Abstract:
A spinal fixation device including two plates, a connector element for either coupling the plates in a fixed manner between the L5 vertebrae and the sacrum, and an anchor element to anchor the spinal fixation device to the sacrum. Each plate is preferably equipped with integral spikes on the inwardly facing surfaces for pressing into the spinal processes and thereby augmenting the purchase between the plates and the spinous processes. Each plate contains a central aperture through which the connector element passes in order to couple the plates together.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Application No. 61/514,442, which was filed on Aug. 2, 2011. The contents of U.S. Application No. 61/514,442 are incorporated by reference as part of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates generally to spinal surgery, and more particularly to devices for fusing adjacent spinous processes to stabilize the vertebral segment associated with the particular spinous processes or with a spinous process and an adjacent vertebrae or sacrum. 
     II. Discussion of the Prior Art 
     The human spinal column is made up of two basic components, vertebrae (bone) and intervertebral discs (gel-like cushions that absorb pressure and prevent vertebrae from rubbing together). Vertebrae and intervertebral discs stack together to form a column that provides support and structure for the body while still allowing a large degree of motion and flexibility. The spinal column also serves to protect the spinal cord (a bundle of nerves linking the brain to the rest of the body) that runs through an opening formed in the center of the column. Two nerve roots exit the spinal column at each level through spaces formed between the vertebrae. Various traumatic events and degenerative conditions may result in undesirable motion or changes in disc height, both of which may cause chronic pain for the affected individual. The pain is generally caused when changes in disc height and improper motion allow adjacent vertebrae to impinge upon exiting nerve roots. The degree and treatment of pain varies by individual but in many instances the pain can be disabling and uncontrollable by non-invasive means, leaving surgery as the only viable option. Often in such a case, two or more vertebrae are fused together, employing various instrumentation and methods to correct disc height and prevent improper movement of the vertebrae while fusion occurs, thereby eliminating or at least reducing the pain of the affected individual. 
     While there are a variety of systems and methods for effecting spinal fixation while fusion occurs, one of the more common methods involves securing pedicle screws into the pedicles of the two or more adjacent vertebrae to be fixed. The challenge in this method is securing the pedicle screws without breaching, cracking, or otherwise compromising the pedicle wall, which may occur if the screw is not properly aligned with the pedicle axis. If the pedicle (or more specifically, the cortex of the medial wall, lateral wall, superior wall and/or inferior wall) is breached, cracked, or otherwise compromised, the patient may experience pain or neurological deficit due to unwanted contact between the pedicle screw and delicate neural structures, such as the spinal cord or exiting nerve roots. This may necessitate revision surgery, which is disadvantageously painful for the patient and costly, both in terms of recovery time and hospitalization. 
     Alternative systems and methods include attaching two spinous processes by way of a device. The challenge in this method is securing the device to two or more spinous processes when one spinous process is damaged or broken. Another challenge is securing the device to the sacrum which has an extremely small, if any, spinous process. 
     The present invention is directed to overcome one or more shortcomings encountered with current fixation devices and systems. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a spinal fixation device designed to be attached to spinous processes of neighboring vertebrae, or to a spinous process at one end and to the sacrum at the other end, of the spine for immobilizing the vertebrae in order to promote fusion therebetween. The spinal fixation device may be used alone (that is, without any supplemental fusion devices, such as interbody fusion implants) or with supplemental fixation devices. In either event, the spinal fixation device allows fusion to occur between the adjacent spinous processes by maintaining them in an immobilized, locked relationship such that a boney bridge can form therebetween. The formation of the fusion bridge between the adjacent spinous processes may be augmented or facilitated by placing fusion-enhancing compounds between the spinous processes, including but not limited to allograft bone, autograft bone, bone morphogenic protein (BMP), calcium hydroxyapatite, demineralized bone matrix, collagen bone graft matrix (e.g. Formagraft®), and stem cell material (e.g. Osteocel®) and/or any number of suitable biomaterials. 
     According to one embodiment of the present invention, the spinal fixation device includes two plates, a connector element for coupling the plates in a fixed manner about adjacent spinous processes of the spine and an anchor element for anchoring the spinal fixation device to a vertebra or the sacrum. Each plate is preferably equipped with integral spikes on the inwardly facing surfaces for pressing into the spinal processes and thereby augmenting the purchase between the spinous processes and the plates. Each plate contains a central aperture through which the connector element passes in order to couple the plates together. Each plate also contains a fin for coupling the plates to the adjacent vertebrae. 
