Abstract:
An instrument for spinal rotation that aligns and holds direct vertebral rotation (DVR) lever arms relative to each other to achieve an initial axial alignment of a segment of vertebrae and allows the final DVR rotation by rotating the instrument and lever arms together. A method of direct vertebral rotation that allows rotating the vertebrae to be aligned relative to each other, and collectively rotating the vertebrae to be aligned relative to adjacent spinal segments by rotating the direct vertebral rotation instrument. A system for direct vertebral rotation having at least two pedicle screws. The system also includes at least two levers attachable to the pedicle screws and a clamping instrument configured to clamp the levers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/889,847, filed on May 8, 2013, which is a divisional application of U.S. application Ser. No. 12/152,834, filed on May 16, 2008, which claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/930,770, filed May 18, 2007, the disclosures of which are hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an alignment linkage such as a direct vertebral rotation instrument for creating, restraining and/or maintaining horizontal rotation of the vertebrae during posterior spinal fusion operations. The present invention also relates to a method for creating, restraining and/or maintaining horizontal rotation of the vertebrae during posterior spinal fusion operations. 
       BRIEF DESCRIPTION OF THE PRIOR ART 
       [0003]    During spine surgery for conditions such as scoliosis, the surgeon seeks to achieve a three-dimensional correction of the spinal column shape by realigning and instrumenting the vertebrae in order to achieve an eventual fusion of the vertebral bodies in the desired alignment. Typically, the misalignment of the patient&#39;s vertebral bodies is readily apparent in the sagittal and coronal planes, either visually or by radiography. More difficult to see and correct is rotational misalignment of the vertebrae about the axis in the defined along the length of the spine. This rotation is often characterized in the scoliosis patient by projection of the ribs of the back creating a so-called rib hump on one side of the back caused by the rotation of the thoracic vertebrae and the attached ribs. While the axis of rotation actually changes along the length of the spine due to the spines natural curvature, for convenience of discussion the axis will be discussed as if it is a vertical line. 
         [0004]    In order to correct such a rotational misalignment, the surgeon must axially rotate the vertebrae in the opposite direction so that they are correctly oriented about the longitudinal axis of the spine. A corrective rotation of this type is often referred to as a “derotation.” 
         [0005]    Direct vertebral rotation, hereinafter “DVR,” is one method of horizontally rotating and re-aligning vertebral bodies. To use DVR, screws are implanted in the pedicles of the vertebrae and then a horizontal torque is applied by a lever arm or extension tube mounted to the screw head. As mentioned above, the indication is frequently scoliosis, but other deformity issues may be addressed through DVR. Tubular lever arms are then placed on the screws in line with the axis of the screw. A force is then applied to the lever arms to rotate the spinal vertebrae. This brings the vertebrae into the desired positions and in line with one another. The surgeon and the surgeon&#39;s assistants face the difficult task of manually rotating and aligning the various lever arms to eventually fasten the pedicle screw assemblies to rods and form a construct holding the vertebrae in the desired alignment. 
         [0006]    Polyaxial pedicle screw assemblies have, by way of example, a cage shaped to receive a bone screw, a rod and a blocker or set screw engaging screw threads. Generally, cages have two arms that extend away from the screw and define a slot through which the rod can pass transverse to the axis of the cage. Often, such cages are referred to as tulip shaped. The cage can move polyaxially about the head of the bone screw until the assembly is fixed in a position. Once the rod is in place, the blocker is threaded within or on the outside of the cage. The blocker engages, directly or indirectly, the rod which in turn engages the head of the bone screw seated in the cage or engages the cage itself. The blocker thus locks or immobilizes the assembly. 
         [0007]    A monoaxial pedicle screw assembly generally includes a bone screw with an integral cage or head to receive the rod and blocker or nut. 
         [0008]    For DVR, the lever arms apply torque to the bone screw and the bone screw, in turn, applies the torque to the vertebrae. Either a polyaxial or monoaxial screw assembly may be used. The lever must fit tightly and grasp the screw head in order to apply the torque. If a polyaxial screw assembly is used, the head should be immobilized in the direction of axial rotation to allow the transmission of torque. A polyaxial screw also has a limited extent of free travel and can create torque on the vertebra once the range of movement of the head is exceeded. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention fills the need described above by providing a system and method for rotation of vertebral segments for posterior spinal fusion. 
