Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/618,640 which was filed on Mar. 30, 2012 and U.S. Provisional Patent Application No. 61/618,687 which was filed on Mar. 31, 2012. The contents of U.S. Application Nos. 61/618,640 and 61/618,687 are incorporated by reference as part of this application. 
    
    
     FIELD 
     The present invention relates generally to spinal surgery and, more particularly, to a device for spinal fusion comprising a spinal fusion implant of non-bone construction to be introduced into any variety of spinal target sites. 
     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. Introducing the intervertebral implant from an anterior approach 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 
     In a preferred aspect, the spinal fusion implant includes a body configured for implantation via an anterior approach (e.g. anterior lumbar interbody fusion or anterior cervical discectomy and fusion) between a superior and inferior vertebra, having a top surface and a bottom surface, an anterior height and a posterior height, and a fusion aperture defined by an anterior wall, a posterior wall, and first and second lateral walls. In some implementations, the anterior height of the body is greater than the posterior height of the body, such that the top surface creates a posterior-to-anterior angle relative to the horizontal axis. The posterior-to-anterior angle may be between 0° and 15°. In some implementations, the body will have a medial support extending from the anterior wall to the posterior wall through the fusion aperture. The medial support is defined by a first and second lateral wall, having a top and bottom surface, and an aperture extending through the anterior wall to receive a drive screw. The medial support has a horizontal axis extending from the midpoint of the anterior wall through the midpoint of the posterior wall. 
     The body may be constructed of radiolucent, non-bone material. At least one of the top surface and bottom surface may include anti-migration features. The body may also include at least one radiopaque marker. In some implementations, the body may include an engagement groove in the lateral walls dimensioned to receive a gripping element of an inserter. 
     The spinal fusion implant includes a drive screw aperture at the midpoint of the anterior wall, extending through the anterior wall into the implant along the horizontal axis. The drive screw aperture is dimensioned to receive a drive screw for insertion into the implant. The drive screw has a head, a shank and a collar disposed between the head and shank. The collar and shank of the drive screw may be at least partially threaded. 
     The spinal fusion implant also includes a plurality of fastener apertures extending through the anterior wall at oblique angles relative to a horizontal axis. Each of the fastener apertures is dimensioned to receive a bone fastener for insertion into one of the superior or inferior vertebrae. The bone fasteners may have a head, a shank and a collar disposed between the head and shank. The bone fasteners are of a material that can flex or deform to accommodate the aperture angle upon insertion, but is still rigid enough to penetrate the superior and inferior vertebral processes. 
     The bone fasteners are connected such that they can be driven into the implant with the screwing in of the drive screw. This may be accomplished with an intermediary plate or a drive screw collar. The intermediary plate or drive screw collar has a driving screw aperture for receiving a drive screw. The drive screw will be used to advance bone spikes through the implant apertures by pulling the intermediary plate to the implant. 
     Implementations may include one or more of the following features. For example, fastener apertures extending through the anterior wall of the implant body may at angles between 35° and 55° relative to the horizontal axis. Preferably, the fastener apertures extend through the anterior wall of the body at a 45° angle relative to the horizontal axis. 
     The fastener apertures may also extend through the anterior wall at angles oblique to the longitudinal axis. In some implementations, the angles oblique to the longitudinal axis may be divergent. Preferably, the angles are between 5° and 15° relative to the longitudinal axis. More preferably, the fastener apertures extend through the anterior wall at a 12° angle relative to the longitudinal axis. 
     In a preferred embodiment, the spinal fusion implant includes four fastener apertures and one drive screw aperture. Two of the apertures may be dimensioned to receive bone fasteners for insertion into the inferior vertebra, two of the apertures may be dimensioned to receive bone fasteners for insertion into the superior vertebra, and the drive screw aperture is dimensioned to receive a drive screw that can be fully contained by the implant. 
