Abstract:
A method and devices for placing spinal implants including placing the implants completely within a spaced defined between adjacent vertebral bodies where the implants are supported by the cortical bone of the vertebral bodies. An insertion instrument places the implants in pairs with a variable-sized space placed in between. The implants are made of a biocompatible material and are particularly suited for anterior lumbar interbody fusion surgery. The spinal implants used to facilitate spinal fusion, correct deformities, stabilize and strengthen the spine.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/793,616, filed on Mar. 15, 2013 and titled, “Anterior Lumbar Fusion Method and Device,” the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to methods and devices for placing spinal implants. More particularly, the invention is directed to spinal implants used to facilitate spinal fusion and correct deformities and stabilize and strengthen the spine. The implants are inserted in pairs with a variable-sized space placed in between. The implants are made of a biocompatible material and are particularly suited for anterior lumbar interbody fusion surgery. 
       BACKGROUND OF THE INVENTION 
       [0003]    Anterior lumbar interbody fusion (ALIF) is a surgical procedure used to join two or more vertebrae. Interbody fusion includes removing an intervertebral disc and replacing the disc with an implant. The implant may be naturally occurring, for instance bone tissue, or it may be a non-naturally occurring substance, such as a plastic or plastic derivative. Often, supplementary bone tissue is used in conjunction with non-natural implants to fuse the vertebrae. Spinal fusion procedures are performed to alleviate pain due to abnormal motion of the vertebrae usually caused by degenerative conditions. However, spinal fusion is also the preferred way to treat spinal deformities. 
         [0004]    In ALIF, the vertebral disc space is fused by approaching the spine through the abdomen instead of through the lower back. A three-inch to five-inch incision is made on the left side of the abdomen and the abdominal muscles are retracted to the side. The anterior abdominal muscle in the midline runs vertically and therefore does not need to be cut and easily retracts to the side. 
         [0005]    Interbody spinal fusion places the implant between the vertebrae in the area usually occupied by the intervertebral disc. In preparation for the spinal fusion, the disc is removed entirely. A device may be placed between the vertebra to maintain spine alignment and disc height. After surgery, fusion occurs between the endplates of the vertebrae. Fusion is augmented by a process called fixation, where metallic screws, rods or plates, or cages are used to stabilize the vertebra and facilitate bone fusion. 
         [0006]    Spinal implants generally have a structure which allows for the fusion of adjacent vertebral bodies by promoting growth of bone through the implant. The implant is sized to fit (both in length and width) in the space normally occupied by the vertebral disk. However, the size and shape of the implant is limited by the natural contours of the spine and the vertebral body. Present methods often involve drilling or cutting into the vertebrae in order to secure the implant. These procedures may weaken the vertebral structure and may contribute to failure of the implant. Therefore, one challenge encountered in spinal implant surgical procedures is manufacturing an implant that replicates the general dimensions of the intervertebral disk. An implant that matches the dimensions of the intervertebral disk will more securely reside in the disk space. Elimination, or at least minimization, of movement promotes faster and more efficient fusion with the vertebrae. It may therefore be advantageous to insert multiple implants of a smaller size into the vertebral disk area to insure a better fit. The size of the implants and the spacing of these multiple implants within the disk area will vary depending on the anatomy of the individual patient. What is needed in the art, therefore, is an anterior lumbar interbody fusion method and device which allow for custom spacing of multiple implants. 
       SUMMARY OF THE INVENTION 
       [0007]    In one embodiment, the present invention relates to methods and devices for placing spinal implants. The implants are sized so as to be inserted between vertebral bodies in at least pairs. The interbody implants are placed completely within the space previously occupied by the intervertebral disc and are supported between the cortical bone surfaces of the adjacent vertebrae. The method does not require drilling or boring into the vertebral bone. The height of the implants is larger in the middle than at the ends providing for a convex shape. The convex shape allows the bottom portion of the implant to contact the vertebral body. This maximizes the contact surface area between the implant and the adjacent vertebral bodies and provides improved support to the adjacent vertebrae and thus inhibited movement of the implant after insertion. An insertion instrument places the implant in at least pairs with a variable-sized space placed in between. The spinal implants are used to facilitate spinal fusion, correct deformities, stabilize and strengthen the spine. The implants are made of a biocompatible material and are particularly suited for anterior lumbar interbody fusion surgery. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The disclosure can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Furthermore, like reference numerals designate corresponding parts throughout the several views. 