         [0010]    The invention is directed to an instrument and associated method that aligns and holds the DVR lever arms relative to each other to achieve an initial axial alignment of a segment of vertebrae and allow the DVR rotation by rotating the instrument and lever arms together. 
         [0011]    Joining the lever arms or extension tubes with such a clamping instrument allows the surgeon to more uniformly and easily rotate the tubes together and to stepwise achieve a relative orientation of a segment of vertebrae. The segment of vertebra to be aligned can be aligned collectively relative to adjacent spinal segments. 
         [0012]    In one aspect the invention teaches a method of direct vertebral rotation, wherein the steps include attaching pedicle screws to at least two vertebrae to be aligned and attaching a lever to each of the pedicle screws. The levers are positioning between jaws of a direct vertebral rotation instrument and the jaws held in closed position. The jaws are brought together to rotate the vertebrae to be aligned relative to each other, and the vertebrae to be aligned are collectively rotated relative to adjacent spinal segments by rotating the direct vertebral rotation instrument. 
         [0013]    In another aspect the invention teaches a direct vertebral rotation instrument comprising a first jaw; a second jaw; a hinge connecting the first jaw and the second jaw; and a lock for locking the first jaw to the second jaw. 
         [0014]    In yet another aspect the invention teaches a system for direct vertebral rotation having at least two pedicle screws. The system also includes at least two levers attachable to the pedicle screws and a clamping instrument configured to clamp the levers. 
         [0015]    In one aspect of the present invention, the instrument has substantially parallel jaws to engage or clamp the lever arms in relative alignment for manipulation. 
         [0016]    In another aspect of the invention, the jaws of the instrument have a compliant material for interface with the lever arms in order to assist in gripping the lever arms and thus facilitate the effective adjustment of the longitudinal position of the lever arms. 
         [0017]    A further aspect of the invention includes the method of rotating vertebrae located within a patient&#39;s body about the spinal axis by: implanting a first pedicle screw on a first vertebra; implanting a second pedicle screw on a second vertebra; attaching a first moment arm and a second moment arm to the first screw and the second screw, respectively; locking the first moment arm and a second moment arm in a preliminary angular orientation with respect to the spinal axis by applying pressure using the opposing jaws of an instrument to align and restrain said moment arms; and rotating the instrument, arms and vertebra relative to the spinal axis. 
         [0018]    The present invention may be reduced to practice by a clamping instrument which includes elongate jaws having opposed interior faces and being hingeably or rotatably connected at one end or interior from one end, the jaws having an open position and a closed position, the open position facilitating the instrument to be arranged about a plurality of pedicle screw extension tubes or other lever arms associated with vertebra. The instrument in its closed position holds and initially aligns the lever arms on the interior faces of the jaws. 
         [0019]    In another aspect of the present invention, the above described instrument includes handles to facilitate at least the closing of the jaws. The handles may be in the central area of the jaws and extend transverse to the elongate axis of the jaws, or may be displaced towards or at one end of the jaws, or even as an extension generally in alignment with the elongate axis of the jaws, or a portion of the jaws themselves may serve as portions of handles. 
         [0020]    In another aspect of the present invention, the jaws are hingeably connected at one end or are located interiorly from one end and include a spring mechanism to hold the jaws in a normally open position. This normally open position facilitates arrangement of the jaws about the extension tubes or lever arms to be clamped within the jaws. The hinge may be integral with one or both jaws, or may be a separate element connected to the jaws. 
         [0021]    In another aspect of the present invention, the closing mechanism is provided to hold the jaws in a closed position such that a surgeon or surgeon&#39;s assistant does not need to hold the handles together in order to maintain the instrument in a closed position. In one embodiment, a closing mechanism may be a latching mechanism provided anywhere along the jaws, or even on the handles themselves. In a preferred embodiment, a latching mechanism is provided at the end of the jaws opposite the hinge mechanism, and comprises a pawl and ratchet arrangement which automatically latches the jaws as the jaws are closed. The latching mechanism may have an extension with a finger grip, which may simply be a surface designed to facilitate gripping of one&#39;s finger (knurling, raised gripping ribs, etc.). The finger gripping portion may extend laterally outside of one of the jaws such that a depression on that portion will release the pawl and ratchet mechanism. 
         [0022]    In another aspect of the present invention, the interior faces of the jaws have a surface to facilitate gripping the extension tubes or lever arms. In a preferred embodiment, this may be a compliant material such as rubber. The coefficient of friction of such a material should facilitate the gripping of the lever arms, and the material may also include compliancy such that the lever arms are, upon undergoing a clamping force, forced into the material for gripping purposes. The compliance also allows the lever arms to be gripped at various angles and positions along the length of the jaws. 
