Abstract:
Temporary spinal fixation apparatuses and methods are disclosed for temporarily fixing the relative position of spinal implant assemblies until a permanent fixation position is determined. The disclosed apparatuses and methods enhance the ease of placement of spinal implant assemblies and facilitates the accuracy of positioning of the spinal vertebrae. The invention can reduce the number of steps needed to perform spinal surgery and can decrease the likelihood of post-operative complications.

Description:
FIELD OF THE INVENTION 
     This invention pertains to vertebral stabilization. Specifically, the invention is directed to vertebral implants and rod systems for stabilization of vertebral bodies and includes apparatuses and methods for temporary fixation until final alignment is established for permanent fixation. 
     BACKGROUND OF THE INVENTION 
     Chronic back problems cause pain and disability for a large segment of the population. In many cases, the chronic back problems are caused by intervertebral disc disease and loss of stability of the intervertebral joint. Stabilization and/or arthrodesis of the intervertebral joint can reduce the pain and debilitating affects associated with disc disease. 
     Spinal stabilization systems and procedures have been developed to stabilize diseased intervertebral joints and, in some cases, to fuse the vertebrae that are adjacent to the diseased joint space. One type of spinal stabilization system includes bone implants and rods that are used for many types of spinal conditions including, for example, degenerative disc disease, scoliosis, spondylolithisis, spinal stenosis, etc. Examples of some spinal stabilization systems are disclosed in U.S. Pat. Nos. 6,010,503; 5,946,760; 5,863,293; 5,554,157; 5,549,608; and 5,190,543, the entire disclosures of which are incorporated herein by reference. In these systems, a bone implant (e.g., pedicle screw, bone hook) is typically anchored to each vertebral body to be stabilized and a connecting rod mounted to each implant to fix the vertebrae in a particular position. 
     In many known stabilizing systems, after the implant is positioned in or on the bone, a connecting rod is mounted and secured to the implant by, for example, a locking nut that fixes the rod in position as the nut is tightened. Often times adjustment of the position of the vertebrae (e.g., compression, distraction, rotation, etc.), the implant or the rod necessitates repeated loosening and retightening of the locking nut until a satisfactory position is achieved. However, repeated loosening and tightening of the locking nut not only adds additional steps to the surgical procedure, and thus can increase the duration of the surgery, but the long term integrity of the implant, rod or implant assembly can potentially be compromised due to repeated threading and unthreading of the nut before arriving at a satisfactory final position. 
     Accordingly, there is a continuing need for instrumentation and procedures that enhance the ease of performing positional corrections, reduce surgical time and preserve the integrity of the implanted system to reduce the likelihood of post-operative complications. The present invention is directed to addressing these needs. 
     SUMMARY OF THE INVENTION 
     The invention is directed to temporary spinal fixation apparatuses and methods for temporarily fixing the relative position of vertebral bodies or spinal implants until a permanent fixation position is determined. The disclosed apparatuses and methods can enhance the ease of placement of spinal implant assemblies, facilitate the accuracy of positioning of spinal vertebrae and preserve the integrity of the fixation system. 
     It will be noted that in several places throughout the specification, guidance is provided through lists of examples. In each instance, the recited list serves only as a representative group. It is not meant, however, that the list is exclusive. 
     In one embodiment, a surgical instrument of the invention includes a temporary fixation device having a proximal end, a distal end and a fixing member passed within the lumen of an inner cannula that is passed within the lumen of an outer cannula. According to this embodiment, the fixing member can be axially mobile within the lumen of the inner cannula and the inner cannula axially mobile within the lumen of the outer cannula. The distal end of the instrument provides for mounting to a portion of the spinal implant assembly and the proximal end can be used for operating the device. 
     In another embodiment, a surgical instrument according to the invention can include an anti-torque device to reduce the amount torque applied to spinal vertebrae while performing a spinal implant procedure. 
