Abstract:
A prosthetic implant for restoring lamina after a laminectomy. The implant is generally a lamina-sized construct having a hollow interior. The lamina removed during the laminectomy may be converted to autologous bone that may then be placed inside the hollow interior of the implant. The implant may then be secured to the spine at the site of the laminectomy so that lamina restoration can occur as the hollow interior of the implant solidifies with bone growth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation of U.S. patent application Ser. No. 13/940,217, filed Jul. 11, 2013, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/670,581 filed Jul. 11, 2012, and these applications are incorporated herein by reference in their entireties for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to the field of lamina replacement. 
         [0004]    2. Description of the Related Art 
         [0005]    Laminectomies, removal of the spinal lamina, are the most common surgical procedures in spinal surgery. Laminectomies are routinely performed in the cervical and lumbar spine to allow decompression of key areas of the spine. 
         [0006]    Cervical laminectomies allow decompression of the spinal cord and nerve roots. Patients may present with a radiculopathy (pain in the arms), myelopathy (weakness in arms and legs), or a combination of both. Cervical laminectomies are performed over multiple cervical levels and are an effective technique for cervical decompression and relief of symptoms. Removal of the posterior spinal elements, the cervical lamina, predisposes the patient to develop spinal instability, deformity, and pain. The posterior spinal elements, lamina, allow posterior structural support for the spine and an attachment for the posterior neck muscles. Some surgeons will perform a spinal fusion after cervical laminectomy to prevent spinal deformity. Cervical fusion creates an unnatural state for the neck, however, as the entire fused neck segment is non-mobile. There is a high risk of adjacent level segment instability after cervical fusion since all of the force with motion is transferred to the segment above and below the fusion. 
         [0007]    Cervical laminoplasty has been devised for decompression and reconstruction of the cervical lamina, but has certain limitations that have decreased its usefulness in spinal surgery. The primary issue is the technical difficulty of cervical laminoplasty. A “trough” needs to be drilled on one side of the junction of the lamina and lateral mass. This is a technically challenging technique. After a complete trough is formed on one side of the lamina-lateral mass junction, a partial trough is then formed on the opposite side. The lamina is then lifted off the dura and a wedge of bone is secured between the lifted-up side of the lamina Therefore, current cervical laminoplasty techniques allow adequate decompression of only one side of the spinal cord and nerve roots. 
         [0008]    Lumbar laminectomies are performed for decompression of the cauda equina and nerve roots. As a large laminectomy defect is created, however, spinal instability can occur. There can also be additional scar formation, as the muscle has to rest directly on the dura after a traditional laminectomy. Some surgeons use hemilaminotomies, where only a portion of the lamina is removed to decompress the nerve roots. However, hemilaminotomies are technically difficult, time consuming, and cannot adequately decompress the bilateral nerve roots and central dura. Lumbar fusions are routinely performed after lumbar laminectomies, but represent a plethora of technical difficulties and predispose the patient to “adjacent level” instability as forces are displaced above or below the fusion. A fusion also involves the placement of large pedicle screws through the pedicle of the vertebral body. Misplacement of the screws has resulted in cerebrospinal fluid (CSF) leaks, nerve injury, and paralysis. 
         [0009]    As such, there is still a need for a prosthetic implant for restoring the lamina after laminectomies while providing complete relief for the patient. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed towards a prosthetic implant for restoring lamina after a laminectomy. The implant is generally a lamina-sized construct having a hollow interior. The lamina removed during the laminectomy may be converted to autologous bone that may then be placed inside the hollow interior of the implant. The implant is then secured to the remaining portion of the spine at the site of the laminectomy. An attaching agent, such as one or more plates with screws, may be used to secure the implant to the spine. Over time, the autologous bone inside the hollow interior of the implant will solidify as bone grows through the interior of the implant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a perspective view of the spine with the lamina removed. 
           [0012]      FIG. 2A  shows a rear view of the cervical region of the spine with the lamina removed with an embodiment of the present invention in place. 
           [0013]      FIG. 2B  shows a rear view of the lumbar region of the spine with the lamina removed with an embodiment of the present invention in place. 
           [0014]      FIG. 3  shows a perspective view of an embodiment of the present invention with its parts separated and the attachment sites of the spine. 
           [0015]      FIG. 4  show a cross-sectional perspective view of an embodiment of the present invention secured to the spine. 
           [0016]      FIG. 5  shows a cross-sectional isometric top view of an embodiment of the present invention secured to the spine after bone growth. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The detailed description set forth below in connection with the appended drawings is intended as a description of presently-preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed and/or utilized. The description sets forth the functions and the sequence of steps for constructing and operating the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions, features, and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. 
         [0018]    The present invention represents a novel implant and technique for the restoration of the lamina after cervical decompression or lumbar decompression. As seen in  FIG. 1 , when a surgeon performs a cervical or lumbar laminectomy by removing the lamina  102  of a spine  100 , a gap is formed. In one embodiment of the present invention, an appropriately sized lamina replacement implant  200  may then be selected for attachment to the spine  100  on each side  106  of the gap. 
         [0019]    This embodiment of the present invention, therefore, includes a lamina replacement implant  200 . As shown in  FIG. 2A  and  FIG. 2B , it may be secured to the spine  100  at the site of the removed lamina The implant  200  is shaped in a way that allows attachment to the spine  100  while providing support for the spine  100  and/or protection for the spinal cord  108 . In a preferred embodiment, the implant  200  has a hollow body having a first arm  202  terminating at a first end  204 , a second arm  206  terminating at a second end  208 , connected together in a mid-section  210 . The hollow body may be made of PEEK (polyether ether ketone) or other suitable biocompatible material. 
         [0020]    In the embodiment in  FIG. 3 , the body of the implant  200  has a first arm  202  and a second arm  206 , with the first arm  202  and the second arm  206  connected to form the mid-section  210 . In this embodiment, the first arm  202  and second arm  206  are connected in a movable way to allow for adjustments to their orientation. Examples include the use of hinges, pivots, joints, or telescoping features. This allows the implant  200  to be adjusted to fit many of the different sizes of the spine  100  at different spinal levels. Accordingly, one such implant  200  could be adjusted outwardly to fit the largest lumbar spinal level or inwardly to fit a much smaller cervical spinal level so that it may be applicable to many or all of the spinal levels. Alternatively, a larger two-arm implant  200  could be fashioned to fit just the lumbar spinal levels and a smaller two-arm implant could be fashioned to fit just all or a portion of the cervical spinal levels. Once the adjustment has been made such that the ends of the two arms satisfactorily mate with the spine  100 , this particular orientation can be locked in place by a locking mechanism  218 , such as a screw, pin, glue, or any equivalents. The locking mechanism may be made of titanium, solidified bone graft material, or other biocompatible material. The two arms would mate with the lateral mass in the cervical spine and facet/pedicle in the lumbar spine. 
         [0021]    In another embodiment, the body of the implant  200  is one piece or even multiple pieces but without a defined hinge or pivot portion. Such an implant  200  could have several mounting holes or slots so as to be able to mount to a range of spinal levels of several different sizes. Alternatively, such an embodiment could involve two flexible arms  202 ,  206  or a flexible mid-section  210 . The flexible portion could be elastic such that it tends to spring back to a neutral shape until it is fixed to the spine  100 . Yet a further alternative would be that the flexible portion could be designed to readily plastically deform so that there is no significant tendency of the implant  200  to return to a neutral shape once flexed. 
         [0022]    Once the surgeon adjusts the implant  200  and moves it into place, such as in  FIGS. 2 ,  4  and  5 , the surgeon may secure the implant  200  to the spine  100 . This can be done by several different securing means. In the embodiment shown in  FIG. 4 , the implant  200  is secured to the spine  100  using plates, braces, or brackets fixed to the implant  200  and/or the spine  100  by screws  214 ,  216  Implant screws  214  of appropriate length may attach the plates  212  to the arms  202 ,  206  of the implant  200 , and spinal screws  216  of appropriate length may attach the plate  212  to the spine  100 . In one preferred embodiment, the lengths are approximately 6 mm-8 mm for the cervical region and approximately 12 mm-14 mm for the lumbar region. In another embodiment, the plates  212  and screws  214 ,  216  may comprise titanium or a titanium alloy for their biocompatible properties. In other embodiments, the securing means may instead be a malleable strap, a biodegradable material, or a durable or biodegradable adhesive. 
         [0023]    The implant  200  should be attached so as to allow contact between the remaining portions of the exposed spine  100  and a region on or in the implant  200  that comprises a bone graft region  300  that can facilitate bone growth through the implant  200 . In one embodiment, at least a portion of the implant  200  may be hollow. These hollow portions  300  can be fitted securely so any bone graft material  500  will not leak out. In a preferred embodiment, the first and second ends of the arms also comprise bevels to allow the implant to more securely attach to the spine. When that midsection is adjusted, the angle of the bevels may change orientation as well. Because of this, in some embodiments, the mating faces of the arms may also be adjustable, malleable, or realignable so that the bevels are at a correct orientation to securely attach to the lateral mass  106  for ease of mating and alignment with the spine and to better ensure a tight fit therebetween. To further facilitate securement to the spine  100 , the first and second ends may further comprise one or more notches into which remaining portions of the spine are contoured, fitted or wedged. One or more additional buffers, such as linings, gap-filling adhesives, mating gaskets, or cushioning, may be added to prevent any leakages of bone graft material  500  from the secured implant  200  or to better fit and secure the implant to the spine  100 . The spine and/or the ends of the arms may be further shaped to each other&#39;s contours to form a more secure attachment. The inclusion of adjustable mating facings further reduces the time and effort required in contouring, fitting, or wedging the implant or spine. 
         [0024]    Thus, in one embodiment, a hollow interior  300  of the implant  200  may be filled with bone graft material  500  that is intended to solidify through the implant. As shown in  FIG. 5 , the bone graft material  500  may become as strong as bone and provide additional strength for the implant  200 . In one embodiment, after a spinal laminectomy, the removed portions of lamina may be crushed into autologous bone (autograft) and used as bone graft material  500  in the implant  200 . This would aid the implant  200  to solidify over time as bone continues to grow through the implant  200 . Such autologous bone graft material  500  may also decrease the chances that such material will be rejected by the patient&#39;s body. Indeed, PEEK implants in spinal surgery, filled with autograft and fitted in the disc space, have shown to produce robust bone growth through the interior where autograft has been placed. As PEEK has modules of elasticity that resemble that of bone, it may be a preferential template for lamina replacement, although other compositions may be used and new compositions are sure to prove useful with advancements in the field. 
         [0025]    Alternatively, the bone graft material  500  could be composed of autograft material from other portions of the body, allograft material from the bones of other people (such as cadavers, donors, or stem cell cultures), xenograft material from animals, synthetic replacements, other similar substitutes, or a combination thereof. In one embodiment, the implant uses larger bone pieces or fragments or other bone graft material that may have been pre-solidified or partially solidified before it is implanted into a patient. 
         [0026]    In one embodiment, as shown in  FIG. 5 , the surgeon may drill into the exposed sections of the spine  100  and fill the void created thereby with bone graft material  500  that is also used to fill adjacent hollow portions  300  of the implant  200  so that new bone formed inside the ends of the implant and the new bone formed inside the drilled void within the adjacent spine can form together, allowing for a more secure bone attachment. The embodiment in  FIG. 5  shows a drilled area with rounded edges, but other shapes may be used for stronger securement or greater surface areas. In one embodiment, a drill with a hollow center is used so the drilled area has a peg in the middle for greater surface area to promote bone growth. In another embodiment, several holes are drilled in each lateral mass  106  for increased surface area. Alternatively, the implant  200  may include a solid end mass that approximately mates with the interior surface of the void created in the spine  100  and design with a surface material and/or texture that facilitates bone growth or solidification, such surfaces may include nanostructured regions, including nanotextured and nanoporous regions. The solid end mass may also be a solid nub used for anchoring the implant in the bone. This solid nub can be made from titanium, bone made from bone graft material, or other biocompatible material. 
         [0027]    Additionally, the implant portions themselves may be composed of biodegradable materials so that the bone graft material  500  solidifies with the spine  100  and the biodegradable implant later biodegrades ultimately to restore the spinal lamina  102 . 
         [0028]    While the present invention has been described with regards to particular embodiments and some of their equivalents, it is recognized that additional variations of the present invention with their functionally equivalent features may be devised without departing from the inventive concept.