         [0023]    In another aspect of the present invention, a method includes the use of the above broadly described instrument by surrounding a plurality of lever arms with a normally open instrument, positioning the instrument about the lever arms, closing the instrument such that the jaws clamp the lever arms, and manually applying a torque and otherwise manipulating the instrument in order to manipulate the lever arms and thus the vertebra to which the lever arms are connected, directly or indirectly. The clamping of the jaws may achieve an initial desired alignment of the lever arms and vertebrae and then the entire assembly of the lever arms and vertebrae may be further rotated to the final position. The method may also include the steps of fixing spinal rods or other fixation devices arranged with respect to the vertebra to maintain the vertebra in the aligned position, and subsequently releasing the clamping instrument and removing the same from the lever arms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic right side view of four adjacent vertebrae of a spine, with pedicle screws and lever arms as used in DVR. 
           [0025]      FIG. 2  is a plan view as in  FIG. 1  showing the lever arms and establishing a coordinate system relative to the human body. 
           [0026]      FIG. 3  is a schematic right side view of four adjacent vertebrae of a spine, with pedicle screws, lever arms and an instrument according to the present invention. 
           [0027]      FIG. 4  is a plan view as in  FIG. 3  showing the lever arms and instrument of the present invention. 
           [0028]      FIG. 5  is a perspective left side view of four lever arms and an instrument according to the present invention. 
           [0029]      FIG. 6  is a perspective left side view of two lever arms and an instrument according to the present invention. 
           [0030]      FIG. 7  is a perspective view of an instrument according to the present invention in the open position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring to  FIG. 1 , the portion of the spine illustrated includes a first vertebra  1   a , which may be the T10 (Tenth Thoracic) vertebra of a patient, a second vertebra  1   b , which may be the T9 (Ninth Thoracic) vertebra of a patient, a third vertebra  1   c , which may be the T8 (Eighth Thoracic) vertebra of a patient, and a fourth vertebra  1   d , which may be the T7 (Seventh Thoracic) vertebra of a patient. The systems and methods described hereafter may be applicable to any vertebra or vertebrae of the spine and/or the sacrum (not shown). In this application, the term “vertebra” may be broadly interpreted to include the sacrum although rotation is only attempted relative to the sacrum and the sacrum itself is not rotated. 
         [0032]    Pedicle screw assemblies  11   a - 11   d  (collectively screws  11 ) are implanted in the associated pedicles of the vertebrae  1   a - 1   d . In one of many pedicle screw arrangements, pedicle screw assemblies  11   a - 11   d  each have a cage  13  shaped to receive a rod and a set screw that passes through an aperture of the cage. Each screw  11  also has a threaded shaft  15  which is threaded into the vertebra  1  to implant the pedicle screw assembly. 
         [0033]    Connected to the head  13  of each screw  11  are moment arms  21   a - 21   d  (collectively moment arms  21 ). In this embodiment the moment arms  21  are cannulated tubes having an open distal end  23  allowing placement of objects such as the aforementioned locking screws and suitable locking screw drivers through the cannulae of the tubes. These moment arms  21  serve as lever arms in connection with the vertebral rotation system herein. The proximal end  25  of each moment arm  21  removeably engages the head  13  of the respective pedicle screw assembly  11  so as to be able to apply torque to the vertebrae  1 . 
         [0034]      FIG. 2  shows a top view, related to  FIG. 1 , of the distal end of the moment arms  21   a - 21   d . Also shown is a coordinate system defining superior and inferior directions along the spinal axis and left and right directions in the plane defined by the spine axis A-A. Thus, the torque to be applied by the moment arms  21  is in the left or right direction. It can be seen that the distal ends  23  of the moment arms  21  are offset in various left-right and inferior-superior directions depending on the initial geometry of the patient&#39;s spine and the pedicle screw placements as determined by the surgeon. 
         [0035]      FIG. 3  schematically illustrates an embodiment of a clamping instrument  31  according to the present invention. The instrument  31  engages, aligns and restrains the positions of the moment arms  21  by clamping the arms  21  in the distal region outside the patient&#39;s body. 
