Abstract:
A vertebral body replacement includes first and second end plates, and a compliant connector section between the end plates having one or more helical cuts to provide limited compliance between the end plates. The compliant connector section can be provided in a separate spacer that fits between the end plates or directly in one or more of the end plates. The adjoining end plate surfaces, and/or adjoining surfaces of the spacer, include a rotational interlock to inhibit allow the selection an modular stacking assembly of the vertebral body replacement to accommodate a wide range of patients.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/981,665 filed Oct. 22, 2007, entitled “Method and Spacer Device for Spanning Space Formed Upon Removal of an Intervertebral Disc,” the full disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to medical devices and methods. More specifically, the invention relates to vertebral body replacements and methods of spanning a space formed upon removal of an intervertebral disc. 
         [0003]    Back pain takes an enormous toll on the health and productivity of people around the world. According to the American Academy of Orthopedic Surgeons, approximately 80 percent of Americans will experience back pain at some time in their life. In the year 2000, approximately 26 million visits were made to physicians&#39; offices due to back problems in the United States. On any one day, it is estimated that 5% of the working population in America is disabled by back pain. 
         [0004]    One common cause of back pain is injury, degeneration and/or dysfunction of one or more intervertebral discs. Intervertebral discs are the soft tissue structures located between each of the thirty-three vertebral bones that make up the vertebral (spinal) column. Essentially, the discs allow the vertebrae to move relative to one another. The vertebral column and discs are vital anatomical structures, in that they form a central axis that supports the head and torso, allow for movement of the back, and protect the spinal cord, which passes through the vertebrae in proximity to the discs. 
         [0005]    Another form of spinal injury involves injury or deformity of the vertebra themselves. When one or more vertebrae is fracture or deformed by tumor or other causes and results in pain and discomfort, surgery is often required. Traditionally, surgical procedures for vertebral replacement have involved removal of the vertebra and fusion of the two vertebrae above and below the missing vertebra. It is necessary to replace the removed vertebra to maintain spacing of adjacent vertebrae. Oftentimes, pins, rods, screws, cages and/or the like are inserted between the vertebrae to act as support structures to hold the vertebrae and graft material in place while they permanently fuse together. These vertebral body replacement procedures generally focus on rigidly fusing the adjacent vertebrae and preventing motion. 
         [0006]    However, it would be desirable to achieve immobilization of the vertebrae adjacent a removed vertebral body and maintain spacing between the adjacent vertebrae without the complete rigidity of traditional interbody fusion. 
         [0007]    Another problem associated with the typical vertebral body replacement procedure is the subsidence of the cage into the vertebral body. The typical vertebral body replacement cage is formed with a large percentage of open space to allow the bone to grow through and form the bridging bone which immobilizes the vertebrae. However, the large amount of open space means that the load on each segment of the cage is significantly higher than if the cage surface area was larger. This results in the cage subsiding or sinking into the bone over time and allows the space between the vertebrae to collapse. 
         [0008]    Therefore, a need exists for improved vertebral body replacement and method for spanning a space and maintaining spacing between two vertebrae after removal of an intervertebral body. Such improved method and intervertebral body replacement would avoid the need for growth of bridging bone between the remaining vertebrae. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention provide a vertebral body replacement with compliance or shock absorption and methods of spanning a space formed upon removal of vertebral body. 
         [0010]    In accordance with one of numerous aspects of the present invention, a vertebral body replacement for replacing at least one vertebral body between remaining upper and lower vertebral bodies, the vertebral body replacement comprises a first end plate having an upper surface configured to engage against a surface of the upper remaining vertebral body, and a lower surface opposite the upper surface spanning the first end plate, a second end plate having a lower surface configured to engage against a surface of the lower remaining vertebral body, and a compliant connector section between the first end plate lower surface and the second end plate lower surface, the compliant connector section comprising at least one helical cut configured and arranged to permit limited motion between the first end plate and the second end plate. 
