Abstract:
A spinal plate that is self-adjusting along its longitudinal axis to accommodate subsidence that may occur and aid in loading the bone graft to promote boney fusion while providing rigid fixation. The spinal plate is configured to inhibit loosening or backing out of bone screws.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to, and benefit of, U.S. Provisional Patent Application Ser. No. 61/388,639, filed Oct. 1, 2010, the entire disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates generally to a device for use in orthopedic surgeries, and more particularly to a plate that is attachable to the vertebrae, e.g., cervical vertebrae, and is configured and adapted to change its length to maintain constant loading of the vertebrae. 
         [0004]    2. Background of Related Art 
         [0005]    The human spinal column is a highly complex structure. It includes twenty-four discrete bones, known as vertebrae, coupled sequentially to one another to house and protect critical elements of the nervous system. The cervical portion of the spine, which comprises the neck of the spine up to the base of the skull, includes the first seven vertebrae. 
         [0006]    For many reasons, such as aging and trauma, the intervertebral discs can begin to deteriorate and weaken. This may result in chronic pain, degenerative disc disease, or even tearing of the disc. Ultimately, the disc may deteriorate or weaken to the point of tearing and herniation, in which the inner portions of the disc protrude through the tear. A herniated disc may press against or pinch the spinal nerves, thereby causing radiating pain, numbness, and/or diminished strength or range of motion. 
         [0007]    Many treatments are available to remedy these conditions, including surgical procedures in which one or more damaged intervertebral discs are removed and replaced with a prosthetic. However, should the prosthetic protrude from between the adjacent vertebrae and contact the surrounding nerves or tissues, the patient may experience additional discomfort. In procedures for remedying this problem, a spinal plate is affixed to the vertebrae and oriented to minimize such protrusion. In addition, the plate provides fixation and support to maintain spinal stability while the fusion occurs. 
         [0008]    Spinal plates, and cervical plates in particular, are known in the art. Fixed cervical plates generally exhibit unalterable, static dimensions. During the natural subsidence of the spinal column after surgery, the overall length of the spinal column gradually decreases. Fixed cervical plates resist this change due to their fixed axial length, which may eventually stress the spine and cause pain or discomfort. Adjustable cervical plates attend to this predicament by providing a mechanism through which the plate is shortened to accommodate for a measure of subsidence. However, some adjustable plates require subsequent surgical procedures to adjust the axial dimensions of the plate. In addition to accommodating subsidence, it is critical for the plate to provide means to apply constant loading of the bone graft in order to promote fusion of the graft site. 
         [0009]    A common problem associated with the use of spinal plates is the tendency of the bone screws to “back out” or pull away or otherwise withdraw from the bone into which they are mounted. This problem occurs primarily due to the normal torsion and bending motions of the body and spine. As the screws become loose and pull away or withdraw from the bone, the heads of the screws can rise above the surface of the spinal plate from one or more vertebrae. 
       SUMMARY 
       [0010]    Disclosed herein is a bone plate, e.g., cervical bone plate. In an embodiment, the bone plate includes a plurality of segments, each of which is operatively attachable to a vertebra. Each segment is movable relative to at least one other segment for adjusting an overall length of the plate without performing a secondary procedure. This allows the bone plate to shorten in response to subsidence, thereby facilitating constant loading of the bone graft, which helps facilitate healing. The length of the plate adjusts automatically in response to subsidence without requiring additional manipulation, i.e., it occurs automatically. Lengthening the plate necessitates a secondary user operation. The number of segments that the plate includes corresponds to the number of vertebral levels to be bridged. The plate includes at least two segments that are positioned along a longitudinal axis and are movable relative to one another along the longitudinal axis. Movement of the segments apart from one another is inhibited. In addition, non-axial movement, e.g., twisting or rotation, of the segments relative to one another is inhibited. 
         [0011]    Each segment is operatively attachable to a vertebra. Each of the segments may include a bone screw hole for the reception of a bone screw therethrough to operatively couple the segment to a vertebral body. An insert may be placed between the portion of the plate defining the screw hole and the screw to inhibit separation of the screw from the plate. The insert, the plate, and the bone screw may each be formed from materials having different hardnesses to improve the retention of the screw to the plate. 
