Abstract:
Methods and instruments are provided to allow access to a surgical site through a small incision while optimizing visualization of the patient anatomy. The instrumentation provide for the retraction of soft tissue, creation of a working envelope below the skin, and access to intervertebral discs and/or the surrounding bony structures for the purpose of performing various operative procedures including discectomy, laminectomy, and other spinal fixations. One set of disclosed instrumentation provides for the targeting of placement and trajectory of spinal fixation devices while reducing the number of instruments necessary needed to pass through the surgical incision. Another instrument disclosed herein allows for the compression of the intervertebral space through a very small incision. The instrument profile is minimized by using the same instrument that is used for tightening of the pedicle screws as one of the active components of the compression instrument.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to U.S. Provisional Application Ser. No. 61/335,961, filed Jan. 14, 2010, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. 
    
    
     BACKGROUND 
     Spinal fusion is a procedure that involves joining two or more adjacent vertebrae with a bone fixation device to restrict movement of the vertebra with respect to one another. Spinal fixation devices are used in spine surgery to align, stabilize and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation rod, such as, for example, a relatively rigid fixation rod or a dynamic or flexible spinal fixation rod, etc. (collectively referred to herein as a spinal fixation rod), that is coupled to adjacent vertebrae by attaching the spinal fixation rod to various spinal fixation elements, such as, for example, hooks, bolts, wires, screws, such as pedicle screws, and the like. Surgeons may commonly choose to install multiple spinal fixation elements, as well as multiple spinal fixation rods, to treat a given spinal disorder. 
     Conventional surgical techniques for spinal fusion have involved the use of multiple instruments that sometimes require the use of more than one hand to operate. Thus, multiple surgeons often manipulate the instruments used during a spinal fusion surgery. Furthermore, conventional surgical techniques included long incisions that are associated with long and painful recovery times. Recently, minimally invasive surgical procedures for performing spinal fusion have been developed that generally provide access to and perform corrective surgery at a surgical site while imparting reduced trauma to the patient anatomy. 
     SUMMARY 
     In accordance with one embodiment, a surgical instrument includes a driver and an actuator. The driver is configured to apply a torque to a locking cap of a spinal fixation device, so as to lock the locking cap against a spinal fixation rod. The driver defines a proximal end and a distal end opposite the proximal end. The actuator defines a distal end that is configured to fit over the spinal fixation rod, and a proximal end opposite the distal end. The actuator includes a body that defines a recess sized to receive the driver such that the driver extends through the actuator and is rotatable with respect to the actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the preferred embodiments of the application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the surgical instruments and methods of the present application, there is shown in the drawings preferred embodiments. It should be understood, however, that the application is not limited to the specific embodiments and methods disclosed, and reference is made to the claims for that purpose. In the drawings: 
         FIG. 1A  is a rear elevation view of a portion of a spinal region of a human spine, illustrating three adjacent vertebrae separated by respective intervertebral spaces; 
         FIG. 1B  is a rear elevation view of the portion of the spinal region illustrated in  FIG. 1A , whereby a pair of spinal fixation assemblies attached to the vertebrae after a spinal fusion surgery has been performed, the spinal fixation assembly including spinal fixation rods and spinal fixation devices; 
         FIG. 2  is a perspective view of a spinal fixation device of the type illustrated in  FIG. 1B ; 
         FIG. 3  is a perspective view of a bone anchor manipulation instrument constructed in accordance with one embodiment including a torque assembly and an actuator; 
         FIG. 4  is a perspective view of the torque assembly illustrated in  FIG. 3 ; 
         FIG. 5A  is a perspective view of the actuator illustrated in  FIG. 3 , including a distal body portion, a proximal body portion and an intermediate body portion; 
         FIG. 5B  is a top plan view of the intermediate body portion of the actuator illustrated in  FIG. 5A ; 
         FIG. 6  is a perspective view of the bone anchor manipulation instrument illustrated in  FIG. 3 , shown operably coupled to a pair of spinal fixation devices; 
         FIG. 7A  is a perspective view of an anchor delivery instrument constructed in accordance with one embodiment including a handle and a guide; 
         FIG. 7B  is a perspective view of an anchor delivery assembly including the anchor delivery instrument illustrated in  FIG. 7A  and a trocar inserted into the guide of the anchor delivery instrument; 
         FIG. 8  is a top plan view of the guide illustrated in  FIG. 7A ; 
         FIG. 9A  is a schematic radio image of the guide illustrated in  FIG. 8 , shown in a desired orientation; 
         FIG. 9B  is a schematic radio image of the guide illustrated in  FIG. 8 , shown in an undesired orientation; 
         FIG. 10  is a rear elevation view of adjacent vertebrae and intervertebral spaces showing the placement of a pedicle fiducial marker as an intra-operative reference point and a stable mount for various surgical instruments; 
         FIG. 11A  is a side elevation view of a fiducial marker illustrated as a spinal fixation device of the type illustrated in  FIG. 2 ; 
         FIG. 11B  is a side elevation view of a fiducial marker illustrated as a bone anchor of the spinal fixation device of the type illustrated in  FIG. 11A ; 
         FIG. 11C  is a side elevation view of a fiducial marker constructed in accordance with another embodiment; 
         FIG. 11D  is a top plan view of the fiducial marker illustrated in  FIG. 11C ; 
         FIG. 11E  is a side elevation view of a fiducial marker constructed in accordance with another embodiment; 
         FIG. 11F  is a top plan view of the fiducial marker illustrated in  FIG. 11E ; 
         FIG. 11G  is a side elevation view of a fiducial marker constructed in accordance with another embodiment; 
         FIG. 11H  is a top plan view of the fiducial marker illustrated in  FIG. 11G ; 
         FIG. 11I  is a side elevation view of a fiducial marker constructed in accordance with another embodiment; and 
         FIG. 11J  is a top plan view of the fiducial marker illustrated in  FIG. 11I . 
     
    
    
     DETAILED DESCRIPTION 
     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 drawings to which reference is made. The words “proximally” and “distally” refer to directions toward and away from, respectively, the surgeon using the surgical instrument. The words, “anterior”, “posterior”, “superior”, “inferior” and related words and/or phrases designate preferred positions and orientations in the human body to which reference is made and are not meant to be limiting. The terminology includes the above-listed words, derivatives thereof and words of similar import. 
     Referring to  FIG. 1A , a spinal region  1  of the human spine includes a plurality of adjacent vertebrae  2  arranged along a vertical spinal column  3 . Adjacent vertebrae  2  are separated by respective intervertebral disc spaces  4  that can retain a vertebral disc  5 . As illustrated, the spinal region  1  includes a superior vertebra  2   a  disposed above an inferior vertebra  2   b  and separated from the inferior vertebra  2   b  by a respective intervertebral disc space  5   a . It should be appreciated that a discectomy can be performed on one or more intervertebral disc spaces  4  as desired that remove the vertebral disc  5  so as to reveal an intervertebral disc space  5   a  whereby the vertebral disc  5  has been removed. An artificial disc can be implanted in the intervertebral disc space  5   a . Alternatively or additionally, the adjacent vertebrae  2  that define the intervertebral disc space can be fused. 
     For instance, referring to  FIG. 1B , a surgical assembly  41  includes a spinal fixation assembly  10  that is configured to fuse or otherwise attach adjacent vertebrae  2  together. The spinal fixation assembly  10 , and components thereof, can be constructed generally as described in U.S. patent application Ser. No. 12/669,224, filed Jul. 21, 2008, published as U.S. Publication No. 2010/0198272, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. In accordance with the illustrated embodiment, the spinal fixation assembly  10  can includes a plurality of spinal fixation devices  11 , for instance at least a pair of spinal fixation devices  11 , and a spinal fixation rod  12  configured to be coupled to the spinal fixation devices  11 . Accordingly, the spinal fixation rod  12  spans across at least one intervertebral disc space  4 . The spinal fixation devices  11  are implanted into respective vertebrae  2 , for instance into the pedicles of the vertebrae  2 . The spinal fixation rod  12  extends through the spinal fixation devices  11  so as to operatively couple the respective vertebrae  2 . 
     Referring to  FIG. 2 , the spinal fixation assembly  10  includes a plurality of spinal fixation devices  11  connected by a spinal fixation rod  12  that spans between the spinal fixation devices  11 . Each spinal fixation device  11  can generally include a bone anchor  13 , which can be a bone screw such as a pedicle screw, a bone anchor seat  17  and a locking cap  19 . The bone anchor  13  is received within the bone anchor seat  17 , such that the bone anchor seat  17  is coupled to the proximal end of the bone anchor  13 , and the distal end of the bone anchor  13  is configured to be driven into the corresponding underlying vertebra  2 . The bone anchor  13  can include a threaded shaft  60  that extends along a central axis  62 , such that any suitable driver can apply a torsional force or torque to the bone anchor, thereby rotating the bone anchor  13  so as to cause the shaft  60  to be driven into the underlying vertebra  2 . The bone anchor  13  can be inserted through the bone anchor seat  17  and subsequently driven into the underlying vertebra  2 , or can be driven into the underlying vertebra  2  and the bone anchor seat  17  can be subsequently popped downward onto the head of the bone anchor  13 . The bone anchor  13  can be rotated relative to the bone anchor seat  17  prior to locking the locking cap  19  in the bone anchor seat  17 . The bone anchor seat  17  includes a first bearing surface  34  that is configured to receive the spinal fixation rod  12 , and the locking cap  19  includes a second bearing surface  35  that is configured to secure the anchor seat  17  to the spinal fixation rod  12 , such that the spinal fixation rod  12  is captured between the bearing surfaces  34  and  35  when the locking cap  19  is tightened to the bone anchor seat  17 . Once the bone anchor  13  is implanted into the underlying vertebra  2  and attached to the bone anchor seat  17 , the spinal fixation rod  12  can be received against the first bearing surface  34 . 
     For instance, in accordance with the illustrated embodiment, the locking cap  19  defines external threads  61  that mate with internal threads of the bone anchor seat  17 . The locking cap  19  further includes a recess  36  that is configured to receive a driving instrument that is configured to apply a torsional force or torque to the locking cap  19 . Accordingly, the locking cap  19  can be actuated, such as rotated or screwed, between a first unlocked configuration and a second locked configuration whereby the spinal fixation rod  12  is captured between the bearing surfaces  34  and  35 . When the locking cap  19  is in the unlocked configuration, the spinal fixation rod  12  can move with respect to the spinal fixation devices  11 , and the bone anchors  13  can rotate relative to the respective bone anchor seat  17 . When the locking cap  19  is in the locked configuration, such that the first bearing surface  34  and the second bearing surface  35  bear tightly against the spinal fixation rod  12 , the spinal fixation rod  12  is unable to move with respect to the spinal fixation device  11 . Furthermore, the locking cap  19  delivers a force to the bone anchor  13  that prevents the bone anchor  13  from rotating relative to the bone anchor seat  17 . Unless otherwise specified, the spinal fixation assembly  10  and its components can be made from any suitable biocompatible material such as titanium, titanium alloys such as titanium-aluminum-niobium alloy (TAN), implant-grade 316L stainless steel, poly-ether-ether-ketone (PEEK) or any suitable alternative implant-grade material. 
     The spinal fixation devices  11  are each implanted into a corresponding plurality of underlying vertebra  2  disposed in a spinal region  1 . While the spinal fixation rod  12  is illustrated as having a length sufficient to join four spinal fixation devices  11 , it should be appreciated that the spinal fixation rod  12  can have any length suitable for attachment to any desired number of spinal fixation devices  11  configured to attach to any corresponding number of underlying vertebrae  2 . 
     The spinal fixation rod  12  can extend substantially straight between a pair of opposing terminal ends  15   a  and  15   b , and a middle portion  16  disposed between the terminal ends  15   a  and  15   b , thereby defining a profile  14  that is substantially straight. While the profile  14  is substantially straight as illustrated, it should be appreciated that the spinal fixation rod  12  could be constructed as having a curved profile. For instance the middle portion  16  could be disposed posterior with respect to the terminal ends  15   a  and  15   b  when the spinal fixation devices  11  are implanted into the vertebrae  2 , such that the spinal fixation rod  12  is concave with respect to the spinal column  3 , though it should be appreciated that the spinal fixation rod  12  could also be curved when implanted such that the middle portion  16  is disposed anteriorly with respect to the terminal ends  15   a  and  15   b , such that the spinal fixation rod  12  is convex with respect to the spinal column  3 . 
     Referring to  FIG. 3 , the surgical assembly  41  can further include an implant manipulation instrument  20  configured to apply a compressive force against a pair of implanted spinal fixation devices  11 , and subsequently lock the spinal fixation rod  12  in the spinal fixation devices  11 . In accordance with the illustrated embodiment, the implant manipulation instrument  20  includes a torque assembly  21  and an actuator  22  connected such that the torque assembly  21  and the actuator  22  can move with respect to each other in multiple degrees of freedom. As illustrated, the torque assembly  21  and the actuator  22  can rotate, pivot and translate relative to each other while remaining operably connected. 
     The torque assembly  21  is configured as a driver  23  that includes a driver shaft  24  that extends along a central longitudinal axis L between a distal shaft portion  25 , an opposed proximal shaft portion  26 , and an intermediate shaft portion  27  that extends between the distal shaft portion  25  and the proximal shaft portion  26  along the longitudinal axis L. Thus, the distal shaft portion  25  and the proximal shaft portion  26  are spaced along the longitudinal axis L. The driver  23  also includes a handle  28  connected to the proximal shaft portion  26  of the driver shaft  24 , the handle  28  being configured to receive a torque and transfer the received torque to the driver shaft  24 . The actuator  22  includes a body  29  having a distal body portion  30 , a proximal body portion  31  and an intermediate body portion  32  extending between the distal body portion  30  and the proximal body portion  31 . 
     Referring to  FIG. 4 , the driver shaft  24  of the driver  23  extends along the longitudinal axis L, and defines an outer cross-sectional dimension D 1 , such as a diameter. In this regard, it should be appreciated that the driver shaft  24  can be substantially cylindrical or alternatively shaped as desired. The outer cross-sectional dimension D 1  of the driver shaft  24  can vary at different locations along the driver shaft  24  from the proximal shaft portion  26  to the distal shaft portion  25 . The implant manipulation instrument  20  includes a sleeve  33 . The sleeve  33  is a tubular shape that is sized such that the outer cross-sectional dimension D 1  of the driver shaft  24  fits within the sleeve  33 . When the driver shaft  24  is positioned within the sleeve  33 , the sleeve  33  can be coupled to the driver shaft  24  such that the sleeve  33  is able to rotate with respect to the driver shaft  24  about the longitudinal axis L. The implant manipulation instrument  20  can further include a connector  140  that couples the sleeve  33  to the driver shaft  24  as described above. The connector  140  prevents the sleeve  33  from falling off of the driver shaft  24 , such as by translating along the longitudinal axis L, while allowing the driver shaft  24  to rotate with respect to the sleeve  33  about the longitudinal axis L. As illustrated, the connector  140  is a spring clip but it should be appreciated that other connectors or couplings could be used to operably couple the sleeve  33  and drive shaft  24  as described above. 