     The connector element may be any number of devices capable of coupling the first plate to the second plate. In one embodiment, the connector element may be an elongated bolt member having external ridges (as opposed to threads) to engage corresponding features in the aperture of one plate to prevent any backward motion once received through the aperture. This embodiment is advantageous in that the plates can be easily locked together and tightened by simply pushing the connector element through one plate (with the head received within a corresponding region or recess of the first plate) and into the next (with the ridges locking at each point as the ridged section is advanced through the aperture of the second plate, the head may or may not be fully contained within the first plate). In either embodiment, the head may be constructed like a screw head with an internally disposed recess for receiving a driving element (e.g. hexalobe drive, Phillips screw driver, hex driver, etc. . . . ) or may be constructed without such an internally disposed recess and may instead be driven by an exteriorly placed driving element (e.g. wrench). 
     The apertures may be provided in any number of different manners to help facilitate coupling the fixation element to the plates. For example, the aperture of one plate may be equipped with any number of suitable features, such as inwardly facing teeth or ridges that engage with the ridges of the connector element. Moreover, the aperture may include a recess therein configured to house a locking element in the form of a canted coil ring member. The coiled ring member is configured to allow uni-directional movement while in a compressed state and bi-directional movement of the connector element while in a relaxed state. The fin on each plate may be any number of shapes to provide additional stability between adjacent spinous processes. The fins may allow for purchase between adjacent vertebrae where the spinal process is damaged or broken or for purchase between the L5 spinous process and the S1 sacrum. The fins may possess any number of elements including spikes or screws in order to attach the fins to the vertebrae. 
     Any number of suitable instruments may be provided to help facilitate the surgery, including but not limited to instruments for compressing and/or distracting the adjacent spinous processes prior to securing the plates (and thus immobilizing the spinous processes), as well as instruments to facilitate coupling the plates together such as drivers for tightening the connector element to the plates or instruments for compressing the plates together. In one embodiment, the driving or compressing instrument may be equipped with a torque limiting mechanism that produces an audible (e.g. “click”) and/or and a tactile alert that lets the surgeon know he or she has applied optimal torque to the fixation element to fix the plates together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a spinous process fixation system. 
         FIG. 2  is a top view of the spinous process fixation system of  FIG. 1 . 
         FIG. 3  is a side view of an alternative embodiment of the connector element of the spinous process fixation system of  FIG. 1 . 
         FIGS. 4-5  are front and side views of the anchor element used in conjunction with the spinous process fixation system of  FIG. 1 ; 
         FIGS. 6-7  are front and side views of an alternative embodiment of the anchor element shown for use in conjunction with the spinous process fixation system of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The spinous process plate system for spinal fusion disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination 
     The specifics of the spinous process fixation system  10  will now be described with reference to  FIGS. 1-7 . The spinous process fixation system  10  includes a first plate  12 , a second plate  14 , a connector element  16 , a locking assembly  18  and an anchor element  160 . By way of example, the locking assembly  18  is configured to be assembled with the second plate  14  and provides secure coupling of the coupling member, which in turn maintains the first and second plates  12 ,  14  in a desired orientation relative to one another. However, it will be appreciated that a variety of locking assemblies for connecting the connector element  16  to the first and second plates  12 ,  14  known in the art may be used with the spinous process fixation system described herein. 