         [0012]    A method of performing spinal surgery is disclosed. In use, a plate is assembled having a number of movable segments that corresponds to the number of vertebral levels that are to be bridged. A bone plate including a first segment, and a second segment, the first and second segments that are positioned along a longitudinal axis and are movable relative to one another, wherein movement of the segments apart from one another is inhibited is provided. The first segment is secured to a first vertebra, and the second segment is secured to the second vertebra, and the segments are spaced to accommodate the patient&#39;s anatomy. During implantation, inserts may be placed between segments to hold the segments in a predetermined spaced orientation. When such inserts are used, they are removed after implantation to permit movement of the segments relative to one another. 
         [0013]    These and other aspects of the present disclosure will be described in greater detail when read with reference to the appended figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Embodiments of the present disclosure are described herein with reference to the accompanying figures, wherein: 
           [0015]      FIG. 1  is a perspective view of a spinal fixation assembly; 
           [0016]      FIG. 2  is an exploded view of the spinal fixation assembly of  FIG. 1 ; 
           [0017]      FIG. 3  is a top view of the spinal fixation assembly of  FIG. 1 ; 
           [0018]      FIG. 4  is a sectional view of the spinal fixation assembly of  FIG. 1  taken along section line  4 - 4 ; 
           [0019]      FIG. 5  is a sectional view of a screw shown placed within a portion of the spinal fixation assembly of  FIG. 1 ; and 
           [0020]      FIG. 6  is a perspective end view of one segment of the spinal fixation assembly of  FIG. 1  shown with screws. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Embodiments of the present disclosure will now be described in detail with reference to the appended figures, wherein the reference numerals identify similar or identical elements. In the figures and in the following description, the term “proximal” will refer to the device that is closest to the operator, while the term “distal” will refer to the end of the device that is farthest from the operator. In addition, the term “cephalad” is used in this application to indicate a direction toward a patient&#39;s head, whereas the term “caudad” indicates a direction toward the patient&#39;s feet. Further still, for the purposes of this application, the term “medial” indicates a direction toward a side of the body of the patient, i.e., away from the middle of the body of the patient. The term “posterior” indicates a direction toward the patient&#39;s back, and the term “anterior” indicates a direction toward the patient&#39;s front. Additionally, in the drawings and in the description that follows, terms such as front, rear, upper, lower, top, bottom, and similar directional terms are used simply for convenience of description and are not intended to limit the disclosure coupled hereto. 
         [0022]    A plate  10  that allows for adjustment over a specified range, while maintaining the strength and functionality of the plate  10 , will now be described with reference to  FIGS. 1-6 . The plate  10  may generally be operatively coupled to a patient&#39;s spine, and in particular to the cervical vertebrae, i.e., the vertebrae comprising the patient&#39;s neck. The plate  10  includes a plurality of adjacent segments that are axially movable relative to one another. The number of segments that the plate  10  includes corresponds to the number of vertebral levels the plate  10  is to bridge. As shown in  FIGS. 1-3 , the plate  10  may include three (3) segments  12 ,  14 ,  16 . 
         [0023]    As shown best in  FIGS. 1 and 3 , the segments  12 ,  14 ,  16  of the plate  10  include mating or inter-locking surfaces that fit together in a dove-tail or tongue-and-groove mechanism, allowing the segments  12 ,  14 ,  16  to move or slide relative to one another along longitudinal axis “A” thereby facilitating lengthening or shortening of the plate  10 . As will be discussed, a locking mechanism  18  inhibits lengthening of the plate  10 , but facilitates shortening of the plate  10  automatically, without an additional procedure. As shown in  FIG. 3 , the segment  12  includes a groove  5  that is shaped to receive a portion  7  of adjacent segment  14 , which in turn includes a groove  9  that is shaped to receive a portion  11  of adjacent segment  16 . 