     In another embodiment, a surgical instrument of the invention can be contained in a kit including temporary fixation devices having various inner and outer cannula lengths, various sized spinal implants, or other instruments used to perform a surgical procedure according to the invention. 
     The invention also provides methods for stabilizing the spinal column utilizing the instruments and principles disclosed herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of a temporary fixation device according to the invention; 
     FIG. 2 is an exploded perspective view of a low profile version of the temporary fixation device of FIG. 1; 
     FIG. 3 a  is a perspective view of an alternative embodiment of a temporary fixation device of the invention; 
     FIG. 3 b  is the same embodiment of a temporary fixation device of FIG. 3 b  with the driver removed; 
     FIG. 3 c  is the same embodiment of a temporary fixation device of FIG. 3 a  with the outer cannula and driver removed; 
     FIG. 4 is a longitudinal cross section of the temporary fixation device of FIGS. 3 a - 3   c;    
     FIG. 5 is a longitudinal cross section view of the outer cannula of the temporary fixation device of FIG. 1; 
     FIG. 6 is a side view of an inner cannula of a temporary fixation device according to the invention; 
     FIG. 7 is a longitudinal cross section view through lines  7 — 7  of the inner cannula of FIG. 6; 
     FIG. 8 is a side view of one embodiment of a fixing member according to the invention; 
     FIG. 9 is a side view of an embodiment of a handle suitable for use according to the invention; 
     FIG. 10 illustrates one embodiment of an anti-torque arrangement according to the invention; and 
     FIG. 11 illustrates a pedicle screw with a polyaxial head that can be set according to one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to instruments and methods for increasing the ease and accuracy of positioning vertebral bodies for stabilization and maintaining the integrity of spinal implant systems. The invention can reduce the number of steps and time required for placement of a vertebral stabilization system and thus reduce the overall surgery time. The invention is suited for use with known spinal implant assemblies including pedicle screws, laminar/transverse process hooks (collectively “hooks”), securing mechanisms, etc. and rods. The invention also provides unique advantages for pedicle screw systems having heads that provide multiple degrees of rotational or angular freedom. 
     In one embodiment, the invention provides a surgical instrument, particularly, a temporary fixation device (“TFD”), for temporarily fixing a stabilizing rod to a spinal implant prior to permanent fixation of the rod to the implant. A TFD provides enhanced control during positioning of the implant before or after temporary fixation. Moreover, the temporary fixation provided by a herein disclosed TFD permits the surgeon to repeatedly fix and unfix the rod to the implant when maneuvering or correcting the relative position of vertebrae without using the permanent securing arrangement of the implant until a permanent fixation position is established. This ensures the integrity of the permanent securing arrangement of the implant by requiring its use only when a final position is established and not using the permanent securing arrangement during corrective maneuvers that may be made prior to arriving at a final position. The ease and convenience provided by the instruments and methods of the invention permit the surgeon to align vertebrae into optimal position with greater ease and accuracy and in less time and with less chance of post-operative complications due to prolonged surgical time or compromise the integrity of the implant assembly. 
     As used herein, a “spinal implant assembly” refers to the combination of a spinal implant that can be attached, mounted, clasped, coupled, threaded or otherwise “anchored” to a vertebral body (e.g., posterior or anterior body, transverse process, etc.) and a stabilizing rod. At least one spinal implant is usually anchored to each vertebra to be stabilized. The stabilizing rod (“rod”) can be positioned between two or more spinal implants and provides rigid stabilization between the vertebrae. Typically, two implants are positioned on each vertebrae, one on each side of the transverse process, to provide bilateral stabilization. Examples of spinal implants and rods suitable for the invention are known and disclosed in, for example, U.S. Pat. Nos. 6,010,503; 5,964,760; 5,863,293; 5,554,157; and 5,549,608, the entire disclosures of each of which are incorporated herein by reference. 