     Referring to  FIGS. 2 and 4 , the driver shaft  24  defines a distally directed tip  34  that defines a terminal end of the distal shaft portion  25 . The tip  34  is configured to mate with the locking cap  19  in the recess  36 , and can be tapered inwardly as it extends distally so as to facilitate insertion into the recess  36 . The exact shape of the tip  34  and the recess  36  can be any of a number of shapes including but not limited to a flat head, a Phillips or crosshair end, a hex, or any other shape in which the tip  34  and recess  36  have some corresponding features that allow the tip  34  to enter the recess  36  and impart a torque on the locking cap  19  to rotate the locking cap  19  from the unlocked configuration to the locked configuration and vice versa. 
     The handle  28  can extend proximally from the driver shaft  24 , and can be integral with the driver shaft  24  or can alternatively be discreetly attached to the driver shaft  24  via coupling  37 . The coupling  37  is configured to rotationally lock the handle  28  with respect to the driver shaft  24 , such that a torsional force or torque applied to the handle  28  is transferred to through the coupling  37  to the driver shaft  24 . Thus, the coupling  37  can include corresponding engagement members, such as an internal hex and an external hex that mate, on the driver shaft  24  and handle  28  that rotatably couple the handle  28  to the driver shaft  24 . One example of corresponding engagement drives would be an internal hex and an external hex. Handle  28  may also include a built in torque limiter  38  that prevents over tightening of the locking cap  19  when being fixed to the anchor seat  17 . Accordingly, the handle  28  is rotatably coupled to the proximal shaft portion  25 , such that a rotational biasing force applied to the handle  28  is transferred to the distal shaft portion  25  and the tip  34 . 
     The handle  28  can be configured as desired, and includes a substantially T-shaped grip  39  presenting an engagement surface  40 . The grip  39  can be sized to allow a surgeon&#39;s hand to grab and apply a torque to the handle  28 . It should be appreciated that the grip  39  can be any structure or handle suitable for a surgeon to grab and apply a torque to such as but not limited to a knob, crank, protrusion, and the like. The driver  23  is configured to receive a torque, and selectively transfer the torque to the locking caps  19 , so as to move the locking caps to the locked configuration. 
     Referring now to  FIGS. 5A and 5B , the actuator  22  includes an actuator body  29  that has a proximal body portion  31 , an opposed distal body portion  30 , and an intermediate body portion  32  that extends between the proximal body portion  31  and the distal body portion  30 . The body  29  is defined by a top surface  42 , a bottom surface  43 , and opposing side surfaces  44 . Alternatively, the body  29  can have a circular cross-section or can define any suitable alternative shape as desired. 
     The proximal body portion  31  includes a substantially flat panel  45  that is configured to receive a force F and impart that received force F to the distal body portion  30 . The top surface  42  and the bottom surface  43  can be wider at the panel  45  than at the intermediate body portion  32 , such that the actuator body  29  necks down from the panel  45  to the intermediate body portion  32 . The broader top surface  42  and broader bottom surface  43  allow for easier input of a force to the actuator  22  than at the intermediate body portion  32 . The intermediate body portion  32  defines a recess  46  that extends from the top surface  42  through the bottom surface  43 . The recess  46  has a length L 1  defined by a top inner wall  47  and a bottom inner wall  48  and a width W defined by opposing side walls  49 . The width is substantially equal to or slightly greater than the outer cross-sectional dimension D 2  of the driver shaft  24  such that the driver shaft is configured to extend through the recess  46  between the side walls  49 . The distal body portion  30  includes a body tip  50  and a neck  53  that connects the body tip  50  to the intermediate body portion  32 . The neck  53  can extend obliquely with respect to the intermediate body portion  32 , such that the body tip  50  is offset from the rest of the intermediate body portion  32 . The body tip  50  includes a distal end  51  that is configured to slidably and releasably contact the spinal fixation rod  12  (shown in  FIG. 2 ). The distal end  51  can define a curved surface  52  having a curvature that matches the radius of the spinal fixation rod  12  (see  FIG. 2 ). 
     During operation, with further reference to  FIG. 6 , a first spinal fixation device  11  is attached to a first vertebra  2  and a second spinal fixation device  11 ′ is attached to a second vertebra  2 ′ in the manner described above. In particular, each of the bone anchors  13  and  13 ′ of the spinal fixation devices  11  and  11 ′ are received by the anchor seats  17  and  17 ′, respectively. Furthermore, the bone anchors  13  and  13 ′ are attached to the vertebrae  2  and  2 ′ respectively, for instance, by screwing the bone anchors  13  and  13 ′ into the pedicles of the vertebrae  2  and  2 ′. The spinal fixation rod  12  is inserted through each of the anchor seats  17  and  17 ′ and placed in a desired position with respect to at least the second spinal fixation device  11 ′. The locking cap  19 ′ of the second spinal fixation device  11 ′ is moved into the locked configuration such that spinal fixation rod  12  and the second spinal fixation device  11 ′ cannot move with respect to each other. For instance, the tip  34  of the driver  23  is inserted into the recess  36  of the locking cap  19 ′ (see  FIG. 2 ), and the driver  23  is rotated so as to tighten the locking cap  19 ′ against the spinal fixation rod  12 . The locking cap  19  of the first spinal fixation member  11  remains in the unlocked configuration such that the spinal fixation rod  12  and the first spinal fixation member  11  can move with respect to each other. 
