Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Application No. 61/454,571, which was filed on Mar. 20, 2011. The contents of U.S. Application No. 61/454,571 are incorporated by reference as part of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to spinal implants, implant insertion assemblies, and surgical methods for replacing at least a portion of one or more vertebral bodies of the spine. 
     II. Discussion of the Prior Art 
     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 pelvic region of the vertebral column. These fused vertebrae consist of the sacral and coccygeal region of the vertebral column. 
     The main functions of the spine are to provide support and protect the spinal cord. Even slight disruptions to either the intervertebral discs or vertebrae can result in serious discomfort due to decompression of nerve fibers either within the spinal cord or extending from the spinal cord. 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, and breathing). Therefore, it is of great interest and concern to be able to both correct and prevent ailments of the spine. 
     Trauma to the spine (e.g. car accident, sports injury) can cause fracturing of one or more of the vertebrae. Certain diseases affecting the spine (e.g. tumors, osteoporosis) can cause degeneration of the spine. Both trauma and degeneration may result in severe disruption to the spine. In these circumstances, the complete removal of one or more vertebrae may be required. If one or more vertebrae are removed, a replacement support system must be implanted in order to protect the spinal cord and maintain, or improve, the structure and integrity of the spine. 
     SUMMARY 
     According to one broad aspect, a stackable vertebral body replacement is provided comprising variable size upper and lower endcaps and at least one center core, all manufactured from a biocompatible material. For example, the biocompatible material may include, but is not limited to, poly ether ether ketone (PEEK). The upper and lower endcaps comprise a base and a variable height riser connector. The implant endcap has a cavity through the center of the piece to allow for bone fusion. The endcaps connect to the center core by a mating section on one end of the endcap. The mating section allows the endcaps to be joined to opposite ends of the core, and once locked in place they form a complete assembly. The mating section is designed so the vertebral body replacement can be built inside the body or prior to insertion. The endcaps are available in heights ranging from 7 mm to 25 mm and angles ranging from zero to eight degrees, allowing for ideal height reconstruction and restoring lordotic or kyphotic curvature. The center core comprises a body with a hollow center defining a fusion aperture therethrough. Both the top and bottom of this center core comprise mating sections which allow the center core to attach to the endcaps and lock into place. The height of the center core ranges from 10 mm to 80 mm. During lateral insertion, the center core is inserted between the two endcaps using the lateral insertion assembly. If an anterior insertion method is used, either a one-piece vertebral body replacement (endcaps and core body as one complete piece) is inserted or the implant is assembled outside the patient and then inserted as a complete vertebral body replacement. 
     In one embodiment, the vertebral body replacement is radiolucent. The use of radiolucent material is ideal for use in tumor patients since the surgeon can see through the implant on an x-ray and monitor the site post-surgery. According to this embodiment, radiopaque markers are placed in the endcaps and the core for use in positioning and alignment of the vertebral body replacement during insertion. By way of example only, the radiopaque markers may be titanium or tantalum pins. 
     The lateral inserter assembly is constructed from a biocompatible material, such as stainless steel. It is comprised of a core insertion tool between two slide retainers held apart by an adjustable clamp. The lateral inserter assembly is used to properly position the endcaps in the body and guide the core between them inside the body. The center core of the vertebral body replacement is attached and removed from the core insertion tool by means of a quick-release on the top of the tool. The two endcaps are attached to the lateral inserter assembly by screwing them onto endcap retaining rods which slide into holes on each side of the slide retainer. The center core is placed between the two slide retainers using the mating sections on the core as a guide between the two slides. Malleting or sliding of the core between the slides provides the distraction of the vertebral bodies without the requirement for an additional device. Once in place, the core insertion tool is detached from the center core using the quick-release and the lateral inserter assembly are unscrewed from the endcaps. This assembly has the advantage of allowing for a smaller opening for access to the spine, compared to previous approaches, which will reduce patient recovery time. Additionally, the stackable assembly provides a slightly lower cost option than expandable cages, while still being able to provide many of the benefits of the lateral approach. 
