Abstract:
A facet joint is exposed at one side of the spine during surgery. An inclinometer is mounted on an elongated probe, and a pin is fixed on a spinous process near the exposed joint. The probe is swivelled about the pin so that a distal end of the probe contacts the joint and the inclinometer indicates a corresponding first trajectory. A second trajectory from the pin to an unexposed facet joint on the opposite side of the spine is defined as being symmetrical with the first trajectory about the spine axis. The inclinometer is mounted on a guide sleeve, and the sleeve is swivelled about the pin into the second trajectory. A wire is inserted through the sleeve until a tip of the wire penetrates the unexposed joint percutaneously. A facet screw is advanced over the wire and threaded percutaneously into the unexposed facet joint after the sleeve is withdrawn.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/389,906 filed Oct. 5, 2010, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to spinal implant procedures and tools, and particularly to a procedure and tools for implanting facet joint screws percutaneously. 
     Discussion of the Known Art 
     U.S. Pat. No. 7,717,919 discloses a mechanical alignment jig (see FIGS. 17-20) for aligning the axis of an external cannula guide block to coincide with, or run parallel to, a determined internal target path along which a screw is to be delivered percutaneously to either one of two facet joints at a given level of a patient&#39;s spine. Each internal guide path is initially determined by a surgeon using conventional imaging means and by inserting markers. 
     Further, U.S. Patent Application Pub. No. 2010/0023018 describes a bilateral drilling guide (see FIG. 1) that is fixed by a clamp on the spinous process of a vertebral body in a patient&#39;s spine. An extension is mounted to extend laterally from the spinous process, and to rotate 180 degrees between either side of the vertebral body. A pointing device, a protractor, and a drill bushing are mounted on the extension to enable a number of drilling axes to be defined toward the body. 
     U.S. Pat. No. 4,907,577 discloses a transpedicle drill jig having a pair of drill guiding sleeves (see FIGS. 3-6) the distal ends of which can be placed at desired positions on either side of a vertebral body of a patient&#39;s spine. In use, the jig is held against but is not fixed to the vertebral body. 
     New products for facet fixation have been offered to complement the use of unilateral pedicle screws or stand-alone cages in spinal surgery. Many of these products do not fixate rigidly, and/or they are cumbersome to implant properly. Problems have been encountered mainly in the process of targeting and placing the screws in the patient&#39;s spine, rather than in fixation where conventional facet screws have proven to achieve the best results. 
     To achieve a minimally invasive spinal fusion procedure, surgeons may implant pedicle screws unilaterally by exposing the spine only at the side in which the screws are to be inserted, and provide contralateral facet joint fixation by use of facet screws inserted percutaneously with the aid of X-ray imaging and/or other navigation equipment. Notwithstanding the known art, there is a need for tool or system that will enable a surgeon to determine a first drilling axis along which a facet screw can be inserted percutaneously and accurately into a given side of a patient&#39;s spine, based only on the geometry of a second drilling axis determined at the opposite side of the spine, and without a need for X-ray or other navigation techniques. Such a tool could substantially reduce the time required to implant facet screws or other devices percutaneously at the given side of the spine. 
     SUMMARY OF THE INVENTION 
     According to the invention, a surgical tool system for implanting facet joint screws percutaneously in a patient&#39;s spine, includes an elongated probe, and an inclinometer arranged and configured to mount on the probe for sensing angular deviations of the probe from a horizontal and a vertical plane, and for indicating corresponding trajectories of the probe. A guide anchor screw or pin is configured to be fixed on a spinous process on a given spinal vertebra, and the pin has a guide opening or channel for passage of the probe, and for enabling the probe to swivel so that a distal end of the probe contacts an exposed first facet joint on one side of the spine and the inclinometer indicates a first trajectory from the pin to the first facet joint. The system also includes a guide sleeve on which the inclinometer is mounted, and the pin on the spinous process enables the sleeve to swivel about the pin to a position at which the inclinometer indicates a second trajectory from the pin to an unexposed second facet joint on the opposite side of the spine, such that the second trajectory is symmetrical with the first trajectory about the spine axis. A guide wire is dimensioned to be inserted through the guide sleeve so that a distal tip of the wire penetrates the second facet joint percutaneously. A cannulated facet screw is arranged to be advanced over the guide wire after the sleeve is withdrawn, and the screw is threaded percutaneously through the second facet joint. 