     The implant manipulation instrument  20  can further secure the spinal fixation assembly  10 . For instance, the driver  23  is positioned such that the intermediate shaft portion  27  is disposed within the recess  46  of the body  29  of the actuator  22 . Thus, the driver  23  and the actuator  22  intersect. The outer cross-sectional dimension D 1  of the intermediate shaft portion  27  and the width W of the recess  46  are sized such that the driver  23  and the actuator  22  can freely translate longitudinally with respect to each other, rotate about their respective central longitudinal axes with respect to each other, and pivot with respect to each other about respective axes angularly offset, e.g., perpendicular, with respect to their central longitudinal axes. 
     The tip  34  of the driver  23  is moved into the recess  36  of the locking cap  19 . The body tip  50  of the distal body portion  30  is moved into contact with the spinal fixation rod  12  and the second spinal fixation device  11 ′. Specifically, the curved surface  52  of the distal end  51  is manipulated into slidable and releasable contact with the spinal fixation rod  12  and the bottom surface  43  at the body tip  50  of the actuator  22  is manipulated into releasable contact with the anchor seat  17 ′. 
     Once both the tip  34  of the driver  23  and the body tip  50  of the actuator  22  are in contact with the spinal fixation assembly  10  as described above, a force F is applied to the bottom surface  43 ′ of the panel  45  and to the sleeve  33 . The force F biases the proximal body portion  31  toward the driver  23 , thereby causing the actuator  22  to pivot with respect to the driver  23  about a location where the top inner wall  47  contacts the intermediate shaft portion  27 . As the proximal body portion  31  pivots toward the proximal shaft portion  26  the distal body portion  30  pivots toward the distal shaft portion  25 . As a result the second spinal fixation device  11 ′ moves closer to the first spinal fixation device  11 , thereby compressing the vertebrae  2  and  2 ′. Once the desired level of compression is achieved, a torque is applied to the grip  39 , and thus the handle  28 . The applied torque is transferred to the tip  34  that imparts the torque to the locking cap  19 , thereby rotating the locking cap  19  from the unlocked configuration to the locked configuration. The torque can be continuously applied until a specified torque is achieved placing the locking cap  19  in the locked configuration. Because the driver shaft  24  is able to rotate with respect to the sleeve  33  as described above in reference to  FIG. 4 , force F can be applied continuously to the actuator  22  and the sleeve  33  while the locking cap  19  is rotated to the locked configuration. For instance, a single surgeon can apply force F to the actuator  22  and the sleeve  33  with one hand while applying the torque to the grip  39  with the other hand. The rotational coupling of the sleeve  33  and the driver shaft  24  allows the surgeon&#39;s hand to remain in place on the sleeve  33  applying the force F while the driver shaft  24  rotates within the sleeve  33  transferring the torque from the grip  39  to the tip  34 . It should be appreciated that the steps described above for fixing the spinal fixation assembly  10  as described above may be rearranged as desired. 
     Referring to  FIGS. 7A and 8 , the surgical assembly  41  can further include an anchor delivery instrument  300  that is configured to guide a bone anchor to a target location, such as an underlying vertebra, in a desired position and orientation. In accordance with the illustrated embodiment, the anchor delivery instrument  300  includes a handle  301  and a guide  302  connected to the handle  301 . The handle  301  includes a body  303  that is elongate along a central longitudinal axis  306 , and defines a proximal end  304  and a distal end  305  that is spaced from the proximal end  304  along the longitudinal axis  306 . The guide  302  is elongate along a central axis  310  that can be angularly offset with respect to the longitudinal axis  306 , and includes a cannulated body  307  having a first portion  308  that can define a head  318 , and a second portion  309  spaced from the first portion  308  along the central axis  310 . The second portion  309  can define a shaft  320  that extends distally from the head  318 . 
     The handle  301  includes a grip  315 , such that the body  303  supports the grip  315  and connects the grip to the guide  302 . The body  303  includes a first or proximal arm  322  that extends distally from the grip  315  inline with the longitudinal axis  306 , and a second or distal arm  324  that extends distally from the first or proximal arm  322 , and defines the distal end  305  of the handle  301 . The body  303  further includes a transition arm  314  connected between the first or proximal arm  322  and the second or distal arm  324 . The transition arm  314  can extend along a direction that is angularly offset with respect to the longitudinal axis  306 , such that the second or distal arm  324  is offset with respect to the first or proximal arm  322  along a direction angularly offset with respect to the longitudinal axis  306 . For instance, the second or distal arm  324  can be spaced closer to the distal end # of the guide  302 . The distal arm  324  can be attached to the head  318  of the cannulated body  307  as illustrated, or can be connected to the guide  302  at any alternative location along the cannulated body  307 , such as the shaft  320 . 
     The guide  302 , including the cannulated body  307 , can be made from a radiolucent material, meaning that it can be seen through in an x-ray, unless otherwise indicated. The cannulated body  307  defines a first or proximal end  308  and a second or distal end  309  that is spaced from the first or proximal end  308  along the central axis  310 . In accordance with the illustrated embodiment, the handle  301  is attached to the cannulated body  307  at the proximal end  308 , though it should be appreciated that the handle  301  can be attached to the guide  302  at any alternatively location as desired. The head  318  of the cannulated body  307  can define a cross-sectional dimension greater than that of the shaft  320 , though it should be appreciated that the head  318  can define a cross-sectional dimension less than that of the shaft  320 , or substantially equal to that of the shaft  320 . It should be appreciated that the cannulated body  307  can be devoid of the head  318 , such that the shaft  320  of the cannulated body  307  extends from the proximal end  308  of the cannulated body  307  to the distal end  309 . 
