing the fixation rod in a partially extended position; 
           [0047]      FIG. 15   c  is another side view of the implants and tubes of  FIG. 15   b  with the mating tube also shown in cross-section illustrating the fixation rod in a fully extended position, reoriented and positioned within the rod accommodating openings in the mating tube and the transverse opening or channel in the adjacent implant; 
           [0048]      FIG. 16  is another side view of the implants and access tubes showing the cap fully seated in the implant located in the deployment tube and the distal end of the rod positioned near the support surface in the adjacent implant; 
           [0049]      FIG. 17  is another side view of the implants and access tubes with the cap in the adjacent implant about to be fully seated; 
           [0050]      FIG. 18  is a perspective view of the implants of  FIG. 17  installed in simulated vertebrae with both caps fully seated and the access tubes removed; 
           [0051]      FIG. 19  is a perspective view of the implants of  FIG. 18  with the upper portions of the implant posts above the demarcation lines removed; 
           [0052]      FIGS. 20   a  and  20   b  are side elevational views of an alternative access deployment tube arrangement for use in securing a cap/rod subassembly to an implant and; 
           [0053]      FIG. 21  is a side elevational view (partially in cross-section) of the tubes of  FIGS. 20   a  and  20   b  positioned over an installed implant with a cap/rod subassembly lowered into the implant so that the free end of the rod is engaging an edge of the spiral slot beginning to force the rod outwardly of the deployment tube. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0054]    Referring now to the drawings and particularly to  FIGS. 1-3 , an implant  10 , for use in the present invention, has a pair of elongated posts  10   a  which extend upwardly along a longitudinal axis x-x from a bottom support surface  10   b , generally orthogonal to the longitudinal axis. The support surface in conjunction with the posts defines a transverse opening or channel  10   c . The posts are part of a housing  10   m  having a bottom inwardly projecting shelf  10   d  ( FIG. 3 ) which engages the lower semispherical surface of the head  10   e  of a conventional polyaxial pedicle screw having a depending threaded shaft  10   f . A pressure washer  10   g , having a saddle-shaped upper surface  10   b  which forms the lower support surface of the implant, is held in place by pins  10   h  while allowing the washer to be forced downwardly against the screw head via a fixation rod and a set screw (to be described) to lock the housing and pedicle screw together. The implant housing  10   m  ( FIG. 1   c ) may have a length Ph within the range of about 120 mm +/−50 mm (depending on the patient&#39;s anatomy)so that the proximal end  10   k  (opposite the distal end  101 ) extends outside of a patient&#39;s body with the implant installed in a selected vertebral body. The lower portions of the posts are internally threaded at  10   i  and have a weakened demarcation line at  10   j  ( FIG. 3 ) to enable a surgeon to break off the portion of the posts  10   a  above the line once the fixation rod is secured to the installed implants as will be explained. It is to be noted that an implant, designed for traditional open incision procedure, like that shown in the &#39;291 publication, but with slightly extended posts having a weakened demarcation line above an installed cap, has been marketed by SeaSpine under the brand name Malibu Screw System. 
         [0055]    A cap  12 , for use with the implants, is illustrated in  FIGS. 4   a  and  4   b . The cap includes top struts  12   a  (forming the top surface) open at the center through which a wrench, such as an alien wrench, may be inserted to engage the hexagonal wrench engaging surface  12   b  of a set screw  12   c  enclosed within the cap between the top strut, bottom strut  12   d  and flat end walls  12   e . The cap has opposed side wall openings  12   f  inside of the curved side walls  12   g . The cap has a bottom saddle-shaped concave surface  12   h  for engaging a fixation rod. The external set screw threads  12   i  are arranged to engage the internal threads of the implant posts to advance the cap along the posts when the set screw is rotated as is explained in more detail in the &#39;291 publication. 
