Abstract:
Disclosed is a surgical alignment and distraction frame and associated methods of use that facilitates correction of a sagittal imbalance. The alignment and distraction frame works in conjunction with pedicle screw installation guide assemblies to impart the desired correction. The alignment frame can be utilized to ensure the pedicle screw housings are aligned (to facilitate rod coupling) in concert with the completion of a correction maneuver.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application is a non-provisional application claiming the benefit of priority under 35 U.S.C. §119(e) from commonly owned U.S. Provisional Application Ser. No. 61/794,723 filed on Mar. 15, 2013 and entitled “Spinal Alignment Frame,” the entire contents of which is hereby incorporated by reference into this disclosure as if set forth fully herein. 
    
    
     FIELD 
     The present invention relates to the field of spinal surgery and spinal fixation devices, including a system and associated methods for manipulating, distracting and/or reorienting vertebrae of the spine in conjunction with the installation of a spinal fixation construct. 
     BACKGROUND 
     The spine is formed of a column of vertebra that extends between the cranium and pelvis. The three major sections of the spine are known as the cervical, thoracic and lumbar regions. There are 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae, with each of the 24 vertebrae being separated from each other by an intervertebral disc. A series of about 9 fused vertebrae extend from the lumbar region of the spine and make up the sacral and coccygeal regions of the vertebral column. 
     The main functions of the spine are to provide skeletal support and protect the spinal cord. Even slight disruptions to either the intervertebral discs or vertebrae can result in serious discomfort due to compression of nerve fibers either within the spinal cord or extending from the spinal cord. Disruptions can be caused by any number factors including normal degeneration that comes with age, trauma, or various medical conditions. If a disruption to the spine becomes severe enough, damage to a nerve or part of the spinal cord may occur and can result in partial to total loss of bodily functions (e.g., walking, talking, breathing, etc.). Therefore, it is of great interest and concern to be able to treat and correct ailments of the spine. 
     When conservative efforts fail, treating spinal ailments very often includes one of or a combination of spinal fusion and fixation. Generally, spinal fusion procedures involve removing some or all of an intervertebral disc, and inserting one or more intervertebral implants into the resulting disc space. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”) and maintain the height, and/or correct vertebral alignment issues, until bone growth across the disc space connects the adjacent vertebral bodies. Resection of ligaments and/or boney elements from the affected spinal area is also common in order to access the disc space and/or decompress impinged nerve or spinal cord tissue. 
     Fixation systems are often surgically implanted during a fusion procedure to help stabilize the vertebrae to be fused until the fusion is complete or to address instabilities (either preexisting or created by the fusion or decompression procedure itself). Fixation constructs of various forms are well known in the art. Most commonly, the fixation construct is a plate anchored to the anterior column with multiple bone anchors or a posterior fixation construct including multiple anchors and a connecting rod anchored to the posterior elements of the spine. For a posterior fixation construct the anchors (typically pedicle screws) are anchored into the pedicles of each vertebra of the target motion segment. The pedicle is a dense, strong, stem-like structure that projects from the posterior side of the vertebral body. The anchors are then connected by a fixation rod that is locked to each anchor, thus eliminating motion between the adjacent vertebrae of the motion segment. The fixation anchors utilized in posterior fixation constructs generally include an anchor shank and a rod housing. The rod housing includes a pair of upstanding arms separated by a rod channel in which the fixation rod is captured and locked. When constructing the posterior fixation construct the surgeon must align and seat the rod in the rod channel. This can be a challenge as it requires the rod channels of adjacent rod housings to be generally aligned, or alternatively, the rod must be bent to fit. 