           [0009]      FIG. 1  is a lateral view of a human lumbar spine and spinal cord. 
           [0010]      FIG. 2  is top view of a human vertebra. 
           [0011]      FIG. 3  is a lateral view of a human vertebra. 
           [0012]      FIG. 4  is a perspective view of a spinal implant in accordance with an embodiment of the present invention. 
           [0013]      FIG. 5  is a top plan view of the spinal implant of  FIG. 4 . 
           [0014]      FIG. 6  is a bottom plan view of the spinal implant of  FIG. 4 . 
           [0015]      FIG. 7  is an elevational view of a first lateral side of the spinal implant of  FIG. 4 . 
           [0016]      FIG. 8  is an elevational view of a second lateral side of the spinal implant of  FIG. 4 . 
           [0017]      FIG. 9  is an elevational view of a front end of the spinal implant of  FIG. 4 . 
           [0018]      FIG. 10  is an elevational view of a back end of the spinal implant of  FIG. 4 . 
           [0019]      FIG. 11  is a perspective view of a spinal implant insertion tool in accordance with an embodiment of the present invention illustrating the tool holding two of the spinal implants of  FIG. 4 . 
           [0020]      FIG. 12  is an elevational view of a lateral side of a spinal implant engagement device of the spinal implant insertion tool of  FIG. 11 . 
           [0021]      FIG. 13  is a top plan view of the view of the spinal implant engagement device of  FIG. 12 . 
           [0022]      FIG. 14   a  is an elevational view of lateral side of a spinal implant engagement device for use with the spinal implant insertion tool of  FIG. 11  with no spacer. 
           [0023]      FIG. 14   b  is a perspective view of the spinal implant engagement device of  FIG. 14   a.    
           [0024]      FIG. 14   c  is a top plan view of the spinal implant engagement device of  FIG. 14   a.    
           [0025]      FIG. 15   a  is an elevational view of a lateral side of a spinal implant engagement device for use with the spinal implant insertion tool of  FIG. 11  with a first spacer. 
           [0026]      FIG. 15   b  is a perspective view of the spinal implant engagement device of  FIG. 15   a.    
           [0027]      FIG. 15   c  is a top plan view of the spinal implant engagement device of  FIG. 15   a.    
           [0028]      FIG. 16   a  is an elevational view of a lateral side of a spinal implant engagement device for use with the spinal implant insertion tool of  FIG. 11  with a second spacer. 
           [0029]      FIG. 16   b  is a perspective view of the spinal implant engagement device of  FIG. 16   a.    
           [0030]      FIG. 16   c  is a top plan view of the spinal implant engagement device of  FIG. 16   a.    
           [0031]      FIG. 17  is a top plan view of a lumbar vertebral body with a first pair of spinal implants in accordance with an embodiment of the invention. 
           [0032]      FIG. 18  is a top plan view of a lumbar vertebral body with a second pair of spinal implants in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    As  FIG. 1  shows, the spinal column  10  includes a number of uniquely shaped bones, called the vertebrae  12 . The number of vertebrae  12  that make up the spinal column  10  depends upon the species of animal In a human there are twenty-four vertebrae  12 , including seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. 
         [0034]    As  FIGS. 1 to 3  show, each vertebra  12  includes a vertebral body  14 , which extends on the anterior (i.e., front or chest) side of the vertebra  12 . As  FIGS. 1 to 3  show, the vertebral body  14  is in the shape of an oval disk. Referring to  FIG. 2 , the vertebral body  12  includes an exterior formed from compact cortical bone  16 . The cortical bone  16  encloses an interior volume of reticulated cancellous, or spongy, bone  18  (also called medullary bone or trabecular bone) and is raised to form a lip that encircles the cancellous bone. A “cushion,” called an intervertebral disk  20 , is located between vertebral bodies  14 . 
