Abstract:
An artificial vertebral body includes superior and inferior portions wherein said portions are positively engageable. The relative positions of the superior and inferior portions are variable about the sagittal plane. The artificial vertebral body also includes one or more means for engaging adjacent spinal structures to establish placement of the body in the spine.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS  
       [0001]     The present application is a Continuation of PCT application no. PCT/CA2006/000675, filed May 2, 2006, which claims priority from U.S. application No. 60/594,727, filed May 2, 2005. The entire disclosures of these applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to devices and surgical methods for the treatment of various types of spinal pathologies. More specifically, the present invention is directed to vertebral body replacements and procedures for performing such replacements.  
       BACKGROUND OF THE INVENTION  
       [0003]     The spine has four natural curves; two are lordotic and two are kyphotic. The cervical and lumbar curves are lordotic, while the thoracic and sacral curves are kyphotic. While these curves of the spine help to distribute mechanical stress as the body moves, conditions may develop where there are extreme curvatures. For example, while the upper or thoracic region of the spine is normally curved forward, if the curve exceeds 50°, it is considered abnormal or “kyphotic”. Lordosis is an abnormal increase in the normal lordotic curvature of the lumbar spine; excessive lordosis may cause an extreme inward curve in the lower back.  
         [0004]     The techniques, instrumentation and implants for treating conditions or abnormalities of the spine have adapted to address many forms of spinal injury and deformities that can occur due to trauma, disease or congenital effects. One type of spinal deformity, a kyphosis, involves a prolapse of the vertebral column towards the front of the body, often caused by the destruction of the vertebral body itself.  
         [0005]     Several events can distort the spine leading to conditions like accentuated kyphosis or hyper-lordosis. Because the natural tendency of the spine is to curve, a weakness in any component thereof or the supporting structures may lead to such conditions. For example, a diseased thoracic vertebra will ordinarily crumble its forward edge first, increasing the kyphotic curve. Conditions that can do this include cancer, tuberculosis, Scheuermann&#39;s disease, and certain kinds of arthritis. Healthy vertebra can fracture forward with rapid deceleration injuries, such as in car crashes. Osteoporosis may also contribute to such conditions. As result of any of these conditions and their underlying etiology, it may be necessary to consider vertebral body replacement.  
         [0006]     Where it is necessary to replace at least a portion of a vertebral body for the reasons noted above, previous techniques have involved reconstruction of that portion of the vertebral body with a polymerizable paste or a bone graft which is frequently modelled to give it the shape of intact vertebral body. Frequently, autologous bone, such as that extracted from the ilium, is used to bridge the space. The polymerizable paste can include a PMMA bone cement. Various artificial apparatus have also been developed to address structural failure of various parts of the spinal column.  
         [0007]     While there is a need for the replacement of injured and/or diseased vertebral bodies, which cause, or are a result of, various spinal diseases, previous apparatuses and techniques have, however, several drawbacks. They have been fashioned to provide support between adjacent vertebral bodies by creating a fusion across the diseased segment thereby eliminating movement in the spinal column. In addition to reducing range of movement in the spine this can also cause premature degeneration of spinal joints above and below the fusion site. They also require additional instrumentation at the front or back of the spine to secure them in place.  
         [0008]     The present invention, in one aspect, provides an artificial vertebral body that obviates or mitigates at least some of the deficiencies of previous apparatuses and techniques.  
       SUMMARY OF THE INVENTION  
       [0009]     In one aspect, the invention provides an vertebral body for replacing a naturally occurring a vertebral body in a spine.  
         [0010]     Thus, in one aspect, the invention provides an artificial vertebral body comprising:  
         [0011]     a superior portion and an inferior portion, each of the superior and inferior portions having superior and inferior surfaces and lateral sides;  
         [0012]     the superior surface of the inferior portion being in contact and in positive engagement with the inferior surface of the superior portion;  
         [0013]     the superior surface of the superior portion and the inferior surface of the inferior portion having one or more engagement means to engage adjacent spinal structures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Various objects, features and attendant advantages of the present invention will become more fully appreciated and better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views.  
         [0015]     FIGS.  1 ( a ) to ( g ) show various views of embodiments of the present invention.  
         [0016]      FIG. 2  shows a side view of an embodiment of the present invention.  
         [0017]      FIG. 3  shows a perspective view of an embodiment of the present invention.  
         [0018]     FIGS.  4 ( a ) to ( d ) show various views of embodiments of the present invention.  
         [0019]     FIGS.  5 ( a ) to ( c ) show various views of embodiments of the present invention.  
         [0020]     FIGS.  6 ( a ) to ( c ) show various views of embodiments of the present invention.  
         [0021]      FIG. 7  shows side views of an embodiment of the present invention.  
         [0022]      FIG. 8  shows side views of an embodiment of the present invention.  
         [0023]      FIG. 9  shows side view of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     In order that the invention may be more fully understood, it will now be described, by way of example, with reference to the accompanying drawings in which  FIGS. 1 through 9  illustrate embodiments of the present invention.  
         [0025]     In the description and drawings herein, and unless noted otherwise, when discussing anatomical plans of view, it will be understood that the terms “front” and “back” shall be used to refer to the front and back in the coronal or frontal plane. The terms “left” and “right” shall be used to refer to left and right in the sagittal or lateral plane. The terms “up” and “down” shall be used to refer to up and down in the axial transverse. It will be understood that a reference to “medial” shall refer towards the midline of a body. It will be understood that a reference to “lateral” shall refer to away from the midline of a body. It will be understood that a reference to “inferior” shall refer to lower, below or down and “superior” shall refer to upper, above or up. It will be further understood that a reference to “anterior” shall refer to front and “posterior” shall refer to the rear or back.  
         [0026]     The present invention provides an artificial vertebral body that can be used to replace at least a portion of vertebral bodies in different regions of the spinal column or, alternatively, the entire vertebral body or corpus (e.g. the drum shaped structure at the anterior end of the vertebrae) can be replaced. Specifically, different embodiments of the vertebral body according to the present invention may be used in the lumbar, thoracic, and cervical spine regions.  
         [0027]      FIG. 1 ( a ) illustrates an artificial vertebral body  10  in accordance with an embodiment of the present invention. Vertebral body  10  has a superior portion  12  and an inferior portion  12 ′. As shown in  FIG. 1 ( e ), portions  12  and  12 ′ have a generally wedged, trapezoid shape to approximate configuration of a normal vertebral body in a lordotic spine. As shown in  FIG. 1 ( a ), the superior element  12  includes an upper or superior surface  16 , a lower inferior surface  21 , anterior and posterior surfaces  20  and  18 , respectively and left and right lateral side surfaces  19  and  17 , respectively. Similar surfaces are provided on portion  12 ′ except identified as  16 ′,  17 ′,  18 ′,  19 ′,  20 ′ and  21 ′, as shown in  FIGS. 1 and 3 . Anterior surface  20  of portion  12  may extend beyond the anterior surface  20 ′ of portion  12 ′, the function of which will be described below.  
         [0028]     Portions  12  and  12 ′ are affixed together by at least one fastener. As shown in FIGS.  1 ( b ) and ( e ), there are three fasteners in the form of screws  22 ,  24  and  26 .  
         [0029]     Anterior surface  20  is generally convex, while inferior surface  21  is generally concave. Posterior surface  18  is also concave. The anterior surface or side  20 , after insertion into the spinal column, is generally facing anteriorly, namely facing towards the front of the body, while the posterior side  18  is positioned towards the spinal cord contained within the spinal column (towards the back of the body). The superior surface  16  of the vertebral body may be of smaller dimensions than the inferior surface  21 . Similarly the superior surface  16 ′ may be of smaller dimensions that the inferior surface  21 ′, causing asymmetry between upper and lower surfaces, more closely approximating normal anatomical relationships in the cervical spine. This asymmetry may be less pronounced or reversed in cases where the invention is for use in the thoracic or lumbar spine regions.  
         [0030]     Portion  12  is provided with overhang  28  of the convex surface  20  with respect to the sides of vertebral body. Overhang on the sides of the anterior (or front) curved surface of the vertebral body produces an edge of approximately  90  degrees to the true lateral wall of the vertebral body. Portion  12 ′ is similarly shaped. Over hang  28  prevents posterior migration of portion  12  into the spinal cord upon insertion thereof into a surgical vertebrectomy defect. A smooth anterior surface may also reduce postoperative dysphagia by reducing adhesions between the implant and the posterior pharyngeal wall.  
         [0031]     Portions  12  and  12 ′ are joined by way of a toothed or textured curved locking mechanism. Such mechanism is formed with the inferior surface of portion  12  and the superior surface of portion  12 ′ having complementary toothed surfaces. In this manner, when the portions  12  and  12 ′ are positioned together, the toothed surfaces engage to prevent further movement between such surfaces. This locking mechanism is tightened by at least one of the fasteners affixing portions  12  and  12 ′ together. In one embodiment of the present invention, there is provided, as shown in FIGS.  1 ( b ) and ( e ), screws  22 ,  24  and  26  recessed into the midline of the superior surface of portion  12 . Loosening of the locking mechanism allows adjustment of the angular relationship of upper portion  12  to the lower portion  12 ′ of vertebral body  10 . In such a manner, upper surface  16  of vertebral body  10  can be made parallel to lower surface  21 ′ or the two surfaces can be angled or off-set with respect to each other.  FIG. 1 ( f ) shows how surfaces can be offset. In addition, FIGS.  7  to  9  show how the portions can be off set. This accommodates angular variations of lordosis and kyphosis amongst different areas of the spine and variations in the spines of different people.  
         [0032]     In one embodiment, the locking mechanism consists of adjustment fasteners  22 ,  24  and  26  provided generally in the midline of portion  12  and recessed into superior surface  16  of portion  12 . As seen in  FIG. 1 ( e ), a locking plate  25  is provided between portions  12  and  12 ′ and is positioned adjacent to the convex curve of the inferior portion  12 ′ of the vertebral body. The ends of screws  22 ,  24 , and  26  engage locking plate  25 . Locking plate  25  receives the screws  22 ,  24  and  26  and acts like a “blind nut”, which receives a screw that can be subsequently tightened without the nut spinning. Tightening screws  22 ,  24  and/or  26  into locking plate  25  cinches it up against the inside of  12 ′ which in turn then engages against the teeth  27  of toothed or textured curved surface  21  of portion  12 . Teeth  27  are shown in greater detail in  FIG. 4 ( a ). Pressure between the screw heads  22 ,  24 , and  25  against portion  12 , and pressure from the locking plate against portion  12 ′ keep the teeth engaged between  12  and  12 ′ preventing the vertebral body from changing shape. Locking plate  25  may be sufficiently wide or as sufficiently long so as to fit within portion  12 ′. Locking plate  25  is provided against toothed or textured curved surface  21  so as to allow angular motion of portion  12  between angled posterior and anterior positions which allows for the adjustment of the angular relationship of upper portion  12  to the lower portion  12 ′ of vertebral body  10 . As will be understood, such adjustment is made by loosening screws  22 ,  24  and  26 , disengaging the toothed surfaces of the portions  12  and  12 ′ and moving such portions relative to one another to achieve the desired placement.  
         [0033]     As shown in  FIG. 1 ( e ), superior surface  16 ′ of lower portion  12 ′ is adapted to mate with the curved inferior surface  21  of upper portion  12 . The mating of surface  16  and surface  21  provided for an interface that separates the upper portion  12  of vertebral body  10  from lower portion  12 ′. Changes in angle necessitate a degree of translation of the upper half with respect to the lower half of the artificial vertebral body.  
         [0034]     In a further embodiment of the present invention, as shown in  FIG. 1 ( f ), the artificial vertebral body of the invention may include a third portion  30  provided between the portions  12  and  12 ′ in order to produce pure translational adjustments of portion  12  of the vertebral body  10 ′. As shown in  FIG. 1 ( f ), the third portion  30  provides an additional interface between the portions  12  and  12 ′. As shown in  FIG. 1 ( f ) and  FIG. 7 , it will be appreciated that the addition of portion  30  allows the creation of a more kyphotic angle in the vertebral implant without the large degree of offset required in the “two component” version. As shown in  FIG. 1 ( f ), the radius of the curvature is less with the embodiment encompassing three portions  12 ,  12 ′ and  30 , making the curve sharper than in the two piece design. It will be understood, however, that the radius can be varied depending on the application. Similarly the dimensions of the three components shown in  10 ′ ( FIG. 1 ( f )), namely portions  12 ,  12 ′ and  30  may also be varied in length, width, and height.  
         [0035]     Third portion  30  has an upper or superior surface  30 ′ and a lower or inferior surface  30 ″, which engage with surfaces  21  and  16 ′ respectively. Upper surface  30 ′ is generally flat, while lower surface  30 ″ is generally curved to mate with superior surface  16 ′ of portion  12 ′. It will be understood in such an embodiment that inferior surface  21  of portion  12  would be need to be configured to mate with surface  30 ′. This allows the artificial vertebral body to take on a more skewed and kyphotic shape to treat conditions of more severe malalignment. In this embodiment, vertebral body  10 ′ consists of three elements or portions  12 ,  12 ′ and  30 . These elements are affixed by two sets of locking mechanisms similar to those described above through toothed or textured surfaces that interact to form two interfaces. One portion of body  10  translates backwards or forwards on a middle portion. As provided in  FIG. 1 ( e ), portion  12  can move anteriorly or posteriorly as shown by arrows A. Another portion of body  10  angles backwards and forwards on the middle section as well. As provided in  FIG. 1 ( e ), portion  30  can move as provided by arrows B. Adjustment screws are recessed from the exposed upper and lower surfaces of the body lock the pieces together in their desired configuration.  