    
    
     
       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 implant, according to one example embodiment; 
         FIG. 2  is a top view of the spinal implant of  FIG. 1 ; 
         FIG. 3  is a view of the anterior wall face of spinal implant of  FIG. 1 ; 
         FIG. 4  is a perspective view of a drive screw, according to one example embodiment, for use with the spinal implant of  FIG. 1 ; 
         FIG. 5  is a perspective view of the bone nail, according to one example embodiment, for use with the spinal implant of  FIG. 1 ; 
         FIG. 6  is a perspective view of the posterior facing side of an intermediary plate, according to one example embodiment, for use with the spinal implant of  FIG. 1 ; 
         FIG. 7  is a perspective view of  FIG. 6  with four bone nails attached with a ball joint connection to the posterior face; 
         FIG. 8  is a perspective view of the spinal implant assembly of  FIG. 7  and the implant of  FIG. 1  with the drive screw of  FIG. 4  fully inserted in the implant; 
         FIG. 9  is an insertion instrument according to a first embodiment; 
         FIG. 10  is an exploded view of the insertion instrument of  FIG. 9 ; 
         FIG. 11  is a perspective view of the inserter shaft and head; 
         FIG. 12  is an exploded view of the insertion head of the insertion instrument of  FIG. 9  and the driver; 
         FIG. 13  is a perspective view of the outer shaft and housing of the insertion instrument of  FIG. 9 ; 
         FIG. 14  is perspective view of the assembled head of the insertion instrument. 
     
    
    
     DETAILED DESCRIPTION 
     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 anterior lumbar interbody implant disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
     The implant consists of a top surface and a bottom surface, an anterior height and a posterior height, and a fusion aperture defined by an anterior wall, a posterior wall, and first and second lateral walls. In one embodiment, the anterior height of the body is greater than the posterior height of the body, such that the top surface creates a posterior-to-anterior angle relative to the horizontal axis. The implant anterior wall may have a central drive screw aperture and a plurality of bone fastener apertures. In one embodiment, there will be two upper bone fastener apertures and two lower bone fastener apertures, designed to receive bone fasteners. In the one embodiment the bone fasteners are spikes. 
     As best appreciated in  FIGS. 1, 3, and 8 , the upper spike apertures  116  pass through the anterior side  114  at an angle such that when the spikes  140  are inserted into the upper spike apertures  116 , they extend from the implant  110  at an angle and penetrate into the vertebral body superior to the implant  110 . By way of example only, the upper spike apertures  116  may be angled such that the spikes  140  penetrate into the vertebral body at an angle between 35 and 55 degrees, and preferably 45 degrees. Lower spike apertures  118  also pass through the anterior side  114  at an angle, but in the opposite direction of the upper spike apertures  116 . Thus, when the spike  140  is inserted into the lower spike apertures  118 , it extends from the implant  110  at an angle and penetrates the vertebral body inferior to the implant  110 . By way of example, the lower spike apertures  118  may be angled such that the lower spikes  140  penetrate into the vertebral body at an angle between 35 and 55 degrees, and preferably 45 degrees. The lateral spike apertures  116 ,  118  may also be angled such that the distal end of the spikes  140  diverge away from each other. By way of example, the nail apertures may be oriented such that the spikes are angled laterally between 5 and 15 degrees, and preferably 12 degrees. The medial spike apertures  116 ,  118  may also be angled such that the distal end of the spikes  140  diverge away from each other. By way of example, the spike apertures may be oriented such that the spikes are angled laterally between 5 and 15 degrees, and preferably 10 degrees. 
     As demonstrated in  FIGS. 1-3 , a drive screw aperture  120  extends through the anterior wall into the implant. The drive screw aperture  120  is located at the midpoint of the anterior wall  114  and, according to one embodiment, is threaded to receive the drive screw. In one embodiment, the drive screw aperture extends from the anterior wall into a medial support  112  extending from the anterior wall to the posterior wall. The medial support  112  is defined by a top and bottom surface, a first and second lateral wall, the anterior and posterior wall of the implant body, and has a threaded aperture to accommodate the drive screw  130 . The drive screw aperture  120  is centered along a horizontal axis that extends from the mid-point of the anterior wall to the mid-point of the posterior wall. The body of the drive screw, when in the final locked position, is fully contained within the implant. 
     The spikes may be connected to the drive screw by any method such that the spikes may be advanced into the implant without the spikes rotating while turning the drive screw into the implant. The use of a collar around the neck of the drive screw or an intermediary plate is contemplated, but any composition may be used to achieve this purpose. As best seen in  FIGS. 6 and 7 , the spikes are flexibly connected to the intermediary plate  150  and the intermediary plate has a central aperture  154  through which the drive screw can rotate freely. The intermediary plate consists of an anterior surface and a posterior surface. The anterior surface is smooth to reduce abrasion with the spinal anatomy. The posterior surface  152  has features to hold the heads of the bone nails and is designed to interface with the anterior surface of the implant. In one embodiment, the posterior surface has four sockets  156  to hold the heads of four spikes in a ball and socket configuration. The intermediary plate can be of any shape and size, but the preferred embodiment is such that the intermediary plate matches the shape of the anterior side of the implant and has minimal thickness, while maintaining structural integrity. 
     With reference to  FIG. 5 , there is shown a spike  140  for use with the spinal fusion implant  110 . The spike  140  has a shaft  142 , a head  144 , and may have a neck or rim  148 . The head is such that it can be flexibly or rigidly connected to the intermediary plate. As seen in  FIG. 7 , in one embodiment, the head of the spike  144  is connected to the intermediary plate with a ball and socket joint. The spike head  144  may act as the ball in the ball joint. The spike is of a material sufficiently flexible to expand from a fully sheathed position prior to implant to an expanded position at the angle of the implant bone nail aperture when fully deployed. While the spike material is flexible enough to expand through the bone, it also must be rigid enough such that it can penetrate the superior and inferior vertebral processes with minimal deformity. 
     With reference to  FIG. 4 , there is shown a drive screw  130  for use with the spinal fusion implant  110 . The drive screw has a head  134 , a threaded shaft  132 , and may have a neck separating the head and shaft. The drive screw head  134  further comprises a rim  136  and a tooling recess/engagement mechanism  138 , for engaging an insertion tool. The body of the drive screw will fit through the intermediary plate aperture and the diameter of the rim  136  is slightly larger than the diameter of the intermediary plate aperture such that the drive screw head  134  cannot fully pass through the intermediary plate aperture. The drive screw  130  draws the intermediary plate with it as the drive screw enters the implant and holds the plate to the implant, by way of the rim  136 , when in the final locked position. As appreciated in  FIG. 8 , when in the final locked position, the drive screw holds the intermediary plate to the implant and is fully inserted in the implant. With the intermediary plate connected to the implant, the spikes will protrude from the bone fastener apertures such that they extend superior and inferior to the implant to engage vertebral bodies through the endplates, fixing the implant in place. 
     The present invention may include a plurality of inserters which provide the user with a suite of choices for implanting the implant  110 . According to a broad aspect of the present invention, the insertion instruments are capable of gripping and releasing the implant and screwing the drive screw into the implant. As described in  FIGS. 9-14 , one embodiment of the insertion instrument consists of a handle, an outer elongated tubular shaft, an intermediary inserter shaft, an inner drive shaft, two thumbwheels, and gripping elements. 
     The handle  178  is generally disposed at the proximal end of the insertion instrument  170 . The handle  178  may be further equipped with a universal connector  188  to allow the attachment of accessories for ease of handling of the insertion instrument  170  (e.g. a straight handle, or a T-handle, not shown). The handle  178  is fixed to the thumbwheel housing  180  allowing easy handling by the user. By way of example, the thumbwheel housing  180  holds the two thumbwheels  190 , a set screw  192 , and at least one spacer  194 . Because the handle  178  is fixed, the user has easy access to the thumbwheels  190  and can stably turn the thumbwheels  190  relative to the thumbwheel housing  180 . Additionally, the relative orientation of the thumbwheel housing  180  to the handle  178  orients the user with respect to the distal insertion head  186 . The inserter shaft  184  is attached to one of the thumbwheels  190  and is freely rotatable with low friction due to the spacer  194 . The inner drive shaft  185  is attached to the other thumbwheel and is freely rotatable with low friction due to a spacer. The user may then employ the first thumbwheel  190  to rotate the inserter shaft  184  thereby advancing it towards distal inserter head  186 . The user may employ the second thumbwheel to rotate the drive shaft, thereby turning drive the drive screw into the implant. 