     According to another aspect of the invention, a method of implanting facet joint screws percutaneously in a patient&#39;s spine includes exposing a first facet joint at one side of the spine while performing a surgical procedure, providing an elongated probe, and mounting an inclinometer on the probe to indicate angular trajectories of the probe. A guide anchor screw or pin is fixed on a vertebral spinous process in the vicinity of the first facet joint, and the probe is swivelled about the pin so that a distal end of the probe contacts the exposed first facet joint and the inclinometer indicates a corresponding first trajectory from the pin to the first facet joint. A second trajectory from the pin to an unexposed second facet joint on the opposite side of the spine is defined as being symmetrical with the first trajectory about the spine axis. The inclinometer is mounted on a guide sleeve, and the sleeve is swivelled about the pin on the spinous process to a position at which the inclinometer indicates the second trajectory. A guide wire is inserted through the sleeve until a distal tip of the wire penetrates the second facet joint percutaneously. After the sleeve is withdrawn, a facet screw is advanced over the guide wire and threaded percutaneously into the second facet joint. 
     For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawing and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the drawing: 
         FIG. 1  shows a spinal vertebra as viewed in a plane perpendicular the axis of a human spine; 
         FIGS. 2( a ) and 2( b )  are views of the vertebra as in  FIG. 1 , and including a probe to demonstrate a reflective symmetry of the spine, according to the invention; 
         FIGS. 3( a ) and 3( b )  show the vertebra of  FIG. 1 , showing opposite side end portions of the vertebra and the probe to demonstrate reflective symmetry according to the invention; 
         FIG. 4  is a cross sectional image of a lumbar portion of a patient&#39;s spine in a plane transverse the axis of the spine, and showing two facet joints on either side of the spine axis; 
         FIG. 5  shows the lumbar portion of the spine, and a guide anchor screw or pin inserted in the top edge of a spinous process according to the invention; 
         FIG. 6  shows an incision in the patient&#39;s back exposing one side of the spine and the anchor pin inserted in the spinous process; 
         FIG. 7  shows a probe passing through a gap in the anchor pin and defining a first trajectory toward a facet joint on one side of the spine; 
         FIG. 8  shows the probe in  FIG. 7  defining a second trajectory toward a facet joint on the other side of the spine and at the same level as in  FIG. 7 ; 
         FIG. 9  shows another embodiment of the guide anchor pin; 
         FIG. 10  shows the anchor pin in  FIG. 9  with a cap removed; 
         FIG. 11  shows a guide or K-wire passing through a gap in the anchor pin of  FIG. 9 , while being inserted percutaneously into a facet joint at an unexposed side of the spine; and 
         FIG. 12  shows the guide wire in  FIG. 11  removed from the anchor pin prior to guiding a cannulated facet screw to the facet joint for insertion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a tool or system for locating and placing facet screws or other implants in a surgical patient&#39;s spine, typically for the purpose of obtaining a spinal fusion. The inventive system allows certain implants to be placed percutaneously with accuracy and in minimal time. 
     It has been discovered and observed that except for cases of scoliosis, congenital deformity or tumor, the vertebral bones of a normal human spine have what is referred to herein as “reflective symmetry”. See, for example, vertebra  12  in  FIG. 1 . Specifically, when the vertebra  12  is viewed in a plane perpendicular to spine axis A as in  FIGS. 1, 2 ( a ) &amp;  2 ( b ), the body of the vertebra  12  on the left side of a normal line N drawn perpendicular to the spine axis A, is a mirror image physically of the body of the vertebra  12  on the right side of the line N. Accordingly, if a probe  14  is used to form an entry point on the left pedicle of the vertebra  12  as viewed in  FIG. 2( a )  and the probe  14  defines an angle P 1  with line N, the probe  14  will define an angle P 2  equal to P 1  in magnitude with respect to line N when forming a corresponding entry point on the right pedicle of the vertebra  12  as viewed in  FIG. 2( b ) . 