     The anterior inserter assembly is used to easily insert the vertebral body replacement into the spinal cavity and release when properly positioned. For anterior insertion the stackable vertebral body replacement (core and two endcaps) are assembled outside the body prior to insertion. The anterior inserter assembly comprises a quick-release to easily affix and detach the vertebral body replacement from the assembly. For the anterior approach, a separate distractor/sizer will be required. 
     A distractor/sizer assembly is used to open the space between two adjacent vertebrae where the vertebral body replacement will be inserted. The tool is unique since it not only distracts the spinal column, but also measures the desired size of the requirement implant. The distractor/sizer tool comprises two pairs of connected crossed arms with handles at one end (connected by a measurement device) and spreader arms at the other. Opening the space between the handles at one end decreases the distance between the spreader arms at the other end. Affixed to the outside of the spreader arms by a pivoting mount is an endcap with anti-migration elements on the outside face to allow sufficient friction to hold onto the surface of remaining vertebrae during distraction. The vertical distance between the endcaps of the spreader arms can be read from the measurement arm near the handle of the device. The distractor/sizer can accommodate heights from 18 mm to 120 mm. 
     The lateral method for inserting the stackable vertebral body replacement is as follows: (1) the patient is placed in the lateral decubitus position on the operating table and sedated under general anesthesia, (2) The surgeon ensures proper positioning of the vertebrae to be treated using a fluoroscope, (3) The surgeon makes a small incision in the skin in the patient&#39;s side, over the midsection of the disc for a single-level fusion or over the intervening vertebral body for a multi-level fusion, (4) Surgical dissection is performed via the placement of serial dilators, each of which actively provides directional nerve localizing electromyographic (EMG) data to the surgeon for safe navigation near the lumbar nerve plexus. Active neuromonitoring in addition to the use of real-time fluoroscopic guidance insures safety and accuracy as the expandable tubular retractor is carefully advanced through the psoas muscle (for lumbar spine surgeries) to the desired disc space or vertebral body, (5) The endcaps are inserted coupled to the lateral insertion tool, (6) The endcaps are placed into position inside the patient; adjacent the endplates of the vertebral bodies, (7) The clamp holding the two slide retainers is adjusted to the desired width for core insertion, (8) A core is inserted between the two slides and is guided into place between the endcaps, (9) Malleting the core inserter assembly down the slides with the core distraction block attached provides the distraction of the spine. (10) The core is slid down until it locks into place between endcaps, (11) The core is released from the core insertion tool, (12) The insertion tools are removed and the incision is closed. 
     The anterior method for inserting the stackable vertebral body replacement body may be performed as follows: (1) The vertebral body to be replaced is accessed via any anterior approach appropriate for the spinal level, (2) A distractor/sizer is used to distract the endplates of the adjacent vertebral bodies, and to determine the height of the vertebral body replacement (VBR), (3) The vertebral body replacement is built outside the body based on measurements determined from the distractor/sizer and attached to the anterior insertion tool and the distractor/sizer is removed. (4) The insertion tool is detached from the vertebral body replacement and the anterior insertion tool is removed. 