         [0035]      FIGS. 4 to 10  illustrate an interbody spinal implant  100  in accordance with one embodiment of the present invention. Implant  100  has opposed upper portion  102  and lower portion  104  that make contact with adjacent vertebral bodies  14  when inserted into the disc-space between vertebral bodies  14 . In one embodiment, the upper  102  and lower  104  portions have a textured surface for engaging the bone of the vertebral bodies  14  and securing the implant. The embodiment illustrated in  FIGS. 4 to 10  includes barb-like projections with evenly spaced raised rings or ratchets  116 . The ratchets  116  are angled upward in the direction of the anterior end  30  of implant  100 . The ratchets  116  resist forces in the direction of the anterior end  30  of the implant  100  and thus prevent movement of implant  100  out from between adjacent vertebral bodies  14 . The textured surface may take other forms, for example grooves or raised lines. 
         [0036]    Upper portion  102  and lower portion  104  are spaced apart and connected by two opposing sides  106  and  108 . If multiple implants  100  are inserted into the disk space  20 , opposing sides  106  and  108  of opposing implants  100  will be adjacent to one other. Opposed upper portion  102  and lower portion  104  may also include at least one hole  110  for the application of bone growth and fusion preparations. In one embodiment, implant  100  is at least partially hollow, again allowing for bone regrowth between adjacent vertebral bodies  14 . 
         [0037]    Referring now to  FIGS. 4 ,  7  and  8 , implant  100  includes varying heights along its length, as indicated by lines A, B and C. In one embodiment, the length of line B, located at the approximate midpoint of the spacer, is greater than the length of lines A and B. In an additional embodiment, the length of lines A and B may be equal. However, the lengths of lines A and B may not be equal. Implant  100  therefore has a greater height near its center as compared to the anterior  30  and posterior  32  ends, resulting in a convex shape, as will be discussed in more detail below. 
         [0038]    Referring now to  FIGS. 4 ,  7 ,  8  and  10 , anterior end  30  of implant  100  includes female groove  120  which runs the length of the anterior end  30 . Groove  120  accepts contact slots (not shown) from an insertion device (not shown) which will be discussed in more detail below. The anterior end  30  also includes an opening  122 , also used for attachment of the implant  100  to an insertion device (not shown). In one embodiment, opening  122  accepts a screw (not shown) which acts to couple the implant to the insertion device (not shown). 
         [0039]    Implants  100  for use in human ALIF may be made of a variety of materials. The material must exhibit strength characteristics to enable formation of a bond between two vertebral segments in the spine. The material must also provide a foundation and environment to allow the body to grow new bone and fuse a section of the spine together. Possible implant materials include autologous bone taken from the patient and transferred to the portion of the spine to be fused, or bone harvested by a tissue bank or a donor. Use of these types of implants is limited because it is often difficult to obtain a bone section large enough and shaped correctly in order to provide the needed vertebral support. There are a variety of bone graft substitutes that are available for use in spine fusion surgery. In general, these types of bone graft are a synthetic or a manipulated type of a naturally-occurring product. Exemplary graft substitutes include demineralized bone matrix (DBM), synthetic bone graft extenders, bone morphogenetic proteins (BMP) and demineralized bone matrix (DBM). Other synthetic materials are also available. One exemplary non-naturally occurring material is polyether ether ketone (PEEK), a colorless organic polymer thermoplastic. PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties. Because of its robustness, PEEK is one of the few advanced biomaterials used in medical implants. 
         [0040]    In an additional embodiment of the invention, implant  100  is adapted to detachably engage an insertion tool for insertion of the implant  100  into a region of the body. In one embodiment, the anterior end is shaped to engage with an insertion tool.  FIG. 11  shows one embodiment of a tool  200  for performing ALIF, having a proximal and distal end,  202  and  204 , respectively. The tool  200  includes two hollow tube-like structures  212   a  and  212   b  which extend in parallel from the distal end  202  to the proximal end  204 . Hollow tubes  212   a  and  212   b  terminate at the distal end  204  with an engagement device  210  for securing and placing the spinal implants  100  between the intervertebral bodies  14 . Referring now to  FIGS. 12 and 13 , engagement device  210  includes a raised male slot  206  which connects with female groove  120  ( FIGS. 7 ,  8  and  10 ) located on implant  100 , for instance with a snapping or sliding motion. Engagement of slot  210  within groove  120  secures the implant  100  to the tool  200  for insertion of the implant(s) into the vertebral body  14 . 