     As used herein, the term “permanent fixation” refers to the fixation of the vertebrae or implant in a final position with a securing arrangement that secures the rod to the implant at the completion of the surgical procedure and closure of the surgical site. In contrast, “temporary fixation” refers to fixation of the vertebrae or implant during surgery in a position that may or may not be the final position at the completion of the surgical procedure. In contrast to a permanent securing arrangement, a TFD of the invention is generally only used during surgery and is not left in the patient post-operatively. Prior to the invention, temporary fixation was typically provided during surgery by the permanent securing arrangement that secures the rod to the implant at the completion of the procedure. 
     Throughout the specification, unless stated otherwise, the terms “proximal” and “distal” are relative terms, the term “proximal” referring to a location nearest the surgeon and the term “distal” referring to a location farthest from the surgeon. Thus, for example, when describing an instrument, the proximal end is the end that is typically nearest the surgeon and the distal end nearest the patient. 
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     The invention will now be described with reference to the accompanying drawings, wherein like reference numerals identify identical or similar components throughout the several views. The illustrated embodiments and following description are for exemplary purposes to facilitate comprehension of the invention and should not be construed to limit the scope of the invention. 
     FIG. 1 is a perspective view of one embodiment of a temporary fixation device (“TFD”)  10  shown mounted to one embodiment of a spinal implant assembly  100  suitable for the invention. Spinal implant assembly  100  includes spinal implant  101  and stabilizing rod  102 . As illustrated, TFD  10  has a proximal end  1 , a distal end  2  and a longitudinal axis A—A passing therethrough. 
     A shortened version of the TFD  10  of FIG. 1 is illustrated in an exploded perspective view in FIG.  2  and includes an outer cannula  20 , inner cannula  40 , fixing member  60  and driver  80 . As illustrated, fixing member  60  is sized and configured to pass within lumen  41  of inner cannula  40 . Inner cannula  40  is sized and configured to pass within lumen  21  of outer cannula  20 . Driver  80  is sized and configured to pass over outer cannula  20 . 
     FIG. 3 a  is a perspective view of one embodiment of TFD  10  substantially identical to the embodiments of FIGS. 1 and 2 except that the driver engagement region  26  of outer cannula  20  has a splined configuration  27   a  to coaptate with cannula engagement region  81   a  of driver  80  as will be further described below. FIG. 3 b  illustrates the TFD  10  of FIG. 3 a  with driver  80  removed. FIG. 3 c  illustrates the TFD  10  of FIGS. 3 a  and  3   b  with outer cannula  20  removed. FIG. 4 is a longitudinal cross section view of the TFD  10  of FIG. 3 a.    
     The operation and working relationship of the components of TFD  10  will be discussed with reference to spinal implant assembly  100 . It will be appreciated that while the discussion exemplifies use of TFD  10  with spinal implant assembly  100 , TFD  10  can be used with other spinal implant systems. For this discussion, the distal end of spinal implant  101  includes a hook  103  including a saddle region  104  for anchoring to a vertebral lamina or transverse process. Referring to FIG. 2, rod  102  is positioned within rod receiving arrangement  105  comprising cradle region  106  and arms  107  and  108 . Arms  107  and  108  include a distal thread set  109  and a proximal thread set  110 . It will be appreciated that spinal implant  101  includes a longitudinal axis that is concentric with longitudinal axis A—A of TFD  10  when TFD  10  is mounted to spinal implant  101  (see FIGS. 1 and 3 a ). 
     In use, when spinal implant assembly  100  is positioned on a spinal vertebrae, rod  102  can be securely fixed within cradle region  106  when locking nut  111  is threaded along distal threads  109  such that locking nut surface  112  is snugged tight against rod  102 . In this particular spinal implant  101 , the threads  113  of locking nut  111  are configured to force arms  107  and  108  together against rod  102  as locking nut  111  is distally advanced along distal threads  109  to a permanent tightened position. Grooves  116 ,  117  are present in each of arms  107 ,  108 , respectively, between proximal threads  110  and distal threads  109 . Grooves  116  and  117  provide a point at which tabs  118  and  119  of arms  107  and  108 , respectively, can be removed from implant  101  after permanently fixing rod  102  with locking nut  111 . 