    
    
     
       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 the perspective view of a stackable vertebral body replacement according to an exemplary embodiment; 
         FIG. 2  is the top view of a stackable vertebral body replacement of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the vertebral body replacement of  FIG. 1 ; 
         FIG. 4  is a perspective view of the center core section of the vertebral body replacement of  FIG. 1 ; 
         FIG. 5  is the top/bottom view of the core section of the vertebral body replacement implant of  FIG. 4 ; 
         FIG. 6  is the side (left/right) view of the core section of the vertebral body replacement implant of  FIG. 4 ; 
         FIG. 7  is the front/back view of the core section of the vertebral body replacement implant of  FIG. 4 ; 
         FIG. 8  is the perspective view of an endcap of the vertebral body replacement implant of  FIG. 1 ; 
         FIG. 9  is the front view of an endcap of the vertebral body replacement implant of  FIG. 8 ; 
         FIG. 10  is the side (left/right) view of the endcap of the vertebral body replacement implant of  FIG. 8 ; 
         FIG. 11  is the back view of the endcap of the vertebral body replacement implant of  FIG. 8 ; 
         FIG. 12  is the top/bottom view of the endcap of the vertebral body replacement implant of  FIG. 8 ; 
         FIG. 13  is the cross-sectional view of the endcap of the vertebral body replacement implant of  FIG. 8 ; 
         FIG. 14  is the perspective view of the lateral inserter assembly; 
         FIG. 15  is the bottom view of the lateral inserter assembly of  FIG. 14 ; 
         FIG. 16  is the top view of the lateral inserter assembly of  FIG. 14 ; 
         FIG. 17  is the exploded view of the lateral inserter assembly of  FIG. 14 ; 
         FIG. 18  is a perspective view of the bracket assembly of the lateral inserter assembly of  FIG. 14 ; 
         FIG. 19  is an exploded view of the bracket assembly of the lateral inserter assembly of  FIG. 14 ; 
         FIG. 20  is a perspective view of the clamp for the lateral inserter assembly of  FIG. 14 ; 
         FIG. 21  is an exploded view of the clamp for the lateral inserter assembly of  FIG. 14 ; 
         FIG. 22  is a perspective view of the core inserter assembly; 
         FIG. 23  is exploded view of the core inserter assembly of  FIG. 22 ; 
         FIG. 24  is exploded view of top of core inserter assembly of  FIG. 22 ; 
         FIG. 25  is exploded view of bottom of core inserter assembly of  FIG. 22 ; 
         FIG. 26  is perspective view of distractor block of  FIG. 22 ; 
         FIG. 27  is a perspective view of anterior inserter assembly; 
         FIG. 28  is side view of anterior inserter assembly of  FIG. 27 ; 
         FIG. 29  is detailed view of bottom end of anterior inserter assembly of  FIG. 27 ; 
         FIG. 30  is an exploded view of the bottom end of the anterior inserter assembly of  FIG. 27 ; 
         FIG. 31  is further exploded view of the bottom end of the anterior inserter assembly of  FIG. 27 ; 
         FIG. 32  is an exploded view of the top end of the anterior inserter assembly of  FIG. 27 ; 
         FIG. 33  is a perspective view on the distractor/sizer assembly; 
         FIG. 34  is an exploded view of the distractor/sizer assembly of  FIG. 33 ; 
         FIG. 35  is a bottom view of the distractor/sizer assembly of  FIG. 33 ; 
         FIG. 36  is an exploded view of the bottom of the distractor/sizer assembly of  FIG. 33 ; 
         FIG. 37  is a detailed view of the bottom of the distractor/sizer assembly of  FIG. 33 ; 
         FIG. 38  illustrates the steps involved in using the lateral inserter assembly; 
         FIG. 39  illustrates the steps involved in using the anterior inserter assembly; 
     
    
    
     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 stackable vertebral body replacement, anterior and lateral inserter assemblies, distractor/sizer and methods for implantation disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIGS. 1-13  illustrate an exemplary embodiment of a stackable vertebral body replacement  10  according to one embodiment of the present invention. The stackable vertebral body replacement  10  includes a center core section  11  and two endcaps  12 . The core section  11  and the two endcaps  12  are made from a biocompatible material. For example, the components may be machined from implantation-grade polyether ether ketone (PEEK). In one embodiment, six sides comprise the center core  11 . The following sides of the core are opposite each other and are identical: top  34  and bottom  35 , front  36  and back  37 , and left  38  and right  39 . The top  34  and bottom  35  sides of the core sections  11  have mating sections  13 , which allow the core  11  to couple to the mating sections  14  of the endcaps  12 . The core  11  is may vary in height from 10 mm to 80 mm. The core  11  is held in place between the two endcaps  12  by the stops  15  on front  36  and back  37  of the core  11  which lock into the locking assembly  16  on the back of the endcap  12 . A guide  33 , helps position the core  11  into the mating sections  14  on the endcaps  12  during insertion. Additionally, a protrusion  17  on the mating section  13  increases the friction between the core  11  and endcaps  12  holding the assembly together. The top of the core  11  has holes  18  extending longitudinally therethrough, in which radiopaque markers are placed to verify alignment during insertion. On top of the core  11  there are additional holes  19  which allow entry of the core insertion assembly pins  77  for lateral insertion. The side of the core  11  has holes  20  for attachment to the anterior inserter assembly  90  for anterior insertion. Additional holes  21  in the side of the core  11  allow for insertion of additional radiopaque markers for verifying alignment during insertion. 