     In addition to simply stabilizing the spine, components of the fixation system can also be utilized to manipulate the positioning of the vertebrae to achieve the desired alignment before movement is arrested. That is, applying a directional force to the anchor shank through the attached housing, for example, via minimally invasive guides, reduction tools, or other instruments that are commonly engaged to the housing and extend out of the patient, causes the associated vertebra to translate or rotate in the direction of the force, thus allowing the surgeon good control to manipulate the relevant vertebrae into a desired position. However, doing so typically causes the rod housings to move relative to each other. Thus, achieving the desired correction (realignment) of the vertebrae while also aligning the rod channels of the housings to effectively seat a rod is a significant challenge and can create difficulties and delays during the surgery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a spinal fixation system applied to a lumbar spine and having coupled thereto one example embodiment of a spinal alignment frame for facilitating manipulation of spinal anatomy to correct spinal imbalances; 
         FIG. 2  is a perspective view of the alignment frame of  FIG. 1 ; 
         FIGS. 3A through 3C  depict various perspective views of a left-side indicating and readout arm of the spinal alignment frame of  FIG. 1 ; 
         FIG. 3D  is an exploded view of the indicating and readout arm and related frame structure of  FIG. 3A ; 
         FIGS. 4A through 4D  depict various perspective views of a right-side indicating and readout arm of the spinal alignment frame of  FIG. 1 ; 
         FIG. 4D  is an exploded view of the indicating and readout arm and related frame structure of  FIG. 4A ; 
         FIG. 5  is a perspective view of the spinal alignment frame of  FIG. 2 , with left and right indicator arm assemblies detached from the frame; 
         FIG. 6  is a perspective view of the backside of the spinal alignment frame of  FIG. 5  the frame; and 
         FIG. 7  is a flowchart denoting example steps of a method for performing a surgical procedure with the posterior fixation system and alignment frame of  FIG. 1  to perform a surgical correction. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments disclosed herein include surgical measurement frames that can be conveniently used by a surgeon to determine an appropriate surgical correction for a patient suffering from a spinal instability or deformity. For example, the surgical measurement frame may be used to realign sagittal balance during compression fracture reduction, VBR resection, pedicle subtraction osteotomy (PSO), scoliosis correction, or other procedures affecting sagittal balance. 
     With reference to  FIG. 1 , there is shown a spinal fixation construct  10  and associated installation guide assemblies  20 , coupled with an example embodiment of a spinal alignment frame  100 . The spinal fixation construct is of a type commonly known in the art and includes a pair of pedicle screws  12  and a rod  18 . The pedicle screws  12  each include a rod housing  14  and a shank (not pictured) coupled to the housing. The housing  14  has pair of upstanding arms separated by a rod channel  16  in which the fixation rod  18  is captured and locked with a locking cap (not shown). The housing  14  is coupled to the shank in a manner that permits polyaxial rotation of the housing  14  relative to the shank. Locking of the rod  18  within the housing  14  also locks the housing  14 , arresting further movement between the housing and the shank. Additionally, the pedicle screw  12  includes a provisional locking feature, various different embodiments of which are readily known and available in the art, which permits the housing  14  to be locked (again, arresting further movement between the housing  14  and the shank) before locking (or positioning) the rod  18 . The provisional locking feature may be either reversible or irreversible. 
     The installation guide assemblies  20  are also of a type commonly known in the art and includes a generally tubular body  22  with a distal end  24  that releasably couples to the rod housing  14  and a proximal end  26  that extends out of the patient when the pedicle screw  12  is anchored to the vertebra and the distal end  22  is coupled to the housing  14 . A lumen  28  extends through the body  22 , opening in each of the distal end  24  and proximal end  26 . Guide channels  30  passing through the body  20  and opening in the distal end  24 , and preferably extending along a length of the guide toward the proximal end  26 , align with the rod channel  16  when the guide and screw are coupled. The installation guides  20  facilitate rod delivery into the rod channels  16  and also facilitate engagement of various instruments with the pedicle screw. For example, a shank driver may extend through the lumen  28  while coupled to the shank, which also functions as a pseudo provisional lock, as the guide  20  (and thus the housing  14 ) is restrained from movement relative to the shank by the driver. Other instruments, such as a provisional locking tool used to engage (or disengage) the provisional lock, locking caps, and reducers may also be advanced through the lumen  28  to engage the screw  12 . Additionally, the guide assemblies  20  can be manipulated from outside the body to impart force on the shank, via housing  14  (with the housing  14  locked), to adjust the position of the associated vertebra and achieve a desired surgical correction. By way of example, the guides may be manipulated to compress, distract, translate, rotate, and/or bend the associated vertebra relative to other vertebrae. It will be appreciated that while installation guides are generally used to facilitate minimally invasive pedicle fixation, the guides  20  (and the alignment frame  100  with them) may be utilized in open pedicle fixation procedures as well. 