     Best seen in  FIGS. 10 and 13 , the outer elongated tubular shaft  182  is generally cylindrical and of a length sufficient to allow the device to span from the surgical target site to a location sufficiently outside the patient&#39;s body so the handle  178  and thumbwheel housing  180  can be easily accessed by a clinician or a complimentary controlling device. The elongated tubular shaft  182  is dimensioned to receive a spring  196  and the proximal ends of both the inserter shaft  184  and the inner drive shaft  185  into the inner bore  188  of the elongate tubular element  182 . 
       FIGS. 9-14  detail an insertion instrument  170  according to a first embodiment of the present invention, preferably adapted for insertion from an anterior approach. The distal inserter head  186  is comprised of a fixed inserter base  202  extending generally perpendicularly from gripping arm to rotate in relation to the actuating member  204 . Each lateral channel  218  is sized and dimensioned such that the lateral aspect of each gripping arm  206  is seated within the lateral channel  218 . The central protrusion  220  is sized and dimensioned to be slideably received by central slot  214  on the inserter base  202 . As the central protrusion  220  of the actuating member  204  is being advanced by the inserter shaft  184 , it travels along the appropriate path within the central slot  214 . 
     The two gripping arms  206  each contain a laterally-disposed guide post  222 , a medially-disposed pivot pin  224 , and a terminal engagement hook  226 . Gripping arms  206  are seated within the inserter base  202  via the lateral channels  212  and seated within the actuating member  204  via the lateral channels  218 . Gripping arms  206  are attached to the actuating member  204  via the pivot pins  224  received within the pin-receiving apertures  216  on the actuating member  204 . The gripping arms  206  are pivotably disposed within the fixed inserter base  202  via the guide posts  222  positioned within the guide slots  210 . 
     The rotation of the first thumbwheel  190  in the clockwise direction causes the inserter shaft  184  to retreat within the elongate tube member  182 , which will result in pulling the actuating member  204  closer towards the inserter base  202 . This movement will cause the gripping arms  206  to pivot about the pivot pins  224  of the gripping arms  206 . When the inserter shaft  184  is fully retracted within the elongate tubular member  182  and the actuating member  204  has reached a final position with the inserter base  202 , the gripping arms  206  are releaseably engaged to the spinal fusion implant  110  such that the insertion instrument  170  is stabilized relative to the spinal fusion implant  110 . Once the implant  110  has been successfully inserted into the disc space, the second thumbwheel  190  is rotated, thereby drive the drive screw and bone nails into the implant  110 . Once the drive screw is fully inserted into the implant, the first thumbwheel is rotated in a counter clockwise direction, thereby de-coupling the inserter from the implant. 
     According to a broad aspect, the inner drive shaft may be comprised of an elongate shaft portion  302  coupled to a distal drive portion  304 . The distal end of the guided straight driver  312  is placed within the drive screw engagement mechanism  138 . The rotation of the thumbwheel  190  in the clockwise direction causes the driver  312  to advance within the inserter shaft  184  and drives the screw  126  into the implant. 
     It is expected that a standard anterior approach to the spine is performed per surgeon preference. An annulotomy template is placed onto the disc space and a centering pin is placed, penetrating the annulus at the midline. The centering pin may have a length of between 10 and 25 mm, preferably 20 mm. Anterior-posterior fluoroscopy may be used to verify midline placement of the centering pin. Additionally, lateral fluoroscopy may be used to check depth. A surgical knife is used to cut the annulus, using the lateral edges of the annulotomy template as a guide. Additionally, if the spinal fusion implant is to be further used as a partial vertebral body replacement, the necessary resections may also be made to the vertebral body or bodies. A desired trial may be implanted into the annulotomy cut and gently impacted into the disc space such that it is subflush, preferably approximately 2 mm from the anterior lip of the vertebral body. The implant corresponding to the appropriate trial side should be selected and attached to the proper size implant inserter (as described above), and filled with an appropriate graft material. The implant is gently impacted into the disc space. Lateral fluoroscopy may be used to confirm proper implant placement. Once the implant is placed, the screw is driven into the implant and the nails are driven into the superior and inferior vertebral processes. 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that 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 as defined herein.

Technology Category: 1