         [0056]    A modified cap  14  with a stabilization or fixation rod  16  is coupled, e.g., mounted, to the bottom surface thereof is shown in  FIGS. 5   a - 5   d . Like components of the cap are identified with the same letter with the caveat that the bottom of the cap  14  has been reconfigured to support the proximal end  16   a  of the fixation rod  16 . The proximal end of the rod includes a flat surface  16   c  with a centrally located upwardly extending semicircular tongue  16   d . The tongue has a lateral bore  16   e  therethrough which is pivotally mounted within a clevis  14   k  formed in a bottom section  14   i  of the cap via a pin  141  ( FIG. 5   e ). The bottom surface  14   m  of the clevis  14   k  ( FIGS. 5   c - 5   e ) engages the surface  16   c  on the proximal end of the rod to stop the clockwise rotation of the rod ( FIG. 5   c ) at a point within the acute angle  (a range of about 5° to 45°). This limitation on the rod&#39;s rotation relative to the cap&#39;s longitudinal axis  14   o  insures that the rod will exit the access deployment tube as it travels down the implant posts as will be explained more fully. The length of the rod will vary depending upon the number of implants and the distance between the implants to be secured to the rod. As an example, rods may have a length between as little as 30 mm and as great as 110 mm or more. I have found that a lateral distance d3 ( FIG. 5   c ) between the rod&#39;s distal end  16   b  and the axis  14   o  within the range of about 5 to 15 mm is satisfactory for a deployment tube of the type discussed in connection with  FIG. 6 . 
         [0057]    The rod can pivot in a counterclockwise direction ( FIG. 5   e ) through an angle of up to 90° to allow the distal end  16   b  to extend through the rod accommodating openings in the mating tube and into the transverse opening in an adjacent implant. See  FIGS. 15   b - 15   c.    
         [0058]    The percutaneous access tubes will now be described in conjunction with  FIGS. 6 and 7 . The tubes have longitudinal axii  19  which are coincident with the respective longitudinal axii of the implants when positioned thereover. A percutaneous deployment tube  18  has proximal and distal ends  18   a  and  18   b , a lower circular section  18   c , and an upper section  18   d  as shown. The upper section has a tear drop shape, i.e., circular in cross-section through an angle λ of say 240° to 300°, and then extends outwardly about a distance d 2  of ½ to ¾ of the diameter d 1  forming an extended side  18   f  ( FIGS. 6   b  and  6   c ) for accommodating the passage of the cap/rod construct as it travels down the implant posts as is illustrated in  FIG. 14 . 
         [0059]    The deployment tube includes a rod accommodating opening  18   g  which extends in an expanding manner from it&#39;s apogee  18   h  in the upper tear drop section to a rod tip engaging ledge  18   i  in the lower section and then through a diagonally and downwardly extending portion  18   j  to the distal end  18   b  as is shown in  FIGS. 6   a  and  6   b . The ledge  18   i  serves as a kick out point to force the free or distal end  16   b  of the rod out of the deployment tube. The distance h from the distal end  18   b  to the ledge  18   i  is preferably within the range of 0.25-3.00 inches. As the cap/rod construct continues its downward progress along the implant posts, the rod is reoriented upwardly with respect to the tube until it becomes generally parallel to the spine, i.e., about normal to the axis  19  and extends into the rod accommodating openings in the mating tube and the transverse opening of the implant located therein. By continuing the downward movement of the rod/construct and turning the deployment tube (clockwise in  FIGS. 6   a - 6   b ) through, say about 90°, the rod will be lowered to a position near the support surface in the adjacent implant. See  FIGS. 14-16 . 
         [0060]    Referring now to  FIGS. 7   a - 7   c , a mating access tube  20  is circular in cross-section with proximal  20   a  and distal  20   b  ends and opposed rod accommodating openings  20   c  extending upwardly from the distal end sufficiently to receive the free end  16   e  of the rod in its fully extended position. 
         [0061]    The method of installing the implants and cap/rod construct will now be explained in conjunction with  FIGS. 8-19 . Initially conventional K wires or target needles (not shown) are used to locate the targeted pedicles. Next, conventional dilators  22  are placed over the K wires (or target needles) to expand the incision to a diameter large enough to receive the implants leaving the last dilator tube  22   a  in place ( FIGS. 8 and 9 ). 
         [0062]    Next, the implants are inserted into each dilator tube and the screws thereof threaded into the respective pedicles. A tool  23  is illustrated as inserting one implant through the right hand dilator tube in  FIG. 9 . Next, the percutaneous tubes are placed over the dilator tubes. 
         [0063]      FIG. 10  shows the proximal ends of installed implants and dilator and access tubes extending outside the patient&#39;s body  21  with the rod receiving transverse openings or channels  10   c  aligned and readily accessible to the surgeon. 