       FIG. 2  depicts the spinal alignment and distraction frame  100 . The frame  100  includes a pair of guide attachment rings  110  and  110 A, each of which has an internal opening  115  and  115 A sized to fit over a single guide  20 , such as those depicted in  FIG. 1 . Each of the guide attachment rings  110  and  110 A include anterior openings  120  and  120 A for accommodating a set screw (not shown) or other securement feature that allows the ring to be “locked” or otherwise secured to a desired position on the tubular guide  20 . In various embodiments the guide  20  may include one or more grooves, notches, depressions or openings on an outer surface that accommodates the set screw (or clip, lever, etc.), allowing the ring  110  and  110 A to be secured to a predetermined longitudinal and/or rotational position on the guide  20 , or alternatively, the set screw may directly engage the outer surface of the guide body  22 . In various alternative embodiments, attachment mechanisms other than rings could be utilized to attach the frame to the tubular guides, which could include locking tabs, screw and thread mechanisms, quick release tabs, slide locks, collets, inserts, taper and press fits or other connecting arrangements known in the art. For example, one alternative attachment mechanism includes attachment via a cap that clips onto the top of the tubular guides, or that could engage a projection, slot, ring or other feature on or extending outward of the guides. 
       FIGS. 3A through 3D and 4A through 4D  depict various perspective and exploded views of the indicating and readout arms and related frame structures. As best seen in  FIGS. 3D and 4D , each ring  110  and  110 A includes an attached ring shaft  125  and  125 A. The ring shafts  125  and  125 A are sized and configured to fit into corresponding openings  130  and  130 A in first and second attachment blocks  135  and  135 A attached to the frame (not shown). Each ring shaft  125  and  125 A includes a grooved or reduced diameter section  140  and  140 A that accommodates set screws  145  and  145 A that secure through openings  150  and  150 A in the attachment blocks  135  and  135 A. The set screws  145  and  145 A allow the ring shafts  125  and  125 A to be inserted into the openings  130  and  130 A and then the set screws  145  and  145 A can be tightened a sufficient degree to retain the ring shafts  125  and  125 A within the openings  130  and  130 A in the first and second attachment blocks  135  and  135 A, yet allow the ring shafts  125  and  125 A to rotate freely about the longitudinal axes of the ring shafts  125  and  125 A. 
     Each ring shaft  125  and  125 A includes an indicator arm  155  and  155 A which is secured to the ring shaft  125  and  125 A by a pin  156  and  156 A or other feature extending through the ring shaft  125  and  125 A. The pin  156  and  156 A desirably locks the indicator arm to the ring shaft such that rotation of the ring  110  and ring shaft  125  concurrently displaces and rotates the indicator arm  155  and  155 A. 
     Readout arms  160  and  160 A are secured to each of the first and second attachment blocks  135  and  135 A by pins  136  and  136 A, adhesives or other attachment features known in the art. Each readout arm  160  and  160 A includes an opening  165  and  165 A through which the respective ring shaft  125  and  125 A can extend. An indicator scale  170  and  170 A is included on each readout arm  160  and  160 A. Because the readout arms  160  and  160 A are secured to the blocks  135  and  135 A, the readout arms  160  and  160 A do not rotate with the ring shafts  125  and  125 A, but rather are secured relative to the frame (not shown) to which the blocks  135  and  135 A are attached. Because the readout arms  160  and  160 A remain stationary relative to the frame, and the indicator arms  155  and  155 A move with the ring shafts  125  and  125 A, rotation of the rings  110  and  110 A relative to the frame will rotate the indicator arms  155  and  155 A relative to the readout arms  160  and  160 A, and the relative rotational position between each indicator arm  155  and a corresponding readout arm  160  can be determined from each indicator scale  170  and  170 A. 
       FIG. 5  depicts the measuring and distraction frame  100  assembly, showing left and right indicator arm assemblies  180  and  180 A (i.e. rings, ring shafts, indicator arms, and associated coupling features) prior to insertion of the ring shafts  125  and  125 A into the openings  130  and  130 A in the first and second attachment blocks  135  and  135 A. It should be understand that “left” and “right” are used for convenience only, and that various other embodiments could include reversed or other positioning arrangements for the various components described herein. In addition, the substitution of “left” and “right” with “first” and “second” or “cephalad” and “caudad,” or other such conventions, could be used as desired, and are contemplated herein. 