         [0036]     As shown in FIGS.  1 ( e ) and  2 , the artificial vertebral body of the present invention can integrate or co-operate with an artificial intervertebral disc such as a disc that is described in applicants&#39; co-pending application No. 60/594,732 (the entire contents of which is incorporated herein by reference). As described in such application, an artificial disc is provided with one or more “stabilising keels” on at least one of its outer surfaces. As shown in FIGS.  1 ( a ), ( b ), and ( d ) there are provided openings  35  and  36  on surface  16  as well as opening  35 ′ and  36 ′ on lower surface  16 ′. Openings  25 ,  36  as well as  35 ′ and  36 ′ contain fastener openings through which screws extending from endplates of an artificial disc or the like can be secured, fastening the disc endplate tightly to the vertebral body. The keels of the artificial disc endplate fit into the openings so as to align the screw conduits.  
         [0037]     FIGS.  1 ( c ) and  1 ( d ) demonstrate adjacent or integrating surfaces of disc endplate (see  FIG. 1 ( c )) with artificial vertebral body (see  FIG. 1 ( d )). Keels  70  provided on the artificial disc endplate insert into slots  35  and  36  (or  35 ′ and  36 ′) of the vertebral body. Screw holes allow screws to be inserted, attaching the endplates  22   a  and  22   b  to the artificial vertebral body in multilevel disc and body reconstruction. Screw receptacles  23  are shown in the artificial vertebral body diagrams as well as on the keels  70  of the artificial disc.  FIG. 1 ( c ) is a diagram of the surface of the artificial disc endplate that “flips” over and integrates with the vertebral body shown in  1 ( d ). The keels  70  of the disc endplate fit into troughs  35 ,  35 ′,  36 , and  36 ′ of the artificial vertebral body. In one embodiment, screws fix superior endplate  22   b  to inferior surface  16 ′ of the vertebral body, and the inferior endplate  22   a  of the disc to superior surface  16  of the vertebral body. The screws are inserted from the inside surface of the disc endplates—i.e. the disc must be disassembled to attach the endplates to the artificial vertebral body,  
         [0038]     As shown in FIGS.  1 ( a ) and ( d ) as well as  FIG. 3 , there are provided two sets of stabilizing fins  40  and  40 ′ located on each lateral surface of portions  12  and  14  of the vertebral body. Fins  40  and  40 ′ move from a recessed position to an extended position by means of fin set screws, such as fin set screw  41  as shown in  FIG. 1 ( g ). Insertion of vertebral body  10  into the surgical vertebrectomy defect occurs with fins  40  and  40 ′ in a recessed position. Once the vertebral body  10  is inserted in the correct position, fin set screws, such as fin set screw  41  can be tightened causing individual fins of fin sets  40  and  40 ′ to push out from their recessed position in artificial vertebral body  10  engaging surrounding bone and securing vertebrae  10  in place against the remaining native bone inside the patient.  
         [0039]     The individual fins of fin sets  40  and  40 ′ are designed to act against vertebral body extrusion. They are tapered toward their posterior aspect and that of the artificial vertebral body but angled perpendicular to the body along their anterior surface. They act in opposition to the overhang of the curved front surface of the artificial vertebral body, which prevents posterior migration.  
         [0040]     As shown in  FIG. 3 , porous reservoirs  45 ′ and  46 ′ of portion  12 ′, as well as  45  and  46  of portion  12  (not shown) are located behind curved surface  20  or  20 ′ along lateral surfaces  19  and  21  as well as  19 ′ and  21 ′ of portions  12  and  12 ′ respectively. Reservoirs  45 ,  46 ,  45 ′ and  46 ′ act as hollow cages with small perforations in their outside walls. The cages are open at their upper and lower ends to allow for insertion of a substance to promote the growth of bone. The porous reservoirs contain this bone growth substance helping to release it locally in a controlled fashion encouraging bone to actively grow into the perforations and stabilize the artificial vertebral body against normal bone inside the spine of the recipient patient. The porous reservoirs can rest adjacent to similar reservoirs located in the artificial disc endplate. It will be understood that the exterior surfaces of the artificial vertebral body  10  or  10 ′ may also include various physical features such as a porous or pitted surface, a plurality of pins, ribs etc. that promote bony in-growth so as to anchor the prosthesis in place in the spine. Various other such anchoring means will be known to persons skilled in the art.  
