Abstract:
An orthopedic implantable device articulately connecting a first spinal vertebra to an adjacent second spinal vertebra includes a pair of first components adapted to be attached to locations left and right of a midline of the first vertebra, respectively; and a pair of second components adapted to be attached to locations left and right of a midline of the second vertebra, respectively. Each of the first components includes a body and a male articulation member attached to the first component body and each of the second components includes a body and a female articulation member attached to the second component body. The first components are articulately connected to the second components by engaging the male articulation members to the female articulation members, thereby articulately connecting the first vertebra to said second vertebra along lines left and right of the midlines, respectively.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS  
       [0001]    This application is a continuation in part of U.S. application Ser. No. 10/364847 filed on Feb. 11, 2003 and entitled APPARATUS AND METHOD FOR THE REPLACEMENT OF POSTERIOR VERTEBRAL ELEMENTS the contents of which are expressly incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to an apparatus and a method for connecting spinal vertebrae, and more particularly to an apparatus and a method that connects spinal vertebrae while preserving spinal stability and mobility.  
         BACKGROUND OF THE INVENTION  
         [0003]    The human spine  29  comprises individual vertebrae  30  that interlock with each other to form a spinal column, shown in FIG. 1A. Referring to FIGS. 1B, 1C, and  1 D, each vertebra  30  has a cylindrical bony body (vertebral body)  32 , two pedicles  48  extending from the vertebral body  32 , a lamina  47  extending from the pedicles  48 , three winglike projections (two transverse processes  33 ,  35  extending from the pedicles  48  and one spinous process  34  extending from the lamina  47 ), pars interarticularis  36 , two superior facets  46  extending from the pedicles  48  and two inferior facets  45  extending from the lamina  47 . The pars interarticularis  36  connects the superior  46  and inferior  45  facets on either side of the spinous process  34 . The bodies of the vertebrae  32  are stacked one on top of the other and form the strong but flexible spinal column. The spinous process  34 , lamina  47 , pars interarticularis  36 , superior facets  46 , inferior facets  45 , transverse processes  33 , and pedicles  48  are positioned so that the space they enclose forms a tube, i.e., the spinal canal  37 . The spinal canal  37  houses and protects the spinal cord and other neural elements. A fluid filled protective membrane, the dura  38 , covers the contents of the spinal canal. The spinal column is flexible enough to allow the body to twist and bend, but sturdy enough to support and protect the spinal cord and the other neural elements.  
           [0004]    The vertebrae  30  are separated and cushioned by thin pads of tough, resilient fiber known as inter-vertebral discs  40 . Inter-vertebral discs  40  provide flexibility to the spine and act as shock absorbers during activity. There is a small opening (foramen)  42  between each vertebra  30 , through which nerves  44  pass and go to different body parts. When the vertebrae are properly aligned the nerves  44  pass through without a problem. However, when the vertebrae are misaligned or a constriction  45  is formed in the spinal canal, the nerves get compressed  44   a  and may cause back pain, leg pain or other neurological disorders. Disorders of the spine that may cause misalignment of the vertebrae or constriction of the spinal canal include spinal injuries, infections, tumor formation, herniation of the inter-vertebral discs (i.e., slippage or protrusion), arthritic disorders, and scoliosis. In these pathologic circumstances, surgery may be tried to either decompress the neural elements and/or fuse adjacent vertebral segments. Decompression may involve laminectomy, discectomy, or corpectomy. Laminectomy involves the removal of part of the lamina  47 , i.e., the bony roof of the spinal canal. Discectomy involves removal of the inter-vertebral discs  40 . Corpectomy involves removal of the vertebral body  32  as well as the adjacent disc spaces  40 . Laminectomy and corpectomy result in central exposure of the dura  38  and its contents. An exposed dura  38  puts the neural elements and spinal cord at risk from direct mechanical injury or scarring from overlying soft tissues. Scarring is considered a major cause for failed back syndrome in which patients continue to have back and leg pain after spinal surgery. Current methods to decrease the risk of developing this syndrome include covering the dura with fat harvested from the patient&#39;s subcutaneous tissues or using a synthetic material. However, no material as yet has been used that completely or significantly prevents scarring of the dura and nerve roots after spine surgery in humans.  
           [0005]    Furthermore, laminectomy predisposes the patient to instability through the facet joints and may lead to post-laminectomy kyphosis (abnormal forward curvature of the spine), pain, and neurological dysfunction. Therefore the surgeon needs to stabilize the spine after laminectomy procedures and after corpectomy. One spine stabilization method is fusion. Fusion involves the fixation of two or more vertebrae. Fusion works well because it stops pain due to movement of the intervertebral discs  40  or facets  45 ,  46 , immobilizes the spine, and prevents instability and or deformity of the spine after laminectomy or corpectomy. However, spinal fusion limits spinal mobility. Maintaining spinal mobility may be preferred over fusion in some cases to allow more flexibility of the spine and to decrease the risk of junction problems above and below the level of the fixation due to increased stress.  
           [0006]    An arthritic facet joint may also cause back pain. Since the majority of the motion along the spine occurs at the facet joints, fusing the diseased facet would often relieve pain but again at a high cost of fusing across at least one spinal segment thus preventing motion and effectively increasing stresses at the adjacent facet joints. Increased stresses predispose facet joints to accelerated arthritis, pain, and instability requiring additional surgery to fuse these levels. This cyclic process results in an overall decreased mobility of the spine. Therefore, it is an attractive alternative to attempt to replace the diseased facet without resorting to fusion, thus avoiding significant limitation in mobility of the spine. The obvious solution would be to replace the opposing surfaces of each facet to preserve motion between the surfaces. However, any efforts to replace the facets at their natural location necessitate destroying the facet capsule and risks producing an unstable joint. Therefore, it is desirable to achieve spine stabilization that preserves mobility, and does not cause tissue scarring or destroy the facet capsule. It is also desirable to be able to implant the stabilization device percutaneously utilizing minimally invasive surgery.  
         SUMMARY OF THE INVENTION  
         [0007]    In general, in one aspect, the invention features an orthopedic implantable device articulately connecting a first spinal vertebra to an adjacent second spinal vertebra. The orthopedic implantable device includes a pair of first components adapted to be attached to locations left and right of a midline of the first vertebra and a pair of second components adapted to be attached to locations left and right of a midline of second vertebra. Each of the first components comprises a body and a male articulation member attached to the first component body and each of the second components comprises a body and a female articulation member attached to the second component body. The first components are articulately connected to the second components by engaging the male articulation members to the female articulation members, thereby articulately connecting the first vertebra to the second vertebra along lines left and right of the mentioned midlines, respectively.  
           [0008]    Implementations of this aspect of the invention may include one or more of the following features. The male articulation member may comprise a hook and the female articulation member may comprise a loop. The first component body may further comprise at least one female articulation member and the second component body may further comprise at least one male articulation member. The locations left and right of the midlines of the first and second vertebrae are selected from a group including a pedicle, transverse processes, facets, lamina, pars interarticularis, and vertebral body. The body of the first component may be attached to first and second pedicles of the first vertebra and the body of the second component may be attached to first and second pedicles of the second vertebra, respectively. The first and second components may be attached to the first and second vertebrae, respectively, via screws, wires, or hooks. The first component may be articulately connected to the second component via a hinge. The first and second components may have adjustable length and the length may be adjusted between 10 and 200 millimeters. The first and second components may be made of metal, plastic, ceramic, bone, polymers, composites, absorbable material, biodegradable material, and combinations thereof. The female articulation members may be formed within the second component bodies. The male articulation member may be a hook and the female articulation member may be a bar connecting opposite sides of a cavity formed within a bottom surface of the body.  
           [0009]    In general, in another aspect, the invention features a spine stabilization method articulately connecting a first vertebra to a second vertebra including the following steps. First providing a pair of first components and attaching the first components to locations left and right of the midline of the first vertebra, respectively. Each first component comprises a body and a male articulation member attached to the body. Next, providing a pair of second components and attaching the second components to locations left and right of the midline of the second vertebra, respectively. Each second component comprises a body and a female articulation member. Finally, articulately connecting the first component to the second component by engaging the male articulation members to the female articulation members.  
           [0010]    In general, in another aspect, the invention features a spine stabilization method connecting a first vertebra to a second vertebra including the following steps. First attaching first and second screws to first and second locations left and right of a midline, of the first vertebra, respectively. Next attaching third and fourth screws to first and second locations left and right of a midline of the second vertebra, respectively. Next providing a pair first components and a pair of second components. Each of the first components comprises a body and a male articulation member attached to the first component body. Each of the second components comprises a body and a female articulation member attached to the second component body. Next articulately connecting the first components to the second components by engaging the male articulation members to the female articulation members. Next attaching the bodies of the pair of first components to the first and second locations of the first vertebra via the first and second screws, respectively. Next, attaching the bodies of the pair of second components to the first and second locations of the second vertebra via the third and fourth screws, respectively. Finally, tightening of all said screws. This aspect of the invention may further include before attaching the bodies of the first and second components adjusting the length of the bodies of the first and second components.  
           [0011]    Among the advantages of this invention may be one or more of the following. The implantable spinal stabilization device stabilizes the spine, while allowing the patient to retain spinal flexibility by preserving motion between adjacent vertebras. This spinal stabilization device may be implanted percutaneously along the sides left and right of the spine utilizing minimally invasive surgery, i.e., without the need to make a large midline incision and stripping the erector spinae muscles laterally. There is also no need to remove the posterior elements of the veretebrae such as the spinous processes and lamina.  
           [0012]    The spinal stabilization device may be used for the treatment of a multitude of spinal disorders including facet arthritis and spinal stenosis. The implantable device has a compact structure and low profile.  
           [0013]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings and from the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Referring to the figures, wherein like numerals represent like parts throughout the several views:  
         [0015]    [0015]FIG. 1A is a side view of the human spinal column;  
         [0016]    [0016]FIG. 1B is an enlarged view of area A of FIG. 1A;  
         [0017]    [0017]FIG. 1C is an axial cross-sectional view of a lumbar vertebra;  
         [0018]    [0018]FIG. 1D is a perspective view of a lumbar vertebra;  
         [0019]    [0019]FIG. 2 is a schematic posterior view of an implantable spine stabilization device according to this invention;  
         [0020]    [0020]FIG. 3 is a posterior view of a spine stabilization component of the implantable spine stabilization device of FIG. 2;  
         [0021]    [0021]FIG. 4 is a perspective view of a lumbar vertebra with resected spinous process, lamina, and facet joints and the stabilization component of FIG. 3 attached to its pedicles;  
         [0022]    [0022]FIG. 4A is a cross-sectional view of FIG. 3 along AA′ plane;  
         [0023]    [0023]FIG. 5 is a perspective view of the spine stabilization component of FIG. 3;  
         [0024]    [0024]FIG. 5A is a cross-sectional view of FIG. 3 along BB′ plane;  
         [0025]    [0025]FIG. 6 is a cross-sectional side view of the spine stabilization device of FIG. 2 along midline  102 ;  
         [0026]    [0026]FIG. 7 is a posterior view of a spine stabilization component without a tail segment;  
         [0027]    [0027]FIG. 8 is a flow diagram depicting the method of applying the implantable spine stabilization device of this invention; and  
         [0028]    [0028]FIG. 9 is a schematic posterior view of another embodiment of an implantable spine stabilization device according to this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Referring to FIG. 2, an implantable spine stabilization device  100  connects vertebra  92  to adjacent vertebra  94  and vertebra  94  to adjacent vertebra  96 . The spine stabilization device  100  includes modular components  110 ,  120 , and  130 . Modular components  110 ,  120 , and  130  have circular ends  110   a  and  110   b ,  120   a  and  120   b ,  130   a  and  130   b , respectively, that attach to pedicles  92 A,  92 B,  94 A,  94 B,  96 A, and  96 B of vertebra  92 ,  94  and  96 , respectively, via pedicle screws  111   a ,  111   b ,  121   a ,  121   b ,  131   a , and  131   b , respectively. Modular components  110 ,  120 , and  130  replace the resected laminas, pars interarticularis, facets and spinous processes of the vertebra  92 ,  94 , and  96 , respectively. Modular component  110  is articulately connected to component  120  along the midline  102  of the device  100  and the corresponding vertebrae  92  and  94 , shown in FIG. 6. Similarly modular component  120  is articulately connected to component  130 . Additional modular components may be added to extend the spine stabilization device  100  in either caudad  272  or cephalad  270  directions. The modular structure of the spine stabilization device  100  allows a surgeon to replace laminas, facets, pars interarticularis, and spinous processes over any distance and orientation along the entire spine  29 .  
         [0030]    Referring to FIG. 3, modular component  110  comprises a lamina  114 , two circular ends  110   a ,  110   b  extending laterally from opposite sides of the lamina  114 , a tail segment  118  extending from the lower portion of the lamina  114 , and a spinous process  116  protruding posteriorly from the top surface of the lamina  114 . The lamina  114  has a width  81  and a length  82  that depend upon the distance between the pedicles  92 A and  92 B and the length of the vertebra  92 , respectively. The length  83  of the tail segment  118  depends upon the intervertebral distances. In one example, the width  81  is in the range between 20 millimeters and 80 millimeters, length  82  is in the range of 10 millimeters and 80 millimeters, length  83  is in the range of 4 millimeters and 60 millimeters and height  84  is in the range of 4 millimeters and 30 millimeters. Width  81 , length  82 , length  83  and height  84  have different values for the different type of vertebrae, including lumbar, thoracic, sacral and cervical.  
         [0031]    Referring to FIG. 3 and FIG. 5, pedicle screw  111   b  comprises a body portion  140 , a first head portion  142 , a second head portion  144 , and a head  146 . The body portion  140  of the pedicle screw  111   b  has helical threads on its exterior surface and screws into the vertebral body  32  through the pedicle  92 B. A hexagonal screwdriver (not shown) is inserted into a slot  148  formed on the head  146  of the pedicle screw  111   b  and is used to drive the screw  111   b  into the vertebral body  32 . The first head portion  142  is directly above the body portion  140  and has a smooth or serrated outer surface  143  for receiving the circular end  110   b  of modular component  110 . End  110   b  has an aperture  152   b  that allows end  110   b  to slide over the pedicle screw  111   b . The second head portion  144  has a threaded outer surface for receiving locking nut  112   b . Locking nut  112   b  slides over the head  146  of the pedicle screw  111   b  and screws around the threaded outer surface of the second head portion  144 , thus securely attaching the circular end  110   b  to pedicle screw  111   b . In one example, pedicle screw  111   a  has a length  220  of 57 millimeters and a diameter  222  of 6.5 millimeters.  
         [0032]    Referring to FIG. 4 and FIG. 4A, the cross-section of lamina  114  along AA′ has a U-shape and the roof  114   c  of the lamina (top of U-shape) is elevated above the spinal canal  37 . The sides  114   a  and  114   b  of the lamina  114  run first at a gentle slope downwards about 5 degrees and then drop more sharply at about 80 degrees to get to the pedicles  92 A and  92 B, respectively. The U-shape form of the lamina  114  provides space between the spine stabilization device  100  and the spinal canal  37  and is also designed to clear the facets  46  laterally, in case they were not previously resected. This arrangement covers the central spinal canal and protects the neural elements from scar tissue formation or mechanical damage. The lamina  114  has a flared lower portion that extends into the tail segment  118 .  
         [0033]    In the embodiment of FIG. 4A the width  81  of the lamina  114  is extended or contracted via mechanism  90 . In this embodiment the lamina  114  comprises a first segment  92  and a second segment  94 . Segment  94  is allowed to slide in the lateral direction  86  and can rotate around the axis  87 . The lateral motion of segment  94  allows the adaptation of the modular component  110  to vertebrae with various pedicle distances. The rotation of segment  94  around the axis  87  allows accurate positioning of the circular end  110   b  over the pedicle screw  111   b  and accommodates pedicles that are not perfectly aligned in the cephalo-caudad direction. Segments  94  and  92  have overlapping elongated slots  184 A and  184 B, respectively, extending through the thickness of the corresponding segment. A housing  182  slides over the overlapping segments  92  and  94 . Housing  182  has an elongated slot  186  that runs through the thickness of the housing  182  and is aligned with the elongated slots  184 A and  184 B. The position of the overlapping segments  92  and  94  and the housing  182  is secured via a screw  188  that is threaded through the elongated slots  184 A,  184 B, and  186 . In one example, the width  81  of the lamina  114  is 40 millimeters and it can be increased or decreased up to 8 millimeters via the two sliding mechanisms  90 . Circular ends  110   a ,  110   b  have apertures  152   a ,  152   b , respectively. Apertures  152   a  and  152   b  have serrated inner surfaces for receiving a pedicle screw with matching longitudinal serrations  143 , shown in FIG. 5. The top and/or bottom surfaces of circular ends  110   a ,  110   b  have radial extending grooves  88  that match the grooves  89  of the locking nuts  112   a ,  112   b.    
         [0034]    Referring to FIG. 5 and FIG. 5A, the posteriorly protruding spinous process  116  includes a cavity  115  formed in the bottom surface of the lamina  114  within the spinous process  116 . Inside the cavity  115  there is a horizontally extending bar  117  attached to opposite cavity walls  115   a ,  115   b . Referring to FIG. 6, the end of the tail segment  118  of modular component  110  forms a hook  119 . Hook  119  engages around the horizontal bar  117  of the adjacent modular component  120  and forms an articulated connection between the two modular components  110  and  120 . The cavity  115  is contoured to allow smooth gliding of the outer surface  118   a  of the tail segment  118  around the horizontal bar  117 .  
         [0035]    Referring to FIG. 7, a modular component  140  without the tail segment  118  is implanted to the pedicles on the vertebra that is below but adjacent to the lowest ( in the caudad direction  272 ) level that underwent either a laminectomy or facetectomy. This vertebra will still have its natural spinous process and ligamentous attachment to the next lower vertebra. This vertebral level will therefore provide stability to the end of the stabilization assembly  100  since this vertebral level will have preserved facets and ligamentous attachments.  
         [0036]    Referring to FIG. 8, a method  400  of using the spine stabilization device  100  comprises the following steps. Opening an incision in the patient&#39;s back, and exposing first and second vertebrae, the vertebra that is immediately above but adjacent to the first vertebra (cephalad direction), and the vertebra that is immediately below but adjacent to the second vertebra (caudad direction) ( 405 ). Performing laminectomy and/or facetectomy posteriorly of the first and second vertebrae ( 410 ). Placing pedicle screws within the pedicles of the first and second vertebra, the vertebra immediately above the first vertebra, and the vertebra immediately below the second vertebra ( 420 ). Engaging a first modular component to a second modular component. In one example, the modular components are as shown in FIG. 3. Placing the apertures of the two circular ends  110   a ,  110   b  of the first modular component over the two contralateral pedicle screws on the first vertebra, and adjusting the length and orientation of the two end segments  94  of the lamina ( 430 ). Placing the apertures of the two circular ends  110   a ,  110   b , of the second modular component over the two contralateral pedicle screws on the second vertebra, and adjusting the length and orientation of the two end segments  94  of the lamina ( 440 ). Engaging a third modular component without a tail segment, as shown in FIG. 7, to the tail of the second modular component, placing the apertures of the two circular ends  110   a ,  11   ab , of the third modular component over two contralateral pedicle screws on the vertebra that is immediately below the second vertebra, and adjusting the length and orientation of the two end segments  94  of the lamina ( 450 ). Engaging a fourth modular component to the first modular component, placing the apertures of the two circular ends  110   a ,  110   b , of this fourth modular component over the two contralateral pedicle screws on the vertebra that is immediately above the first vertebra, and adjusting the length and orientation of the two end segments  94  of the lamina ( 455 ). Tightening of the nuts over the pedicle screws down on the circular ends ( 460 ) and closing of the incision in the patient&#39;s back ( 470 ).  
         [0037]    Referring to FIG. 9, an implantable spine stabilization device  200  connects vertebra  92  to adjacent vertebra  94 . The spine stabilization device  200  includes modular components  210 ,  220 ,  230  and  240 . Modular components  210 ,  220 ,  230  and  240  have circular ends  211 ,  221 ,  231 , and  241 , respectively, that attach to pedicles  92 B,  94 B,  92 A,  94 A, of vertebrae  92  and  94 , respectively, via pedicle screws  212 ,  222 ,  232 , and  242  respectively. Modular component  210  is articulately connected to component  220  along a line  201  left of the midline  202  of vertebrae  92  and  94 . Modular component  230  is articulately connected to component  240  along a line  203  right of the midline  202  of vertebrae  92  and  94 . Additional modular components may be added left and/or right of the midline  202  to extend the spine stabilization device  200  in either caudad  272  or cephalad  270  directions . Modular components  210  and  230  are articulately connected to modular components  220  and  240 , respectively with an articulation mechanism similar to the one of FIG. 2, and FIG. 6. Modular components  210 ,  230  have hook tail segments  119  similar to the one described in FIG. 6. Modular components  220  and  240  have a cavity  115  with a bar  117  extending across opposite cavity walls, thereby forming a loop similar to the one described in FIG. 5 and FIG. 5A. Hook-shaped tail segment  119  engages around bar  117  into the loop formed in cavity  115 , thereby articulately connecting modular component  210  and  230  to modular components  220  and  240 , respectively. Modular components  210 ,  220 ,  230  and  240  may have adjustable length. The length of the modular components may be adjusted to be in the range of 10 millimeters to 200 millimeters.  
         [0038]    Other embodiments are within the scope of the following claims. For example, the articulation mechanism between the modular components may be a hinge. There may be more than one articulation mechanisms medial or lateral to the medial line  102  on a given vertebra, and/or medial to both the natural facet joints. The ends of the modular components may be secured to pedicle screws via connectors. The ends of the modular components may be attached to the vertebrae via hooks. Other locations where screws, wires, or hooks may be anchored for attaching the stabilization device of this invention include the transverse processes  33 ,  35 , the vertebral body  32 , and the lamina  47 . The modular components may be solid without adjustable ends. Modular components  110 ,  120 ,  130  and  140  may be manufactured from a variety of materials including among others stainless steel, titanium, nickel, composites, ceramics, plastic, bone, bioabsorbable material or combination thereof. Pedicle screws may be manufactured from a variety of materials including among others stainless steel, titanium, gold, silver ceramics, plastic, bioabsorbable material, or alloys thereof.  
         [0039]    Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.