         [0024]    As shown best in  FIG. 2 , one or more rails  20  longitudinally extend from the segments  12 ,  14  and are receivable within slots  27  of the adjacent segments  14 ,  16 , respectively. The length of the rails  20  (as well as the length of tongue  22  and number and positioning of grooves  24   a - c ) determines the range within which the segments  12 ,  14 ,  16  are slidable relative to one another. As shown in  FIG. 3 , the rails  20  of segment  12  are slidably received within segment  14 ; the rails  20  of segment  14  are slidably received within segment  16 . Although shown in the figures as having a circular cross-section, the rail  20  may define an alternate geometrical cross-section, e.g., the rail  20  may alternatively define a square or triangular shape, an I-beam, a C-channel, or the like. The rails  20  may be operatively coupled to the segments  12 ,  14 ,  16  or may be an integral portion of the segments  12 ,  14 ,  16 . 
         [0025]    The rails  20  facilitate movement of the segments  12 ,  14 ,  16  relative to one another along longitudinal axis “A”, and also stabilize the plate  10  by inhibiting movement of the segments  12 ,  14 ,  16  that is not along the longitudinal axis “A”, e.g., rotation and/or twisting. As the rails  20  are inserted into the channels  27  of the adjacent segments  14 ,  16 , the locking mechanism  18  inhibits the backward movement of the segments  12 ,  14 ,  16  away from one another. By inhibiting the backward movement of the segments  12 ,  14 ,  16  away from one another, i.e., expansion of the plate  10 , the integrity and position of the plate  10  is maintained while allowing compression of the anatomy, constant loading of the bone graft, and subsidence of the anatomy, which may occur over time. 
         [0026]    The locking mechanism  18  includes tongue  22  and grooves  24   a - c . Once the rails  20  couple the segments  12 ,  14 ,  16  to one another there is no additional manipulation required for the locking mechanism  18  to be engaged, i.e., the locking mechanism  18  automatically releasably secures the segments  12 ,  14 ,  16  to each other to prevent the segments  12 ,  14 ,  16  from moving apart while permitting the segments  12 ,  14 ,  16  to move together. The tongues  22  and the rails  20  of the segments  12 ,  14  are slidably received within segments  14 ,  16 , respectively. As shown in  FIG. 3 , channels  27  receive rails  20 . The rails  20  facilitate sliding of the tongue  22  of the locking mechanism  18  to slide relatively effortlessly past the grooves  24   a - c  in a releasably locked engagement therewith, i.e., as the tab  22   a  is engaged with one of the grooves  24   a - c . The tongue  22  may also include a guide channel  25   b  to receive a guide pin  25   a  therein to facilitate aligning of the tongue  22  and to minimize off-axis movement of the segments  12 ,  14 ,  16  relative to one another. 
         [0027]    The tongue  22  includes an undercut feature or tab  22   a  at a distal end thereof is configured and adapted to engage the grooves  24   a - c , thereby causing the tongue  22  to releasably lock to one of the grooves  24   a - c , which are spaced at intervals. As shown in  FIG. 3 , segment  12  and segment  14  can be maximally spaced apart by a length x 1 , and segment  14  and segment  16  can be maximally spaced apart by a length x 2 . The lengths x 1 , x 2  by which the segments  12 ,  14  and segments  14 ,  16  are spaced, respectively, correspond to the groove  24   a - c  to which the tab  22   a  of the tongue  22  is releasably secured. After installation, the plate  10  is able to shorten in response to subsidence without the need for a secondary operation, as the segments  12 ,  14 ,  16  move together and the tab  22   a  of the tongue  22  moves into the next adjacent groove  24   b - c.    
         [0028]    The interaction of the tab  22   a  with the grooves  24  allows the segments  12 ,  14 ,  16  to move closer together but not apart, i.e., once one of the grooves  24  engages the tab  22   a , movement of the segments  12 ,  14 ,  16  apart is inhibited. The shape of the tab  22   a  allows the tab  22   a  to disengage the groove  24  in a direction that will move the segments  12 ,  14 ,  16  together, but not in a direction that would move or distract the segments  12 ,  14 ,  16  apart without requiring an additional, secondary user operation. If needed, an instrument may be inserted into the groove  24  in which the tab  22   a  is positioned to disengage the tab  22   a  from the groove  24 , thereby releasing the locking mechanism  18  and allowing the segments  12 ,  14 ,  16  to move apart from one another to allow for surgical adjustment if it is needed. It is desirable to maintain loading on the vertebral bodies so that the healing process, or boney fusion, can continue uninterrupted. Inhibiting the segments  12 ,  14 ,  16  of the plate  10  from moving or distracting apart from each other aids in the healing process by maintaining loading on the vertebrae. 