     The guide  302  defines a cannulation  311  that extends along the central axis  310  through the cannulated body  307 , and can extend through both the first and second ends  308  and  309 . The second end  309  includes a tip  312  that defines at least one tooth such as a plurality of teeth  317 . The tip  312  can be round or substantially circular, or can define any suitable alternative shape as desired. In accordance with the illustrated embodiment, the tip  312  defines a tapered profile along the circumferential direction, so as to define a distal point  331 . The tip  312  can be made from a radio-opaque material, which is more radio-opaque than the radiolucent material. The teeth  317  are configured to be driven into an underlying bone, such as a vertebra so as to secure the anchor delivery instrument  300  to the underlying bone. Thus, during a surgical delivery of a spinal fixation device  11 , a surgical component can be guided through the cannulation  311  to the underlying bone. The surgical component can be, for instance, a bone anchor  13  that is subsequently implanted in the underlying bone, a drill bit that is configured to produce a recess in the underlying bone, such that the recess is configured to receive the bone anchor  13 , a guide wire or Kirschner wire that facilitates implantation of the bone anchor  13  in the underlying bone, a fiduciary marker  7  (see  FIGS. 10-11J ), or any other surgical component as desired. Thus, the cannulation  311  can define a cross-sectional dimension sized substantially equal to or slightly greater than the surgical component that is guided through the cannulation  311 . 
     With continuing reference to  FIGS. 7A and 8 , the guide  302  can include a first set  326  of at least one first radio-opaque marker  313 , such as a plurality of first radio-opaque markers  313   a - 313   d , and a second set  328  of at least one second radio-opaque marker  330  such as a plurality of second radio-opaque markers  330 . For instance, as descried above, the tip  312  can be radio-opaque so as to define the second radio-opaque marker  330 . The first set  326  of radio-opaque markers  313  can be carried by the guide  302  at any location spaced from the second radio-opaque marker  330  as desired. For instance, the first set  326  of radio-opaque markers  313  can be at least partially embedded in the cannulated body  307 . In accordance with the illustrated embodiment, the head  318  includes a radially outer portion  332  and an inner portion  334  that is distally recessed with respect to the outer portion  332 , such that the outer portion  332  defines a radially inner surface  336  that defines a radially outer perimeter of a void  338  that is disposed proximal of the proximally outer surface of the inner portion  334 . The cannulation  311  extends through the inner portion  334  in accordance with the illustrated embodiment. The first plurality of radio-opaque markers  313   a - d  can be driven at least partially into the radially inner surface  336 , and thus at least partially embedded in the head  318 . In accordance with the illustrated embodiment, the first plurality of radio-opaque markers  313  are partially embedded in the head  318 , though it should be appreciated that the first plurality of radio-opaque markers  313  can alternatively be fully embedded in the head  318 . Alternatively still, the first plurality of radio-opaque markers  313  can be carried by the guide at any location proximal of the second radio-opaque marker  330  as desired. For instance, the first plurality of radio-opaque markers  313  can be at least partially embedded in or otherwise carried by the cannulated body  307  at any location proximal of the tip  312 . 
     In accordance with the illustrated embodiment, the first set  326  of at least one radio-opaque markers  313  includes a plurality of radio-opaque markers  313  that are substantially equidistantly spaced circumferentially with respect to each other. While four radio-opaque markers  313   a - d  are illustrated as spaced substantially 90° with respect to each other, the first set  326  of markers  313  can include any number of radio opaque markers  313  greater than or equal to one. It should be further appreciated that the plurality of radio-opaque markers  313  can alternatively be variably spaced from each other as desired. Furthermore, in accordance with the illustrated embodiment, the radio-opaque markers  313  define a first opposed pair  313   a  and  313   c , and a second opposed pair  313   b  and  313   d . The first set  326  of markers  313  further defines a first axis  340  that extends centrally through the first opposed pair  313   a  and  313   c  of radio-opaque markers, and a second axis  342  that extends centrally through the second opposed pair  313   b  and  313   d  of radio-opaque markers. In accordance with the illustrated embodiment, the axes  340  and  342  define an intersection  344 . 
     Referring also to  FIGS. 9A-B , the radio-opaque markers  313  and the circular tip  312  are shown in solid lines to represent their visibility in a radio image while the remainder of the guide  302  is shown in dotted lines to identify radiolucent material in the radio image. In accordance with the illustrated embodiment, the first and second sets  326  and  328  of at least one radio-opaque marker can be spatially positioned as desired to indicate that the guide  302 , and in particular the cannulated body  307 , is in a desired orientation with respect to a target location of an underlying bone. For instance, when distal point  331  of the tip  312  is driven into the underlying bone, such as a pedicle or a vertebra, and the cannulated body  307  is oriented as desired, the surgical component, such as the bone anchor  13  can be driven into the pedicle so as to remain contained in the pedicle as it is driven into the vertebra. It is appreciated that an improperly oriented bone anchor  13  or other surgical component can pierce the outer periphery of the pedicle or otherwise damage the pedicle or vertebra when driven into the vertebra. If the cannulated body  307  is found to be in an undesired orientation after the point  331  has been driven into the underlying target location, the orientation of the cannulated body  307  can be corrected to the desired orientation prior to driving the remainder of the tip  312  into the underlying bone and subsequently implanting the surgical component in the underlying bone. 