     The endcaps  12  comprise a variable length base  22  and a variable height riser  23 . In one embodiment, the endcap base  22  is rectangular with front  133 , back  134 , left  135 , right  136 , top  137 , and bottom  138  sides. The endcaps  12  range in height from 7 mm to 25 mm. The endcap  12  is comprised of a cavity  24  through the piece which runs from the front  133  to the back  134  to allow for bone fusion through the vertebral body replacement. In one embodiment, in addition to the cavity  24 , the endcap base  22  has additional holes  25  which are cut through the base material at opposite ends of the base, also to promote bone fusion with the endcap  12 . On the top  137  and bottom  138  of the endcaps  12  are screw holes  26  to allow for connection to the endplate retaining rods  45  of the lateral inserter system  40 . Additionally on top  137  and bottom  138  of the endcaps  12  are holes  27  for radiopaque markers for proper alignment during insertion and a hole  32  to promote bone fusion. The side of the implant has an additional hole  28  for a radiopaque marker and holes  29  to promote fusion. The front  133  of the endcap  12  has anti-migration elements  30  designed to grip the ends of the vertebrae after implantation in order to maintain its proper spinal alignment. Additionally, there are a plurality of small holes  31  in the front  133  of the endcap  22 , partially through the base for the insertion of radiopaque markers which guide insertion and maintain implant position. 
       FIGS. 14-26  illustrate the lateral inserter system  40  according to one embodiment of the present invention. This embodiment of the lateral inserter system is comprised of two slide retainers  41 , a core inserter  42 , two bracket assemblies  43 , and a clamp assembly  44 . 
     The slide retainers  41  are constructed of a biocompatible material, such as stainless steel and are positioned on either side of the core inserter  42 . Endcap retaining rods  45  are slid into the in the top of the slide retainer  41  and travel the complete length of the slide retainer  41 . On the top of the endcap retaining rod  45  is a knurled knob  46  and the opposite end is a threaded end tip  47 . The threaded end tip  47  can be attached to the top of the endcap  12  in screw hole  26 . The front of the slide retainer  41  has a handgrip  48  to assist the surgeon in handling the device. Below the handgrip  48 , on the front of the slide retainer  41  is a vertical height adjustment section  49 . This vertical height adjustment section  49  allows varying height adjustment of the bracket assembly  43 . On the inside of the slide retainer  41  is a mating section  50  which allows for coupling the core  11  onto the inside of the slide retainer  41  between the two endcaps  12 . 
     The bracket assemblies  43  maintain position of the lateral inserter system  40  in the body during surgery. The vertical position of the bracket assembly  43  along the slide retainer  41  is adjustable in one embodiment by manually retracting the slide locks  51  by pulling the knobs  52  outward on the bracket assembly  43 . The bracket assembly  43  is positioned vertically along the slide retainer  41  as required and the knobs  52  are released when in the desired position. In one embodiment, the slide locks  51  are held extended in the locked position by the extension force of a spring  53  inside the bracket assembly  43 . Here, the slide lock  51  is affixed to the knob  52  by a pin  54  inserted through a hole  55  in the knob and a hole  56  in the top of the slide lock  51 . The inside edges  57  of the bracket assembly  43  are curved to allow the bracket assembly  43  to move along the outside edges of the slide retainer  41 . 
