Patent Abstract:
A vertebral implant comprising a first base configured for securing to a first cut portion of a vertebra, and second base configured for securing to a second cut portion of the vertebra. A connecting member is configured to associate the first and second bases at a preselected spacing from each other, and the implant is preferable adjustable to select the spacing.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 10/859,962 filed on Jun. 4, 2004 and entitled “Variable Laminoplasty Implant,” which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present application relates to an implant for bone surgery, and more specifically to a vertebral implant with an adjustable configuration. 
     BACKGROUND 
     In certain pathologies, the spinal canal extending through a patient&#39;s vertebrae is or becomes too narrow and constricts the spinal cord extending therethrough. The narrowing may be congenital, potentially affecting patients at any age. Narrowing can also be attributable to other causes, such as age, injury or removal of a spinal disk. 
     A condition associated with aging, for instance, is spondylolsis, in which intervertebral disc loose water and become less dense. These degenerative changes near the disk can cause an overgrowth of the bone, producing bony spurs called, “osteophytes” that can compress the spinal cord. The constriction of the spinal cord in the cervical spine, for example, often produces pain, weakness, or loss of feeling in extremities. Other causes for narrowing of the spinal canal include disc shrinkage, which causes the disc space to narrow and the annulus to bulge and mushroom out, resulting in pressure on the spinal cord. Degenerative arthritis of facet joints can cause joints to enlarge, or the vertebra to slip with respect to each other, also compressing the spinal cord. Instability between vertebra, such as caused by stretched and thickened ligaments&#39; can also produce pressure on the spinal cord and nerve roots. 
     Myelopathy, or malfunction of the spinal cord, occurs due to its compression. The rubbing of the spine against the cord can also contribute to this condition, and the spinal cord compression can ultimately compromise the blood vessels feeding the spinal core, further aggravating they myelopathy. 
     Traditional procedures for decompressing the spinal cord include a laminectomy, in which the lamina and spinal processes are removed to expose the dura covering the spinal cord. Another known procedure is a laminoplasty, in which the lamina is lifted off the dura, but not completely removed. Typically, one side of the lamina is cut, while a partial cut is made on the other side to hinge the lamina away from the spinal cord to increase the size of the spinal canal. A laminoplasty plate is then screwed to a facet and to the hinged open lamina. The plate of an appropriate size is selected and bent to the desired shape and preferably has a plurality of screw holes. A strut of bone can be placed in the open portion within the lamina and the facet to help hold the open position of the lamina. Prior to the operation, the surgeon needs to measure the vertebra to determine the size of the plate necessary for implantation. At that point, a plate can be selected with the appropriate dimensions, and implanted at the site. 
     A laminoplasty implant is needed that preferably allows its size to be varied prior to implantation, preferably without changing its overall shape or configuration, so that a plate does not have to be custom selected and intensively shaped and formed prior to each surgery. 
     SUMMARY 
     The present invention relates to a bone implant, and more preferably a vertebral implant. The implant has first and second bases configured for securing two first and second cut portions, respectively, of a vertebra. A connecting member is configured for associating the first and second bases at a pre-selected spacing from each other. Most preferably, the implant is adjustable to select and set the spacing. In the preferred embodiment, the implant is a laminoplasty implant, and the first and second vertebral portions are a lateral mass, its articular mass, or its facet, or a portion of the lamina, and the second vertebral portion can comprise, for example, at least part of the lamina. 
     The first base is preferably in fixed association with the connecting member. One of the connecting members and second base comprises an adjustable member that is adjustable to select the spacing between the bases. The other of these portions of the implant can include a linking member that is associable with the adjustable member. The adjustable member preferably adjusts the length of the connecting member measured from the first base to a connection location at which the linking member is associated with the adjustable member. This length is preferably adjusted without changing the overall shape or configuration of the implant and preferably by changing the length of the connecting member without modifying the general shape of the bases or the size of the position of he bases in contact with the bone when implanted. 
     Also, the adjustable member can define a plurality of mating portions, with the linking member being associable selectively with at least one of the mating portions to select the connection location. The mating portions and linking member are preferably configured for pivotally associating the adjustable member and second base. The mating portions and linking member of the preferred embodiment are configured to be placed into the association at a first pivotal orientation with respect to each other, and for connecting the first and second bases secured to the cup portions in a second pivotal orientation between the linking member and mating portions or connecting member. 
     In one embodiment, the mating portions and/or linking member comprise at least one or more protrusions receivable in one or more notches of the other of these elements to associate the adjustable and linking members a protrusion can be selectively receivable in at least one of the notches for selecting the connection location. At least one of the notches and protrusions is preferably arcuate about axial direction measured with respect to the spinal column, such that the protrusion is received for sliding in the notch and in this manner pivoting of the connecting member with respect to the linking member without sliding in the notch can be restricted if desired. A loading opening can be provided, for example, between a pair of the protrusions to receive the notches of the adjustable member therein for associating the adjustable member and the linking member. The adjustable portion is preferably configured for severing a potion of the connecting member disposed beyond the selected connection location from the first base. 
     At least one of the bases can include a concave contacting surface that is configured for receiving the cut portions of the vertebra. At least one of the bases preferably includes a fastener mount portion configured to attach a bone fastener thereto to secure the base to the vertebra. The fastener mount portion can include a plurality of fastener mount portions that are disposed at different axial locations with respect to the spinal access. This allows attaching bone fasteners depending on the axial spacing between the first and second cut portions. A fastener can be mounted in the fastener mount portions, and in one embodiment the fastener is articularble and includes a universally pivotal head. The head is associable with a vertebra joining member, such as a rod and at least one other vertebra in the spinal column. A further fastener mount potion can be provided, such as in the connecting member, for securing a bone graft thereto. Once the first and second bases are secured to the first and second cut portions of the vertebra, the connecting member preferably fixes the association between the bases, thus fixing the distance therebetween and holding the lamina in a desired hinged position. In a preferred embodiment of an articularble fastener, the fastener has a bone fastener portion configured for fastening to a bone, a head configured for associating with the vertebra joining member, and a universal joint that pivotally associates the fastener portion with the head for relative universal pivoting therebetween. In one embodiment, a passage is cooperatively defined by the head and joint to permit access to the fastener portion to engage it directly with the driver. Thus, a driver can be used to screw the fastener portion into the bone prior to attaching to a rod, or other vertebrae joining member. 
     Consequently, an improved implant is provided that can be used in a laminoplasty procedure without requiring the intensive customization of a bone plate or the selection from a wide size variety of bone plates prior to implantation. Preferably the implants can be customized in situ to best fit the patients anatomy substantially reducing the amount of time and costs to perform the operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments disclosed herein will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1 and 2  are perspective views of a laminoplasty implant constructed according to a preferred embodiment of the invention, adjusted to different lengths; 
         FIGS. 3 and 4  are perspective views of alternative embodiments of implants with different fastener mount portions; 
         FIGS. 5 and 6  are a bottom view and a perspective rear view of another embodiment of an implant; 
         FIGS. 7 and 8  are a perspective and axial view of an implant fixed with other vertebrae; 
         FIGS. 9 and 10  are cross-sectional views of other embodiments of inventive universally pivotable screws; and 
         FIG. 11  is a perspective view of another embodiment of an articulated fastener. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , in a preferred laminoplasty procedure, an osteotomy is performed in which a complete cut is made through vertebra  16 , approximately between the lamina  20  and lateral mass  14 , such as the articular mass or facet portion therof. A partial-depth cut  11  is made on the opposite lateral side, also approximately between the lamina  20  and other lateral mass  14 . The lamina  20  is then hinged open about the partial cut  11  to increase the cross-sectional size of the spinal canal to decompress the spinal cord therein. 
     A preferred embodiment of a laminoplasty implant  10  includes a lateral base  12  that is configured for securing to a lateral mass  14  of a vertebra  16 . A lamina base  18  is configured for securing to a portion of a lamina  20  that has been cut and hinged away from the lateral mass  14 . For alternative surgical procedures, the base can be configured for securing to different parts of the vertebra, a differently prepared vertebra, or to different bones, as desired. 
     Preferably, one or both bases  12 , 18  have concave contacting surfaces  22 , 24  that are configured for receiving the cut portions of the vertebra  16 , such as at the lateral mass  14  and lamina  20 . The lateral base  12  of the embodiment shown has an outside portion  26  that is preferably placed against the posterior surface of the lateral mass  14  outside the spinal canal  30 , and against an inside portion  28  that is preferably placed against a wall of the vertebrae at an angle to the position facet surface at the cut  32  location, preferably in the interior of the spinal canal  30 . Together, the outside and inside portions  26 , 28  of the lateral base  12  define the concave surface  22  for receiving and capturing the cut portion of the lateral facet  14 . The individual surfaces of the outside and inside portions  26 , 28  can also be concave, preferably by a slight amount. 
     In the embodiment shown, the angle between the outside and inside potions  26 , 28  at the concave surface is about a right angle, but can be varied depending on the location of the implantation and the angle of the cut that is made. Preferably, the angle is between about 30.degree. and 150.degree., and more preferably between about 60.degree. and 100.degree. In one embodiment, the angle can be up to about 180.degree., such as by employing an intermediate portion to connect the outside and inside portions. The inside portion  28  can be constructed as a lip to capture the edge of the lateral mass  14  at the cut, to assist in the proper placement of the implant  10  and prevent or restrict movement thereof after implantaion. 
     The lamina base  18  also preferably has an outside portion  34 , which is preferably placed against the posterior surface of the lamina  20  outside the spinal canal  30 . An intermediate portion  36  is configured and disposed for placement against a narrow edge of the lamina  20 , and an inside portion  38  is placed against an anterior surface of the lamina  20  inside the spinal canal  30 . Together, the outside, intermediate, and inside portions  34 , 36 , 38  of the lamina base  18  define the concave surface  24  for receiving and capturing the cut portion of the lamina  20 , preferably surrounding the cut portion of the lamina  20 . The inside portion  38  can be configured as a lip to help prevent pivoting of the lamina  20  tending to close the spinal canal  30  prior to the bone healing. 
     The angle between the outside and intermediate portions  34 , 36  in the preferred embodiment and between the intermediate and inside potions  36 , 38  at the concave surface are about right angles, but can be varied depending on the location of the implantation and the angle of the cut that is made. In one embodiment, only two angled portions are used, such as by providing a lip to capture the edge of the cut lamina, as is shown for the lateral base  12 . The angle between the outside and inside portions is preferably about 180.degree., but can alternatively be as low as about 30.degree., more preferably as low as about 60.degree., and most preferably as low as about 90.degree. The concave surface  24  captures the edge of the lamina  20  at the cut, to assist in the proper placement of the implant  10 . 
     The bases  14 , 18  preferably include fastener mount portions  40  configured for attaching a bone fastener thereto. If bone screws  42  are to be used, then the fastener mount portions can define suitable openings for receiving and fastening the bone screws  42 . The fastener mount portions  40  are preferably disposed for accessing and inserting the fasteners  42  from the outside of the bone, to facilitate implantation. 
     The lateral base  12  shown has two fastener mount portions  40  aligned laterally with respect to each other. The lamina base  18  shown, on the other hand, has two fastener mount portions  40  disposed axially with respect to each other. The position of the fastener mount portions  40  can be varied according to the bone available at the implantation site. For instance, the implant  44  of  FIG. 3  has facet and lamina bases  46 , 48 , each with a fastener mount portion  50 , 52  configured to attach a single bone screw  42 . The implant  54  of  FIG. 4 , however, has a lamina base  56  with fastener mount portions  58  configured for receiving and attaching up to three bone screws  42 . Alternative bases can secure to other numbers of fasteners in other arrangements. Similar fastener mount portion arrangements can be used for the lateral base. 
     The fastener mount portions of implant  54 , shown in  FIG. 4 , has three fastener mount portions  58  oriented generally along the apices of a triangle. Two of the fastener mount portions  58  are disposed generally at a same lateral location, and at least two of the three are preferably disposed at different axial locations along the spinal axis when implanted. Since the vertebral laminae are displaced downwardly in an axial direction with respect to the facets of the same vertebrae, axially displaced fastener mount portions, such as in lamina base  56  in  FIG. 4  and lamina base  18  in  FIG. 1 , can help ensure that at least one or more of the fastener mount portion  40 , 58  is disposed over bone into which a fastener can be placed. 
     As shown in  FIG. 4 , the upper fastener mount portion  58  is empty, as it is not completely over lamina bone. On the other hand, the other two fastener mount portions  58  are fully disposed over bone, and each has a bone screw  42  secured therethrough. The leftmost fastener mount portion  58 , disposed closest to the lateral base  12 , is preferably disposed axially between the other two fastener mount portions  58  in a position likely to always be able to engage the bone with a fastener. If the implant  54  were used on the right side of a vertebra, instead of on the left side as shown, the other of the two fastener mount portions  58  that are is a close axial position would be over bone and used for securing a fastener, while the fastener mount portion that is shown with a bone screw  42  in  FIG. 4  would be empty. In an alternative embodiment, the triangle may be reversed, with a pair of fastener mount portions provided towards the lateral base, and a single fastener mount portion provided further therefrom than the other two. An alternative embodiment has an asymmetrical arrangement of fastener mount portions, and one embodiment has two positioned along a line that is diagonal to the lateral direction between the facet and lamina bases. 
     Referring again to  FIG. 1 , implant  10  has a connecting member  60  that associated the facet and lamina bases  12 , 18  at a preselected spacing  62  from each other. The spacing  62  is selected to determine the hinged position in which the cut lamina will be maintained when the surgery is complete. The connecting member  60  preferably acts as a strut holding the bases  12 , 18  apart. 
     The preferred connecting member  60  and/or its association with at least one of the bases  12 , 18  is adjustable for selecting the desired spacing  62 . In the preferred embodiment, one of the bases  12 , 18 , preferably the lateral base  12 , is in fixed association, and preferably integral with or of unitary construction with the connecting member  60 . The other base, preferably the lamina base  18 , has a linking member  64  that is associable with the connecting member  60 . The preferred linking member  64  has at least one protrusion, such as parallel D-rings, that is associable with any of a plurality of notches  66  defined between ledges  68  on the connecting member  60  to select a location for the connection between a notch  66  and the D-ring. 
     Prior completing the implantation, such as after the lamina base  18  is secured to the cut lamina  20  but before the lateral base  12  is secured to the lateral mass  14 , at least one of the ledges  68  of the connecting member  60  is inserted into a loading opening, such as a slot  70  defined in the linking member  64  and extending into the facing D-rings, which slot  70  preferably has a larger cross-section than the cross-section of the ledges  68  along a plane parallel to the notches  66 . 
     Once a ledge  68  is placed within the slot  70 , the mated connecting member  60  and linking member  64  are pivotally associated, and the connecting member  60  can be pivoted about an axis that is preferably generally parallel to the spinal axis to place the lateral base  12  against the vertebra lateral mass  14 , where it can be secured. When both bases  12 , 18  are engaged with each other and secured to the respective bone portions, the connecting member  60  preferably maintains the bases  12 , 18  in fixed association with each other, preferably substantially preventing movement between the bases  12 , 18 . 
     The connecting member  60  is adjustable in length, and preferably comprises an adjustable member  72 , which includes the notched  66  and ledges  68 . The adjustable member  72  is adjustable to adjust a length of the connecting member  60  and thus the spacing  62 . By selecting the notch  66  to be mated with the linking member  64  D-rings, the length of the connecting member  60  can be incrementally adjusted. Once the anatomy of the vertebra is measured and preferably verified by mating the connecting member  60  with the lamina base  14  and pivoting the connecting member  60  and lateral base  12  portion to contact the lateral mass  14 , the connecting member  60  can be separated from the lamina base  18 . The adjustable member  72  of the connecting member  60  can then be clipped on the opposite side of the desired notch  66  from the lateral base  12  to shorten the connecting member  60  and eliminate unneeded material.  FIG. 2  shows an implantation of the implant  10  with the connecting member adjusted and clipped to a shorter length than in  FIG. 1 , thus fixing the lamina  20  at a smaller open hinged angle than in  FIG. 1 . The shorter arrangement of  FIG. 2  can also be used for smaller vertebrae. 
     Referring to  FIGS. 5 and 6 , another implant  74  embodiment is shown with a fastener mount portion  76 , which is preferably associated with connecting member  78  and faces the spinal canal  30 . Fastener mount portion  76  is preferably positioned and configured for securing a bone graft fragment  80  to help support the hinged lamina  20  in the open position, and ultimately for fusing with the vertebral bone when the vertebra heals. A fastener, such as a bone screw  84  is fastened through the fastener mount portion  76  to the one fragment  80 . 
     In the embodiment shown, the connecting member  78  is substantially straight. Alternatively, the connecting member can be curved, preferably bowed outwardly from the spinal canal to increase its expanded cross-sectional size. 
     The bone fragment  80  is shaped to preferably contact both sides of the cut  32  in the vertebra  16 . The bone fragment  80  is preferably also provided with a notch  86  to receive the inside portion  28  of lateral base  82  to extend around the cut portion of the lateral mass  14 . Although a similar notch can be provided for the lamina base  88 , the lamina base  88  of this embodiment does not have a third portion that extends inside the spinal canal  30 . As shown in  FIG. 5 , the ledges are arcuately curved about an axial direction with respect to the spinal column, preferably following the curved shape of the D-rings of linking member  64  and further controlling the relative orientation between the connecting member  78  and the linking portion  64 . 
     As shown in  FIG. 7 , an implant embodiment  90  has a lateral base  46  that is secured to lateral mass  14  by an articulated bone fastener  92 , which is itself secured to at least one adjacent vertebra  16 . Fastener  92  comprises a fastener portion  94 , which is preferably a bone screw portion fastened to the vertebra  16 , and a head  96  that is configured for associating with a vertebra joining member, such as a rod  98 . A locking mechanism, such as a set screw  102 , preferably locks the rod  98  to the head  96 . A joint  100 , which is preferably substantially universally pivotable and also preferably rotatably, pivotally associates the head  96  with the fastener portion  94 . 
     As shown in  FIG. 8 , an embodiment of the joint  100  includes a link  104  configured with two spherical portions  106 , 108 , preferably of different sizes. Each spherical portion  106 , 108  is received in a socket  110  of the head  96  or the fastener portion  94 . The sockets  110  preferably extend more than half way around the spherical portions  106 , 108  to retain the spherical portions  106108  therein. A double ball and socket joint is thus provided, preferably allowing rotation, and most preferably unlimited rotation, at least about the axis of the head  96  or fastener portion  94 . Pivoting is preferably allowed through an arc of between about 10.degree. and 80.degree., and more preferably between about 20.degree. and 70.degree., preferably in any direction about the spherical portions  106 , 108 . 
     A passage  120  is preferably defined cooperatively by aligned openings in the head  96  and joint  100  configured to receive a driver, such as a screw driver, to engage directly with the fastener portion  49  to secure it to the bone. The passage  120 , preferably is aligned with a driver receptacle  122  in the fastener portion  94 . 
     The articulated fasteners  92  thus allow other vertebrae to support each other and can be useful where vertebrae are to be fused. As shown in  FIG. 7 , a similar arrangement of articulated fasteners  92  and rods  98  can also be employed on the opposite facets  14  to improve support and possibly fixation with other vertebrae. 
     Another embodiment of a pivoted fastener  112  is shown in  FIG. 9 , in which a double ball and socket joint  114  includes a link  116  with two spherical portions  118  associated with head  124  and fastener portion  94 . The joint  128  articulated fastener  126  of  FIG. 10  includes a double-socket member  130  that receives spherical portions  132 , 134 , which are respectively integral or unitary with the head  136  and fastener portion  138 . The articulated fastener  140  of  FIG. 11  has a joint  142  with a link  144  that has a cylindrical portion  146  associated with a spherical portion  148 , which are received in complementary sockets  150 ,  152  in head  156  and fastener portion  158 , respectively. Although the spherical portion  148  can rotate about an axis joining the fastener portion  158  and head  156 , the cylindrical portion  146  is restricted against such rotation. 
     Referring again to  FIG. 8 , a unitary facet-base/connecting-member portion has the connecting member  160  offset from the interior edge of the lateral base  46 , which is disposed closest to the spinal canal  30 , by an offset amount  164 , measured laterally in this embodiment. This offset  146  is preferably of similar or greater thickness as the thickness of the bone graft  80 . In an alternative embodiment, greater or lesser offsets can be provided, including substantially no offset at all. In embodiments without a bone graft, the offset  154  can provide additional room for the expanding spinal cord. Also, the connecting member preferably extends at an angle of between about 100.degree. and 140.degree. from the lateral base. 
     The preferred materials for use in the embodiments of the implants of the present invention include titanium, PEEK (polyetheretherketone) and absorbable materials such as a polylactic or polyglycolic acid material. Other suitable materials may alternatively be used. The preferred spacing  62  provided by the connecting member  60  is between about 5 mm and 30 mm, depending on the location in the spine in which it is desired to be employed. For example, cervical implants will typically be between about 10 mm and 20 mm, while lumbar implants will typically be between about 20 mm and 30 mm. The bone screw diameters can also vary according to the size of the implant and the implant location, and typically vary between about 3 mm and 6 mm, with a length of about 8 mm to 20 mm. 
     While illustrative embodiments of the invention are disclosed herein, it will be appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments that come within the spirit and scope of the present invention

Technology Classification (CPC): 0