         [0041]     In another embodiment, sets of stabilizing fins  40  and  40 ′ and/or reservoirs  45 ,  46 ,  45 ′ and  46 ′ in one portion of the vertebral body  10  might be partially or completely substituted for a depression or indentations, as shown in  FIGS. 4, 5  and  6 . These depressions serve as insertion points for artificial pedicles that are adapted to be received within the depressions. The pedicle is the part of each side of the neural arch of a vertebra. It connects the lamina with the vertebral body. In one embodiment of the present invention, the artificial pedicle might be hollow to allow a drill to be positioned inside of it, and used to drill through the depression into the body of the artificial vertebrae. A screw might then be inserted through the pedicle tightening into the artificial vertebral body and securing the pedicle against the artificial vertebral body. As shown in  FIG. 6 ( a ), there is provided pedicle fastener  60  in artificial pedicle  61 , which rests in depression or aperture  65  of vertebral body  70  (see also FIGS.  6 ( b ) and ( c )). As can also be seen in  FIG. 6 ( a ) a drill bit  61  advances into a lateral surface of vertebral  70 .  
         [0042]     In yet a further embodiment, as shown in  FIG. 5 , the aperture or depression might extend farther into a portion of the vertebral body forming a pedicle fastener receptacle or sleeve that doesn&#39;t require drilled as shown in  FIG. 6 . As shown in FIGS.  5 ( a ), ( b ) and ( c ), receptacle  80  is angled tangential to the side of vertebral body  85  to generally cross from one lateral surface towards the anterior surface or towards the midline of the front of the artificial vertebral body. Receptacle  80  may have threads in its walls to receive a threaded fastener of appropriate dimensions. The receptacle or pedicle screw sleeve can be embodied by a hollowed-out portion of the vertebral body or may be fashioned as a separate component, assembled into the artificial vertebral body as shown in  FIG. 5 .  
         [0043]     As shown in FIGS.  4 ( a ) to ( d ), a receptacle or pedicle screw sleeve  100  can be fashioned as a separate component and assembled into the artificial vertebral body. Posts  102  and  104  arising from the upper and lower surfaces of the sleeve can act as a hinge recessed inside the artificial vertebral body (as shown in  FIG. 1 ( d )) so that the pedicle sleeve  100  can rotate about post. This allows the pedicle screw sleeve  100  to accommodate pedicle screws from different angles (as shown in  FIG. 1 ( d )). The outer end of the pedicle screw receptacle is expanded so that an artificial pedicle can be inserted into it, locking it in place with respect to the receptacle and the artificial vertebral body.  
         [0044]     The posts arising from the upper and lower surfaces of the pedicle screw receptacle can be embedded in recessed grooves running front to back in the artificial vertebral body. The grooves provide a track along which the pedicle sleeve can move forwards or backwards in relation to the artificial vertebral body while maintaining angular motion about the posts.  
         [0045]     The grooves can be angled inwards or outwards (front to back) to prevent forwards or backwards migration of the artificial pedicles once they have been secured to the artificial vertebral body. It is envisioned that the artificial pedicles will be directly or indirectly connected to each other from behind in addition to their connection to the artificial vertebral body. The additional connection prevents the artificial pedicles from sliding along their posts inside grooves on either side of the vertebral body that point in opposing directions.  
         [0046]     Additionally, a separate rectangular compartment built into the wall of the artificial vertebral body may house the grooves containing the pedicle screw sleeve. This rectangular housing could be connected to the artificial vertebral body by two side rails protruding into it at each end. The side rails (tongue in groove) prevent the housing from extruding outside or inside of the artificial vertebral body but allow the housing to move upwards and downwards within the wall of the artificial vertebral body. This is illustrated in  FIGS. 4   b  and  4   d.    
         [0047]     The side rails can be angled in towards the middle of the artificial body or out towards the sides (from the top downwards) to prevent the rectangular compartment from moving once the artificial pedicles have been secured to the artificial vertebral body. It is envisioned that the artificial pedicles will be directly or indirectly connected to each other from behind in addition to their connection to the artificial vertebral body. The additional connection prevents the artificial pedicles and their respective rectangular housings from sliding up or down on rails that point in opposing directions on either side of the artificial vertebral body.  
         [0048]     The artificial vertebral body can be used with artificial discs to reconstruct multiple levels in the spinal column. It can be manufactured in a variety of widths, heights, and depths.  
         [0049]     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the purpose and scope of the invention as outlined herein. The entire disclosures of all references recited above are incorporated herein by reference.