     The clamp assembly  44  allows for both measuring the space between vertebral bodies in the spine and maintaining the proper space between the slide retainers  41  during lateral insertion. The clamp assembly  44  is made of a biocompatible material, such as stainless steel. The upper arm  58  of the clamp assembly  44  is affixed to the slide retainer  41  by means such as a screw  59  and a retaining nut  60 . The lower arm  61  of the clamp assembly is attached to the opposite slide retainer  41  in similar fashion. The measurement bar  62  is mounted into the end of the upper arm  58  opposite the slide retainer  41  attachment point. The lower arm  61  travels along the measurement bar  62  with the opposite end affixed to the slide retainer mount  41 . The lower arm  61  is held in place by a locking device  68  which is attached to the lower arm  41  by the mounting pin  65 . A handle  63  is attached to a locking screw  64  inside the lower arm. Turning the handle  63  engages and disengages the locking device  68 , restricting and allowing travel of the lower arm  41  along the measurement bar  62  which changes the distance between the slide retainers  41 . 
     The core inserter  42  is made of biocompatible material, such as stainless steel. In one embodiment, the core inserter  42  comprises an outer container  66 , an inner rod  67 , a core distractor block  80 , a quick release  69  and a locking nut  70 . The inner rod  67  slides within the hollow outer container  66  and is attached at the upper end by release pins  71  which travel through holes in the inner rod and into slots  72  in the outer container which limit the travel of the rod. The quick-release  69  fits around and is attached to the outer container  66  by two lock pins  73 . The inside of the locking nut  70  is threaded and fits around the outer container  66  and screws onto the threaded area  74  on the outside of the container. A spring  75  fits around the outer container  66  between the quick-release  69  and the locking nut  70 . The spring  75  is compressed and the force on the spring is translated as a downward force on the inner rod  67 , keeping the arms  77  at the end of the core inserter  42  extended unless upward force is applied to the quick-release  69  counteracting spring  75  force. The lower end of the inner rod  67  is attached to the center pin  76  holding the core inserter arms  77  together. Two pivot pins  78  allow the core inserter arms  77  to pivot around the center pin  76 , opening and closing the arms. 
     With the core inserter arms  77  together, the outer container  66  slides into the distractor block  80 . The distractor block  80  is made of biocompatible material. For example, the components may be machined from implantation-grade polyether ether ketone (PEEK). The distractor block  80  is held onto the core inserter  42 , in one case, by two ball detents  78  on both sides of the core inserter  42 . The top  139  and bottom sides  139  of the distractor block  80  have a mating section with connectors  81  which are smaller than those of the center core  11  in order to take the downward load off the core  11  during distraction. The center of the distractor block  80  is hollow to allow the bottom of the outer container  66  to slide into and attach to the distractor block  80 . On the inside of the left  143  and right  144  sides of the distractor block  80  are recessed holes  83  where the ball detents  79  from the outer container  66  meet with and attach the distractor block  80  to the outer container  66 . Pulling the distractor block  80  vertically down off the outer container  66  will release the ball detents  79 , allowing the distractor block  80  to be removed from the outer container  66 . 
       FIGS. 27-32  illustrate the anterior inserter system  90  according to one embodiment of the present invention. The anterior inserter system  90  is comprised of a hollow outer container  91  a collet  92 , a lock  93 , a bracket assembly  94 , an inner shaft  95  and two bracket arms  96  which attach to the center core  11 . The anterior inserter system  90  is constructed from biocompatible material, such as stainless steel. The end of the bracket arms  96  are machined to enable them to affix to the core  11  by traveling through holes  20  on the core  11  and grasping the inside edge of the core material. Both bracket arms  96  are connected to the end of the inner shaft  95  by means such as a center pin  97 . The bracket arms  96  are also connected to the bracket  94  by two pivot pins  98 . The bracket assembly  94  allows vertical movement of the inner shaft  95 , which pivots the bracket arms  96  around the pivot pins  98  causing the bracket arms  96  to open and close. The pivot pins travel through holes  99  on the bracket  94  which affix the bracket arms  96  to the bracket assembly  94 . 
