Abstract:
Prosthetic replacement for a posterior element of a vertebra comprising portions that replace the natural lamina and the four natural facets. The prosthetic replacement may also include portions that replace one or more of the natural spinous process and the two natural transverse processes. If desired, the prosthesis replacement may also replace the natural pedicles. A method for replacing a posterior element of a vertebra is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/276,617, filed Oct. 19, 2011, which is a continuation of U.S. application Ser. No. 12/328,964, filed on Dec. 5, 2008, now issued as U.S. Pat. No. 8,066,741, which is a continuation of U.S. application Ser. No. 11/083,710, filed Mar. 18, 2005, now issued as U.S. Pat. No. 7,566,345, which is a continuation of U.S. application Ser. No. 10/196,716, filed Jul. 16, 2002, now issued as U.S. Pat. No. 6,902,580, which is a continuation of U.S. application Ser. No. 09/797,309, filed Mar. 1, 2001, now issued as U.S. Pat. No. 6,419,703, U.S. Ser. No. 12/328,964, filed on Dec. 5, 2008, is also a continuation-in-part application of U.S. application Ser. No. 11/456,509, filed Jul. 10, 2006, now issued as U.S. Pat. No. 7,618,455, which is a continuation of U.S. application Ser. No. 10/420,467, filed Apr. 22, 2003, now issued as U.S. Pat. No. 7,074,237, which is a continuation of U.S. application Ser. No. 09/736,103, filed Dec. 13, 2000, now issued as U.S. Pat. No. 6,565,605. 
     All of the foregoing are incorporated herein by reference entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to surgical devices and methods in general, and more particularly to surgical devices and methods for restoring a damaged, diseased or otherwise painful spinal joint. 
     2. Description of Related Art 
     Traumatic, inflammatory, metabolic, synovial, neoplastic and degenerative disorders of the spine can produce debilitating pain that can have severe socioeconomic and psychological effects. 
     One of the most common surgical interventions today is arthrodesis, or spine fusion, in which two or more adjacent vertebral bodies are fused together in order to alleviate pain associated with the disc(s) located between those vertebral bodies. Approximately 300,000 such procedures are performed annually in the United States alone. Clinical success varies considerably, depending upon technique and indications, and consideration must be given to the concomitant risks and complications. 
     For example, while spine fusion generally helps to eliminate certain types of pain, it has also been shown to decrease function by limiting the range of motion for patients in flexion, extension, axial rotation and lateral bending. Furthermore, it is believed that spine fusion creates increased stresses on (and, therefore, accelerated degeneration of) adjacent non-fused motion segments. Additionally, pseudoarthrosis, resulting from an incomplete or ineffective fusion, may reduce or even totally eliminate the desired pain relief for the patient. Also, the fusion device(s) used to effect fusion, whether artificial or biological, may migrate out of the fusion site, thereby creating significant new problems for the patient. 
     Recently, several attempts have been made to recreate the natural biomechanics of the spine through the use of an artificial disc. Artificial discs are intended to restore articulation between vertebral bodies so as to recreate the full range of motion normally allowed by the elastic properties of the natural disc, which directly connects two opposed vertebral bodies. However, the artificial discs developed to date do not adequately address the mechanics of motion of the spinal column. 
     In addition to the foregoing, posterior elements called the facet joints help to support axial, torsional and shear loads that act on the spinal column. Furthermore, the facet joints are diarthroidal joints that provide both sliding articulation and load transmission features. However, the facet joints can also be a significant source of spinal disorders and, in many cases, debilitating pain. For example, a patient may suffer from arthritic facet joints, severe facet joint tropism or otherwise deformed facet joints, facet joint injuries, etc. There is currently a lack of good interventions for facet joint disorders. Facetectomy, or the removal of the facet joints, may provide some relief, but it is also believed to produce significant decreases in the stiffness of the spinal column (i.e., hypermobility) in all planes of motion: flexion and extension, lateral bending, and axial rotation. Furthermore, problems with the facet joints can also complicate treatments associated with other portions of the spine. By way of example, contraindications for artificial discs include arthritic facet joints, absent facet joints, severe facet joint tropism or otherwise deformed facet joints. 
     U.S. Pat. No. Re. 36,758 (Fitz) discloses an artificial facet joint where the inferior facet, the mating superior facet, or both, are covered with a cap. This cap requires no preparation of the bone or articular surfaces; it covers, and therefore preserves, the bony and articular structure. 
     The capping of the facet has several potential disadvantages, however. If the facet joint is osteoarthritic, a cap will not remove the source of the pain. Additionally, at least in the case of surface replacements for osteoarthritic femoral heads, the capping of articular bone ends has proven to lead to clinical failure by means of mechanical loosening. This clinical failure is hypothesized to be a sequela of disrupting the periosteum and ligamentum teres femoris, both serving a nutrition delivery role to the femoral head, thereby leading to avascular necrosis of the bony support structure for the surface replacement. It is possible that corresponding problems could develop from capping the facet. Another potential disadvantage of facet capping is that in order to accommodate the wide variability in anatomical morphology of the facets, not only between individuals but also between levels within the spinal column, a very wide range of cap sizes and shapes is required. 
     U.S. Pat. No. 6,132,464 (Martin) discloses a spinal facet joint prosthesis that is supported on the lamina (which is sometimes also referred to as the posterior arch). Extending from this support structure are inferior and/or superior blades that replace the cartilage at the facet joint. Like the design of the aforementioned U.S. Pat. No. Re. 36,758, the prosthesis of U.S. Pat. No. 6,132,464 generally preserves existing bony structures and therefore does not address pathologies which affect the bone of the facets in addition to affecting the associated cartilage. Furthermore, the prosthesis of U.S. Pat. No. 6,132,464 requires a secure mating between the prosthesis and the lamina. However, the lamina is a very complex and highly variable anatomical surface. As a result, in practice, it is very difficult to design a prosthesis that provides reproducible positioning against the lamina so as to correctly locate the cartilage-replacing blades for the facet joints. 
     Another approach to surgical intervention for spinal facets is disclosed in International Pat. Publication No. WO9848717A1 (Villaret et al.). While this publication teaches the replacement of spinal facets, the replacement is interlocked in a manner so as to immobilize the joint. 
     Thus it will be seen that previous attempts to provide facet joint replacement have proven inadequate. 
     In some circumstances, additional structures of a vertebra beside the facets may have been compromised by disease or trauma. For example, the lamina, the spinous process and/or the two transverse processes may have been compromised by disease or trauma. In such a circumstance, it would be useful to have a prosthesis which would allow the replacement of the same. 
     SUMMARY OF THE INVENTION 
     As a result, one object of the present invention is to provide a novel prosthesis tier the replacement of all four of the facets so as to remove the source of traumatic, arthritic or other disease-mediated pain. 
     Another object of the present invention is to provide a novel prosthesis for the replacement of different combinations of the posterior elements of a vertebra. 
     And another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the lamina, the four facets, the spinous process and the two transverse processes. 
     Still another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the lamina, the four facets and the spinous process. 
     Yet another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the lamina, the four facets and the two transverse processes. 
     Another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the lamina and the four facets. 
     And another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the two pedicles, the lamina, the four facets, the spinous process and the two transverse processes. 
     Still another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the two pedicles, the lamina, the four facets and the spinous process. 
     Yet another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the two pedicles, the lamina, the four facets and the two transverse processes. 
     Another object of the present invention is to provide a novel prosthesis for the replacement of a posterior element of a vertebra that replicates the two pedicles, the lamina and the four facets. 
     These and other objects are addressed by the present invention which, in one preferred embodiment, comprises a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic mounts; a prosthetic lamina extending from the two prosthetic mounts; a pair of prosthetic superior facets extending from the two prosthetic mounts and the prosthetic lamina; a pair of prosthetic inferior facets extending from the prosthetic lamina, a prosthetic spinous process extending from the prosthetic lamina; and a pair of prosthetic transverse processes extending from the two prosthetic mounts. 
     In another form of the invention, there is provided a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic mounts; a prosthetic lamina extending from the two prosthetic mounts; a pair of prosthetic superior facets extending from the two prosthetic mounts and the prosthetic lamina; a pair of prosthetic inferior facets extending from the prosthetic lamina; and a prosthetic spinous process extending from the prosthetic lamina. 
     In another form of the invention, there is provided a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic mounts; a prosthetic lamina extending from the two prosthetic mounts; a pair of prosthetic superior facets extending from the two prosthetic mounts and the prosthetic lamina; a pair of prosthetic inferior facets extending from the prosthetic lamina; and a pair of prosthetic transverse processes extending from the two prosthetic mounts. 
     In another form of the invention, there is provided a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic mounts; a prosthetic lamina extending from the two prosthetic mounts; a pair of prosthetic superior facets extending from the two prosthetic mounts and the prosthetic lamina; and a pair of prosthetic inferior facets extending from the prosthetic lamina. 
     In another form of the invention, there is provided a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic pedicles; a prosthetic lamina extending from the two prosthetic pedicles; a pair of prosthetic superior facets extending from the two prosthetic pedicles and the prosthetic lamina; a pair of prosthetic inferior facets extending from the prosthetic lamina; a prosthetic spinous process extending from the prosthetic lamina; and a pair of prosthetic transverse processes extending from the two prosthetic pedicles. 
     In another form of the invention, there is provided a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic pedicles; a prosthetic lamina extending from the two prosthetic pedicles; a pair of prosthetic superior facets extending from the two prosthetic pedicles and the prosthetic lamina; a pair of prosthetic inferior facets extending from the prosthetic lamina; and a prosthetic spinous process extending from the prosthetic lamina. 
     In another form of the invention, there is provided a prosthesis for the replacement of a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic pedicles; a prosthetic lamina extending from the two prosthetic pedicles; a pair of prosthetic superior facets extending from the two prosthetic pedicles and the prosthetic lamina; a pair of prosthetic inferior facets extending from the prosthetic lamina; and a pair of prosthetic transverse processes extending from the two prosthetic pedicles. 
     In another form of the invention, there is provided a prosthesis for the replacement posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the prosthesis comprising a pair of prosthetic pedicles; a prosthetic lamina extending from the two prosthetic pedicles; a pair of prosthetic superior facets extending from the two prosthetic pedicles and the prosthetic lamina; and a pair of prosthetic inferior facets extending from the prosthetic lamina. 
     In another form of the invention, there is provided a method for replacing a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the two natural pedicles, the method comprising the steps of making a resection at the most dorsal aspect the two natural pedicles; and attaching a prosthesis to the resected vertebra, the prosthesis comprising a pair of prosthetic mounts, a prosthetic lamina extending from the two prosthetic mounts, a pair of prosthetic superior facets extending from the two prosthetic mounts and the prosthetic lamina, and a pair of prosthetic inferior facets extending from the prosthetic lamina. 
     In another form of the invention, there is provided a method for replacing a posterior element of a natural vertebra, wherein the natural vertebra comprises a natural vertebral body, a pair of natural pedicles extending from the natural vertebral body, a natural lamina extending from the two natural pedicles, a pair of natural superior facets extending from the two natural pedicles and the natural lamina, a pair of natural inferior facets extending from the natural lamina, a natural spinous process extending from the natural lamina, and a pair of natural transverse processes extending from the natural pedicles, the method comprising the steps of making a resection at the junction of the natural vertebral body and the two natural pedicles; and attaching a prosthesis to the resected vertebra, the prosthesis comprising a pair of prosthetic pedicles, a prosthetic lamina extending from the prosthetic pedicles, a pair of prosthetic superior facets extending from the two prosthetic pedicles and the prosthetic lamina, and a pair of prosthetic inferior facets extending from the prosthetic lamina. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
         FIG. 1  is a perspective view of a lumbar vertebra; 
         FIG. 2  is a perspective view of a novel prosthesis that replaces the lamina, the four facets, the spinous process and the two transverse processes of a vertebra; 
         FIG. 3  is an anterior view of the prosthesis shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of a vertebra which has been resected to receive the prosthesis shown in  FIG. 2 ; 
         FIG. 5  is a perspective view of the prosthesis shown in  FIG. 2  mounted to the resected vertebra shown in  FIG. 4 ; 
         FIG. 6  is a dorsal view attic prosthesis shown in  FIG. 2  mounted to the resected vertebra shown in  FIG. 4 ; 
         FIG. 7  is a lateral view of the prosthesis shown in  FIG. 2  mounted to the resected vertebra shown in  FIG. 4 ; 
         FIG. 8  is a perspective view of a novel prosthesis that replaces the lamina, the four facets and the spinous process of a vertebra; 
         FIG. 9  is a perspective view of a novel prosthesis that replaces the lamina, the four facets and the two transverse processes of a vertebra; 
         FIG. 10  is a perspective view of a novel prosthesis that replaces the lamina and the four facets of a vertebra; 
         FIG. 11  is a perspective view of a novel prosthesis that replaces the two pedicles, the lamina, the four facets, the spinous process and the two transverse processes of a vertebra; 
         FIG. 12  is a lateral view of the prosthesis shown in  FIG. 11 ; 
         FIG. 13  is an anterior view of the prosthesis shown in  FIG. 11 ; 
         FIG. 14  is a perspective view of a vertebra which has been resected to receive the prosthesis shown in  FIG. 11 ; 
         FIG. 15  is a perspective view showing the prosthesis of  FIG. 11  mounted to the resected vertebra shown in  FIG. 14 ; 
         FIG. 16  is a perspective view of a novel prosthesis that replaces the two pedicles, the lamina, the four facets and the spinous process of a vertebra; 
         FIG. 17  is a perspective view of a novel prosthesis that replaces the two pedicles, the lamina, the four facets and the two transverse processes of a vertebra; 
         FIG. 18  is a perspective view of a novel prosthesis that replaces the two pedicles, the lamina and the four facets of a vertebra; and 
         FIG. 19  is a perspective view showing an alternative arrangement for mounting the prosthesis of  FIG. 1  to a vertebra. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , there is shown a natural lumbar vertebra  5  comprising a natural vertebral body  10 , a pair of natural pedicles  15  extending from natural vertebral body  10 , a natural lamina  20  extending from natural pedicles  15 , a pair of natural superior facets  25  extending from natural pedicles  15  and natural lamina  20 , a pair of natural inferior facets  30  extending from natural lamina  20 , a natural spinous process  35  extending from natural lamina  20 , and a pair of natural transverse processes  40  extending from natural pedicles  15 . 
     Looking next at  FIGS. 2 and 3 , there is shown a novel prosthesis  100  which is adapted to replace the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 . To this end, prosthesis  100  comprises a pair of prosthetic mounts  115 , a prosthetic lamina  120  extending from prosthetic mounts  115 , a pair of prosthetic superior facets  125  extending from prosthetic mounts  115  and prosthetic lamina  120 , a pair of prosthetic inferior facets  130  extending from prosthetic lamina  120 , a prosthetic spinous process  135  extending from prosthetic lamina  120 , and a pair of prosthetic transverse processes  140  extending from prosthetic mounts  115 . 
     In the use of prosthesis  100 , natural lumbar vertebra  5  is resected at its natural pedicles  15  so as to remove the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , leaving a pair of pedicle end surfaces  41  ( FIG. 4 ). Then the prosthesis  100  may be attached to the natural pedicles  15 , e.g., by placing prosthetic mounts  115  against pedicle surfaces  41  and then passing screws  145  through screw holes  147  and into natural pedicles  15 , as shown in  FIGS. 5-7 . As seen in the drawings, the relative size, shape and positioning of the prosthetic lamina  120 , the two prosthetic superior facets  125 , the two prosthetic inferior facets  130 , the prosthetic spinous process  135 , and the two prosthetic transverse processes  140  essentially mimic the relative size, shape and positioning of the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , whereby to effectively restore the vertebra. If desired, holes  150  may be provided in the prosthetic spinous process  135  and/or the two prosthetic transverse processes  140  so as to facilitate re-attaching soft tissue to these structures. 
     Looking next at  FIG. 8 , there is shown a novel prosthesis  200  which is adapted to replace natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , and natural spinous process  35 . To this end, prosthesis  200  comprises a pair of prosthetic mounts  215 , a prosthetic lamina  220  extending from prosthetic mounts  215 , a pair of prosthetic superior facets  225  extending from prosthetic mounts  215  and prosthetic lamina  220 , a pair of prosthetic inferior facets  230  extending from prosthetic lamina  220 , and a prosthetic spinous process  235  extending from prosthetic lamina  220 . 
     In the use of prosthesis  200 , natural lumbar vertebra  5  is resected at its natural pedicles  15  so as to remove the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the spinous process  35  and the two natural transverse processes  40 , leaving a pair of pedicle surfaces  41  ( FIG. 4 ). Then the prosthesis  200  may be attached to the natural pedicles  15 , e.g., by placing prosthetic mounts  215  against pedicle surfaces  41  and then passing screws  145  through holes  247  and into natural pedicles  15 . As seen in the drawing, the relative size, shape and positioning of prosthetic lamina  220 , the two prosthetic superior facets  225 , the two prosthetic interior facets  230 , and the prosthetic spinous process  235  essentially mimic the relative size, shape and positioning of the natural lamina  20 , the two natural superior facets  25  the two natural inferior facets  30 , and the natural spinous process  35 , whereby to effectively restore the vertebra. If desired, holes  150  may be provided in the prosthetic spinous process  235  so as to facilitate re-attaching soft tissue to this structure. 
     Looking next at  FIG. 9 , there is shown a novel prosthesis  300  which is adapted to replace the natural lamina  20 , the two natural superior facets  25 , the two natural interior facets  30 , and the two natural transverse processes  40 . To this end, prosthesis  300  comprises a pair of prosthetic mounts  315 , a prosthetic lamina  320  extending from prosthetic mounts  315 , a pair of prosthetic superior facets  325  extending from prosthetic mounts  315  and prosthetic lamina  320 , a pair of prosthetic inferior facets  330  extending from prosthetic lamina  320 , and a pair of prosthetic transverse processes  340  extending from prosthetic mounts  315 . 
     In the use of prosthesis  300 , natural lumbar vertebra  5  is resected at natural pedicles  15  so as to remove natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35  and the two natural transverse processes  40 , leaving a pair of pedicle surfaces  41  ( FIG. 4 ). Then the prosthesis  300  may be attached to the natural pedicles  15 , e.g., by placing prosthetic mounts  315  against pedicle surfaces  41  and then passing screws  145  through holes  347  and into natural pedicles  15 . As seen in the drawing, the relative size, shape and positioning of the prosthetic lamina  320 , the two prosthetic superior facets  325 , the two prosthetic inferior facets  330 , and the two prosthetic transverse processes  340  essentially mimic the relative size, shape and positioning of the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , and the two natural transverse processes  40 , whereby to effectively restore the vertebra. If desired, holes  150  may be provided in the two prosthetic transverse processes  340  so as to facilitate re-attaching soft tissue to these structures. 
     Looking next at  FIG. 10 , there is shown a novel prosthesis  400  which is adapted to replace the natural lamina  20 , the two natural superior facets  25 , and the two natural inferior facets  30 . To this end, prosthesis  400  comprises a pair of prosthetic mounts  415 , a prosthetic lamina  420  extending from prosthetic mounts  415 , a pair of prosthetic superior facets  425  extending from prosthetic mounts  415  and prosthetic lamina  420 , and a pair of prosthetic inferior facets  430  extending from prosthetic lamina  420 . 
     In the use of prosthesis  400 , natural lumbar vertebra  5  is resected at pedicles  15  so as to remove the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , leaving a pair of pedicle surfaces  41  ( FIG. 4 ). Then the prosthesis  400  may be attached to the natural pedicles  15 , e.g., by placing prosthetic mounts  415  against pedicle surfaces  41  and then passing screws  145  through holes  447  and into natural pedicles  15 . As seen in the drawing, the relative size, shape and positioning of prosthetic lamina  420 , the two prosthetic superior facets  425 , and the two prosthetic inferior facets  430  essentially mimic the relative size, shape and positioning of the natural lamina  20 , the two natural superior facets  25  and the two natural inferior facets  30 , whereby to effectively restore the vertebra. 
     Looking next at  FIGS. 11-13 , there is shown a novel prosthesis  500  which is adapted to replace a pair of natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 . To this end, prosthesis  500  comprises a pair of prosthetic pedicles  515 , a prosthetic lamina  520  extending from prosthetic pedicles  515 , a pair of prosthetic superior facets  525  extending from prosthetic pedicles  515  and prosthetic lamina  520 , a pair of prosthetic inferior facets  530  extending from prosthetic lamina  520 , a prosthetic spinous process  535  extending from prosthetic lamina  520 , and a pair of prosthetic transverse processes  540  extending from prosthetic pedicles  515 . 
     In the use of prosthesis  500 , natural lumbar vertebra  5  is resected at the bases of natural pedicles  15  so as to remove two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , leaving a vertebral body end face  42  ( FIG. 14 ). Then the prosthesis  500  may be attached to the natural vertebral body  10 , e.g., by placing prosthetic pedicles  515  against vertebral body end face  42  and then passing screws  145  through holes  547  and into natural vertebral body  10 , as shown in  FIG. 15 . As seen in the drawings, the relative size, shape and positioning of the two prosthetic pedicles  515 , the prosthetic lamina  520 , the two prosthetic superior facets  525 , the two prosthetic inferior facets  530 , the prosthetic spinous process  535 , and the two prosthetic transverse processes  540  essentially mimic the relative size, shape and positioning of the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , whereby to effectively restore the vertebra. If desired, holes  150  may be provided in prosthetic spinous process  535  and the two prosthetic transverse processes  540  so as to facilitate re-attaching soft tissue to these structures. 
     Looking next at  FIG. 16 , there is shown a novel prosthesis  600  which is adapted to replace the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , and the natural spinous process  35 . To this end, prosthesis  600  comprises a pair of prosthetic pedicles  615 , a prosthetic lamina  620  extending from prosthetic pedicles  615 , a pair of prosthetic superior facets  625  extending from prosthetic pedicles  615  and prosthetic lamina  620 , a pair of prosthetic inferior facets  630  extending from prosthetic lamina  620 , and a prosthetic vinous process  635  extending from prosthetic lamina  620 . 
     In the use of prosthesis  600 , natural lumbar vertebra  5  is resected at the bases of natural pedicles  15  so as to remove the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35  and the two natural transverse processes  40 , leaving a vertebral body end face  42  ( FIG. 14 ). Then the prosthesis  600  may be attached to the natural vertebral body  10 , e.g., by placing prosthetic pedicles  615  against vertebral body end face  42  and then passing screws  145  through holes  647  and into natural vertebral body  10 . As seen in the drawing, the relative size, shape and positioning of the two prosthetic pedicles  615 , the prosthetic lamina  620 , the two prosthetic superior facets  625 , the two prosthetic inferior facets  630 , and the prosthetic spinous process  635  essentially mimic the relative size, shape and positioning of the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , and the natural spinous process  35 , whereby to effectively restore the vertebra. If desired, holes  150  may be provided in prosthetic spinous process  635  so as to facilitate re-attaching soft tissue to this structure. 
     Looking next at  17 , there is shown a novel prosthesis  700  which is adapted to replace the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , and the two natural transverse processes  40 . To this end, prosthesis  700  comprises a pair of prosthetic pedicles  715 , a prosthetic lamina  720  extending from prosthetic pedicles  715 , a pair of prosthetic superior facets  725  extending from prosthetic pedicles  715  and prosthetic lamina  720 , a pair of prosthetic inferior facets  730  extending from prosthetic lamina  720 , and a pair of prosthetic transverse processes  740  extending from prosthetic pedicles  715 . 
     In the use of prosthesis  700 , natural lumbar vertebra  5  is resected at the bases of natural pedicles  15  on as to remove the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , leaving a vertebral body end face  42  ( FIG. 14 ). Then the prosthesis  700  may be attached to the natural vertebral body  10 , e.g., by placing prosthetic pedicles  715  against vertebral body end face  42  and then passing screws  145  through holes  747  and into vertebral body  10 . As seen in the drawing, the relative size, shape and positioning of the two prosthetic pedicle  715 , the prosthetic lamina  720 , the two prosthetic superior facets  725 , the two prosthetic interior facets  730 , and the two prosthetic transverse processes  740  essentially mimic the relative size, shape and positioning of the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , and the two natural transverse processes  40 , whereby to effectively restore the vertebra. If desired, holes  150  may be provided in the two prosthetic transverse processes  740  so as to facilitate re-attaching soft tissue to these structures. 
     Looking next at  FIG. 18 , there is shown a novel prosthesis  800  which is adapted to replace the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , and the two natural inferior facets  30 . To this end, prosthesis  800  comprises a pair of prosthetic pedicles  815 , a prosthetic lamina  820  extending from prosthetic pedicles  815 , a pair of prosthetic superior facets  825  extending from prosthetic pedicles  815  and prosthetic lamina  820 , and a pair of prosthetic inferior facets  830  extending from prosthetic lamina  820 . 
     In the use of prosthesis  800 , natural lumbar vertebra  5  is resected at the bases of natural pedicles  15  on as to remove the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , the two natural inferior facets  30 , the natural spinous process  35 , and the two natural transverse processes  40 , leaving a vertebral body end face  42  ( FIG. 14 ). Then the prosthesis  800  may be attached to natural vertebral body  10 , e.g., by placing prosthetic pedicles  715  against vertebral body end face  42  and then passing screws  145  through holes  847  and into natural vertebral body  10 . As seen in the drawing, the relative size, shape and positioning of the two prosthetic pedicles  815 , the prosthetic lamina  820 , the two prosthetic superior facets  825 , and the two prosthetic inferior facets  830  essentially mimic the relative size, shape and positioning of the two natural pedicles  15 , the natural lamina  20 , the two natural superior facets  25 , and the two natural inferior facets  30 , whereby to effectively restore the vertebra. 
     It should also be appreciated that prostheses  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700  and  800  may be attached to natural vertebra  5  with apparatus other than the screws  145  discussed above. Thus, for example, prostheses  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700  and  800  may be attached to natural vertebra  5  with rods or posts, etc. See, for example,  FIG. 19 , where prosthesis  500  is shown attached to natural vertebra  5  with rods  146  which pass through, and snap into engagement with, prosthetic pedicles  515 . 
     Having thus described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the embodiments shown herein are provided by way of example only, and that various changes and modifications may be effected by one skilled in the art without departing from the scope or spirit of the invention as defined in the claims.