         [0029]    The plate  10  includes screw holes  28  adapted for the reception of bone screws  40  ( FIG. 6 ) therethrough. An insert  30  may be press-fitted into each screw hole  28 . In an embodiment, the inserts  30  may be removable. The inserts  30  may be formed from a material that is softer than that forming the bone screws  40 . For example, the insert  30  may be formed from commercially pure implant grade titanium. An inward facing lip  31  is configured and adapted to engage threads  41  of the bone screw  40 . The harder material, e.g., implant grade titanium alloy, of the bone screw  40  deforms the softer material, e.g., commercially pure titanium, forming the lip  31  of the insert  30 . This engagement inhibits the screw from migrating out of the plate  10 , as well as the bone, as is described in U.S. Patent Publication No. 2011/0106172 and U.S. Pat. No. 6,322,562, both of which are incorporated herein by reference. Although the plate  10  is shown as having screw holes  28 , it is contemplated that a plate may be used that lacks holes  28 . For example, a plate may be attached to a bone by using screws that are self-starting or self-tapping or drills may be used to prepare holes within a plate for screws. 
         [0030]    Other structures for locking screws to plates are known and can be used. In addition, the inserts  30 , although shown and described as being part of the plate  10 , may be used with a static plate that does not include movable or adjustable segments. The inserts  30  when used with a bone plate, whether adjustable or static, would provide enhanced screw retention within the screw holes of such plates. 
         [0031]    As discussed, the screws  40  may be formed from a biocompatible material. By way of example, the plate  10  may be formed from a PEEK or titanium alloy, the inserts  30  formed from commercially pure implant grade titanium, and the screws  40  formed from a titanium alloy. The use of materials having different characteristics, such as different hardness, facilitates screw-plate engagement, and inhibits screw back out. 
         [0032]    In an embodiment, the plate  10 , locking mechanism  18 , and rails  20  are made from a relatively hard material, e.g., implant grade titanium alloy, and the inserts  30  are made from a relatively softer material, e.g., commercially pure implant grade titanium. In another embodiment, the plate  10  and/or rails  20  may be made of another implant grade material, such as, but not limited to, commercially pure titanium, titanium alloys, cobalt chrome alloys, PEEK, and the like. 
         [0033]    In use, the segments  12 ,  14 ,  16  of the plate  10  may be maximally spaced apart thereby facilitating the greatest degree of adjustment to fit the anatomy of the patient. The tab  22   a  of tongue  22  may be received within the outward most groove  24   a  such that the segments  12 ,  14 ,  16  are maximally spaced apart, but are inhibited from moving apart from one another without a secondary user operation to disengage the tab  22   a  from the groove  24   a . The plate  10  is placed onto the vertebral bodies such that screw holes  28  are located on the anterior portion of the most cranial vertebral body. Screws  40  are placed into the two most cranial screw holes  28  to anchor the plate  10  in place. The next adjacent segment is adjusted to align the holes  28  with the next vertebral body so that the screws  40  can be inserted through the holes  28  and into the vertebral body. This process is repeated for each additional vertebral segment. 
         [0034]    A standard plate holder (not shown) can be used to facilitate placement of the plate  10  and holding of the plate  10  during insertion of the screw  40 . In addition, instruments known in the art may be used to help expand or contract the adjacent segments  12 ,  14 ,  16  during use. Removable wedges (not shown) may hold segments  12 ,  14 ,  16  in a predetermined spaced orientation during implantation by being positioned between the segments  12 ,  14 ,  16  and impeding movement of the segments  12 ,  14 ,  16  toward one another in a predetermined spaced orientation during the implantation of the plate  10 . After implantation of plate  10 , the removable wedges are removed from the plate  10 , thereby permitting the segments  12 ,  14 ,  16  to move relative to one another after surgery. 
         [0035]    Each of the embodiments described above are provided for illustrative purposes only. It will be understood that various modifications may be made to the embodiments of the present disclosure. Therefore, the above description should not be construed as limiting, but merely as exemplifications of embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present disclosure.