     The actual orientation of the cannulated body  307  can be determined as desired or undesired based on a spatial relationship between the first and second sets  326  and  328  of radio-opaque markers. For instance, when the cannulated body  307  is oriented as desired, the radio image of the tip  312  is disposed at a desired location with respect to at least one of the first set  326  of radio-opaque markers  313 . When the cannulated body  307  is undesirably oriented, the radio image of the tip  312  is disposed at a location other than the desired location with respect to at least one of the first set  326  of radio-opaque markers  313 . For instance, in accordance with the illustrated embodiment, the desired location of the tip  312  relative to the at least one radio-opaque marker  313  of the first set  326  of radio-opaque markers  313  is substantially centered with respect to the radio-opaque markers  313   a - d . In accordance with the illustrated embodiment, the intersection  344  of the axes  340  and  342  of the radio-opaque markers  313   a - d  is disposed substantially at the centroid  346  of the tip  312 , as illustrated in  FIG. 9A . When the cannulated body  307  is undesirably oriented, the radio image of the tip  312  is positioned such that the centroid  346  of the tip  312  is offset with respect to intersection  344  of the axes  340  and  342 . It should be appreciated that the actual orientation of the cannulated body  307  can be compared to the desired orientation to determine if the actual orientation is in the desired orientation or an undesirable orientation from a view substantially inline with the central axis, or other known desired orientation, with respect to the underlying target location, which can be the pedicle of the underlying vertebra. Thus, the view can be an anterior-posterior view of a fluoroscopic image, or the view can be laterally oblique with respect to an anterior-posterior view. 
     Referring now to  FIG. 7B , the surgical assembly  41  can further include an anchor delivery assembly  131  that includes the anchor delivery instrument  300  and a trocar  348  that is configured to be inserted through the cannulation  311  of the guide  302 , and driven into the cortical wall of the underlying bone, e.g., pedicle, once the actual orientation of the cannulated body  307  has achieved the desired orientation. The trocar  348  can include a head  350  and a shaft  352  that extends distally from the head  350 , and a tip  354  that extends distally from the shaft  352 . The shaft  352  has a cross-sectional dimension substantially equal to or slightly less than that of the cannulation  311 , such that the cannulated body  307  can guide the shaft  352  distally as the shaft  352  translates in the cannulation  311 . The head  350  defines a cross sectional dimension greater than that of the shaft, such that the head  350  abuts the proximal end of the guide  302  when the trocar  348  has been fully translated distally within the cannulation  311 . Once the trocar  348  has been fully translated distally, the tip  354  protrudes distally beyond the point  331  of the tip  312  of the shaft  320 , such that the tip  354  of the trocar  348  can pierce the cortical wall of the underlying bone at an insertion point without causing the tip  312  of the cannulated body  307  to also pierce the cortical wall of the underlying bone. The tip  354  can be driven through the cortical wall and into the cancellous portion of the target bone. 
     Accordingly, during operation, a radio image of the guide  302  and spinal region is examined to determine whether the guide  302  is in the desired orientation or an undesired orientation. If the guide  302  is in an undesired orientation, the cannulated body  307  can be pivoted until it is determined that the cannulated body  307  is in the desired orientation. Once the actual orientation of the cannulated body  307  is the same as the desired orientation, the trocar  348  can be tapped, for instance at the head  350 , using a mallet or any suitable alternative device so as to drive the trocar tip  354  through the cortical wall of the underlying target bone so as to create a pilot hole in the underlying bone. It should be further appreciated that the teeth  317  can be caused to grip the underlying bone before or while the guide  302  is oriented as desired. For instance, a mallet or any suitable alternative device can tap the proximal end  308 , or head  318 , of the cannulated body  307  so as to cause the teeth  314  to bite into the cortical wall of the underlying bone prior to driving the trocar through the cortical wall. 
     Next, the trocar  348  can be translated proximally so as to remove the tip  354  from the underlying bone and further remove the trocar  348  from the cannulation  311 , and a surgical component can next be inserted into the cannulation  311  and driven distally into the pilot hole created by the trocar  348 . For instance, the bone anchor  13 , without the bone anchor seat  17  attached, can be inserted into the cannulation  311 , which can be sized substantially equal to or slightly greater than the head of the bone anchor  13 . The driver instrument of the bone anchor  13  can translate the bone anchor  13  distally through the cannulation  311 , and rotate the bone anchor  13  such that the tip of the threaded bone anchor shaft  60  is driven into the underlying bone through the pilot hole created by the trocar  348 . Once the bone anchor  13  has been driven into the underlying bone, the guide  302  can be removed from the bone anchor  13  by translating the cannulated body  307  proximally until the cannulation  311  has cleared the bone anchor head. Once the guide  302  has been removed, the bone anchor seat  17  can be popped downward onto the head of the bone anchor  13  as described above. 