         [0064]      FIG. 11  illustrates, in a side view, partially in cross-section, the implants as installed and surrounded by the deployment and mating tubes with the dilator tubes removed. Items  25  and  26  represent the vertebral bodies receiving the pedicle screws. 
         [0065]      FIG. 12  illustrates a tool  24  for grasping the end walls  14   e  of the cap  14  carrying the pivotally mounted fixation rod in preparation for inserting the cap side wall openings  14   f  over the posts  10   a  of an implant. The tool  24  includes a concentrically arranged rotatable tool (not shown), such as an allen wrench, for engaging the hexagonal cavity  14   b  to rotate the set screw  14   c  to advance the cap along the threaded portion of the posts. 
         [0066]      FIG. 13  illustrates the insertion of the cap/rod construct onto the implant posts located within the proximal end of the deployment tube  18 . The same tool  24  may be used to insert the cap  12  onto the posts in the implant positioned in the mating tube  20 . 
         [0067]      FIG. 14  shows the cap  14  and rod  16  proceeding downwardly along the implant posts within the deployment tube with the distal end of the rod extending into the expanded area  18   f  in the teardrop section of the tube. 
         [0068]      FIG. 15   a  shows the distal end  16   b  of the rod engaging the kick out ledge  18   i  in the lower section of the deployment tube. 
         [0069]      FIG. 15   b  shows the rod being reoriented by the ledge as the cap  14  moves further down the implant posts. 
         [0070]      FIG. 15   c  shows the cap/rod construct advanced along the implant posts in the deployment tube to reorient the rod at a right angle to the tube&#39;s longitudinal axis with the rod extending through the two rod accommodating openings  20   c  in the mating tube and the transverse opening  10   c  in the implant positioned in the mating tube. 
         [0071]      FIG. 16  shows the deployment tube rotated, say through 90°, as the cap is lowered to its final position. This lowers the rod so that it is positioned slightly above the support surface  10   b  in the adjacent implant. The cap  14  is also shown in its locked position.  FIG. 17  shows the cap  12  extending down the posts in the adjacent implant, but not in a fully locked positioned. 
         [0072]      FIG. 18  shows the implants installed in simulated adjacent vertebral bodies  25  and  26  with both caps in a locked position and the access tubes removed.  FIG. 19  is the same view as  FIG. 18  with the portions of the posts above the demarcation lines  10   j  broken off and removed. 
         [0073]    It is to be noted that while the drawings illustrate only one side of the spine as receiving the implants, locking caps and stabilizing rods, the system and method is equally applicable for treating the opposite side of the spine. In addition the length of the pivotally mounted fixation rod is not limited to that required to span only the length between two implants. More than two implants may be locked to a single rod. 
         [0074]      FIGS. 20   a  and  20   b  are side elevational views of an alternative embodiment of a deployment tube comprising elongated inner and outer tubes  28   a  and  28   b , respectively. The inner tube  28   a  extends from a distal end  28   c  to a proximal end formed by collar  28   d . The inner tube includes a spiral slot  28   e  extending upwardly from the distal end to the collar. The outer tube also extends from a distal ( 28   f ) to a proximal ( 28   g ) end and is provided with a longitudinally extending rod accommodating slot or opening  28   h  along one side. 
         [0075]      FIG. 21  is a side view, partially in cross-section, showing the tubes in a nested condition surrounding an implant. By manipulating the inner tube  28   a  while the cap/rod construct  14 / 16  travels down the two tubes the surgeon can set the point at which the rod  16  emerges from the deployment tube. The rod free end  16   b  will remain inside of the deployment tube until the rod free end is aligned with the slots  28   e  and  28   h , at which point the rod starts exiting the tube. The edge of the spiral slot contacting the rod will reorient the rod into an angle paralleling the spine.  FIG. 21  shows the free end of the rod engaging an edge  28   i  of the spiral. 
         [0076]    There has thus been described a novel system and method for immobilizing adjacent vertebral bodies with minimal disturbance of the muscle and soft tissue surrounding the targeted vertebrae. Modifications and perhaps improvements to the system and method may occur to those skilled in the art without involving a departure of the spirit and scope of the present invention as defined by the appended claims.