     Referring to FIGS. 2 and 5 (FIG. 5 is a longitudinal cross section view through outer cannula  20 ), it will be appreciated that the interior surface  22  at the distal end of outer cannula  20  includes a coaptating region  23  having a hexagonal configuration  24  for coaptating with the external hexagonal configuration  120  of locking nut  111 . Tab  24   a  provides an inwardly directed force to hold locking nut  111  in place within coaptating region  23 . 
     As best seen in FIG. 2, the exterior surface  25  of outer cannula  20  also includes a driver engagement region  26  having a hexagonal configuration  27  for engaging cannula engagement region  81  at the distal end of lumen  82  of driver  80 . As discussed earlier, the driver engagement region  26  of TFD  10  can have a splined configuration  27   a  complimentary to cannula engagement region  81   a  of driver  80  as shown in FIGS. 3 a - 3   c.    
     Thus, when cannula engagement region  81  of driver  80  is positioned over driver engagement region  26  of cannula  20  and the coaptating region  23  of cannula  20  is positioned around locking nut  111 , rotation of driver  80  causes rotation of locking nut  111  to threadedly apply locking nut  111  onto threads  109  and  110 . FIGS. 1,  3   a ,  3   b  and  4  illustrate that outer cannula  20  can substantially cover the external hexagonal configuration  120  of locking nut  111  when coaptating region  23  is mounted to locking nut  111 . The proximal end of driver  80  can include a handle receiving region  84  for mounting a handle (not shown) to facilitate rotation of driver  80 . Suitable handles for rotating driver  80 , including torque limiting handles, are known and can be used. 
     FIG. 6 is a side view of one embodiment of an inner cannula  40  according to the invention and FIG. 7 is a longitudinal cross section of the inner cannula  40  of FIG. 6 taken through line  7 — 7 . As illustrated, the interior surface  42  of lumen  41  of inner cannula  40  can include threads  43  at the distal end. In this embodiment, threads  43  are sized to threadedly mate with proximal threads  110  of spinal implant  101 . 
     Referring to FIGS. 4-7, when inner cannula  40  is positioned within lumen  21  of outer cannula  20 , outer cannula  20  is axially movable over inner cannula  40  between a distally advanced and proximally retracted position. In the illustrated embodiment, the limits of the proximally retracted and distally advanced positions, of outer cannula  20  are determined by the interaction of inner cannula distal stop  44  and inner cannula proximal stop  45  with outer cannula distal stop  30  and outer cannula proximal stop  31 . In the illustrated embodiment, inner cannula distal stop  44  comprises an external helical thread  46  and inner cannula proximal stop  45  comprises ridge  47 . Outer cannula distal stop  30  comprises an internal helical thread  32  which can threadedly mate with external helical thread  46  of inner cannula  40 . The outer cannula proximal stop  31  comprises one or more fingers  33  positioned to abut against ridge  47  of inner cannula  40 . 
     Axial mobility of outer cannula  20  over inner cannula  40  may be best understood by referring to FIGS. 4,  5  and  6 . Initially, inner cannula  40  is passed into outer cannula  20  and axially rotated such that external helical threads  46  of inner cannula distal stop  44  threadedly engage internal helical threads  32  until external helical threads  46  of internal cannula  40  pass distally beyond and disengage from internal helical threads  32  of outer cannula  20 . Once external helical threads  46  are advanced distally beyond internal threads  32  (see FIG. 4) outer cannula  20  can be slid proximally until fingers  33  of outer cannula proximal stop  31  abuts against ridge  47  of inner cannula proximal stop  45 . From the proximally retracted position, outer cannula  20  can be distally advanced until the proximal aspect  37  of internal helical threads  32  of outer cannula  20  abut against the distal aspect  50  of external helical threads  46  of inner cannula  40 . The relative position of the fingers  33  of outer cannula proximal stop  31  and ridge  47  of inner cannula proximal stop  45  can be seen with outer cannula  20  in the distally advanced position in FIG.  1  and in the proximally retracted position in FIG. 3 b.    