       FIGS. 1-2  illustrate an exemplary embodiment of a spinous process fixation system  10  dimensioned for achieving fixation between the L5 spinous process and the sacrum of a spine. The spinous process fixation system  10  includes a first plate  12 , a second plate  14 , a connector element  16 , and a locking assembly  18 . Each of the first plate  12  and second plate  14  includes a fin  1 ,  2 . The spinous process fixation system  10  is designed to be attached to a spinous process (e.g. at L5) and the sacrum of the spine for immobilizing the spinous process and sacrum to promote fusion therebetween. The system  10  may be used alone (that is, without any supplemental fusion devices, such as interbody fusion implants) as shown in  FIGS. 1-2 . Alternatively, the system  10  may be used with supplemental devices, for example such as a fusion implant. In any event, the system  10  allows fusion to occur between the adjacent vertebrae by maintaining them in an immobilized, locked relationship such that a boney bridge can form therebetween. The formation of the fusion bridge between the adjacent vertebrae may be augmented or facilitated by placing fusion-enhancing compounds between the spinous processes (such as, e.g. between the plates  12 ,  14  or within a fusion implant or other supplemental device), including but not limited to allograft bone, autograft bone, bone morphogenic protein (BMP), calcium hydroxyapatite, demineralized bone matrix, collagen bone graft matrix (e.g. Formagraft®), and stem cell material (e.g. Osteocel®) and/or any number of suitable biomaterials. 
     An exemplary embodiment of the first plate will now be described with specific reference to  FIGS. 3-4 . The first plate  12  includes a central body portion extending between a pair of end portions  34 ,  36 . The first plate  12  further includes a first surface  38  dimensioned to face medially, or toward the second plate  14  when assembled and a second surface  40  dimensioned to face laterally, or away from the second plate  14  when assembled. The first plate  12  may be augmented through the use of a plurality spike elements  42 , disposed on the first surface  38  of the first plate  12 , at the end portions  34 ,  36 . These spike elements  42  are designed to become embedded in the lateral surface of the spinous process when the spinous process fixation system  10  is compressed in place. The first plate also includes fin  1  which integrally extends laterally from end  34  and presents a face that transects the first surface  38  such that the face of fin  1  may rest flush against the sacrum, increasing stability for the plate  12 . The fin  1  may contain one or more spikes of any number of suitable sizes. 
     The first plate  12  may be constructed from any of a variety to suitable materials without departing from the scope of the invention, including but not limited to titanium, polymeric materials (e.g. plastics such as poly-ether-ether-ketone) carbon fiber, and/or any other biologically acceptable material. The first plate  12  may also be provided with any number of suitable dimensions without departing from the scope of the invention. For example, according to one embodiment, the width of the central body portion may range from 5 mm to 20 mm, the width of the end portions  34 ,  36  may range from 7.5 mm to 25 mm, the length of the central body portion  32  may range from 1 mm to 65 mm, the length of the end portions  34 ,  36  may range from 7.5 mm to 25 mm, and the thickness of the first plate  12  may range from 1.5 mm to 15 mm. It will be appreciated, however, that these dimensions are provided as examples of those that may be employed with the spinous process fixation system  10  of the present invention and any number of suitable modifications may be made depending upon a variety of factors without departing from the scope of the invention. 
     The second plate  14  includes similar general features as the first plate  12 . The second plate  14  includes a central body portion extending between end portions  56 ,  58 . The second plate  14  further includes a first surface  60  dimensioned to face medially, or toward the first plate  12  when assembled and a second surface  62  dimensioned to face laterally, or away from the first plate  12  when assembled. The second plate  14  may be augmented through the use of a plurality spike elements  66 , disposed on the first surface  60  of the second plate  14 , at the end portions  56 ,  58 . These spike elements  66  are designed to become embedded in the lateral surface of the spinous process when the spinous process fixation system  10  is compressed in place. 
     The second plate  14  may be constructed from any of a variety to suitable materials without departing from the scope of the invention, including but not limited to titanium, polymeric materials (e.g. plastics) carbon fiber, and/or any other biologically acceptable material. The second plate  14  may also be provided having any number of suitable dimensions without departing from the scope of the invention. For example, according to one embodiment, the width of the central body portion may range from 5 mm to 20 mm, the width of the end portions  56 ,  58  may range from 7.5 mm to 25 mm, the length of the central body portion may range from 1 mm to 65 mm, the length of the end portions  56 ,  58  may range from 7.5 mm to 25 mm, and the thickness of the second plate  14  may range from 1.5 mm to 15 mm. It will be appreciated, however, that these dimensions are provided as examples of those that may be employed with the spinous process fixation system  10  of the present invention and any number of suitable modifications may be made depending upon a variety of factors without departing from the scope of the invention. 