         [0041]    In the embodiment illustrated in  FIGS. 11 to 13 , hollow tubes  212   a  and  212   b  each contain a screw-like device  208   a  and  208   b  within their interior. The screws  208   a  and  208   b  extend through the entirety of hollow tubes  212   a  and  212   b  and protrude from the distal end  204  into the engagement device  210  ( FIGS. 12 and 13 ). The protruding ends of screws  208   a  and  208   b  serve to secure the implant  100  to the tool  200  during insertion of the implant(s) into the vertebral body  14 . Referring again to  FIG. 11 , tool  200  further includes handle  214  so that the user may manipulate the device. Knob  216  is placed at the proximal end  202  of the tool. Rotational movement of knob  216  causes a concurrent rotational movement of disks  218   a  and  218   b.  Rotation of disks  218   a  and  218   b  initiates rotation of screws  208   a  and  208   b  into or out of opening  122 . As a result, rotation of knob  216  in a first direction acts to secure the implant  100  to the insertion tool  200  (by rotating and inserting screws  208   a  and  208   b  into the opening  122 ) while rotation of knob  216  in the opposite direction acts to release the implant  100  from the vertebral body  14  (by rotation and withdrawing screws  208   a  and  208   b  from opening  122 ). 
         [0042]    In one embodiment of the invention, tool  200  secures at least two implants  100  for insertion into the vertebral body  14 . The at least two implants  100  are secured to the tool  200  in such a manner that one opposing side  106  of a first implant is adjacent to one opposing side  108  of a second implant. The present invention is not limited to a tool  200  including two implants as presently described and thus contemplates other numbers of implants  100 .  FIGS. 14 to 16  illustrate the placement of two implants  100  within the engagement device  210 .  FIG. 14   a  illustrates an implant  300  secured to the engagement device  210  via connection of a raised male slot  206  to the female groove  120 , and via insertion of screws  208   a  and  208   b  into opening  122 . Engagement of slot  210  within groove  120  detachably secures the implant  100  to the tool  200  during insertion of the implant(s) into the vertebral body  14 .  FIG. 14   b  shows a set of implants  300   a  and  300   b  secured to the engagement device  210 . The two implants  300   a  and  300   b  are separated, or spaced, at a distance E ( FIG. 14   c ). Opposing side  310   a  of the first implant  300   a  is adjacent to the opposing wall  310   b  of implant  300   b.  Turning now to  FIGS. 15   a - c,  implants  400   a  and  400   b  are detachably secured to engagement device  210  via connection of a raised male slot  206  to the female groove  120 , and via insertion of screws  208   a  and  208   b  into opening  122 . The two implants  400   a  and  400   b  are separated, or spaced, at a distance F ( FIG. 15   c ). The distance F is maintained by insertion of spacer  402  into the engagement device  210 . Spacer  402  includes a protruding peg  404  which is detachably mated with a matching hole (not shown) in the center of the engagement device  210 . In this embodiment, the distance F is greater than the distance E ( FIG. 14   c ), resulting in a greater spacing between implants  400   a  and  440   b  (as compared to spacers  300   a  and  300   b  as illustrated in  FIG. 14   c ). Opposing side  410   a  of the first implant  400   a  is adjacent to the opposing wall  410   b  of implant  400   b.  Similarly, as illustrated in  FIGS. 16   a - c,  implants  500   a  and  500   b  are detachably secured to engagement device  210  via connection of a raised male slot  206  to the female groove  120 , and via insertion of screws  208   a  and  208   b  into opening  122 . The two implants  500   a  and  500   b  are separated, or spaced, at a distance G ( FIG. 15   c ). The distance G is maintained by the detachable insertion of spacer  502  into the engagement device  210 . Spacer  502  includes a protruding peg  504  which mated with a matching hole (not shown) in the center of the engagement device  210 . Opposing side  510   a  of the first implant  500   a  is adjacent to the opposing wall  510   b  of implant  500   b.  In this embodiment, the distance G is greater than the distances E ( FIG. 14   c ) and F ( FIG. 15   c ), resulting in a greater spacing between implants  400   a  and  440   b  (as compared to spacers illustrated in  FIGS. 14   c  and  15   c ). 