         [0036]      FIG. 4  shows a top schematic view, related to  FIG. 3 , of the distal end of the moment arms  21   a - 21   d  and of the clamping instrument  31 . The instrument  31  has longitudinal jaws  33  that are capable of being moved toward and away from each other in the lateral left and right directions to clamp onto the moment arms  21  and consequently align and restrain them. Each jaw  33  has a compliant material  35 , such as a polymer or rubber, to conform to each moment arm  21  and accept the arms at various inferior-superior angles along the length of the jaws  35 . The compliant material assists in gripping the moment arms  21 . 
         [0037]    End portions  37  of the clamping instrument  31  connect the jaws  33  to complete an approximately rectangular structure having a central opening for the moment arms  21 . A first end portion  37  incorporates a hinge or other mechanism for allowing the jaws to come together and a second end portion  37  incorporates, in the preferred embodiment, a latching mechanism or other closing mechanism that restrains the jaws  33  in the closed position. The clamping instrument  31 , once closed on the moment arms  21 , are capable of being moved toward and away from each other in the lateral left and right directions to align and restrain the moment arms  21 . 
         [0038]    The clamping instrument  31  has two different functions for aligning the vertebrae. The first alignment is achieved by the closing and latching of the jaws  33  as shown by the relative rotations of the moment arms  21  shown between  FIGS. 2 and 4 . Thus, moment arm  21   b  is rotated leftward relative to arm  21   a , moment arm  21   c  rightward relative to arm  21   b  and so on. Consequently, each vertebra is rotated relative to adjacent vertebrae to achieve an initial rotation within the instrumented segment of vertebrae. If straight moment arms  21  are used, the degree of initial rotation for each vertebra  1  depends primarily on the positioning and orientation of each pedicle screw assembly  11 . If desired, a special moment arm  21  with an offset distal portion may be used to increase or decrease the preliminary rotation of a given vertebra  1 . 
         [0039]    The second alignment is achieved by manually rotating the clamping instrument  31  and the clamped moment arms  21  together to align the instrumented spinal segment. Thus, the clamping instrument  31  can achieve rotation both on a vertebra-to-vertebra basis and of an entire segment of the spine relative to the rest of the spine. 
         [0040]      FIG. 5  shows a perspective view of a preferred embodiment of the invention with the clamping instrument  31  restraining four moment arms  21 , each of which has a passage  27  at its proximal end to accommodate a spinal rod. Mounted to the longitudinal jaws  33  are handles  45 . The handles  45  serve the dual purposes of assisting in the closing of the jaws for the initial rotation and then allowing manipulation of the entire instrument for the final rotation. The handles  45  may be placed in any suitable position on the clamping instrument  31 . In the illustrated embodiment, the handles  45  are shown in a central location, but in other embodiments these may be closer to or at the latch end opposite the hinge end. 
         [0041]    As also seen in  FIG. 6 , hinge  41  is at one end of the clamping instrument  31 , and a latch  43  is at the opposite end. In one embodiment, no latch is required as the handles can hold the instrument in the closed position when being held by a surgeon or surgeon&#39;s assistant. In another embodiment, a latching device can be provided on or associated with the handles as opposed to directly on the jaws of the clamping instruments. 
         [0042]    As shown best in  FIG. 6 , the instrument  31  may accommodate the moment arms  21  at various angles in the inferior/superior plane. The resilient material  35  assists in this regard as it conforms to and grips the arms  21  at various angles. As shown, the instrument  31  may be also be used in a left-right orientation, and the moment arms  21   a  and  21   d  may be attached to pedicle screws on either side of the spinous process of the same vertebra. This arrangement creates a triangulated structure that can apply a greater torque to a vertebra while decreasing the bending moment on the pedicle screws. This approach can be used in conjunction with a second instrument  31  oriented in the superior-inferior direction to first create an initial alignment using the first instrument  31  and then restrain the vertebra with respect to other vertebrae using the second instrument  31 . 
         [0043]      FIG. 7  shows the clamping instrument  31  in an open position and more clearly shows portions of its structure, particularly the hinge and latching structures. In the preferred embodiment, a spring-loaded hinge biased toward the open position is employed. Also in a preferred embodiment, a spring-loaded ratchet and pawl type latch  43  is employed. Thus, one handed operation is facilitated. The clamping instrument  31  can be arranged about the moment arms  21 , i.e., extension tubes, closed and latched, all with one hand. Disengagement of the latch  43  is facilitated by the latch extension and finger grip which lies outside of one jaw. A simple depression of this extended finger grip portion will disengage the ratchet and pawl arrangement. 
         [0044]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention.