Abstract:
The present invention relates generally to medical devices and methods for use in spinal surgery. In particular, the disclosed devices relate to a spinal fixation system and an intervertebral spinal implant assembly sized and dimensioned for the lumbar spine implantable via an anterior or anterolateral approach. The devices include an implant, bone screws, and an improved locking mechanism to prevent the back out of screws.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional patent application claiming the benefit of priority from U.S. Provisional Patent Application Ser. No. 61/437,006, filed on Jan. 28, 2011, the entire contents of which are hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein. 
    
    
     FIELD 
     The present invention relates generally to spinal surgery and, more particularly, to devices for spinal fixation and spinal fusion having an improved mechanism to prevent the back out of screws. 
     BACKGROUND 
     Currently there are nearly 500,000 spine lumbar and cervical fusion procedures are performed each year in the United States. One of the causes of back pain and disability results from the rupture or degeneration of one or more intervertebral discs in the spine. Surgical procedures are commonly performed to correct problems with displaced, damaged, or degenerated intervertebral discs due to trauma, disease, or aging. Generally, spinal fusion procedures involve removing some or the all of the diseased or damaged disc, and inserting one or more intervertebral implants into the resulting disc space. Anterior lumbar interbody fusion (ALIF) procedures provide unparalleled access to a desired spinal target site. The ALIF technique involves approaching the spine through the abdomen and exposing the front of the spine, as opposed to the side or the back. Approaching the spine this way generally allows for greater exposure and a more complete excision of the damaged disc. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”), which reduces if not eliminates neural impingement commonly associated with a damaged or diseased disc. 
     SUMMARY 
     According to one embodiment, a surgical fixation system is described including a plate dimensioned to span at least two bony segments, a plurality of apertures dimensioned to receive anchor elements, a plurality of anchor elements and plurality anti-backout elements disposed adjacent to each of the apertures dimensioned to receive anchor elements. 
     According to an exemplary embodiment, the anti-backout element comprises a biasing member and a locking slide. The biasing member is elastically deformable. In a first position, the biasing member urges the locking slide in a first direction in which at least a portion of the locking slide enters the aperture in the plate. Upon insertion of an anchor element, the anchor element may force the locking slide to move in a second direction opposite the first direction, deforming the biasing member and moving the biasing member to a second position such that the locking slide does not reside in the aperture of the plate. Once the anchor element is fully inserted through the plate and passed the locking slide, the biasing member urges the locking slide in the first direction into the aperture such that at least a portion of the locking slide covers the proximal end of the anchor element preventing the anchor element from backing out of the plate. 
     According to another embodiment, a spinal fusion implant assembly is described. The spinal fusion implant assembly includes a plate coupled to a U-shaped body, a plurality of apertures in the plate dimensioned to receive anchor elements, a plurality of anchor elements and a plurality of anti-backout elements. 
     The anti-backout element includes a biasing member and locking slide and operates in the same way as described above for the surgical fixation system. 
     According to an exemplary aspect, the plate and the U-shaped body of the spinal fusion implant assembly are constructed of different materials. When fully assembled, the spinal fusion implant assembly is dimensioned to be contained entirely within an intervertebral disc space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
         FIG. 1  is a perspective view of a spinal fixation system, according to an exemplary embodiment; 
         FIG. 2  is a top view of the spinal fixation plate of  FIG. 1 ; 
         FIG. 3  is a bottom view of the spinal fixation plate of  FIG. 1 ; 
         FIG. 4  is a cross-section of the width of the spinal fixation plate of  FIG. 1 ; 
         FIG. 5  is a perspective view of the spinal fixation plate of  FIG. 1 , without the anti-back-out mechanism; 
         FIG. 6  is a cross-section along the longitudinal axis of the spinal fixation plate of  FIG. 1 ; 
         FIG. 7  is a perspective view of a spinal fusion implant assembly according to an exemplary embodiment; 
         FIG. 8  is a perspective view of the spinal fusion implant assembly of  FIG. 7 ; 
         FIG. 9  is a front view of the spinal fusion implant assembly of  FIG. 7 ; 
         FIG. 10  is a perspective view of the spinal fusion implant assembly according to an alternate embodiment. 
         FIG. 11  is an exploded view of the spinal fusion implant assembly of  FIG. 10 ; 
         FIG. 12  is a top view of the spinal fusion implant assembly of  FIG. 10 . 
         FIG. 13  is a front view of an alternative embodiment of the body of the implant assembly of  FIGS. 7-12 . 
     
    
    
     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 spinal implants disclosed herein boast a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIGS. 1-6  illustrate an example of a surgical fixation system, according to an exemplary embodiment. The surgical fixation system comprises a surgical fixation plate  10 , a plurality of screws  38  (only two of four shown), and a plurality of anti-backout elements  20 . As will be explained in greater detail below, the surgical fixation system may be used to provide temporary or permanent fixation along an orthopedic target site, including but not limited to adjacent vertebral levels within the spine (e.g. cervical spine during anterior fusion surgery, lumbar spine for anterior fusion surgery, etc. . . . ). To do so, the plate  10  is first positioned over the target site such that the screws and anti-backout elements  20  may thereafter be employed to couple the plate  10  to the target site. According to one aspect of the present invention, the screws  38  are prevented from backing out of the target site after placement through the use of the anti-backout elements  20  installed within the plate  10 . 
     The surgical fixation plate  10  includes a first surface  12 , a second surface  14 , and a plurality of bone screw apertures  30  extending between the first and second surfaces  12 ,  14 . Each bone screw aperture  30  has a corresponding anti-backout element  20  for preventing back-out of only one screw  38 . The anti-backout element  20  resides in a recess  40  in first surface  12  of the plate  10  adjacent to the bone screw aperture  30 . 
     The plate  10  may be provided having any number of different peripheral profiles, including but not limited to the generally rectangular peripheral profile set forth by way of example in the figures. The plate  10  may also be provided with or without a viewing aperture  40  formed between the first and second surfaces  12 ,  14  and positioned generally in the central portion of plate  10 . The viewing aperture  40  functions to provide the ability to see or visualize the spinal target site after the plate  10  has been secured to the patient&#39;s vertebrae. It will be appreciated that the viewing aperture  40  may be provided in any number of suitable shapes or configurations without departing from the scope of the invention. Insertion tool recesses  32  may be provided on the lateral sides of the plate  10  for receiving at least a portion of an insertion instrument. By way of example only, the plate  10  shown in  FIGS. 1-6  includes a pair of insertion tool recesses  32 , with one located at each side of the plate  10 . 
       FIGS. 1-6  illustrate a plate  10  having an anti-backout element  20  according to an exemplary embodiment. The anti-backout element  20  includes a locking slide  22  and a biasing member  24 . The biasing member  24  is coupled to the plate  10  medial to the locking slide  22 , and urges the locking slide  22  toward the screw aperture  30 . The biasing member  24  is elastically deformable, such that when a bone screw  38  is inserted into the screw aperture  30 , the head of the screw will urge the locking slide  22  away from the screw aperture  30  against the biasing member  24 , thereby deforming the biasing member  24 . Upon passage of the screw head past the locking slide  22 , into the screw aperture  30 , the biasing member  24  will urge the locking slide  22  back toward the screw aperture  30 . At least a portion of the locking slide  22  will project into the screw aperture  30  (as best shown in  FIG. 3 ), and over the proximal edge of the screw head, thereby preventing the screw from backing out of the screw aperture  30  of the plate  10  after insertion. 
     The locking slide  22  has a medial face  36  for engaging the biasing member  24  and a lateral face  34  for engaging the head of a bone screw  38 . According to the exemplary embodiment shown in  FIGS. 1-6 , the lateral face  34  that engages the head of a bone screw has a chamfered surface  28 , such that during insertion of a bone screw  38  into a bone screw aperture  30  of the plate  10 , when the head of the bone screw contacts the chamfered surface  28  of the locking slide  22 , the medial surface  36  of the locking slide  22  will be urged against the biasing member  24  as discussed above. The locking slides may engage with the spinal fixation plate  10  within a recess  40  in the spinal fixation plate  10 , wherein said recess  40  is located medially to a pair of screw apertures  30  (as best shown in  FIG. 5 ). According to an exemplary embodiment, the locking slides  22  have a recess  44  that corresponds to a track  42  in the recess  40  in superior surface  12  of the plate  10 . The track  42  engages the locking slide  22  via the recess  44  in the locking slide  22  and maintains the locking slide  22  within the plate  10 . As such, the locking slide  22  is capable of sliding in a first direction toward its corresponding screw aperture  30  and in second direction, opposite the first direction, away from a corresponding screw aperture  30  and toward the biasing member  24 . 
       FIGS. 7-8  illustrate a spinal fusion implant assembly  100  according to an exemplary embodiment. The spinal fusion implant assembly  100  is a two-piece assembly including a plate  110  having locking elements  220 , a plurality of bone screws  306  and a generally U-shaped body  120 . The assembled two-piece implant  100  is dimensioned to be contained entirely within the intervertebral space when implanted. According to the exemplary embodiments, the plate  110  and body  120  are constructed of different materials. For example, the plate  110  may be constructed of any biocompatible metal, such as titanium. The body  120  may be constructed of any suitable non-bone composition having suitable radiolucent characteristics, including but not limited to polymer compositions (e.g. poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK)) or any combination of PEEK and PEKK. According to an exemplary embodiment shown if  FIG. 12 , the arms of the U-shaped body may have chamfered surfaces where the body  120  engages the plate. 
     The spinal fusion implant assembly  100  includes a top surface  90 , a bottom surface  95 , two lateral sides, an anterior side  80 , and a posterior side  85  (each defined relative to the regions of the target disc space when implanted). According to a preferred method of implantation the spinal fusion implant  100  may be implanted from an anterior approach such that anterior side  80  is the trailing side and posterior side  85  is the leading side during insertion. The plate  110  defines the anterior side  80  of the implant and includes a plurality of bone screw apertures  302 ,  304  each for receiving a bone screw therethrough. According to the exemplary embodiments, the screw apertures  302 ,  304  are positioned such that there is a lateral upper screw hole, a medial upper screw aperture, a lateral lower screw aperture, and a medial lower screw aperture. 
     The upper screw apertures  302  pass through the plate  110  at an angle such that when the bone screws  306  are inserted into the upper screw apertures  302 , they extend from the plate  110  at an angle and penetrate into the vertebral body inferior to the implant assembly  100 . By way of example only, the upper screw apertures  302  may be angled such that the bone screws penetrate into the vertebral body at an angle between 35 and 55 degrees, and preferably 45 degrees. Lower screw apertures  304  also pass through the plate  110  at an angle, but in the opposite direction of the upper screw apertures  302 . Thus, when the bone screw  306  is inserted into the lower screw apertures  304 , it extends from the plate  110  at an angle and penetrates the vertebral body superior to the implant assembly  100 . By way of example, the lower screw apertures  304  may be angled such that the lower bone screws  306  penetrate into the vertebral body at an angle between 35 and 55 degrees, and preferably 45 degrees. The screw apertures  302 ,  304  may also be angled such that the distal end of the bone screws  306  converge towards each other. By way of example, the screw apertures  302 ,  304  may be oriented such that the bone screws  306  are angled medially between 5 and 15 degrees. 
     According to the exemplary embodiment illustrated in  FIGS. 7-8 , the plate  110  further includes an anti-backout element  220  that corresponds to each individual screw aperture  300 . The anti-backout element  220  includes a locking slide  222  and a biasing member  224 . The anti-backout element  220  functions in a way that is similar to the anti-backout element  20  described with respect to the spinal fixation plate  10  discussed above. A pair of locking elements  220  resides in a recess in the anterior surface of the plate  110  between a pair of screw apertures  300 . The biasing member  224  is elastically deformable, such that when a bone screw  306  is inserted into the screw aperture  300 , the head  308  of the screw will urge the locking slide  222  away from the screw aperture  300  against the biasing member  224 , thereby deforming the biasing member  224 . Upon passage of the screw head  308  past the locking slide  222 , into the screw aperture  30 , the biasing member  224  will urge the locking slide  222  back toward the screw aperture  300 . At least a portion of the locking slide  222  will project into the screw aperture  300 , and over proximal end of the screw head  308 , thereby preventing the screw  306  from backing out of the screw aperture  300  of the plate  110  after insertion. 
     According to one embodiment, the body  120  includes at least one radiopaque marker  126 . Further, the body  120  may also include anti-migration elements. Anti-migration features are designed to increase the friction between the spinal fusion implant assembly  100  and the adjacent contacting surfaces of the vertebral bodies so as to further prohibit migration of the spinal fusion implant  100  after placement and during the propagation of natural bony fusion. Such anti-migration features may include ridges (or teeth) provided along at least a portion of the top surface  90  and/or bottom surface  95 . 