         [0043]    It can be appreciated by these embodiments that the distance between two implants may be adjusted by inserting the desired sized spacer between the implants and securing the spacer to the engagement device, as herein described. The size of the spacing (and thus the spacer) will vary depending on multiple factors, for instance the size and age of the patient, the health condition currently under treatment and the dimensions of the patient anatomy, as is known to one of skill in the art. The present invention is not limited to use of identically sized implants  100  and instead contemplates insertion of differently sized implants  100  into the vertebral body  14  utilizing the presently described insertion tool. 
         [0044]      FIG. 17  shows a top plan view of the endplate region of a vertebral body  14  with the outline of the presently disclosed spinal implants  600   a  and  600   b  inserted on each side of the vertebral body  14 . Here, the implants  600   a  and  600   b  are placed so that the bottom side  104  rests on the cortical bone  16 , located on the periphery of the vertebral body  14 . The cortical bone  16  is the strongest portion of vertebral body  14  and is therefore the most appropriate weight bearing structure. Placement of the implants  600   a  and  600   b  on the cortical bone  16  provides support and prevents the necessity of drilling into any of the bones of the vertebral body, thus weakening of the vertebra  12  in general. The two implants  600   a  and  600   b  are spaced at an appropriate distance H as determined by a health care professional based upon the physical dimensions of the vertebral body. 
         [0045]      FIG. 18  illustrates a top plan view of the endplate region of a vertebral body  14  similar to that shown in  FIG. 17 . The outline of the presently disclosed implants  700   a  and  700   b  are illustrated as inserted on each side of the vertebral body  14 . Implants  700   a  and  700   b  are placed so that the bottom side  104  rests in the cortical bone  16 , located on the periphery of the vertebral body  14 . The two implants  700   a  and  700   b  are spaced at an appropriate distance I as determined by a health care professional based upon the physical dimensions of the vertebral body. Here, the physician has determined that a larger spacing H is appropriate to separate implants  700   a  and  700   b.  As with the previously described  FIG. 17 , implants  700   a  and  700   b  sit over the cortical bone  16 , located on the periphery of the vertebral body  14 . Placement in this manner provides the necessary strength and structure needed to support implants  700   a  and  700   b  within vertebral body  14 . 
         [0046]    The overall physical dimensions of the vertebral body  14  limits the size of the implant  100  which may be inserted. Insertion of multiple smaller implants allows for a better fit within the vertebral body  14 . Insertion of multiple smaller implants  100  allows for a more precise and more secure fit in the vertebral body  14 . The multiple implants  100  provide greater overlap of the cortical bone  16 , thus offering greater support and stability. 
         [0047]    The present invention is also related to a method of inserting a plurality of spinal inserts between vertebral bodies of a patient. In general, a patient in need of spinal fusion surgery is placed on the operating table in a supine position, i.e., lying down with the face up. The spine may be extended slightly at the surgeon&#39;s discretion. A three-inch to five-inch transverse or oblique incision is made just to the left of the umbilicus (belly button). The abdominal muscles are gently spread apart, but are not cut. The peritoneal sac is retracted to the side, as are the large blood vessels. Special retractors are used to allow the surgeon to visualize the anterior aspect of the intervertebral discs. After the retractor is in place, an x-ray is used to confirm that the appropriate spinal level(s) is identified. 
         [0048]    The intervertebral disc  20  is then removed using special biting and grasping instruments. Because of the concave shape of the presently described implants  100 , removal of bone in the vertebral body  14  is unnecessary. Excessive scraping of the bone may weaken the endplate (not shown in the figures). Special distractor instruments are used to restore the normal height of the disc, as well as to determine the appropriate size of implant to be placed. The physician then inserts a series of differently sized metal or plastic trial plates (not shown) between the adjacent vertebral bodies  14 , beginning with a smaller size (length and width) and incrementally increasing the size until a tight fit is obtained. The trial plates act as guides to assist the surgeon in determining the proper size of the spinal implants necessary for insertion into the disc space between the vertebral bodies. Using the trial plates, the surgeon may also determine the optimal spacing between the multiple implants  100  needed to ensure that the implants rest on and are supported by the hard cortical bone  16 . This may be done by inserting trial spacers (not shown) between the trial plates in order to obtain the proper spacing. It is important to use the tallest possible implant  100  to provide maximize stability to the vertebral body  14 . It is possible that two differently sized implants are utilized concurrently to properly support the adjacent vertebra  12  due to the non-symmetrical nature of the vertebral body  14 . Exemplary trial plates are shown and described in U.S. Pat. No. 8,454,699. 