     Further, when the lateral side ends of the vertebra  12  are viewed in planes parallel to the spine axis A as in  FIGS. 3( a )  &amp;  3 ( b ), the side end portions of the vertebra  12  are also mirror images of one another in three-dimensional space. That is, if the probe  14  as it is viewed in  FIG. 3( a )  defines an angle P 3  with a vertical line V, the probe  14  will define an angle P 4  equal to P 3  in magnitude with respect to line V as the probe  14  is viewed in  FIG. 3( b ) . The inventive system uses to advantage the reflective symmetry of the spine to allow a facet screw or other fixation device to be implanted in the vertebra  12  percutaneously and accurately along a first drilling axis in one side of the vertebra, according to the geometry of a second drilling axis that is determined while the opposite side of the vertebra is exposed during a spinal fusion procedure. 
     EXAMPLE 
     Posterior Unilateral Approach 
     A hybrid construct for a L4-L5 fusion is desired using unilaterally placed pedicle screws and contralateral facet fixation. An incision is made in preparation for placement of the pedicle screws at the side of the patient&#39;s spine corresponding to the patient&#39;s right side, which is toward the left as viewed in  FIG. 4 . Before exposing and removing the facet joint RF in  FIG. 4  in order to accommodate the construct, a tool guide anchor screw or pin P according to the invention is inserted in the L3 spinous process SP so that the head of the pin P protrudes vertically above the top edge of the spinous process, and above the incision as depicted in  FIGS. 5 and 6 . A gap opening G is formed at the head of the guide pin P for supporting a probe that passes through the opening G (see  FIGS. 7 &amp; 8 ), and for allowing the probe to swivel on the head of the pin so that the distal end of the probe can swing toward the exposed right facet joint RF. 
     As illustrated in  FIGS. 4 and 7 , a trajectory T is determined for the probe D when passing through the opening G at the head of the anchor pin P, and a position X on the right facet joint RF at which a facet screw would be inserted in the event a fixation of the joint RF were to be performed. The trajectory T may be defined by use of a conventional inclinometer, for example, a model H4PD1-22 inclinometer available from Rieker™ which provides dual axis inclination sensing using an element referenced to gravity over a wide temperature range. Inclinometers have been incorporated in devices or probes for determining a trajectory for placement of pedicle screws. See, e.g., U.S. Patent Application Pub. No. 2010/0087823 (Apr. 8, 2010) and Pub. No. 2010/0036384 (Feb. 11, 2010), both of which are incorporated by reference. 
     As shown in  FIG. 7 , a probe  18  with an associated inclinometer  20  operatively fixed on the outside circumference of the probe, passes through the opening G formed at the top of the anchor pin P inserted in spinous process SP. The distal tip of the probe  18  is visibly positioned by the surgeon at a point X on the facet joint RF where a facet screw would be inserted if a fixation of facet joint RF were to be performed. 
     The trajectory T of the probe  18  from the head of the anchor pin P to the insertion point X on the facet joint RF is then defined by the inclinometer  20  with respect to the head of the anchor pin P by, e.g., (a) degrees HOR relative to the spine axis A in a horizontal plane, as shown in  FIG. 4 , and (b) degrees VER downward relative to the spine axis A in a vertical plane, as shown in  FIG. 7 . Signals corresponding to both of the angular measurements HOR and VER are transmitted from the inclinometer  20  over an associated cable  22 , or wirelessly, and are processed in a known manner to determine the magnitudes of the angles. 
     Both of the angles HOR and VER are stored and/or displayed for later reference. The right facet joint RF is then removed, and pedicle screws and rods are placed by the surgeon in the L4-L5 level at the exposed side of the patient&#39;s spine. Prior to removing the facet joint RF, the surgeon can determine the length of a facet screw need to fix the left facet joint LF on the opposite side of the spine, by measuring the exposed right facet joint RF. 