         [0011]    In accordance with another aspect of the invention, a method of replacing at least one vertebral body comprises removing said at least one vertebral body between two remaining vertebral bodies, placing a vertebral body replacement between said two remaining vertebral bodies, the vertebral body replacement comprising first and second end plates and a compliant connector section between the first and second end plates, the compliant connector section having at least one helical cut and configured and arranged to limit motion to less than 10 degrees between said remaining vertebral bodies, and maintaining the space between the two remaining vertebral bodies with the vertebral body replacement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a vertebral body replacement according to one embodiment of the present invention; 
           [0013]      FIG. 1A  is an exploded, perspective view of the vertebral body replacement of  FIG. 1 ; 
           [0014]      FIG. 2  is a perspective view of a vertebral body replacement according to a second exemplary embodiment of the present invention; and 
           [0015]      FIG. 3  is a perspective view of a vertebral body replacement according to a third exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Various embodiments of the present invention generally provide for a vertebral body replacement having upper and lower plates or surfaces connected by a central connector portion which provides some limited amount of axial compliance and/or rotational motion between the upper and lower plates or surfaces. The compliant vertebral body replacement according to the present invention can maintain disc height and prevent subsidence with a large surface area while improving outcomes by allowing some limited motion and providing improved fixation. The compliance of the vertebral body replacement also functions to reduce loading on the interface between the bone and vertebral body replacement. 
         [0017]    One example of a vertebral body replacement  10  for replacement of a vertebral body and maintaining disc height between two adjacent vertebral discs is shown in  FIG. 1 . The body  10  includes at least one end plate  20  having a vertebral body contacting surface  24 , a second end plate or body end  30  opposite the end plate  20 , and a compliant connector or connector section  32  interposed between, or interconnecting, the two ends  20 ,  30 . As will be described below, some limited rotational and axial motion may be provided between the two plates or sections  20 ,  30  to reduce loading on the interface between the adjacent vertebral bodies and the body  10 . According to an exemplary device embodying principles of the present invention, the compliance of the connector  32 , as well as some small amount of translation and rotation, is provided by lateral cuts or slots  70  extending into the connector  32 . The body  10  when implanted between two vertebrae maintains a desirable space between the two adjacent vertebrae similar to that provided by a natural vertebra. 
         [0018]    Although the body  10  has been shown as generally oblong in cross section, other shapes may be used, including circular, oval, elliptical, or rectangular. Although the connector section  32  has been illustrated in  FIG. 1  as integral with the end section  30 , according to other embodiments, the connector can include one or more separate compliant connectors or spacers in other configurations and at other locations. By way of example, a compliant connector may be the same or substantially the same diameter, size, and shape as the plates, multiple connectors can be arranged in a rectangular pattern, or a hollow cylindrical connector can be used. Further optionally, while the surfaces  24  are illustrated being perpendicular to the vertical axis of the body  10 , one or both of the surfaces  24  can be somewhat wedge-shaped, formed with one or two lordosis angles, as well known to those of ordinary skill in the art. The modular design of the upper plate  20  and the lower plate section  30  allows the creation of a complete bodies  10  of different sizes to correspond to the particular space for each patient. 
         [0019]    The upper plate  20  and the lower plate or plate section  30 , and connector  32 , may be constructed from any suitable metal, alloy or combination of metals or alloys, such as but not limited to cobalt chrome alloys, titanium (such as grade  5  titanium), titanium based alloys, tantalum, nickel titanium alloys, stainless steel, and/or the like. They may also be formed of ceramics, biologically compatible polymers including PEEK, UHMWPE (ultra high molecular weight polyethylene) or fiber reinforced polymers. However, when polymer is used for the body  10 , the contacting surfaces  24  may be coated or otherwise covered with metal for fixation. The upper plate  20  and the lower plate or plate section  30 , and connector  32 , may be formed of a one piece construction or may be formed of more than one piece, such as different materials coupled together. When the body  10  is formed of multiple materials, these materials are fixed together to form a unitary one piece spacer without separately moving parts. 
         [0020]    Different materials may be used for different parts of the body  10  to optimize imaging characteristics. For example, the upper plate  20  and the lower plate or plate section  30  may be formed of titanium, while the connector  32  is formed of cobalt chromium alloy for improved imaging of the plates. Cobalt chrome molybdenum alloys, when used for the plates  20 ,  30  may be treated with aluminum oxide blasting followed by a titanium plasma spray to improve bone integration. Other materials and coatings can also be used such as titanium coated with titanium nitride, aluminum oxide blasting, HA (hydroxylapatite) coating, micro HA coating, and/or bone integration promoting coatings. Any other suitable metals or combinations of metals may be used as well as ceramic or polymer materials, and combinations thereof. Any suitable technique may be used to couple materials together, such as snap fitting, slip fitting, lamination, interference fitting, use of adhesives, welding and/or the like. 
         [0021]    In some embodiments, the outer surface  24  is planar. Oftentimes, the outer surface  24  will include one or more surface features and/or materials to enhance attachment of the body  10  to vertebral bone. For example, as shown in  FIG. 1 , the outer surface  24  may be machined to have serrations  40  or other surface features for promoting adhesion of the plates  20 ,  30  to a vertebra. In the embodiment shown, the serrations  40  are pyramid shaped serrations extending in mutually orthogonal directions, but other geometries such as teeth, grooves, ridges, pins, barbs or the like would also be useful. When the bone integration structures are ridges, teeth, barbs or similar structures, they may be angled to ease insertion and prevent migration. These bone integration structures can be used to precisely cut the bone during implantation to cause bleeding bone and encourage bone integration. Additionally, the outer surface  24  may be provided with a rough microfinish formed by blasting with aluminum oxide microparticles or the like to improve bone integration. In some embodiments, the outer surface may also be titanium plasma sprayed or HA coated to further enhance attachment of the outer surface  24  to vertebral bone. 
         [0022]    The outer surfaces  24  may also carry one or more upstanding fins  50 ,  52  which also extend laterally in an anterior-posterior direction. The fins  50 ,  52  are configured to be placed in slots in the vertebral bodies. Preferably, the fins  50 ,  52  each have a height greater than a width and have a lateral length greater than the height. In one embodiment, the fins  50 ,  52  are pierced by transverse holes  54  for bone ingrowth. The transverse holes  54  may be formed in any shape and may extend partially or all the way through the fins  50 ,  52 . In alternative embodiments, the fins  50 ,  52  may be rotated away from the anterior-posterior axis, such as in a lateral-lateral orientation, a posterolateral-anterolateral orientation, or the like. 
         [0023]    The fins  50 ,  52  provide improved attachment to the bone and prevent rotation of the plates  20 ,  30  in the bone. In some embodiments, the fins  50 ,  52  may extend from the surface  24  at an angle other than 90°. For example, on one or more of the plates  20 ,  22  where multiple fins  52  are attached to the surface  24 , the fins may be canted away from one another with the bases slightly closer together than their edges at an angle such as about 80-88 degrees. The fins  50 ,  52  may have any other suitable configuration including various numbers angles and curvatures, in various embodiments. In some embodiments, the fins  50 ,  52  may be omitted altogether. The embodiment of  FIG. 1  illustrates a combination of one plate with a single fin  50  and another plate with a double fin  52 . This arrangement is useful for double level disc replacements and utilizes offset slots in the vertebral body to prevent the rare occurrence of vertebral body splitting by avoiding cuts to the vertebral body in the same plane for multi-level implants. The combination of the single fin  50  and double fin  52  can also assist the surgeon in placement of the spacer in the correct orientation. 
         [0024]    The body  10  has been shown with the fins  50 ,  52  as the primary fixation feature; however, the fins may also be augmented or replaced with one or more screws extending through the plates and into the bone. For example in the body  10  of  FIG. 1 , the upper fin  50  may be augmented or replaced with one or more screws (not illustrated) while the two lower fins  52  remain. The plates  20 ,  30  can be provided with one or a series of holes  60  to allow screws to be inserted at different locations at the option of the surgeon. However, the holes  60  should not be of such size or number that the coverage of the plate  20 ,  30  is decreased to such an extent that subsidence occurs. Alternately, the screws can pass laterally through one or more of the holes in the fins. When one or more screws are provided, they may incorporate a locking feature to prevent the screws from backing out. The screws may also be provided with a bone integration coating. 
         [0025]    Some limited holes may also be provided in the plate to allow bone ingrowth. However, if the outer surfaces  24  have holes therein, the holes advantageously cover less than 40 percent of the outer surface  24  which contacts the bone to prevent subsidence of the plates into the vertebral bodies. Preferably the holes will cover less than 25 percent, and more preferably less than 10 percent of the outer bone contacting surfaces. At the option of the surgeon, when the small holes are present in the plates  20 ,  30 , bone graft can be placed in the holes to allow bone to grow through the plates. The embodiments illustrated in  FIGS. 1-3  also illustrate the optional inclusion of countersunk screw holes  60  extending between a lateral surface of the plates  20 ,  30  and the end surfaces  24 , in which bone screws may optionally be inserted to further stabilize the body  10 . The holes  60  can alternatively extend vertically through the end plates, or the end plates can include combinations of vertical and angled holes. 
         [0026]    The vertebral body replacement  10  shown herein is configured for placement in the vertebral column from an anterior approach. It should be understood that other approaches can be used, and the particular shape of the vertebral body replacement would be modified depending on the approach. For example, for a lateral approach, the vertebral body replacement may be formed in a more elongated, kidney bean, or banana shape with a transversely oriented fin. 
         [0027]    As shown in  FIG. 1 , the vertebral body replacement  10  is provided with shock absorption or some other limited motion between the two plates  20 ,  30  by providing a compliant connector  32 . The limited motion provided by the compliant connector  32  is designed to reduce forces on the interface between the outer surfaces  24  and the bone to improve long term fixation of the spacer. The compliance of the connector  32  allows motion between the vertebral bodies to be accommodated by the compliance in the body  10  rather than causing one or both of the vertebral bodies to pull away from the plates  20 ,  30 . The compliant connector  32  provides limited relative motion between the plates, which may include compliance in a vertical direction of up to about 6 mm, rotation in an anterior/posterior direction, lateral direction, or axial rotation of less than about 10 degrees, and/or translation of up to about 1 mm. 
         [0028]    In the vertebral body replacement  10  of  FIG. 1 , the compliance, as well as some small amount of translation and rotation, is provided by the cuts or slots  70  extending into the connector  32 . In the embodiment of  FIG. 1 , the slots  70  are spiral slots, however, other shaped slots may also be used. The compliant connector  32  is advantageously formed as a unitary member with at least one lateral cut or slot  70  positioned between the upper and lower plates  20 ,  30 , permitting the plates to move resiliently toward and away from each other. The replacement  10  can also be formed as multiple parts where different properties are desired from the different parts, such as different radiopacities, different strengths, or different flexibility properties and for flexibility in creating the size and configuration of spacer suited to the patient. The lateral cuts  70  in the connector  32  allow the connector to function as a compliant member without affecting the function of the upper and lower plates of the body  10 . 
         [0029]      FIG. 2  illustrates an alternative embodiment of a body  10  having multiple parts including end plates  20 ,  30  and spacers  90 . The spacers  90  include lateral cuts  70  in place of the spiral cuts of  FIG. 1 . The material remaining after the cuts  70  are made is called a column. A shallow cut, that is, one that extends laterally into the connector a relatively small distance, and a large column provides a stiffer spacer, while a deeper cut and smaller column provides a more compliant spacer. In the embodiment shown in  FIG. 2 , the cuts  70  are at least 60% of the way through the spacer width or diameter, and preferably at least 75% of the way through the connector width. 
         [0030]    Optionally, a variable stiffness shock absorbing connector  32  ( FIG. 1 ) or spacer  90  ( FIG. 2 ) can be constructed with lateral cuts  70  with tapering widths. For cuts with such tapering widths, the cut  70  is smallest where the cut terminates adjacent the column and is largest at the edge of the connector  32  furthest from the column. In this version, each of the lateral cuts  70  causes the connector  32  to act as a non linear spring providing progressively stiffer behavior upon larger compression. This is due to the fact that progressively more material on the sides of the cuts  70  is in contact as the connector  32  or spacer  90  is compressed. The non-linear spring can be incorporated in any of the other embodiments described herein to provide a softer stop to the compliant action of the core. The tapered width cuts  70  can provide the additional benefit of providing a flushing action during operation that moves any accumulated material out of the cuts. 
         [0031]    The cuts  70  also advantageously include a stress relief  74  at the end of the cuts which increases the fatigue life of the device by reducing the stress concentration at the ends of the slots. 
         [0032]    In the exemplary embodiments illustrated herein, a shock absorbing connector  32  includes either one or more planar cuts  70  ( FIG. 2 ), or alternatively one or more spiral or helical cuts  70  ( FIG. 1 ) to form one or more continuous spring coil elements  72  which provide compliance to the connector. Although the spiral cut connector  32  is illustrated in  FIG. 1  with two spiral cuts, only one, or three or more spiral cuts may also be employed. For example, two or more spiral cuts  70  arranged in opposite directions can be formed in the connector  32 , as illustrated in  FIG. 1 . Furthermore, when more than one spiral cut  70  is provided, the cuts can optionally be nested one inside the other (not illustrated), as in the manner of a multi-start thread, and/or can include combinations of both nested and adjacent cuts (such as those illustrated in  FIGS. 1-2 ). The compression of a spiral cut connector  70  can result in some small amount of relative rotation between the upper and lower surfaces  20 ,  30 . In cases where it is desirable to eliminate this rotation, a connector  32  having multiple spiral cuts in opposite directions can be used. For example, a connector  32  can be formed with a first spiral cut  70  at a top of the connector in a first direction and a second spiral cut  70  at a bottom of the core in an opposite second direction. The first and second spiral cuts can offset rotation of each other resulting in a non rotating compliant connector. The double spiral embodiment of the connector is also more stable in shear than the single coil. Furthermore, coils  74  provide significantly more surface area between the adjoining surfaces of the cuts  70  than do planar cuts, which can be advantageous to allow limited rotational motion. The spiral cuts  70  can be made parallel to the end surfaces of the body  10  or can be angled, as in a cone shape. When the spiral cuts  70  are angled to form a cone shaped spring the cone shaped surfaces can limit the translational movement of the spring. 
         [0033]    In each of the shock absorbing connectors described herein, the interconnected sections within the connector and the plate(s) are designed for minimal or no motion between contacting parts to prevent particulate generation. However, since the plates and connectors are made entirely of hard materials such as metals, some minimal rubbing contact may be accommodated. In the exemplary embodiments illustrated in figures herein, a rotational interlock  80  is provided between the lower surface of the end plate  20  and the adjoining upper surface of the connector section  32  of the end plate  30 . With reference to  FIG. 2 , the exemplary interlock  80  includes complementary portions  82 ,  84 , formed on the adjoining faces of the end plate  20  and the connector section  32 , in the exemplary body  10 , taking the shape of simple raised portions or ribs  84  which mate with correspondingly sized and shaped recesses  82 . The rotational interlock  80  is not limited to the particular shapes or orientations illustrated in the drawing figures, and can take any shape or orientation which resists, and advantageously prevents, the plate  20  and the connector section  32  from rotating relative to each other. The rotational interlock  80  on the top and bottom surface of a spacer  90  can be different to allow the complete body  10  to be assembled only in a particular desired configuration. 
         [0034]    Further optionally, as illustrated in  FIG. 1A , the body  10  can include one or more blind cavities  86  extending vertically through the connector section  32 , which provides the interior side of the spiral cut  70 . The blind cavities  86  can also vary in cross sectional size and shape to tailor the rigidity of the connector section  32  in different directions. More specifically, the cavity or cavities  86 , only one of which is illustrated in  FIG. 1A , when left hollow, provides a less rigid connector  32 . To increase the rigidity of the connector section  32 , other material can be used to partially or completely fill the cavity  86 , such as pins or rods (not illustrated) inserted in the cavity. 
         [0035]    When implanted between vertebrae, the shock absorbing connector  32  can resiliently absorb shocks transmitted vertically between upper and lower vertebrae of the patient&#39;s spinal column. This shock absorption is related to the material properties, design, and dimensions of the connector. In general, an increased number and width of the cuts  70  will increase absorption of shocks, with more elastic, or springy compression between the vertebrae. 
         [0036]    Preferably the connector  32  is made of metal such as titanium, cobalt chromium alloy, stainless steel, tantalum, nickel titanium or a combination thereof. These materials also can be designed to provide a device which is deformable in the elastic region of the stress/strain curve and will not plastically deform during compression. 
         [0037]    In the embodiments illustrated herein, the number, pitch, lead, lead angle, handedness, and total vertical length of each of the spiral cuts or slots  70 , as well as the combination of multiple cuts if provided, can be varied to change the amount of compliance of the connector  32 . When a load is applied to the upper and lower plates  20 ,  30 , the connector  32  will compress with each of the cuts  70  closing and the total amount of compression possible depending on the number, arrangement, and height of the cuts. The cuts  70  form spiral coils  74  between the ends of the cut, which function like springs to allow the connector  32  to be compressed. The cuts  70  may be modified to be non-uniform to provide preferential deflection in one or more bending directions. Preferential deflection is useful to provide increased anterior-posterior compliance and less lateral compliance, or the other way around. 
         [0038]    According to one embodiment of the invention, the cuts  70  in the shock absorbing connector  32  according to any of the embodiments described herein may be manufactured by wire EDM (electrical discharge machining), molding, laser cutting, or the like. A number of cuts  70  can vary from 1 to about 50, preferably about 6 to about 20, for a vertebral body replacement. A width of the lateral cuts  70  in the direction of the height of the body  10  is about 0.01 mm to about 2 mm, preferably about 0.05 to about 1 mm. 
         [0039]    In one embodiment of the present invention, for a cervical application, the maximum deformation of the shock absorbing body is about 0.5 to about 4 mm, and is preferably about 1 to about 2 mm. For a lumbar application, the maximum deformation of the shock absorbing body is about 1 to about 6 mm, and is preferably about 1 to about 3 mm. 
         [0040]    Although motion between the plates  20 ,  30  of the body  10  has been described herein as provided by cuts  70 , it should be understood that this motion can be provided in a number of other known manners, such as use of resilient materials, or movable joints as long as the motion is limited to the small amount of motion allowable in a patient requiring a fusion procedure including compliance or vertical motion between the plates of up to about 6 mm, rotation between the plates of less than 10 degrees, and translation between the plates of up to about 1 mm. 
         [0041]    The body  10  can be provided in different sizes, with different plate sizes, angles between plates, lordosis angles, and heights for different patients or applications. In addition, the shock absorbing connector section  32  can be provided in different compliances for different patients. In addition, the compliance and/or height of the body  10  can be adjustable, such as by rotating an adjustment screw before or after implantation, and/or bonding portions of one or more of the portions of a coil  74 . The body  10  preferably is sized to provide substantial coverage of the vertebral surfaces. For example, in an anterior procedure, the plates  20 ,  30  are preferably sized to cover at least 50 percent of the vertebral surface. In posterior or lateral procedures, the coverage of the vertebral surface may be somewhat smaller due to the small size of the access area, i.e., the posterior or lateral spacers may cover about 40 percent or more of the vertebral surface with a one or two part spacer. 
         [0042]    Turning now to  FIG. 2 , a second exemplary embodiment of a body  10 , adhering to principles of the present invention, is illustrated. In contrast to the embodiment illustrated in  FIGS. 1 and 1A , the body  10  illustrated in  FIG. 2  includes one or more separate compliant connector spacers  90  positioned between plates  20 ,  30 , rather than a connector section  32  of a plate  30 . Each of the spacers  90  includes one or more cuts  70 , which can be either planar cuts or forming one or more coils, as described above with reference to the embodiment of  FIGS. 1 and 1A . The adjoining surfaces of the plates  20 ,  30  and the spacers  90  are also provided with rotational interlocks  80 , as described herein; while  FIG. 2  suggests that the interlocks  80  are the same, differently configured interlocks can alternatively be provided for different non-adjoining surfaces, for example to prevent the spacers  90  from being assembled in a way other than that designed for a body  10  configured for the particular patient. By way of non-limiting example, a first rotational interlock, formed of rectangular ribs and recesses on adjoining surfaces of the end plates and/or the spacers, as illustrated in  FIG. 1A , can be provided on the adjoining surfaces of the plate  20  and the adjacent first spacer  90 ; a second rotational interlock, formed of vertically oriented cylindrical pins, can be provided on the opposite face of the first spacer  90  and the adjoining surface of the adjacent spacer or plate  30 . Because the two interlocks  80  are incompatible and do not mate, there is only a single configuration of the pieces that will permit them to be assembled into a body  10 . 
         [0043]      FIG. 3  illustrates a third exemplary embodiment of a body  10 , adhering to principles of the present invention. In addition to the features previously described with reference to  FIGS. 1-2 , the embodiment illustrated in  FIG. 3  includes a vertical adjustment mechanism  100  for fine tuning of the vertical size of the body  10 , either prior to or after implantation of body  10  into a patient. While numerous configurations of the adjustment mechanism  100  can be provided, one exemplary embodiment includes a threaded post or tube  102  extending from either an upper surface  106  of the end plate  30  or a lower surface  104  of the section  32 , which mates with a correspondingly configured and threaded hole or post in the other of the end plate  30  and section  32 . Rotation of the post  102  causes the two portions of the body  10  to move toward or away from each other, and thus decreases or increases the vertical size of the body  10 , respectively. According to one version of the adjustable height vertebral body replacement an adjustment mechanism with oppositely threaded ends is inserted in the upper and lower parts  104 ,  106  and is adjustable after positioning in the patient. 
         [0044]    According to one exemplary method adhering to principles of the present invention, a patient in need of a vertebral body replacement is prepped and surgical access is made to the particular vertebral body to be removed. Access to the surgical site is generally made anteriorly through the abdominal cavity for a lumbar procedure. One or more target vertebral body or bodies is removed in one of numerous manners known to those of ordinary skill in the art, between upper and lower remaining vertebral bodies in the patient&#39;s spine, and a vertebral body replacement  10 , embodying principles of the present invention, is selected based on the measurement of the spacing for proper spinal alignment. The vertebral body replacement  10  is assembled and implanted in the space created by removal of the original vertebral body or bodies. Optionally, one or more spacers  90  are assembled into the body  10 , prior to installation of the body  10  into the patient, and/or the vertical length of the body  10  is adjusted to better fit in the space. Further optionally, when the body  10  includes one or more cavities  86 , additional material is inserted into the cavity, prior to implantation of the body, to tailor the rigidity of the body  10 , or for other purposes. 
         [0045]    While the exemplary embodiments have been described in some detail, by way of example and for clarity of understanding, those of skill in the art will recognize that a variety of modifications, adaptations, and changes may be employed. Hence, the scope of the present invention should be limited solely by the appended claims.