         [0049]    Once the properly sized trial plates and trial spacers have been determined, the physician removes the trial plates and spacers and obtains implants  100  and spacers  220  ( FIG. 13 ) with sizes corresponding to these trial plates and spacers. With the screws  208  in the retracted position, a first male slot  206  of an implant tool  200  is mated with the female groove  120  of a first appropriately sized implant  100 . The appropriately sized spacer is then inserted into the engagement device  210  by inserting the protruding peg (not shown) into a matching hole (not shown). Next, a second male slot  206  of an implant tool  200  is mated with the female groove  120  of a second appropriately sized implant  100 . The second implant is located adjacent to the first implant. The two implants are separated by spacer  220 . The physician then grasps tool  100  by the handle  215  and rotates knob  216 . The rotational force of knob  216  turns rotating disks  218  in a direction causing screws  208  to rotate and engage the opening  122 , thus securing the implants  100  to the engagement device  210 . 
         [0050]    The surgeon then inserts the secured implants  100  into the previously evacuated disc space between the adjacent vertebral bodies  14 . The posterior ends  32  of the secured implants are first inserted in a linear direction into the space, moving in a direction from the anterior (front) portion of the body to the posterior (back) portion of the body. The implants  100  should be properly size and spaced as their dimensions were determined using the trial plates and the trial spacers as previously detailed. The concave shape of implants  100  (see  FIGS. 4 ,  7  and  8 ) allows the bottom opposing side  104  to make contact with the surface of the lower vertebral body  14  and the top opposing side  102  to make contact with the adjacent vertebral body  14  and prevents their movement beyond the vertebral body  14 . In this embodiment of the invention, when implants  100  are inserted between two adjacent vertebral bodies  14 , implants  100  are completely contained there between. No portion of implants  100  protrude from the spine, minimizing injury to the spinal cord or any major blood vessels. 
         [0051]    The surgeon then verifies that the implants  100  are (1) securely inserted between the vertebral body  14 , (2) fully resting on the cortical bone  16  and (3) completely contained between the vertebral bodies  14 . This may be accomplished in a number of ways as are known to one in the art, for instance by X-ray analysis or fluoroscopy. The surgeon then grasps tool  100  by the handle  215  and rotates knob  216  in the direction opposite of that used to secure the implants  100  as described above. The rotational force of knob  216  turns rotating disks  218  in a direction causing screws  208  to rotate and disengage from opening  122 . The insertion tool  200  is then gently moved to dislodge the male slot  206  of the implant tool  200  from the female groove  120  of implants  100 , thus releasing the implants  100  from the engagement device  210 . The insertion tool  200  is then removed from between the vertebral bodies  14  while the implants remain. The ratchets  116  located on the top side  102  and bottom side  104  of implant  100  resist forces in the direction of the anterior end  30  of the implant  100  and thus prevent movement of implant  100  out from between the vertebral bodies  14 . Spacer  220  remains engaged with the engagement device  210  and is therefore removed from between the vertebral bodies upon retraction of the insertion tool  200 . The physician may again verify that the implants are properly inserted within the vertebral body space. 
         [0052]    In an additional embodiment, a bone graft substance, for instance implant materials as described previously, is then injected within the hollow interior of inserts  100 . The substance may also include ground bone mixed with other growth promoting materials, such as bone morphogenic proteins. In one embodiment, the bone graft substance is injected through opening  100 , to promote bone regeneration around the implants and fusion of the affected vertebrae. The substance may alternatively be placed into the hollow spaces of the implants prior to implantation. Fusion may be augmented by the insertion of metallic screws, rods or plates, or cages on the periphery of the vertebrae.