     As shown in FIG. 7, the interior surface  42  of lumen  41  of inner cannula  40  also includes an axially directed shoulder  55 . Shoulder  55  can affirmatively stop distal advancement of inner cannula  40  against the proximal edge  122  of implant  101  when threads  43  of inner cannula  40  are threadedly advanced along thread set  110  of implant  101 . 
     Referring to FIG. 8, fixing member  60  includes a distal tip  62  and an operating end  63  including a handle receiving portion  64  configured for receiving a handle such as handle  150  shown in FIG. 9. A centering guide  75  such as annular collar  76  can be provided to maintain fixing member  60  centered within lumen  41  of inner cannula  40 . Referring to FIGS. 4 and 7, fixing member  60  also includes a portion of a temporary securing arrangement  70  to temporarily secure the fixing member in a position to temporarily fix rod  102 . In the illustrated embodiment, temporary securing arrangement  70  includes threads  61  on fixing member  60  which threadedly engage proximal internal threads  71  on inner cannula  40 . Threadedly rotating threads  61  of fixing member  60  relative to proximal internal threads  71  of inner cannula  40  provides for selective axial advancement and retraction of fixing member  60  within inner cannula  40  to secure fixing member  60  against the surface of rod  102  for temporary fixation of rod  102  in cradle region  106  of spinal implant  101 . While the illustrated embodiment utilizes threads for advancing, retracting and securing fixing member  60 , alternative temporary securing arrangements can be used including, for example, a locking cam, pneumatic pressure, etc. 
     According to one method of the invention, a spinal implant  101  can be anchored to the vertebral body using known procedures (e.g., threads, hooks, etc.). A rod securing arrangement, such as locking nut  111  can be positioned into the coaptating region  23  of outer cannula  20  of TFD  10 . At this stage, driver  80  of TFD  10  may be absent and thus TFD  10  appears substantially as shown in FIGS. 1 and 3 b . Locking nut  111  can then be threaded beyond distal threads  109  and just started onto proximal threads  110  of arms  107  and  108  by rotating outer cannula  20 . At this stage, the appearance of TFD  10  relative to spinal implant  101  will be substantially as shown in FIG. 3 b . As locking nut  111  is advanced distally onto the distal threads  109 , inner threads  43  at the distal end of lumen  41  of inner cannula  40  begin to engage proximal threads  110 . In FIG. 3 a , outer cannula  20  has been removed to visualize the appearance of the relationship between the inner cannula  40  and spinal implant  101  at this stage of the procedure. 
     Rod  102  can then be positioned in cradle region  106 . A handle, such as handle  150  (FIG. 9) can be mounted to handle receiving portion  64  at the proximal end of fixing member  60  and fixing member  60  rotated until fixing member  60  exerts a sufficient force to immobilize rod  102  with the force exerted by fixing member  60  preferably being exerted along an axis concentric with the longitudinal axis A—A of TFD  10  and spinal implant  101 . Fixing member  60  can then be alternately loosened and tightened as necessary during correction maneuvers until the vertebral bodies are in desired position for permanent fixation. 
     In addition to providing temporary fixation, fixing member  60  also ensures that the rod  101  is fully seated within the cradle  106  of the spinal implant  101 . It will be appreciated that at this stage of the procedure, although there may be repeated loosening and tightening of fixing member  60  against rod  102 , the locking nut  111  that will maintain permanent fixation of rod  102  within spinal implant  101  post-operatively, has not yet been passed over the distal threads  109 , leaving these threads and threads  113  of locking nut  111  in a pristine condition until finally used for permanent fixation. Thus, in one embodiment, in contrast to permanent fixation, TFD  10  provides for temporary fixation of rod  102  within cradle region  106  to permit the surgeon to secure and unsecure rod  102  within cradle region  106  without forcing arms  107  and  108  together against rod  102  with locking nut  111  until a final position of rod  102  is determined for permanent fixation. 
