Abstract:
The invention discloses devices, methods and systems for implanting articulating devices on the human spine. In some embodiments, three or more vertebrae are movable interconnected with artificial joints. Some embodiments are particularly well suited for implanting in the lumbosacral area of the spine. Some embodiments employ hybrid systems combining translaminar fixation with pedicular fixation of the device components. Some embodiments combine facet joint replacement with disc replacement.

Description:
CROSS-REFERENCE  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/782,932 to Ohrt et al., filed Mar. 15, 2006, the disclosure of which is incorporated herein as if fully set forth. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to devices and surgical methods for treatment of various spinal pathologies. More specifically, the present invention is directed to configurable and anatomically adaptable implantable devices for use in a spine and surgical procedures for altering the biomechanics of a spine, either temporarily or permanently. The devices alter, replace and/or revise existing anatomy and/or previously implanted devices.  
       BACKGROUND OF THE INVENTION  
       [0003]     Back pain, particularly in the small of the back, or lumbosacral region (L 4 -S 1 ) of the spine (see,  FIG. 1 ), is a common ailment. In many cases, the pain severely limits a person&#39;s functional ability and quality of life. Back pain interferes with work, routine daily activities, and recreation. It is estimated that Americans spend $50 billion each year on low back pain alone. It is the most common cause of job-related disability and a leading contributor to missed work.  
         [0004]     Through disease or injury, the laminae, spinous process, articular processes, facets and/or facet capsules of one or more vertebral bodies along with one or more intervertebral discs can become damaged which can result in a loss of proper alignment or loss of proper articulation of the vertebra. This damage can result in an anatomical change, loss of mobility, and pain or discomfort. For example, the vertebral facet joints can be damaged by traumatic injury or as a result of disease. Diseases damaging the spine and/or facets include osteoarthritis where the cartilage of joints is gradually worn away and the adjacent bone is remodeled, ankylosing spondylolysis (or rheumatoid arthritis) of the spine which can lead to spinal rigidity, and degenerative spondylolisthesis which results in a forward displacement of the lumbar vertebra on the sacrum. Damage to facet joints of the vertebral body often results in pressure on nerves, commonly referred to as “pinched” nerves, or nerve compression or impingement. The result is pain, misaligned anatomy, a change in biomechanics and a corresponding loss of mobility. Pressure on nerves can also occur without facet joint pathology, e.g., as a result of a herniated disc.  
         [0005]     One conventional treatment of facet joint pathology is spine stabilization, also known as intervertebral stabilization. Intervertebral stabilization desirably controls, prevents or limits relative motion between the vertebrae, through the use of spinal hardware, removal of some or all of the intervertebral disc, fixation of the facet joints, bone graft/osteo-inductive/osteo-conductive material positioned between the vertebral bodies (with or without concurrent insertion of fusion cages), and/or some combination thereof, resulting in the fixation of (or limiting the motion of) any number of adjacent vertebrae to stabilize and prevent/limit/control relative movement between those treated vertebrae.  
         [0006]     Although spine fusion surgery is an efficacious treatment alternative, complications can, nonetheless, result. Patients undergoing spine surgery frequently continue to experience symptoms. For surgical procedures in the lumbar spine, failure rates as high as 37% have been reported after lumbar fusion and 30% for surgery without fusion. See Eichholz, et al., “Complications of Revision Spinal Surgery,”  Neurosurg Focus  15(3): 1-4 (2003). Post-operative problems can include: decompression related problems, and fusion related problems. Decompression related problems (i.e., loss of normal spine balance resulting in the head and trunk no longer being centered over the pelvis) include, for example, recurrent disc herniation, spinal stenosis, chronic nerve injury, infection, and decompression. Fusion related problems can include, pain from the bone harvest site, failure of a fusion to develop, loosening of the implanted devices, nerve irritation caused by the devices, infection, and poor alignment of the spine.  
         [0007]     Stabilization of vertebral bodies can also be achieved (to varying degrees) from a wide variety of procedures, including the insertion of motion limiting devices (such as intervertebral spacers, artificial ligaments and/or dynamic stabilization devices), devices promoting arthrodesis (rod and screw systems, cables, fusion cages, etc.), and complete removal of some or all of a vertebral body from the spinal column (which may be due to extensive bone damage and/or tumorous growth inside the bone) and insertion of a vertebral body replacement (generally anchored into the adjacent upper and lower vertebral bodies). Various devices are known for fixing the spine and/or sacral bone adjacent the vertebra, as well as attaching devices used for fixation, including devices disclosed in: U.S. Pat. Nos. 6,585,769; 6,290,703; 5,782,833; 5,738,585; 6,547,790; 6,638,321; 6,520,963; 6,074,391; 5,569,247; 5,891,145; 6,090,111; 6,451,021; 5,683,392; 5,863,293; 5,964,760; 6,010,503; 6,019,759; 6,540,749; 6,077,262; 6,248,105; 6,524,315; 5,797,911; 5,879,350; 5,885,285; 5,643,263; 6,565,565; 5,725,527; 6,471,705; 6,554,843; 5,575,792; 5,688,274; 5,690,630; 6,022,350; 4,805,602; 5,474,555; 4,611,581; 5,129,900; 5,741,255; 6,132,430; and U.S. Patent Publication Nos. 2002/0120272, 2005/0143818, 2005/0240265, 2005/0240266, 2006/0058791 and 2006/0149375.  
         [0008]     More recently, various treatments have been proposed and developed as alternatives to spinal fusion. Many of these treatments seek to restore (and/or maintain) some, or all, of the natural motion of the treated spinal unit, and can include intervertebral disc replacement, nucleus replacement, facet joint resurfacing, and facet joint replacement. Such solutions typically include devices that do not substantially impair spinal movement. See, U.S. Pat. Nos. 6,610,091; 6,811,567; 6,902,580; 5,571,171; and Re 36,758; and PCT Publication Nos. WO 01/158563, WO 2004/103228, WO 2005/009301, and WO 2004/103227. Thus, spinal arthroplasty has become an acceptable alternative to fusion, particularly in cases of degenerative disc disease. Arthroplasty devices can be particularly useful because the devices are designed to create an artificial joint or restore the functional integrity and power of a joint.  
       SUMMARY OF THE INVENTION  
       [0009]     It is being discovered that spinal arthroplasty methods and devices that are suitable for use at various levels of the spine do not perform adequately at other levels of the spine. For example, implantable devices that work well at replacing the facet joints at level T 11 -T 12  or L 1 -L 2  may or may not perform adequately at levels L 4 -L 5  or L 5 -S 1 . What is needed are devices that can reliably be used at specific levels of the spine, particularly multiple adjacent levels.  
         [0010]     For the sake of description herein, the tools and prostheses that embody features of the invention are identified as either “cephalad” or “caudal” with relation to the portion of a given natural facet joint they replace. As previously described, a natural facet joint, such as facet joint  32  ( FIG. 3 ), has a superior half and an inferior half. In anatomical terms, the superior half of the joint is formed by the vertebral level below the joint, which can thus be called the “caudal” portion of the facet joint because it is closer to the feet of the person. The inferior half of the facet joint is formed by the vertebral level above the joint, which can thus be called the “cephalad” portion of the facet joint because it is closer to the head of the person. Thus, the prosthesis that is used in the replacement of the caudal portion of a natural facet joint (i.e., the superior half) will be called a “caudal” prosthesis. Likewise, the prosthesis that is used in the replacement of the cephalad portion of a natural facet joint (i.e., the inferior half) will be called a “cephalad” prosthesis.  
         [0011]     In certain patients, it may be desirable to replace the natural facet joints at more than one level. According to aspects of the invention, when facets joints are being replaced at two different levels, particularly if they are adjacent levels, a single implantable device, or multiple devices sharing one or more common components may be utilized. In such an embodiment, a portion of the device may serve as both a “caudal” prosthesis (to replace a lower portion of the facet joint located above the device) and a “cephalad” prosthesis (to replace an upper portion of the facet joint located below the device.  
         [0012]     The invention relates to an implantable spinal arthroplasty devices and methods for their use. Some embodiments of the invention include a device with a first portion adapted to engage a vertebra at the L 5  level of the spine and second portion adapted to engage a portion of a sacrum. The first and second portions of the device, per embodiments of the invention, cooperate to form at least one artificial facet joint between the L 5  level and the sacrum.  
         [0013]     The vertebra has two pedicles, a lamina, and a spinous process. In some embodiments of the device, the first portion of the device is configured to engage the pedicles of the L 5  vertebra. In some of these embodiments, first portion includes a first attachment member and a second attachment member, and each attachment member is configured to connect to one of the pedicles, the first portion further comprising a cross arm spanning between the first and the second attachment members.  
         [0014]     In some embodiments of the device, the first portion is configured to engage the lamina of the L 5  vertebra. In some of these embodiments the first portion is configured to hook over an upper surface of the lamina.  
         [0015]     In some embodiments of the device, the first portion includes two generally vertical members configured to be located on laterally opposite sides of a spinal process at the L 5  level as well as a cross member configured to interconnect the generally vertical members and to be located beneath the spinal process.  
         [0016]     In some embodiments of the device, the first portion includes at least one threaded fastener configured to penetrate the lamina. In other embodiments, the first portion includes at least one threaded fastener configured to press against an outer surface of the lamina.  
         [0017]     Some embodiments of the device further include a joint interconnecting the first and the second portions of the device, the joint have a generally ball-shaped portion and a cup portion, wherein the ball-shaped portion may slide relative to the cup portion.  
         [0018]     Embodiments of the invention include a method of implanting embodiments of the above-summarized spinal arthroplasty device; the method includes the attaching the device to the spine of a patient. The method may further include replacing at least a portion of a natural disc located adjacent to L 5  vertebra with an artificial disc implant.  
         [0019]     Embodiments of the invention also include a multi-level implantable spinal arthroplasty device with a first portion connectable to a first vertebra, a second portion connectable to a second vertebra located beneath the first vertebra, and a third portion connectable to a third vertebra located beneath the second vertebra. This embodiment includes at least one upper artificial joint interconnecting and allowing relative movement between the first and the second portions, and it includes at least one lower artificial joint interconnecting and allowing relative movement between the second and the third portions.  
         [0020]     In some embodiments of this multi-level device, the first, the second, and third vertebrae are adjacent to one another. In some of these embodiments the first and second vertebrae are at the L 4  and L 5  levels, respectively, and the third vertebra is part of the sacrum. In some of the multi-level device embodiments, the first portion is configured to attach to a lamina of the first vertebra. In some of the multi-level device embodiments, the second portion is configured to attach to at least one pedicle of the second vertebra. In some of the multi-level device embodiments, the third portion is configured to attach to at least one pedicle of the third vertebra. In some of the multi-level device embodiments, the first portion is configured to attach to a lamina of the first vertebra and the second portion is configured to attach to at least one pedicle of the second vertebra; and in some such embodiments, the third portion is configured to attach to the sacrum.  
         [0021]     In some embodiments of the multi-level device, the first portion includes two elongated bar elements, each element configured to pass diagonally through a lamina of the first vertebra. In some of these embodiments, at least one upper artificial joint includes a convex member and a concave member, the two members being configured to inter-engage to provide relative movement between the first and the second portions, one of the two members being located on a lower end of one of the elongated bar elements. In some of these embodiments, the at least one lower artificial joint includes a generally ball-shaped portion and a cup portion, wherein the ball-shaped portion may slide relative to the cup portion.  
         [0022]     In embodiments of the multi-level device, the second portion includes a first attachment member and a second attachment member, each attachment member configured to connect to a pedicle of the second vertebra, the second portion further including a cross arm spanning between the first and the second attachment members.  
         [0023]     Embodiments of the invention include a method of implanting embodiments of the above-summarized multi-level spinal arthroplasty device; the method includes attaching the device of claim B 1  to the spine of a patient. In some embodiments of this method, the multi-level device is attached to three adjacent vertebrae. In some embodiments, the first vertebra is at the L 4  level, the second vertebra is at the L 5  level, and the third vertebra is part of the sacrum. The method may further include replacing at least a portion of a natural disc adjacent to any of the first, the second, and/or third vertebrae with an artificial disc implant.  
       INCORPORATION BY REFERENCE  
       [0024]     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:  
         [0026]      FIG. 1  is a lateral elevation view of a normal human spinal column;  
         [0027]      FIG. 2  is a superior view of a normal human lumbar vertebra;  
         [0028]      FIG. 3  is a lateral elevational view of two vertebral bodies forming a functional spinal unit;  
         [0029]      FIG. 4  is a posterolateral oblique view of a vertebrae from a human spinal column;  
         [0030]      FIG. 5  is a perspective view of the anatomical planes of the human body;  
         [0031]      FIG. 6  is a posterior oblique view of an implantable spinal arthroplasty device;  
         [0032]      FIG. 7  is a posterior elevational view of an implantable spinal arthroplasty device;  
         [0033]      FIG. 8  is an oblique partial cutaway view of the device of  FIG. 7 ;  
         [0034]      FIG. 9  is an exploded view of a portion of the device of  FIG. 7 ;  
         [0035]      FIG. 10  is a lateral elevational view of a translaminar cephalad anchoring device implanted in a vertebra;  
         [0036]      FIG. 11  is a partially exploded lower plan view of the device of  FIG. 10 ;  
         [0037]      FIG. 12  is an oblique cross-sectional view of the device of  FIG. 10 ;  
         [0038]      FIG. 13  is an oblique cross-sectional view of another translaminar cephalad anchoring device implanted in a vertebra;  
         [0039]      FIG. 14  is an oblique cross-sectional view of yet another translaminar cephalad anchoring device implanted in a vertebra;  
         [0040]      FIG. 15  is a posterior elevational view of an arthroplasty device shown implanted on an L 5  vertebra and a sacrum;  
         [0041]      FIG. 16  is a posterolateral oblique view of the device of  FIG. 15  before implantation;  
         [0042]      FIG. 17  is a posterior elevational view of an arthroplasty device shown implanted on an L 5  vertebra and a sacrum;  
         [0043]      FIG. 18  is a posterolateral oblique view of a caudal anchoring device implanted on a sacrum;  
         [0044]      FIG. 19  is a perspective view of a portion of the device of  FIG. 18 ;  
         [0045]      FIG. 20  is an oblique side view of one embodiment of a caudal bearing cup;  
         [0046]      FIG. 21  is an oblique side view of another embodiment of a caudal bearing cup;  
         [0047]      FIG. 22  is a posterior elevational view of an arthroplasty device shown implanted on an L 5  vertebra and a sacrum;  
         [0048]     FIGS.  23  is a posterior elevational view of a hybrid, multilevel arthroplasty device shown implanted on L 4  and L 5  vertebrae and a sacrum;  
         [0049]      FIG. 24  is a posterolateral oblique view of another hybrid, multilevel arthroplasty device shown implanted on L 4  and L 5  vertebrae and a sacrum; and  
         [0050]      FIG. 25  is a posterolateral oblique view of yet another hybrid, multilevel arthroplasty device shown implanted on L 4  and L 5  vertebrae and a sacrum. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]     The invention relates generally to implantable devices, apparatus or mechanisms that are suitable for implantation within a human body to restore, augment, and/or replace soft tissue and connective tissue, including bone and cartilage, and systems for treating spinal pathologies. In some instances the implantable devices can include devices designed to replace missing, removed or resected body parts or structure. The implantable devices, apparatus or mechanisms are configured such that the devices can be formed from parts, elements or components which alone or in combination comprise the device. The implantable devices can also be configured such that one or more elements or components are formed integrally to achieve a desired physiological, operational or functional result such that the components complete the device. Functional results can include the surgical restoration and functional power of a joint, controlling, limiting or altering the functional power of a joint, and/or eliminating the functional power of a joint by preventing joint motion. Portions of the device can be configured to replace or augment existing anatomy and/or implanted devices, and/or be used in combination with resection or removal of existing anatomical structure.  
         [0052]     The devices of the invention are designed to interact with the human spinal column  10 , as shown in  FIG. 1 , which is comprised of a series of thirty-three stacked vertebrae  12  divided into five regions. The cervical region includes seven vertebrae, known as C 1 -C 7 . The thoracic region includes twelve vertebrae, known as T 1 -T 12 . The lumbar region contains five vertebrae, known as L 1 -L 5 . The sacral region is comprised of five fused vertebrae, known as S 1 -S 5 , while the coccygeal region contains four fused vertebrae, known as Co 1 -Co 4 . An example of one of the vertebra is illustrated in  FIG. 2  which depicts a superior plan view of a normal human lumbar vertebra  12 . Although human lumbar vertebrae vary somewhat according to location, the vertebrae share many common features. Each vertebra  12  includes a vertebral body  14 . Two short boney protrusions, the pedicles  16 ,  16 ′, extend dorsally from each side of the vertebral body  14  to form a vertebral arch  18  which defines the vertebral foramen  19 . At the posterior end of each pedicle  16 , the vertebral arch  18  flares out into broad plates of bone known as the laminae  20 . The laminae  20  fuse with each other to form a spinous process  22 . The spinous process  22  provides for muscle and ligamentous attachment. A smooth transition from the pedicles  16  to the laminae  20  is interrupted by the formation of a series of processes.  
         [0053]     Two transverse processes  24 ,  24 ′ thrust out laterally, one on each side, from the junction of the pedicle  16  with the lamina  20 . The transverse processes  24 ,  24 ′ serve as levers for the attachment of muscles to the vertebrae  12 . Four articular processes, two superior  26 ,  26 ′ and two inferior  28 ,  28 ′, also rise from the junctions of the pedicles  16  and the laminae  20 . The superior articular processes  26 ,  26 ′ are sharp oval plates of bone rising upward on each side of the vertebrae, while the inferior processes  28 ,  28 ′ are oval plates of bone that jut downward on each side. See also  FIG. 4 .  
         [0054]     The superior and inferior articular processes  26  and  28  each have a natural bony structure known as a facet. The superior articular facet  30  faces medially upward, while the inferior articular facet  31  (see  FIG. 3 ) faces laterally downward. When adjacent vertebrae  12  are aligned, the facets  30 ,  31 , which are capped with a smooth articular cartilage and encapsulated by ligaments, interlock to form a facet joint  32 . The facet joints are apophyseal joints that have a loose capsule and a synovial lining.  
         [0055]     As discussed, the facet joint  32  is comprised of a superior facet and an inferior facet (shown in  FIG. 4 ). The superior facet is formed in the vertebral level below the joint  32 , and the inferior facet is formed in the vertebral level above the joint  32 . For example, in the L 4 -L 5  facet joint shown in  FIG. 3 , the superior facet of the joint  32  is formed by bony structure on the L 5  vertebra (i.e., a superior articular surface and supporting bone  26  on the L 5  vertebra), and the inferior facet of the joint  32  is formed by bony structure on the L 4  vertebra (i.e., an inferior articular surface and supporting bone  28  on the L 4  vertebra). The angle formed by a facet joint located between a superior facet and an inferior facet changes with respect to the midline depending upon the location of the vertebral body along the spine. The facet joints do not, in and of themselves, substantially support axial loads unless the spine is in an extension posture (lordosis). As would be appreciated by those of skill in the art, the orientation of the facet joint for a particular pair of vertebral bodies changes significantly from the thoracic to the lumbar spine to accommodate a joint&#39;s ability to resist flexion-extension, lateral bending, and rotation.  
         [0056]     An intervertebral disc  34  located between each adjacent vertebra  12  (with stacked vertebral bodies shown as  14 ,  15  in  FIG. 3 ) permits gliding movement between the vertebrae  12 . The structure and alignment of the vertebrae  12  thus permit a range of movement of the vertebrae  12  relative to each other.  FIG. 4  illustrates a posterolateral oblique view of a vertebrae  12 , further illustrating the curved surface of the superior articular facet  30  and the protruding structure of the inferior facet  31  adapted to mate with the opposing superior articular facet. As discussed above, the position of the inferior facet  31  and superior facet  30  varies on a particular vertebral body to achieve the desired biomechanical behavior of a region of the spine.  
         [0057]     Thus, overall the spine comprises a series of functional spinal units that are a motion segment consisting of two adjacent vertebral bodies, the intervertebral disc, associated ligaments, and facet joints. See Posner, I, et al. “A biomechanical analysis of the clinical stability of the lumbar and lumbosacral spine.” Spine 7:374-389 (1982).  
         [0058]     As previously described, a natural facet joint, such as facet joint  32  ( FIG. 3 ), has a superior facet  30  and an inferior facet  31 . In anatomical terms, the superior facet of the joint is formed by the vertebral level below the joint, which can thus be called the “caudal” portion of the facet joint because it is anatomically closer to the tail bone or feet of the person. The inferior facet of the facet joint is formed by the vertebral level above the joint, which can be called the “cephalad” portion of the facet joint because it is anatomically closer to the head of the person. Thus, a device that, in use, replaces the caudal portion of a natural facet joint (i.e., the superior facet  30 ) can be referred to as a “caudal” device. Likewise, a device that, in use, replaces the cephalad portion of a natural facet joint (i.e., the inferior facet  31 ) can be referred to a “cephalad” device.  
         [0059]     When the processes on one side of a vertebral body  14  are spaced differently from processes on the other side of the same vertebral body, components of the devices on each side would desirably be of differing sizes as well to account for anatomical difference that can occur between patients. Moreover, it can be difficult for a surgeon to determine the precise size and/or shape necessary for an implantable device until the surgical site has actually been prepared for receiving the device. In such case, the surgeon typically can quickly deploy a family of devices possessing differing sizes and/or shapes during the surgery. Thus, embodiments of the spinal devices of the present invention include modular designs that are either or both configurable and adaptable. Additionally, the various embodiments disclosed herein may also be formed into a “kit” or system of modular components that can be assembled in situ to create a patient specific solution. As will be appreciated by those of skill in the art, as imaging technology improves, and mechanisms for interpreting the images (e.g., software tools) improve, patient specific designs employing these concepts may be configured or manufactured prior to the surgery. Thus, it is within the scope of the invention to provide for patient specific devices with integrally formed components that are pre-configured.  
         [0060]     A configurable modular device design, such as the one enabled by this invention, allows for individual components to be selected from a range of different sizes and utilized within a modular device. One example of size is to provide caudal and cephalad stems of various lengths. A modular implantable device design allows for individual components to be selected for different functional characteristics as well. One example of function is to provide stems having different surface features and/or textures to provide anti-rotation capability. Other examples of the configurability of modular implantable device of the present invention as described in greater detail below.  
         [0061]     Implantable devices of the present invention are configurable such that the resulting implantable spinal device is selected and positioned to conform to a specific anatomy or desired surgical outcome. The adaptable aspects of embodiments of the present invention provide the surgeon with customization options during the implantation or revision procedure. It is the adaptability of the present device systems that also provides adjustment of the components during the implantation procedure to ensure optimal conformity to the desired anatomical orientation or surgical outcome. An adaptable modular device of the present invention allows for the adjustment of various component-to-component relationships. One example of a component-to-component relationship is the rotational angular relationship between a crossbar mount and the crossbar. Other examples of the adaptability of modular device of the present invention as described in greater detail below. Configurability may be thought of as the selection of a particular size of component that together with other component size selections results in a “custom fit” implantable device. Adaptability then can refer to the implantation and adjustment of the individual components within a range of positions in such a way as to fine tune the “custom fit” devices for an individual patient. The net result is that embodiments of the modular, configurable, adaptable spinal device and systems of the present invention allow the surgeon to alter the size, orientation, and relationship between the various components of the device to fit the particular needs of a patient during the actual surgical procedure.  
         [0062]     In order to understand the configurability, adaptability and operational aspects of the invention, it is helpful to understand the anatomical references of the body  50  with respect to which the position and operation of the devices, and components thereof, are described. There are three anatomical planes generally used in anatomy to describe the human body and structure within the human body: the axial plane  52 , the sagittal plane  54  and the coronal plane  56  (see  FIG. 5 ). Additionally, devices and the operation of devices are better understood with respect to the caudal  60  direction and/or the cephalad direction  62 . Devices positioned within the body can be positioned dorsally  70  (or posteriorly) such that the placement or operation of the device is toward the back or rear of the body. Alternatively, devices can be positioned ventrally  71  (or anteriorly) such that the placement or operation of the device is toward the front of the body. Various embodiments of the spinal devices and systems of the present invention may be configurable and variable with respect to a single anatomical plane or with respect to two or more anatomical planes. For example, a component may be described as lying within and having adaptability in relation to a single plane. For example, a stem may be positioned in a desired location relative to an axial plane and may be moveable between a number of adaptable positions or within a range of positions. Similarly, the various components can incorporate differing sizes and/or shapes in order to accommodate differing patient sizes and/or anticipated loads.  
         [0063]     Turning now to  FIG. 6 , an isometric view of a modular, configurable and adaptable implantable spinal arthroplasty device  100  is depicted. The spinal arthroplasty device  100  is illustrated implanted into vertebral bodies  14 .  
         [0064]     The arthroplasty device  100  and the various other devices disclosed herein can be formed of a variety of materials. For example, where the devices have bearing surfaces (i.e. surfaces that contact another surface), the surfaces may be formed from biocompatible metals such as cobalt chromium steel, surgical steel, titanium, titanium alloys, tantalum, tantalum alloys, aluminum, etc. Suitable ceramics and other suitable biocompatible materials known in the art can also be used. Suitable polymers include polyesters, aromatic esters such as polyalkylene terephthalates, polyamides, polyalkenes, poly(vinyl) fluoride, PTFE, polyarylethyl ketone, and other materials that would be known to those of skill in the art. Various alternative embodiments of the spinal arthroplasty device could comprise a flexible polymer section (such as a biocompatible polymer) that is rigidly or semi rigidly fixed to the adjacent vertebral bodies whereby the polymer flexes or articulates to allow the vertebral bodies to articulate relative to one another.  
         [0065]     The spinal arthroplasty device  100  includes a pair of cephalad translaminar anchors  105 ,  105 ′ and a pair of caudal pedicle anchors  110 ,  110 ′. The caudal pedicle anchors  110 ,  110 ′ are supplemented with a crossbar  115 . In this exemplary embodiment, translaminar anchors  105 ,  105 ′ each support a spherical cephalad bearing surface  120 ,  120 ′ mounted on their lower ends and held flush to the cephalad facet. Pedicle anchors  110 ,  110 ′ each support a concave caudal bearing surface  125 ,  125 ′ adjacent to a cephalad bearing surface  120 ,  120 ′. In this embodiment the natural facet joints of the spine ( FIG. 3, 32 ) are replaced by the cooperative metal-on-metal (e.g. cobalt chromium) operation of the cephalad bearing surfaces  120 ,  120 ′ with the caudal bearing surfaces  125 ,  125 ′. The components of the spinal facet arthroplasty device  100  are designed to provide appropriate configurability and adaptability for the given disease state, patient specific anatomy and spinal level where the implant occurs.  
         [0066]     Each end of the crossbar  115  may be mounted to a caudal pedicle anchor  110 ,  110 ′ with a multi-axis tulip  130 ,  130 ′. A crossbar  115  may be selected from a variety of straight, curved or complex shaped crossbars depending on the particular application and anatomy of the patient.  
         [0067]     Another implantable arthroplasty device  200  is illustrated in  FIGS. 7-9 .  FIG. 7  shows the artificial joint structure mounted to the pedicles of a vertebra for replacing the natural facets (see  FIG. 4, 30  and  30 ′). The caudal structure  200  is designed to mate with a cephalad structure or structures, similar to the embodiment shown in  FIG. 6 . Caudal structure  200  includes caudal pedicle anchors  210 ,  210 ′. The caudal pedicle anchors  210 ,  210 ′ are supplemented with a crossbar  215 . In this embodiment, crossbar  215  includes three bends to avoid adjacent spinal anatomy. Pedicle anchors  210 ,  210 ′ each support a concave caudal bearing surface  225 ,  225 ′.  
         [0068]     As best seen in  FIG. 9 , caudal bearing surfaces  225 ,  225 ′ are formed on modular bearing elements  230 ,  230 ′. Modular bearing elements  230 ,  230 ′ in turn are connected to pedicle anchors  210 ,  210 ′, such as with mating tapered dovetail surfaces  235 ,  240  as shown.  
         [0069]     As shown in  FIGS. 8 and 9 , pedicle anchors  210 ,  210 ′ are configured to be mounted to lamina pedicles with pedicle screws  245 . Pedicle screws  245  include a driver portion  250  to allow the screw to be rotatably driven into the vertebra with a mating driving tool (not shown). Once pedicle screw  245  is placed in the vertebra, pedicle anchor body  255  may be slidably attached to the head of screw  245 , such as by a T-shaped slot  260  in body  255  inter-engaging with a flange  265  on the screw head as shown. Crossbar lock  270  may then be placed in the bore of pedicle anchor body  255 . Crossbar lock  270  may include a groove  275  formed in one end for receiving crossbar  215 . The entire pedicle anchor assembly  210  may be secured by inserting threaded fastener  280  in the bore of pedicle anchor body  255  over crossbar  215  and tightening it down. As fastener  280  is turned in the threaded upper portion of the bore of body  255 , fastener  280  bears down on crossbar  215 . Crossbar  215  in turn bears down on crossbar lock  270 , which bears down on the head of screw  245 , thereby locking the crossbar  215 , anchor body  255 , and bearing element  230  onto the pedicle screw  245 .  
         [0070]     Referring now to  FIGS. 10-12 , another embodiment of translaminar cephalad anchors  300  is shown. Each anchor  300  comprises a pin  305 , a cap  310 , a spring washer  315  and a nut  320 . Pin  305  is provided with a knob portion  325  at one end and a first threaded portion  330  and a second threaded portion  335  adjacent an opposite end. Cap  310  includes a recess  340  for receiving the knob portion  325  of pin  305 . Cap  310  can lock onto knob portion  325  by utilizing a snap fit or by having a key-hole shaped lateral access channel in the cap that the knob portion  325  may slide into. Such an arrangement allows some angular misalignment between cap  310  and pin  305 . In some embodiments, cap  310  is provided with teeth  345  around its outer periphery, as shown in  FIG. 11 , to allow cap  310  to better grip the outer surface of the lamina.  
         [0071]     To install anchors  300  in a vertebra, the inferior facets are removed to leave a generally flat mounting surface  350  as shown. Transverse holes are drilled in the lamina as shown to receive pins  305 . A counterbore may also be made in the lower side of each hole to receive a portion of cap  310 , as best seen in  FIG. 12 . Cap  310  may be connected to the knob portion  325  of a pin  305  before it is inserted into the hole. Spring washer  315  may then be placed over the portion of pin  305  protruding from the opposite end of the hole and secured by tightening nut  320  on the second threaded portion  335  of pin  305  until spring washer  315  is snug against the bone.  
         [0072]     Spring washer  315  is configured in a petal design to allow the washer edges to conform to an irregular bone surface. The springiness of the washer desirably creates tension which better secures the device to the bone. The washer can be used at any location where a device is adapted to engage bone and is suitable for use with any of the embodiments disclosed herein. The washer may also incorporate a textured or bony in-growth surface to facilitate bony fixation.  
         [0073]     Nut  320  may be provided with a spherical surface on one or both sides as shown. Such a spherical surface may engage with spring washer  315  to allow the washer to better conform to a bone surface that is not completely perpendicular to pin  305 . In this embodiment, once nut  320  is tightened against spring washer  315 , the first threaded portion of pin  305  is exposed to allow additional hardware to be attached to anchor  300 , if desired. Cap  310  itself may serve as a cephalad bearing surface for creating an artificial facet joint, or it may be used to secure other such hardware.  
         [0074]     Referring now to  FIG. 13 , another embodiment of a cephalad anchor  400  is shown. In this embodiment, the fixation element comprises a cable  405  and cannulated tube  410 , with the cannulated tube passing through the targeted bony structure of the lamina and/or spinous process and encircling the cable along at least a portion of its length. The cable  405  would desirably facilitate flexibility of the implanted artificial facet joint, while the cannulated tube would, among other things, significantly increase the cross-sectional surface area of the cable, thereby reducing the opportunity of the cable to “pull-out” of the bone laterally. A bearing engages one end of the cable and an anchor engages the opposing end. Alternatively, the fixation element may comprise a solid rod  505  having a flexible or adjustable engagement member  510  (see  FIG. 14 ) allowing for some variation between the orientation of the cephalad bearing and the longitudinal axis of the rod. In these embodiments, the cross-section of the cable/rod is desirably of a sufficient size to prevent the force applied by the cable in the lamina from exceeding the ability of the lamina to resist the force; i.e., a cable of insufficient diameter could present a force great enough to tear through the lamina. Moreover, the cross-section of the cable/rod need not be circular, but may be any shape, including irregular shapes, to desirably present a surface to the surrounding bone that is (1) large enough (and/or flat enough) to resist “pull-out” through the bone (e.g. along the length of the cable), (2) non-circular to resist rotation of the cable/rod, and/or (3) of increased surface area to facilitate bony in-growth into the cable/rod. The anchors can further be adapted to provide internal threads such that the anchors can be secured to the cable by screwing the anchor onto a threaded end of the cable, or can be adapted to provide an aperture that enables the anchor to be snap fit onto the end of the cable. Other configurations will be apparent to those skilled in the art.  
         [0075]     Referring now to  FIGS. 15 and 16 , isometric views of an implantable spinal arthroplasty device  600  are depicted with the device attached to the L 5  level and sacrum of a spine ( FIG. 15 ), and with the device shown by itself ( FIG. 16 ). At certain levels of the spine, such as in the lumbosacral region, devices and methods of attaching them that work well at other levels of the spine may not work well or at all. For example, the thickness and/or orientation of a lamina in the lumbosacral region may not be sufficient to support a translaminar cephalad anchor as described above. Accordingly, new devices and attachment methods may be needed when attaching arthroplasty devices in the lumbosacral region.  
         [0076]     Device  600  comprises a cephalad portion  605  and a caudal portion  610 . In this embodiment, the cephalad portion  605  includes two arms  615 ,  615 ′ that have a hooked portion  620 ,  620 ′ on their upper ends that engage the upper edge of the lamina (such as the lamina of L 5  as shown). When device  600  is implanted as depicted in  FIG. 15 , arms  615 ,  615 ′ reside on opposite sides of the spinous process, and in this embodiment are inter-connected by a crossbar  625  which engages the underside of the spinous process. Crossbar  625  may be secured to arms  615 ,  615 ′ by clamp screws, set screws, crimping, adhesive, or other methods known to those skilled in the art. Crossbar  625  may alternatively be formed from a plurality of pieces and/or formed integrally with arms  615 ,  615 ′. A variety of crossbar and/or arm configurations may be provided in the operating room such as in kit form to allow a custom cephalad portion  605  to be created to suit a particular application and/or anatomy of each patient.  
         [0077]     Mounting screws  630  may be located on arms  615 ,  615 ′ for further securing cephalad portion  605  of device  600 . Screws  630  may be configured to penetrate the lamina to hold arms  615 ,  615 ′ down against the lamina. Alternatively, screws  630  may be configured with flat tips as shown to press down against the lamina, thereby securing cephalad portion  605  on the vertebra by driving the distal regions of hooked portions  620 ,  620 ′ against the underside of the lamina and the crossbar  625  against the underside of the spinous process.  
         [0078]     In this embodiment, the ends of arms  615 ,  615 ′ opposite the hooked portions  620 ,  620 ′ are bent laterally outward and anteriorly, and comprise spherical cephalad bearing elements  635 ,  635 ′. Bearing elements  635 ,  635 ′ are slidably received in caudal cups  640 ,  640 ′ which are part of the caudal portion  610  of device  600 . In the embodiment shown, caudal cups  640 ,  640 ′ are separate elements from caudal anchor bases  645 ,  645 ′ to further increase the modularity of implantable device  600 . Caudal cups  640 ,  640 ′ may be selected from a variety of different caudal cups to suit the particular application and/or patient anatomy, and may be attachable to the caudal anchor bases  645 ,  645 ′ by interlocking surfaces  650  and  655 . Caudal anchor bases  645 ,  645 ′ may be attached to one or more vertebra, such as S 1  as shown, with anchor screws  660  and  665 . Anchor screws  660  and  665  may be set at different angles as shown-to take advantage of adjacent bone structures in providing more secure anchoring. While a single anchor screw may be used to secure each anchor base  645 ,  645 ′, the use of at least two anchor screws for each base ensures that the base will not spin about the screw axis when subjected to a moment load.  
         [0079]     Referring now to  FIG. 17 , an isometric view of an implantable spinal arthroplasty device  700  is depicted with the device attached to the L 5  vertebra and sacrum of a spine. Device  700  comprises a cephalad portion  705  and a caudal portion  710 . Similar to the embodiment of  FIGS. 15 and 16 , cephalad portion  705  of device  700  is secured to a vertebra at least in part by hooking over an upper edge of its lamina and under the spinous process. Supralaminar hook body  715  may be formed as an integral unit having one or more hook members for extending from a cephalad surface to a caudal surface of the lamina. Anchor screws  720  may be provided for screwing into or against the lamina, spinous process, or a portion of the vertebra where the spinous process joins the lamina.  
         [0080]     A spinous process clamp or crossbar  725  may be connected to the hook body  715  by a pair of connecting arms  730 ,  730 ′. Connecting arms  730 ,  730 ′ may be integrally formed with hook body  715 , or provided as separate elements as shown to allow different length arms to be selected depending on the application and/or particular anatomy of the patient. Crossbar  725  may be secured to connecting arms  730 ,  730 ′ with fasteners  735 ,  735 ′. In this embodiment, fasteners  735 ,  735 ′ have external threads for engaging internal thread formed within bores in crossbar  725 . As fasteners  735 ,  735 ′ are tightened down, they compress connecting arms  730 ,  730 ′ against a complementary shaped surface formed in crossbar  725 , or against a lock insert such as crossbar lock  270  shown in  FIGS. 8 and 9  and described above. Once cephalad portion  705  is assembled around the spinous process, it may be secured in place by tightening anchor screws  720  to drive crossbar  725  against the underside of the spinous process and hook portions of the hook body  715  against the underside of the lamina.  
         [0081]     Outriggers  740 ,  740 ′ may be adjustably attached to the laterally outward ends of crossbar  725 , such as with multi-axis joints  745 ,  745 ′. Cephalad bearing elements  750 ,  750 ′ may be mounted on the laterally outward ends of outriggers  740 ,  740 ′ such that they can be positioned to engage with mating caudle cups  755 ,  755 ′ and locked into position relative to crossbar  725  by multi-axis joints  745 ,  745 ′. Caudal cups  755 ,  755 ′ may be mounted to the sacrum or other vertebra in a manner similar to that shown in  FIGS. 15 and 16  as described above, and/or as will be further described below.  
         [0082]     Referring to  FIGS. 18-21 , additional caudal anchoring details are shown.  FIG. 18  shows a caudal bearing assembly  800  attached to a sacrum. Caudal assembly  800  may be used in conjunction with any of the cephalad assemblies disclosed or referred to herein to form artificial facet joints, particularly between an L 5  vertebra and a sacrum. Caudal assembly  800  of this embodiment is formed by a pair of caudle cups  805 ,  805 ′ mounted on bases  810 ,  810 ′, which in turn are mounted to the spine by anchor screws  815  and  820 . With this arrangement, bases  810 ,  810 ′ may be securely mounted either with bases contacting the spine, or with bases elevated from a surface of the spine as shown. Such a mounting system allows for greater flexibility in positioning the caudal cups  805 ,  805 ′ where they are desired in each procedure. In the embodiment shown, bases  810 ,  810 ′ are L-shaped, although other layouts may also be used.  
         [0083]     As shown in  FIG. 19 , anchor screws  815  and  820  each have a pair of flats,  825  and  830  respectively, so that they may be turned with a wrench or other tool when inserting them into the bone. Each screw  815  and  820  also has a shoulder portion,  835  and  840  respectively, which provides a surface for supporting the bottom of a base  810 ,  810 ′. Anchor screw  815  includes an internally threaded bore  845  for receiving a screw  850 . Screw  850  passes through hole  855  in a base  810 ,  810 ′ and into threaded bore  845  to tighten the base down onto shoulder portion  835 . Anchor screw  820 , on the other hand, has an externally threaded portion  860  extending above flats  830  such that it may be received in hole  865  in a base  810 ,  810 ′. Nut  870  may then be engaged with threaded portion  860  to tighten base  810 ,  810 ′ down onto shoulder portion  840  of anchor screw  820 . With base  810 ,  810 ′ secured to anchor screws  815  and  820  in this manner, it may be securely positioned on or above the bone. The same type of screw  815 ,  820  or other screw may be used at all locations if desired.  
         [0084]     Referring to  FIGS. 20 and 21 , additional embodiments of caudal cups  875  and  880  are shown. Caudal cups  805 ,  805 ′ (both shown in  FIG. 18 ),  875  and  880  may be attached to a base  810 ,  810 ′ using locking attachment surfaces  885  which mate with complementary shaped surfaces (not shown) located on bases  810 ,  810 ′. As seen in  FIGS. 20 and 21 , the bearing surfaces  890  and  895  of caudal cups  875  and  880  each have different configurations. For example, the bearing surface  890  of caudal cup  875  shown in  FIG. 20  has more symmetrical anterior and posterior portions that are also inclined at shallower angles than the corresponding portions of bearing surface  895  of caudal cup  880  shown in  FIG. 21 . Many other variations of caudal cups may be provided in kit form for use in operating rooms. As will be appreciated by those skilled in the art, particular configurations of bearing surfaces may be selected to provide desired types and ranges of motion depending on the mounting position and other factors of each application.  
         [0085]     Referring to  FIG. 22 , an isometric view of an implantable spinal arthroplasty device  900  is depicted with the device attached to the L 5  vertebra and sacrum of a spine. Device  900  comprises a cephalad portion  905  and a caudal portion  910 . Cephalad portion  905  comprises a pair of anchor screw assemblies  915 ,  915 ′ which are attached by screws to the pedicles of the L 5  vertebra in this embodiment. Anchor screw assemblies  915 ,  915 ′ are configured to receive ends of crossbar  920  which spans between the assemblies. Assemblies  915 ,  915 ′ are also configured to receive the proximal ends of cephalad bearing arms  925 ,  925 ′. Generally spherically shaped cephalad bearing members  930 ,  930 ′ may be provided at the distal ends of arms  925 ,  925 ′ for engaging with caudal bearing cups of caudal portion  910 .  
         [0086]     Crossbar  920  provides additional stability to anchor screw assemblies  915 ,  915 ′, such as securing them from rotational moments caused by forces on cephalad bearing members  930 ,  930 ′ at the distal ends of arms  925 ,  925 ′. Crossbar  920  may be straight, curved or have a complex shape to avoid adjacent anatomy, such as the spinous process of an adjacent vertebra. Anchor screw assemblies  915 ,  915 ′ may be constructed and mounted in a manner similar to that of anchors  210 ,  210 ′ shown in  FIGS. 7-9  and described above. Further construction details of assemblies  915 ,  915 ′ may be obtained from U.S. patent application publication number 2005/0240265, published Oct. 27, 2005, for example in  FIG. 16A-16F . Caudal portion  910  of device  900  may be constructed and mounted in a similar manner to the previous embodiments described above.  
         [0087]     Referring to  FIG. 23 , an isometric view of a hybrid, multi-level implantable spinal arthroplasty device  1000  is depicted with the device attached to the L 4  and L 5  vertebrae and sacrum of a spine. While shown and described at this spinal location in this exemplary embodiment, device  1000  or a modified version thereof may be employed at other locations along the spine. Arthroplasty device  1000  comprises three main portions: a first or cephalad portion  1005 , a second or middle portion  1010 , and a third or caudal portion  1015 . Cephalad portion  1005  and middle portion  1010  cooperate to form artificial facet joints  1020 . In this embodiment, artificial joints  1020  replace the natural facet joints that have been removed from the L 4 -L 5  level of the spine. Similarly, middle portion  1010  and caudal portion  1015  cooperate to form artificial facet joints  1025 . In this embodiment, artificial joints  1025  replace the natural facet joints that have been removed from the L 5 -S 1  level of the spine. In this manner, middle portion  1010  of device  1000  serves as the caudal portion of joints  1020  and the cephalad portion of joints  1025 . As previously mentioned, this arrangement may be used at other levels of the spine, and may involve more than three vertebrae such as by adding additional sections.  
         [0088]     In the embodiment shown in  FIG. 23 , cephalad portion  1005  comprises translaminar cephalad anchors  300 . These may be the same as described above in conjunction with  FIGS. 10-12 . Alternatively, other translaminar cephalad anchor designs may be used, such as those shown in  FIGS. 13 and 14 . Anchors for cephalad bearing surfaces  310  may also be mounted to the pedicles of the vertebra, in this example vertebra L 4 .  
         [0089]     Middle portion  1010  and caudal portion  1015  of device  1000  may be constructed in manner similar to that of device  900  shown in  FIG. 22  and described above. However, in contrast to device  900 , the anchor screw assemblies  1030 ,  1030 ′ of device  1000  include medially extending arms  1035 ,  1035 ′ for supporting caudal bearing members  1040 ,  1040 ′. Caudal bearing members  1040 ,  1040 ′ are positioned adjacent to and cooperate with cephalad bearing surfaces  310  to form artificial facet joints  1020 .  
         [0090]     Referring to  FIG. 24 , an isometric view of another hybrid, multi-level implantable spinal arthroplasty device  1100  is depicted. Device  1100  is similar to device  1000  described above, and is also shown in an exemplary embodiment attached to the L 4  and L 5  vertebrae and sacrum of a spine, although it may be used at other locations of the spine. Middle portion  1105  of this embodiment has two main differences from the middle portion  1010  of device  1000  shown in  FIG. 23 . First, arms  1110 ,  1110 ′ are mounted to crossbar  1115  rather than directly to anchor screw assemblies  1120 ,  1120 ′. This arrangement allows arms  1110 ,  1110 ′ and the cephalad bearing member  1125 ,  1125 ′ mounted on their distal ends to be laterally adjusted by sliding arms  1110 ,  1110 ′ along crossbar  1115  and locking them in place with fasteners  1130 ,  1130 ′. Second, anchor screw assemblies  1120 ,  1120 ′ are provided with two pairs of screws  1135 ,  1135 ′ and  1140 ,  1140 ′. Screws  1135 ,  1135 ′ serve to secure the ends of crossbar  1115  to anchor screw assemblies  1120 ,  1120 ′. Screws  1140 ,  1140 ′ serve to secure anchor screw assemblies  1120 ,  1120 ′ to the vertebra. In this embodiment, screws  1140 ,  1140 ′ screw into the pedicles of the L 5  vertebra. In other embodiments, multiple screws may be used to secure each anchor screw assembly to the vertebra.  
         [0091]     Referring to  FIG. 25 , an isometric view of yet another hybrid, multi-level implantable spinal arthroplasty device  1200  is depicted. Device  1200  is similar to devices  1000  and  1100  described above. Middle portion  1205  of device  1200  comprises cephalad bearing arms  1210 ,  1210 ′ which are adjustably secured at their proximal ends to anchor screw assemblies  1215 ,  1215 ′. Cephalad bearing members  1220 ,  1220 ′ are located at the distal ends of arms  1210 ,  1210 ′. Each end of crossbar  1225  is adjustably mounted to one of the arms  1210 ,  1210 ′. With this modular and adjustable arrangement, the position of cephalad bearing members  1220 ,  1220 ′ may be located precisely with respect to caudal bearing cups  1230 ,  1230 ′ and locked into place.  
         [0092]     In the embodiment shown in  FIG. 25 , caudal bearing cups  1230 ,  1230 ′ face laterally outward rather than medially. Accordingly, unlike the previous example provided above, cephalad bearing arms  1210 ,  1210 ′ enter caudal cups  1230 ,  1230 ′ from the laterally outward side rather than from the medial side. Caudal cups  1230 ,  1230 ′ also have a G-shaped cross-section which creates an overhanging posterior surface  1235 ,  1235 ′ over a portion of caudal cups  1230 ,  1230 ′. Bearing surface  1235 ,  1235 ′ prevents movement of a vertebra, in this case L 5 , in a posterior direction when in its natural state. It is to be understood that features of any of the embodiments disclosed herein may be used in combination with other embodiments.  
         [0093]     In some embodiments, the devices described herein and variations thereof may be implanted in conjunction with one or more artificial discs. In this way, correction of spinal degradation in one part of the spine does not cause spinal loads to be transmitted to adjacent spinal members that may also be failing. The various devices disclosed herein may be implanted before, after or in conjunction with disc replacement devices.  
         [0094]     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.