       FIGS. 9-11  illustrate an alternative embodiment of the spinal fusion implant assembly  100 . This embodiment includes all of the same features as the exemplary embodiment of  FIGS. 7-8 . According to this embodiment, the plate  110  is generally U-shaped and the body  120  is generally U-shaped. The screw apertures  300  extend through the plate  110  from the anterior surface  80  through the top surface  90  (for lower screw apertures) of the plate  110  or the bottom surface  95  (for upper screw apertures) of the plate  110 . 
     With regard to the embodiment shown in  FIGS. 7-11 , it is contemplated that the spinal fusion implant assembly  100  can be assembled prior to insertion into the intervertebral space and implanted as a single complete implant, or the implant assembly  100  can be assembled within the intervertebral disc space in a multi-step process including inserting the body  120  into the intervertebral space, packing the body  120  and/or disc space adjacent the body  120  with bone growth enhancing material, then inserting the plate  110  and coupling the plate  110  to the body  120 , thereby enclosing bone growth material in the interior space of the implant assembly  100 . Both methods of implantation are preferably achieved through a standard anterior approach. In order to facilitate assembly of the implant  100  within the intervertebral space, the body  120  includes an insertion tool aperture  124  to enable the body  120  of the assembly to be implanted in the intervertebral space before the plate  110 . 
     According to the embodiments shown in  FIGS. 7-11 , the body further includes apertures  122  dimensioned to receive a guide element, such as a pin or wire (not shown). By way of example only, the guide element apertures  122  may be threaded to receive a guide element with a threaded distal end. Accordingly, the plate  110  also includes apertures  112  dimensioned to allow passage of a guide element therethough. The guide apertures  122  in the body align with the guide apertures  112  in the plate, such that after the body  120  is implanted in the intervertebral space with guide elements attached, the plate  110  can be inserted to align with the body  120 . The plate  110  further includes engagement features  140  that correspond to engagement features  150  on the body to facilitate coupling of the plate  110  to the body  120  upon insertion of the plate  110  into the intervertebral space. Once the plate  110  is coupled to the body  120  within the disc space, the guide elements may be removed from the implant assembly  100 . 
     The spinal fusion implant assembly  100  may be used to provide temporary or permanent fixation along an orthopedic target site. Once deposited in the intervertebral disc space, the spinal implant assembly  100  effects spinal fusion over time as the natural healing process integrates and binds the implant  100  within the intervertebral space by allowing a bony bridge to form through the implant  100  and between the adjacent vertebral bodies. Top surface  90  and opposed bottom surface  90  are both adapted for contact with the upper and lower vertebra adjacent the disc space. Bone screws may be introduced through the screw apertures  300  and into the adjacent vertebral bodies to fix the implant assembly  100  in the desired position within the disc space. 
     According to an additional embodiment, the top and bottom surfaces  90 ,  95  may be angled between the anterior side  80  and posterior side  85 . In lumbar and cervical applications, the posterior side  85  will preferably be shorter in height than the anterior side  80  such that the implant  100  tapers down from anterior side  80  to posterior side  85 . For example, the posterior-to-anterior angle of the tapered top and bottom surfaces  80 ,  85  may range from 5° and 15° relative to a horizontal axis, and preferably 8° to 12°. In this manner, the implant  100  helps maintain the adjacent vertebral bodies in lordosis, which is the natural curvature found in the lumbar and cervical regions of the spine. The top and bottom surfaces  80 ,  85  may be configured in any number of suitable shapes to better match the natural contours of the vertebral end plates, such as, for example, concave, convex, or a combination of concave and convex. 
     Fusion may be facilitated or augmented by introducing or positioning various osteoinductive materials within cavity between the plate  110  and the body  120  and/or adjacent to the spinal fusion implant assembly  100  within the intervertebral space. Such osteoinductive materials may be introduced before, during, or after insertion of the exemplary spinal fusion implant assembly  100 , and may include (but are not necessarily limited to) autologous bone harvested from the patient receiving the spinal fusion implant assembly  100 , bone allograft, bone xenograft, any number of non-bone implants (e.g. ceramic, metallic, polymer), bone morphogenic protein, and bio-resorbable compositions, including but not limited to, any of a variety of poly (D, L-lactice-co-glycolide) based polymers.