     Once the optimal position of the vertebral bodies is determined, handle  150  can be removed from fixing member  60 . Driver  80  can then be passed onto TFD  10  such that cannula engaging region  81  of driver  80  engages the corresponding exterior surface contour  26  of outer cannula  20 . The outer cannula  20  can then be rotated by driver  80  to advance locking nut  111  distally along distal threads  109  to secure surface  112  of locking nut  111  against rod  102 . A handle such as handle  150  (FIG. 9) or a “T” handle or other known handle can be used to rotate driver  80 . In one preferred embodiment a torque limiting wrench can be used to finally tighten all locking nuts on all implants used. The appearance of the spinal assembly  100  and TFD  10  at the final stage of the procedure is substantially as shown in FIG.  1 . Note that at this stage, axially extending fingers  33  at the proximal end of outer cannula  20  are distally advanced away from ridge  47  of outer cannula  20 . 
     To remove the TFD  10 , fixing member  60  is threadedly retracted away from rod  102 . The outer cannula  20  can then be proximally retracted such that the coaptating region  23  at the distal end of outer cannula  20  is free from locking nut  111 . Inner cannula  40  can then unthreaded from the proximal thread set  110  of spinal implant  101 . If present, tabs  118  and  119  of arms  107  and  108  can be broken free from the spinal implant at grooves  116  and  117 , respectively. The surgical incision can then be closed using known methods. 
     FIG. 10 illustrates one embodiment of an anti-torque arrangement  200  suitable for use with a TFD  10  according to the invention. As illustrated, anti-torque arrangement  200  can include a handle  201  for gripping and a rod stabilizing arrangement  202  for grasping a portion of rod  102 . Thus, when driver  80  is rotated in the direction of arrow  205  to tighten a locking nut, such as locking nut  111 , handle  150  can be used to provide an anti-torque force in the direction of arrow  206  to counteract the forces on the assembly  100  during final tightening of the locking nuts. 
     In another embodiment, a TFD  10  can be advantageously used to “set” or cold fuse the polyaxial head of a pedicle screw having a polyaxial head, such as disclosed in U.S. Pat. Nos. 5,964,760 and 6,010,503. FIG. 11 illustrates one embodiment of a pedicle screw  300  having a polyaxial head  301 . Typically, the mobility of polyaxial head  301  is set when locking nut  302  is advanced distally along distal threads  303  to force rod  304  against insert  305  which tightens around screw head  306  to set polyaxial head  301  in a fixed position. Once the position of polyaxial head  301  is fixed, locking nut  302  can be loosened, if it is necessary to reposition rod  304 , without concern that the position of polyaxial head  301  will change. However, rather than tightening and loosening locking nut  302  to fix polyaxial head  301 , a TFD  10  can be used to set polyaxial head  301  to maintain distal thread set  303  in a pristine condition until permanent fixation. 
     According to this embodiment, internal threads  43  of inner cannula  40  are threaded onto proximal threads  310  of pedicle screw  300 . Fixing member  60  can then be distally advanced to exert a force against rod  304  and insert  305  to set polyaxial head  301  in a fixed position on screw head  306 . Corrective maneuvers can then be performed with TFD  10  as described above without movement of the position of polyaxial head  301  and without the need to advance locking nut  302  along distal threads  303 , until a permanent fixation position is determined. 
     From the foregoing detailed description it will be evident that modifications and variations can be made in the devices and methods of the invention without departing from the spirit or scope of the invention. Therefore, it is intended that all modifications and variations not departing from the spirit of the invention come within the scope of the claims and their equivalents.