     In one exemplary embodiment, the ring  110  of the left indicator arm assembly  180  can be slid over or otherwise engaged to a guide  20  and the ring shaft  125  inserted into the opening  130  in the first attachment block  135 . The set screw (not shown) could then be tightened a sufficient amount to secure the ring shaft  125  to the first attachment block  135 , yet allow the ring shaft  125  to rotate relative to the block  135 , as previously discussed. Similar actions could be taken with the right indicator arm assembly  180 A for another guide  20 , which can be connected to the second attachment block  135 A in a similar manner. 
       FIG. 6  depicts an upper perspective view of the alignment and distraction frame  100 , showing an elongated rack  210 , a left housing  215  and a right housing  220 . The left housing  215  connects the first attachment block  135  to the elongated rack  210 . The right housing  220  connects the second attachment block  135 A to the elongated rack  210 , with the right housing  220  capable of translation along the elongated rack, such that the spacing between the left housing  215  and the right housing  220  can be varied. The right housing  220  also includes a rotating adjustment thumb screw  230  that rotates a pinion engaged with rack  210  and a selective locking mechanism  240 . 
     The elongated rack  210  includes a linear gear bar or toothed portion  245  along one side which extends through the right housing. Inside the right housing  220 , a pinion or circular gear  250  engages with the toothed portion  245 , with the circular gear  250  attached to the enlarged drive plate of the thumb screw  230 . The selective locking mechanism of the right housing includes a locking tooth  260  at one end which engages with the toothed portion  245  of the elongated rack  210  to prevent translation of the right housing in an undesirable manner when the lock is engaged. The other end of the locking mechanism includes a push plate  265  which can be depressed to overcome the force of a biasing spring  270  that maintains the locking tooth  260  in contact with the toothed portion  240  of the elongate rack  210 . 
     In this embodiment, to slide the right housing along the elongated rack  240 , a user can depress the push plate  265 , which disengages the locking tooth  260  from the toothed portion  245 . The thumb screw  230  can then be rotated in a clockwise or counterclockwise direction, which rotates the circular gear  250  against the toothed portion  240  of the elongated rack  210  and drives the right housing  220  away from or towards the left housing. Once movement of the right housing  220  is no longer desired, the push plate  265  can be released, and the locking tooth  260  will re-engage with the toothed portion  245  of the rack  210 . The locking plate itself may include a secondary lock (not shown) that holds the push plate in the disengaged position to relieve the user of the need to maintain continuous pressure on the push plate while also operating the thumb screw  230 . 
     In alternative embodiments, the locking mechanism could include a variety of locking and/or unlocking modes, including a “free wheeling” or unlocked mode (i.e., an unlocked mode which allows the right housing to freely slide), a “closing detent” mode (i.e., a detent mechanism that allows sliding of the right housing towards the left housing, but inhibits motion in the other direction), an “opening detent” mode (i.e., a detent mechanism that allows sliding of the right housing away from the left housing, but inhibits motion in the other direction), a powered mechanism, linear sliders, and/or any other mechanism desired or known. The unlocked mode could be particularly useful during initial placement of the frame onto the tubular guides, as well as during the various distraction and/or correction operations, as it may be desirous to adjust the spacing between the housings to accommodate the initial placement of the left and right indicator arm assemblies and/or to facilitate the surgeon&#39;s manual movement of the guides  20  during rotation, distraction/compression and/or other corrective maneuvers. 