     Without making another incision or opening to expose the other side of the patient&#39;s spine, a contralateral facet screw is placed percutaneously and rapidly according to the angular measurements HOR and VER as obtained above. As shown in  FIG. 8 , a drill bit guide sleeve  30  has the same or an equivalent inclinometer  20 ′ fixed along its outer circumference and aligned in the same orientation with respect to the sleeve as the inclinometer  20  on the probe  18 . The inner diameter of the sleeve  30  should be sufficient to allow passage of a drill bit, and an inner, second guide sleeve  32  may be routed concentrically inside the outer sleeve  30  and have an inner diameter dimensioned for passage of a conventional surgical drill bit guide wire or “K-wire”. The sleeve  30  with the inner sleeve contained 32 inside, is passed through the opening G in the anchor pin P atop the spinous process SP as shown in  FIG. 8 . The surgeon swivels the sleeve  30  over the unexposed side of the spine in a horizontal plane by HOR degrees, that is, by the same number of degrees the probe  18  was swung horizontally over the exposed side of the spine when determining the trajectory for placing a screw in the facet joint RF (now removed). The surgeon swivels the sleeve  30  downward in a vertical plane by VER degrees, that is, by the same number of degrees the probe  18  was swung downward to determine the proper trajectory for screw placement in facet joint RF. The sleeve  30  is advanced percutaneously into contact with the left facet joint LF (see  FIG. 11 ). Thus, the sleeve  30  defines a correct trajectory for inserting a screw in the left facet joint LF, based on the geometry of the trajectory determined for the right facet joint RF on the opposite side of the patient&#39;s spine. 
     A drill bit guide wire or “K-wire”  40  is inserted in the proximal end of the inner guide sleeve  32  contained in the outer sleeve  30 , and the wire is advanced percutaneously toward the unexposed side of the patient&#39;s spine until the tip of the wire contacts the left facet joint LF. See  FIG. 11 . The proximal end of the wire may be fastened to a drill, and the tip of the wire drilled or manually urged to a certain depth into the joint LF. The inner guide sleeve  32  is withdrawn from the outer sleeve  30  and the guide wire  40 , and a conventional cannulated drill bit is slid over the guide wire and through the sleeve  30 . The drill bit is advanced percutaneously into contact with the facet joint LF, and then driven a sufficient distance through the joint LF as to allow a conventional facet screw to be threaded through the joint for fixation. 
     The drill bit and the outer sleeve  30  are then withdrawn from the guide wire  40 , and a cannulated facet screw is passed over the guide wire. To facilitate passage of the facet screw over the guide wire, the wire may be brought outside of the gap opening G, for example, by urging the wire sideways through a narrow slot formed at the periphery of the opening G and away from the anchor pin P. The facet screw is advanced percutaneously on the guide wire toward the facet joint LF, and is driven by a cannulated drive bit through the opening formed in the joint LF by the drill bit. The drive bit and the guide wire are then withdrawn from the joint LF, and the anchor pin P is removed from the spinous process SP. 
       FIGS. 9 and 10  show a preferred embodiment of the anchor pin P in the form of a polyaxial surgical screw including a swivel head  50  and a threaded cap  52 . Gap opening G is bounded by an open channel  54  formed across the top of the swivel head  50  and the cap  52  threaded onto the head  50 . As shown in  FIG. 12 , once the distal end of the guide wire  40  is fixed in the facet joint LF, the guide wire may be removed from within the gap opening G in the anchor pin P by unscrewing the threaded cap  52  from the swivel head  50  as in  FIG. 10 . With the guide wire removed from the anchor pin P, neither the cannulated facet screw nor the drill bit would need to be able to pass through the gap opening G formed in the pin P. 
     It is contemplated that a surgical tool system kit for placement of facet joint screws according to the invention may be provided to include, for example: 
     (a) an elongated probe; 
     (b) an inclinometer configured to mount on the probe in such a position as to sense an angular deviation of the probe from a horizontal and a vertical plane, and to output corresponding signals for processing; 
     (c) a guide anchor screw or pin with a polyaxial swivel head and a guide opening or channel formed in or on the head; 
     (d) a length of guide wire or K-wire; 
     (e) a drill bit guide sleeve with a removable concentric inner sleeve; 
     (f) a cannulated drill bit; and 
     (g) cannulated facet screws of one or more different lengths. 
     The inventive tool system may also be adapted to place a screw or an implant into other parts of the spine such as, e.g., a pedicle, transverse process, lamina, etc, as long as the targeted anatomic structures have reflective symmetry with the corresponding structures on the opposite side of the spine. Moreover, facet screws or other implants may still be placed percutaneously at one side of the spine in a traditional manner based on X-ray and/or other imaging techniques, and the inventive tool system can then be used to place implants percutaneously at the other side of the spine in significantly less time. 
     While the foregoing represents preferred embodiments of the invention, it will be understood by those skilled in the art that various modifications and changes may be made without departing from the spirit and scope of the invention, and that the invention includes all such modifications and changes as are within the bounds of the following claims.