     The connector element  16  may be constructed from any of a variety of suitable materials without departing from the scope of the invention, including but not limited to titanium, polymeric materials (e.g. plastics) carbon fiber, and/or any other biologically acceptable material. The connector element  16  may also be provided having any number of suitable dimensions without departing from the scope of the invention. For example, according to one embodiment, the width of the connector element  16  may range from 3 mm to 10 mm, the length of the connector element  16  may range from 15 mm to 50 mm, and the ridged portion  124  may range from 5 mm to 47 mm. It will be appreciated, however, that these dimensions are provided as examples of those that may be employed with the spinous process fixation system  10  of the present invention and any number of suitable modifications may be made depending upon a variety of factors without departing from the scope of the invention. 
     The connector element  16  may be modified in order to receive an anchor element  160  to fix the spinous process fixation system  10  to the sacrum. By way of example only, the connector element  16  may have an anchor aperture  150  through the transverse axis of the shaft  122  (best seen in  FIG. 3 ). The coupling aperture  150  will allow the placement of an anchor element, e.g. a screw (not shown) to be inserted through the shaft  122  of the connector element  16 . Upon insertion through the shaft  122  of the connector element  15 , the screw can be inserted directly into the sacrum. This configuration will provide additional stabilization and ensure the spinous process fixture system  10  remains in place. The size of the coupling aperture  150  can vary with the size of connector element  16  but may range from a radius of 1 mm to 4 mm. It will be appreciated, however, that these dimensions are provided as examples of those that may be employed with the spinous process fixation system  10  of the present invention and any number of suitable modifications may be made depending upon a variety of factors without departing from the scope of the invention. 
     Another exemplary embodiment of an anchor element  160  for providing fixation between the spinous process fixation system  10  and the sacrum is shown in  FIGS. 4-5 . The anchor element  160  described herein may be used with any spinous process fixation device  10  dimensioned for use at the L5-S1 level of the spine and having a connector element  16  as shown by way of example in  FIGS. 1-2 . The anchor element  160  includes a body  163  having a screw aperture  161 , a rotational device  162 , a sacrum screw  165 , and coupling hook  166 . The body  163  has at least one open side parallel to the sacrum screw  165 . The sacrum screw  165  will be inserted into the screw aperture  161  and then into the sacrum. According to this embodiment, the coupling hook  166  is specifically sized and designed to fit snuggly on the connector element  16  of the spinous process fixation system  10 . The rotational device  162  is attached to both the body  163  and the coupling hook  166 . The coupling hook  166 , with the ability to rotate freely, can be placed over the connector element  16  of the spinous process fixation device  10  before the insertion of the sacrum screw  165  into the sacrum. Upon advancing the sacrum screw  165  through the screw aperture  161  and into the sacrum, the coupling hook  166  of the anchor element  160  will firmly grasp the connector element  16  of the spinous process fixation system  10 , securing the spinous process fixation system  10  in place and to the sacrum by fixing the distance between the connector element  16  and the sacrum. 
     The anchor element  160  may have a number of end pieces in lieu of the coupling hook  166 . For example,  FIGS. 6-7  illustrate an alternative embodiment of the coupling hook  166  with the same function. According to this embodiment, the anchor element  160  is coupled to the connector element  16  of the spinous process fixation system  10  via a coupling sleeve  170  having a sleeve aperture  171  through which the connector element  16  passes. The connector element  16  is inserted though the coupling sleeve  170  prior to attachment of the connector element  16  to the first and/or second plates  12 , 14  and prior to insertion of the spinous process fixation system  10  into the patient. The anchor element  160  works in substantially the same way whether the coupling hook  166  or coupling sleeve  170  embodiment is utilized. 
     The anchor element  160  may be constructed from any of a variety of suitable materials without departing from the scope of the invention, including but not limited to titanium, polymeric materials (e.g. plastics) carbon fiber, and/or any other biologically acceptable material. The anchor element  160  may also be provided having any number of suitable dimensions without departing from the scope of the invention. For example, according to one embodiment, the width of the anchor element  160  may range from 3 mm to 30 mm, the length of the anchor element without the sacrum screw  165  may range from 10 mm to 40 mm, and the length of the sacrum screw  165  may range from 5 mm to 40 mm. It will be appreciated, however, that these dimensions are provided as examples of those that may be employed with the spinous process fixation system  10  of the present invention and any number of suitable modifications may be made depending upon a variety of factors without departing from the scope of the invention.