     With reference to  FIG. 7 , one example method utilizing the spinal alignment and distraction frame  100  to correct a sagittal misalignment and fixate the correction is described. Initially, in step  300  first and second pedicle screws  12  are anchored into a superior vertebral body and an inferior vertebral body that are each adjacent to a fractured, compressed, misaligned, or resected vertebral body located there between. The vertebral body may be fractured, compressed, misaligned, or resected due a wide variety of pathologies, including osteoporosis, trauma, metastatic disease or other causes. The pedicle screws  12  are anchored with their respective guides  20  engaged to the housing  14  and extending out of the incision(s) used for installation. Drivers used to drive the screw shanks are left engaged to the shank and extending out of the guide lumen  28 . Next the spinal alignment and distraction frame  100  is coupled to the installation guides  20  by sliding the ring connectors  110  and  110 A over a respective guide (Step  302 ). Alternatively, the connection rings  110  and  110 A can be attached to the guides  20  first, and thereafter the ring shafts  125  and  125 A can be coupled to the frame. The frame permits one or more of the ring connectors to slide relative to the frame, allowing the spacing between the rings to be widened and/or narrowed as needed, and facilitating the sliding of the ring connections over the guides  20  (and drivers) and engaging set screws through the apertures  120  and  120 A. For step  304 , with the ring connectors  110  and  110 A unlocked (that is, able to rotate relative to the frame), an initial angle reading is taken for each guide/ring connector combination. For example purposes, initial readings will be denoted as A I  and B I , with A I  representing an angle value between the axis of the ring connector  110  (and attached guide  20 ) and the rack, and B I  representing an angle value between the axis of the ring connector  110 A (and attached guide  20 ) and the rack. Initial angle readings are noted for future reference. With the drivers sill engaged to the screw shanks (to in essence effect a provisional locking of the housing  14  relative to the shank), the guides  20  are manipulated to achieve the desired realignment or correction of the vertebrae (step  306 ) (which can be monitored or verified using fluoroscopy or other visualization techniques). When the desired correction is achieved, corrected angle readings are taken, denoted as A C  and B C  (for example purposes), from the readout indicators  170  and  170 A (step  308 ). The readings A C  and B C  represent the angle of the respective guides  20 , and thus the housings  14  also, relative to the rack  210 . In step  310  the total angulation values needed to achieve the desired correction is determined, denoted herein (for example purposes) as A T  and B T . A T  and B T  are determined by calculating the delta between the corrected angle readings (A C  and B C ) and the initial angle readings (A I  and B I ), respectively. This can be accomplished by subtracting A C  from A I  and B C  from B I . Thus for example purposes only, if A I  equals negative 3 and A C  equals negative 8, then A T  equals positive  5 . Likewise, if B I  equals positive  2  and B C  equals negative 4, the B T  equals positive  6 . (In step  312 , the correction may be released, and the drivers removed from the guides  20  (effectively unlocking the housing  14  relative to the shank). With the housings  14  free to move relative to the shanks, in step  314  the guides  20  are again manipulated, this time to align the guides  20  with the angle readings A T  and B T . While maintaining the angles A T  and B T , the provisional locking feature of the screws  12  is engaged (step  316 ), locking the housings relative to the shanks in the positions A T  and B T . This may be accomplished, for example, by advancing a provisional locking tool through the lumen  28  of each guide and engaging the locking mechanism. 
     Moving to step  318 , the guides  20  are manipulated again, this time to maneuver the guides to the zero angle position. This adjustment to zero will provide the desired correction while simultaneously aligning the housings  14  generally parallel to each other such that the rod  18  can be passed (step  320 ) without custom bending and locked in place with locking caps. 
     Prior to locking the rod completely, the surgeon may also choose to lock the ring connectors  110  and  110 A such that the rack may be utilized to apply parallel compression or distraction to the vertebrae by operating the thumb screw  230  to translate the housing  220  along the rack  210  in the appropriate direction. Once the final desired corrections and/or spinal alignment have been obtained (which may include desired lordotic or other curvature corrections, at the surgeon&#39;s options) the rod is finally locked. The frame  100  and guides  20  are disengaged and removed. 
     The disclosed system desirably provides for the accurate alignment and locking of polyaxial screw heads in desired rotational positions relative to their respective screw shanks already implanted into vertebral bodies in such a manner that later distraction and/or reduction of the vertebral bodies to a desired orientation can be accomplished using distraction, torque and rotational forces on the vertebral bodies through the attached pedicle screw shanks, with the resulting alignment of the pedicle screw heads being optimized for securement to a longitudinal spinal rod or other instrumentation without requiring bending of the rod or the use of specialized adapters. The described frame also facilitates the distraction and/or compression of the relevant spinal segment in a controlled fashion after a surgical correction and/or appropriate lordosis/curvature of the spine has been obtained but before final fixation of the spinal anatomy using instrumentation has been accomplished. 
     While specific embodiments have been shown by way of example in the drawings and described herein in detail, it will be appreciated that the invention is susceptible to various modifications and alternative forms (beyond combining features disclosed herein). The description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.