     At the opposite end of the anterior inserter system  90  from the bracket assembly  94  is the release assembly. The release assembly is comprised of the collet  92 , a lock  93  a spring  100  and two release pins  101 . The release pins  101  go through the top of the inner shaft  95  and through slots  102  in the outer container  91 . The release pins  101  ride in the slots  102  allowing for some limited, vertical movement of the inner shaft  95  within the outer container  91 . A spring  100  is placed on the inside of the outer container  91  at the end, between the end of the outer container  90  and the end of the inner shaft  95  allowing for tension being placed upon the inner shaft  95 . The force of the spring  100  causes downward force on the inner shaft  95  which causes the bracket arms  96  to pivot around the pivot pins  98  and the bracket arms  96  to spread out. The spread bracket arms  96  of the anterior inserter  90  affix the center core  11  to the anterior inserter  90 . Upward force on the collet  92 , causes the inner shaft  95  to move upwards, causing the bracket arms  96  to move toward the center (retract), allowing the anterior inserter system  90  to be removed from the center core  11  after being property positioned in the body. The outer container  91  is travels through the hole in the center of the collet  92  and the collet  92  is affixed to the outer container  91  by the release pins  101  which travel through the collet  92 , the outer container  91  and inner shaft  95 . Located just above the collet  92  on the outer container is a threaded area  103 . The inside of the lock  93  is threaded. The top of the outer container  91  is placed through the center of the lock  93 . The lock  93  is then screwed onto the outer container  91  onto the threaded area  103  until it meets the edge of the collet  92 . The lock  93  is used to maintain the collet  92  in the desired position during insertion of the vertebral body replacement. Adjusting the position of the lock  93  on the threaded area  103  allows for movement in the collet  92  on the outer container  91 . 
       FIGS. 33-37  illustrate the distractor/sizer  110  according to one embodiment of the present invention. The distractor/sizer  110  is constructed from a biocompatible material such as stainless steel and is comprised of lower arms  111  held together in the center of the arm by the lower center screw  112 . The top of the lower arms  111  are affixed to the bottom of the upper arms  113  by two screws  114 . The upper arms  113  pivot around the upper center screw  115 . The outer edges of the upper arms  113  are curved to form a handgrip  116 . A pair of flexible bars  117  are affixed between the upper arms  113  by mounting pins  118 . The flexible bars  117  hold the upper arms  113  apart and provide some resistance as the upper arms  113  are closed together. As the upper arms  113  are moved together (closed), the bottom end of the upper arms  113  move apart. This movement causes the upper end of the lower arms  111  to move apart and the bottom of the lower arms  111  with the endplates  119  to move apart, causing distraction. A measurement bar  120  is affixed to one end of the upper arms  113  by a mounting pin  121 . The other end of the measurement bar  120  travels through a hole  122  on the other upper arm  113 . A collar  123  is attached to the end of the measurement bar  120  by an endcap  124  affixed to the end of the measurement bar  120 . The endplates  125  are affixed by threaded screws  126  and caps  127  to endcap brackets  128  which have an attaching point  129  which affix the endcap brackets  128  to the bottom end of the lower arms  111  via a pivot pin  130 . The outside edges of the endplates  125  have anti-migration elements  131  to maintain the proper position of the distractor/sizer  110  on the vertebral bodies during distraction. The measurement bar  120  is calibrated to allow the surgeon to determine the size of vertebral body replacement required for the patient. The distractor/sizer  110  allows for distraction and sizing to be completed with one surgical tool. 
     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