     As described above, the surgical component can define a fiduciary marker  7 , which can include the bone anchor  13 , or any alternative structure that can be implanted in the underlying bone (see  FIGS. 10-11J ). Thus, the fiduciary marker  7  can be driven through the cannulation  311  and into the pilot hole created by the trocar  348  as described above with respect to the bone anchor  13 . Alternatively or additionally, once the trocar  348  has been driven through the cortical wall of the underlying bone and subsequently removed, a drill bit can be driven distally through the cannulation  311  and into the pilot hole created by the trocar  348 , and subsequently further into the underlying bone. The drill bit can subsequently be removed, and the bone anchor  13  or other fiduciary marker  7  can be subsequently inserted in the pilot hole created by the drill bit. 
     Referring now to  FIG. 10 , the fiduciary marker can be configured as the bone anchor  13  as described above, or any alternative radiographically visible pedicle reference implant. For instance, the fiducial marker  7  is inserted into a patient&#39;s vertebra  2 , such as the pedicle, and provides a distinct reference marker to aid the surgeon in fluoroscopically navigating the surgical workspace. The fiducial marker  7  provides a reference point from which the surgeon can generally identify several noteworthy areas of the spinal region  1  including the lamina  6 , disc space  4 , exiting nerve roots, and other anatomical structures of a vertebra  2  prior to, and during, decompressive surgical procedures. For instance, Zone  1  identifies the boney region immediately adjacent to the fiducial marker  7 . This area provides a desired navigational reference location, such as the pedicle. Zone  2 , as illustrated, can be bounded by the disc space  4  at the cranial aspect (typical surgical target) and the exiting nerve root in the lateral, caudal quadrant. Zone  3 , as illustrated, can extend to the cranial-most side of both the cranial disc space  4  adjacent to the boney region identified by Zone  1  and the caudal disc space  4  adjacent to the boney region identified by Zone  1 . By marking a known pedicle position, the surgeon can maintain a navigable reference even after the patient&#39;s anatomy has been significantly altered during the surgical procedure. 
     Referring now to  FIGS. 11A-11J , the fiducial markers  7  can provide non-ambiguous anchoring locations or mounting posts for attachment of various surgical instruments, such as access ports, retractor blades, suction tubes, targeting devices, drill guides or endoscopic instruments, that may be used when performing decompression, fusion, and fixation procedures of the spine. The various fiducial markers  7  can be constructed as desired, for instance as illustrated by the fiducial markers  7   a - 7   f  illustrated in  FIGS. 11A-11J , or alternatively as illustrated by the bone anchor  13 . 
     Referring to  FIG. 11A , the fiducial marker  7   a  is illustrated as a spinal fixation device  11 , including the bone anchor  13  and the bone anchor seat  17  as described above. Referring to  FIG. 11B , the fiducial marker  7   b  is illustrated as the bone anchor  13  of  FIG. 11A , including a shaft  8  presenting external threads  9 , and a head  137  having a substantially spherical outer surface  139 . As described above, the bone anchor seat  17  can be popped onto the outer surface  139  of the head  137  after the shaft  8  has been driven into the underlying bone. As illustrated in  FIGS. 11C-G , the fiducial markers  7   c - 7   e  can include a shaft  8  and a head  137  disposed at the proximal end of the shaft  8 . The heads  137  can be constructed in accordance with any embodiment as desired. Various heads are illustrated in  FIGS. 11C-G . It should be appreciated, however, that the fiducial markers  7  can be provided without heads, and that the shafts  8  can be constructed in accordance with any embodiment as desired. For instance, as illustrated in  FIG. 11I , the shaft  8  can be unthreaded. Each of the fiducial markers  7   a - 7   f  can define a cannulation extending longitudinally through the shaft  8  that is configured, for instance, to receive a guide wire that extends into the underlying bone. The markers  7   a - 7   f  may be further designed to accommodate any number of degrees of freedom of movement of the attached instrumentation. The mechanisms to orient and/or secure the instruments in the surgical site may be a function of the markers  7   a - 7   f , the surgical instrument, or both. The markers  7   a - 7   f  can be removed prior to closing the surgical site or, alternately, the markers  7   a - 7   f  can be retained as one of the elements of the fixation hardware to be used in the surgical procedure, such as the embodiment shown for marker  7   a , in which a spinal fixation device  11 , including a bone anchor  13  and an anchor seat  17 , is used as the marker device, or the embodiment shown for marker  7   b , in which a bone anchor  13  is used as the marker device and a bottom-loading or “pop-on” anchor seat  17  is coupled over the head  137  of the bone anchor  13 . Pedicle targeting aids, such as the anchor delivery instrument  300  described above can also be coupled to the various fiducial markers  7   a - 7   f . The void created in the underlying bone during insertion of the fiducial markers  7   a - 7   f  may subsequently define a pilot hole for placing permanent hardware, such as spinal fixation devices  11 , after removal of the fiducial marker  7 . The markers  7   a - 7   f  may be formed of radio-opaque material or include radio-opaque portions or elements for fluoroscopic visibility. In some embodiments, the fiducial markers  7   a - 7   f  and/or other components of the related system can be disposable. 
     Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For instance, it should be appreciated that the cross-sectional dimensions described herein can define diameters, unless otherwise indicated. Moreover, the scope of the present disclosure is not intended to be limited to the particular embodiments described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure.