Abstract:
An interlaminar fixation device (“ILFD”) and related tools for implanting and extracting the ILFD in surgical procedures to provide support for patients having degenerative spinal conditions. The ILFD comprises an implant body, a pair of fixation pin assemblies, and a locking plug. The body may be a boxlike structure made of a material such as polyetheretherketone (PEEK) or other material with similar beneficial properties. An implant-sizing tool is provided for determining the appropriately sized ILFD. An implant-grasper tool is provided for grasping the ILFD for insertion and positioning of the ILFD. A bone-punch tool is provided for creating openings aligned for insertion of fixation pins. A pin-inserter tool is provided for urging fixation pins into position. A locking-plug inserter tool is provided for inserting the locking plug into the body of the ILFD. A locking-plug extractor tool is provided for removing the locking plug.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Nos. 62/092,640 and 62/268,285, filed on Dec. 16, 2014 and Dec. 16, 2015, respectively. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to an interlaminar fixation device of the type used in surgical procedures to provide support for patients having degenerative spinal conditions. 
       BACKGROUND 
       [0003]    This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
         [0004]    The treatment of degenerative lumbar spinal stenosis is conventionally treated by wide laminectomy and decompression of the spinal canal with or without spinal fusion. Spinal fusion, when required because of destabilization from the decompression, is usually associated with internal fixation making it a major procedure with significant morbidity to the patient. 
         [0005]    Degenerative lumbar spinal stenosis causes neurological symptoms in the lower extremities and/or back pain. The symptoms may be constant with variations in intensity, depending upon position and activity, or may be intermittent and brought on by certain activities, particularly walking and standing. 
         [0006]    The positional nature of the symptoms may be due to instability but most often is due to the fact that the normal posture of the lumbar spine is one of lordosis, which decreases the cross-sectional area of the spine. When the patient is sitting, lordosis decreases, increasing the cross-sectional area and relieving the symptoms. 
         [0007]    Interspinous mechanical blocking devices, such as X-Stop by Medtronic, are commercially available. Such devices are pushed through the interspinous ligament and work by blocking extension of the spine. Unfortunately, such device has a very high failure rate, largely because the spinous process is the weakest part of the vertebra, but also because the population demographics of people requiring this type of operation are such that many of them suffer from osteoporosis. 
         [0008]    Recently, another device, Coflex® by Paradigm Spine, LLC, was commercially released in the United States. This device is inserted by resecting the interspinous ligament and some of the inferior edge of the superior spinous process at the level which the device is to be inserted. Flanges at each end of the device can be pressed down so that they grasp the spinous process above and below. The flanges also contain holes through which small screws can be inserted. 
         [0009]    This device also has a relatively high failure rate. The device has a fairly large diameter curve to make insertion of the device easier. This design results in forces which contain a vector attempting to displace the device back outwards from its position in the spine. If no securing screws have been placed, the device tends to dislocate posteriorly, resulting in a return of symptoms. If one screw is used, the device tends to pivot around that screw as it dislocates posteriorly, resulting in the same return of symptoms due to failure to prevent increased lumbar lordosis. When two screws are used, particularly where there is osteoporosis in the spinous process, the spinous process may fracture through the screw hole(s), resulting in posterior displacement. 
         [0010]    Accordingly, there is a need for a blocking device for alleviating back pain. There is a need for such a blocking device to be easily inserted with a smaller incision than with insertion of conventional devices. There is further a need for such a blocking device to remain in place. There is still further a need for such a blocking device to be capable of extraction. There is a still further a need for tooling for easily inserting and extracting such a blocking device. 
       SUMMARY OF THE INVENTION 
       [0011]    Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
         [0012]    The present invention provides an interlaminar fixation device (“the ILFD”) and insertion tools. The ILFD is inserted into the back of the spine to prevent a patient from bending too far backward at the narrowed segment, a position that for patients with spinal stenosis can cause leg pain (sciatica) and/or lower back pain. The ILFD is designed to avoid or at least significantly reduce the effect of posteriorly dislocating vector forces acting upon the implant. It is an almost boxlike construct with small radii on the corners. It is fixed with pins that engage the spinous processes in the sagittal plane and which do not restrict motion in flexion, only blocking extension. The surgical incision required to implant the ILFD is significantly less than of that required to insert conventional devices. Additionally, conventional devices require transversal bolt insertions which have several disadvantages. Insertion of the ILFD requires less muscular dissection which results in less physical invasion, faster healing, less pain, and lower risk of infection. An additional advantage of the present invention is that it requires less penetration of the colidal surface of the spinal process, and does not require grasping the spinal process to insert, thus lowering the risk of damage on insertion. The ILFD of the present invention is designed to be used in combination with removal of the ligamentum flavum, which further assists in decompressing the spine. 
         [0013]    The ILFD comprises four components: an implant body, a pair of fixation pin assemblies (or spike strips), and a locking plug. The body may be a boxlike structure made of a material such as polyetheretherketone (PEEK) or other material with similar beneficial properties. 
         [0014]    The ILFD may be produced in multiple sizes to accommodate the difference in the size of the patients. Titanium or tantalum rods may be embedded in the plastic so that the position of the ILFD can be assessed radiologically. The spike strips may be made of a titanium alloy. The strip may have a square section and have, at a distance from the inserted end, a breakoff notch. Between the inserted end and the notch, there are two cephalad spikes and two caudad spikes. The tips of the spikes are preferably oval. 
         [0015]    The plug may be made of either PEEK or titanium or similar material. There is either a single threaded hole or dual clean holes for engagement of a plug-inserter tool at the dorsal surface. The ventral surface of the plug may be rounded for easier insertion into the implant body. There is a small ridge ventral to the dorsal surface which engages a notch on the inside of the body and thus prevents backing out. The notch may be present on only one side, but there may be two grooves on the inside of the body, one on the left and one on the right, so that the plug can be inserted without reference to the orientation of the ridge. In yet another embodiment, the plug has a orientation slot. 
         [0016]    The present invention provides tooling. An implant-sizing tool is provided for determining the appropriately sized ILFD. An implant-grasper tool is provided for grasping the ILFD for insertion and positioning of the ILFD. A bone-punch tool is provided for creating openings aligned for insertion of fixation pins. A pin-inserter tool is provided for urging fixation pins into position. A locking-plug inserter tool is provided for inserting the locking plug into the body of the ILFD. A locking-plug extractor toll is also provided for removing the locking plug. 
         [0017]    Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of the embodiments without limitation to the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0019]      FIG. 1  depicts a side view of an embodiment of an interlaminar fixation device (“ILFD”) exemplified after implantation in a spine. 
           [0020]      FIG. 2  depicts an isometric view of the ILFD of  FIG. 1  exemplified as fully assembled. 
           [0021]      FIG. 3  depicts an exploded view of the ILFD of  FIG. 2 . 
           [0022]      FIG. 4  depicts an isometric view of the implant body of the ILFD of  FIG. 2 . 
           [0023]      FIG. 5  depicts a cross-sectional view of the implant body of  FIG. 4  taken along section line  5 - 5 . 
           [0024]      FIG. 6  depicts a close-up view of the implant body of  FIG. 4  taken along line  6 - 6 . 
           [0025]      FIG. 7  depicts a cross-sectional view of the implant body of  FIG. 4  taken along section line  7 - 7 . 
           [0026]      FIG. 8  depicts an isometric view of a cephalad fixation-pin assembly of the ILFD of  FIG. 2 . 
           [0027]      FIG. 9  depicts a cross-sectional view of the cephalad fixation-pin assembly of  FIG. 8 . 
           [0028]      FIG. 10  depicts an isometric view of a caudal fixation-pin assembly of the ILFD of  FIG. 2 . 
           [0029]      FIG. 11  depicts a cross-sectional view of the caudal fixation-pin assembly of  FIG. 10 . 
           [0030]      FIG. 12  depicts an isometric view of a first embodiment of a locking plug of the ILFD of  FIG. 2 . 
           [0031]      FIG. 13  depicts a cross-sectional view of the locking plug of  FIG. 12 . 
           [0032]      FIG. 14  depicts an isometric view of an implant-sizing tool. 
           [0033]      FIG. 15  depicts an isometric view of a first embodiment of an implant-grasper tool for use in combination with a first embodiment of a locking-plug inserter tool (see  FIGS. 22-29 ) for implanting the ILFD illustrated in  FIG. 2 . 
           [0034]      FIG. 16  depicts a side view of the implant-grasper tool of  FIG. 15  in a closed position. 
           [0035]      FIG. 17  depicts a side view of the implant-grasper tool of  FIG. 15  in an open position. 
           [0036]      FIG. 18  depicts an isometric view of an upper element of the implant-grasper tool of  FIG. 15 . 
           [0037]      FIG. 19  depicts an isometric view of a lower element of the implant-grasper tool of  FIG. 15 . 
           [0038]      FIG. 20  depicts an isometric view of a grasper-lock mechanism of the implant-grasper tool of  FIG. 15 . 
           [0039]      FIG. 21  depicts a side view of the grasper-lock mechanism of  FIG. 20 . 
           [0040]      FIG. 22  depicts an isometric view of a first embodiment of a locking-plug inserter tool for use in combination with the implant-grasper tool of  FIG. 15  for implanting the ILFD of  FIG. 2 . 
           [0041]      FIGS. 23-24  depict side views of a handle element of the locking-plug inserter tool of  FIG. 22 . 
           [0042]      FIGS. 25-26  depict side views of a plunger element of the locking-plug inserter tool of  FIG. 22 . 
           [0043]      FIG. 27  depicts an isometric view of a collet element of the locking-plug inserter tool of  FIG. 22 . 
           [0044]      FIG. 28  depicts a side view of the collet element of  FIG. 27 . 
           [0045]      FIG. 29  depicts a cross-sectional view of the collet element of  FIG. 27  taken along section line  28 - 28 . 
           [0046]      FIG. 30  depicts an isometric view of a bone-punch tool for use during implantation of the ILFD of  FIG. 2 . 
           [0047]      FIGS. 31-32  depict side views of an element of the bone-punch tool of  FIG. 30 . 
           [0048]      FIG. 33  depicts an isometric view of a pin-inserter tool for use during implantation of the ILFD of  FIG. 2 . 
           [0049]      FIGS. 34-35  depict side views of an element of the pin-inserter tool of  FIG. 33 . 
           [0050]      FIGS. 36-52  depict perspective views exemplifying the sequence of steps for implanting the ILFD of  FIG. 2  using tooling shown in  FIGS. 14-35 . 
           [0051]      FIG. 53  depicts an isometric view of a second embodiment of an implant-grasper tool for use in combination with a second embodiment of a locking-plug inserter tool (see  FIGS. 63-69 ) and a second embodiment of a locking plug (see  FIGS. 60-62 ). 
           [0052]      FIG. 54  depicts a side view of the implant-grasper tool of  FIG. 53  exemplified in an open position. 
           [0053]      FIG. 55  depicts a side view of the implant-grasper tool of  FIG. 53  exemplified in an closed position. 
           [0054]      FIGS. 56-57  depict isometric views of elements of the implant-grasper tool of  FIG. 53 . 
           [0055]      FIG. 58  depicts an isometric view of a locking mechanism of the implant-grasper tool of  FIG. 53 . 
           [0056]      FIG. 59  depicts a side view of the locking mechanism of  FIG. 58 . 
           [0057]      FIG. 60  depicts an isometric view of the second embodiment of a locking plug for use in combination with the second embodiment of the implant-grasper tool of  FIGS. 53-59  and a second embodiment of a locking-plug inserter tool (see  FIGS. 63-69 ). 
           [0058]      FIG. 61  depicts a cross-sectional view of the locking plug of  FIG. 60  taken along section line  61 - 61 . 
           [0059]      FIG. 62  depicts a side view of the locking plug of  FIG. 60  taken along view  62 - 62 . 
           [0060]      FIG. 63  depicts an isometric view of the second embodiment of a locking-plug inserter tool for use in combination with the implant-grasper tool of  FIGS. 53-59  and the locking plug of  FIGS. 60-62 . 
           [0061]      FIGS. 64-66  depict side views of the locking-plug inserter tool of  FIG. 63 . 
           [0062]      FIG. 67  depicts a side view of an inserter housing of the locking-plug inserter tool of  FIG. 63 . 
           [0063]      FIGS. 68-69  depict side views of an inserter plunger of the locking-plug inserter tool of  FIG. 63 . 
           [0064]      FIG. 70  depicts an isometric view of a locking-plug extractor tool for use in combination with the second embodiment of the locking plug of  FIGS. 60-62 . 
           [0065]      FIG. 71  depicts an isometric view of an extractor body of the locking-plug extractor tool of  FIG. 70 . 
           [0066]      FIGS. 72-73  depict side views of the extractor body of  FIG. 71 . 
           [0067]      FIGS. 74-75  depict side views of an extractor cam of the locking-plug extractor tool of  FIG. 70 . 
           [0068]      FIG. 76  depicts an isometric view of a bobbin of the locking-plug extractor tool of  FIG. 70 . 
           [0069]      FIG. 77  depicts an isometric view of an extractor nut of the locking-plug extractor tool of  FIG. 70 . 
           [0070]      FIGS. 78-81  depict perspective views exemplifying the sequence of steps for implanting the ILFD of  FIG. 2  using the second embodiments of tooling shown in  FIGS. 53-69 . 
           [0071]      FIGS. 82-84  depict perspective views exemplifying the sequence of steps for extracting the locking plug of  FIGS. 60-62  using the locking-plug extractor tool of  FIGS. 78-81 . 
       
    
    
     DETAILED DESCRIPTION 
       [0072]    One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0073]    When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, any use of “top,” “bottom,” “above,” “below,” other directional terms, and variations of these terms is made for convenience, but does not require any particular orientation of the components. The terms “helical” and “spiral” are not intended to require perfectly mathematical helix or spirals, and are particularly intended to include square ended, closed ended, and ground versions of springs of these types, and also as the channels that would receive any of these shapes. 
         [0074]    Turning to  FIG. 1 , a side view of interlaminar fixation device (“ILFD”)  100  is exemplified having been implanted in spine  10  (only two vertebrae shown) of a patient. Spine  10  is oriented as shown by arrow  30 , wherein arrow  30  points cephalad (towards the head of the patient). Spine  10  comprises cephalad vertebra  14  having cephalad spinous process  16  and caudal vertebra  18  having caudal spinous process  20 . Disc  12  is located between the cephalad and caudal vertebrae  14  and  18  as shown. Supra spinous ligament, ligament flavum, interspinous ligament, etc. of spine  10  have been omitted for clarity. ILFD  100  is shown implanted between cephalad spinous process  16  and caudal spinous process  20  using the tooling and procedures described herein. 
         [0075]    Referring to  FIGS. 2-3 , ILFD  100  is exemplified in fully assembled form prior to detachment of breakaway portions (discussed below) of cephalad fixation-pin assembly  130  and caudal fixation-pin assembly  150 . ILFD  100  comprises implant body  110 , cephalad fixation-pin assembly  130 , caudal fixation-pin assembly  150 , and locking plug  170  (or alternatively locking plug  900 ). 
         [0076]    Referring to  FIGS. 4-7 , implant body  110  is shown in more detail. Implant body  110 , preferably fabricated from polyetheretherketone (PEEK), has: left surface  112   a  and an opposite right surface  112   b ; caudal surface  112   c  and an opposite cephalad surface  112   d ; and dorsal surface  112   e  and an opposite ventral surface  112   f . Orientation indicator  120  is provided on dorsal surface  112   e  to indicate visually proper orientation during implantation. Notches  114  are provided through left surface  112   a  and similarly on right surface  112   b  (not shown). Placement-detection rods  116  are provided as shown and are preferably tantalum rods or another material, such as titanium, that can be radiologically assessed. Fixation-pin openings  118  are provided through caudal surface  112   c  and similarly through cephalad surface  112   d  (not shown). Slot  122  is provided through dorsal surface  112   e  and is configured for receiving cephalad fixation-pin assembly  130 , caudal fixation-pin assembly  150 , and locking plug  170 . Implant body  110  has height h 1 . Preferably, implant bodies of various sizes will be on hand during implantation procedure and one of appropriate size for the patient is selected. Preferably, implant body  110  has two versions, one with height h 1  equal to 14 mm and the other with height h 1  equal to 16 mm. Preferably, implant body  110  has a depth (from dorsal surface  112   e  to ventral surface  112   f ) equal to 16 mm and a width (from left surface  112   a  to right surface  112   b ) equal to 8 mm. 
         [0077]    Referring to  FIGS. 8-9 , cephalad fixation-pin assembly  130  is provided. Fixation-pin  130  comprises rod  132  and cephalad fixation pins  134   a  and  134   b . Rod  132  has embedded portion  132   a  and breakaway portion  132   b , which are separated by breakaway notch  136 . Fixation pins  134   a  and  134   b  have a depth d 1 , which is preferably equal to 6 mm, and are preferably 1.5 mm in diameter at their base. Rod  132  preferably has a 2 mm×2 mm square cross section. Fixation pins  134   a  and  134   b  have tips or ends that are ogival as shown. Preferably, rod  132  and fixation pins  134   a  and  134   b  are fabricated from Tivanium®, however other suitable materials may be used. 
         [0078]    Referring to  FIGS. 10-11 , caudal fixation-pin assembly  150  is provided. Fixation-pin  150  comprises rod  152  and caudal fixation pins  154   a  and  154   b . Rod  152  has embedded portion  152   a  and breakaway portion  152   b , which are separated by breakaway notch  156 . Fixation pins  154   a  and  154   b  have a depth d 2 , which is preferably equal to 8 mm, and are preferably 1.5 mm in diameter at their base. Rod  152  preferably has a 2 mm×2 mm square cross section. Fixation pins  154   a  and  154   b  have tips or ends that are ogival as shown. Preferably, rod  152  and fixation pins  154   a  and  154   b  are fabricated from Tivanium®, however other suitable materials may be used. 
         [0079]    Referring to  FIGS. 12-13 , a first embodiment  170  of a locking plug in accordance with the present invention is provided. Locking plug  170  comprises plug body  172  having rounded-insertion surface  174 . Catch  176  is formed on one surface of plug body  172 . Two grasper-pin openings  178  are provided in plug body  172  in the side opposite rounded-insertion surface  174 . Preferably, locking plug  170  is 2 mm wide, 13 mm deep, and 6 mm high (for a 14 mm height implant body) or 8 mm high (for a 16 mm height implant body). Locking plug  170  is preferably fabricated from polyetheretherketone (PEEK). 
         [0080]    Referring to  FIG. 14 , implant-sizing tool  200  is provided. Implant-sizing tool  200  comprises handle  202 , handle linkage  204 , and trial implant  206 . Trial implant  206  has a threaded opening for connection with handle linkage  204  (not shown). Trial implant  206  is substantially similar to implant body  110 . Trial implant  206  has height h 2 . Preferably in practice, two trial implants are provided, one having height h 2  equal to 14 mm and another equal to 16 mm. Handle  202 , handle linkage  204 , and trial implant  206  are fabricated preferably from AISI 314L stainless steel. 
         [0081]    Referring to  FIGS. 15-21 , a first embodiment  300  of an implant-grasper tool is provided in accordance with the present invention. Implant-grasper tool  300  comprises: upper element  320  pivotally connected to lower element  350  by fastener  302 ; slot  306  when implant-grasper tool  300  is in the closed position (see  FIG. 16 ); fulcrum  310 ; and grasper portion  314 . Components of implant-grasper tool  300  are preferably fabricated from AISI 314L stainless steel. 
         [0082]    Upper element  320  comprises handle  322 , handle linkage  324 , fastener opening  326 , lock-mechanism opening  328  (optional), and lower portion  330 . Fulcrum protrusion  332  is formed at the medial end of lower portion  330  and is connected to grasper linkage  334 . Grasper detent  336  is formed at the distal end of grasper linkage  334 . Grasper plate  338  is connected to the distal end of grasper linkage  334  as shown and has grasper flange  340 . Grasper pins  342  are formed on one side of grasper plate  338  and are configured to mate with grasper-pin openings  178  on implant body  110  (see  FIG. 4 ). 
         [0083]    Lower element  350  comprises handle  352 , handle linkage  354 , fastener opening  356 , and lower portion  360 . Fulcrum protrusion  362  is formed at the medial end of lower portion  360  and is connected to grasper linkage  364 . Grasper plate  368  is connected to the distal end of grasper linkage  364  as shown and has grasper flange  370 . Grasper pins  372  are formed on one side of grasper plate  368  and are configured to mate with grasper-pin openings  178  on implant body  110  (see  FIG. 4 ). First grasper bar  376  is connected to the lower portion of grasper linkage  364  and grasper plate  368  as shown. Second grasper bar  378  is connected to grasper plate  368  and grasper flange  370  as shown. Grasper bars  376  and  378  protrude in parallel towards grasper plate  338  when implant-grasper tool  300  is in the closed position (see  FIG. 15 ). 
         [0084]    Optional, locking mechanism  390  is connected to upper element  320  at opening  328  by fastener  304  and is used to secure implant-grasper tool  300  in the closed position. Locking mechanism  390  comprises upper portion  392 , lateral portion  394 , and locking portion  396 . Fastener opening  398  is formed in lateral portion  394 . In yet other embodiments, locking mechanism may be connected to lower element  350  instead of upper element  320 . Alternatively, other means for locking implant-grasper tool  300  in the closed position may be used. 
         [0085]    Referring to  FIGS. 22-29 , a first embodiment  400  of a locking-plug inserter tool is provided. Locking-plug inserter tool  400  comprises handle element  410  pivotally connected to plunger element  440  by fastener  402 . Components of locking-plug inserter  400  are preferably fabricated from AISI 314L stainless steel. 
         [0086]    Handle element  410  comprises linkage portion  412 , grip portion  414 , pivot-point-engagement portion  418 , and fastener portion  420  as shown (see  FIGS. 23-24 ). Grip portion  414  is preferably knurled for enhanced gripping. Pivot-point-engagement portion  418  is configured to pivotally engage fulcrum  310  of implant-grasper tool  300 . 
         [0087]    Plunger element  440  comprises fastener portion  442  having fastener opening  444 , linkage portion  446 , threaded portion  448 , and deflectable-grasper portion  450  (see  FIGS. 25-26 ). Deflectable-grasper portion  450  has first deflectable member  452  and second deflectable member  454  defining closable gap  456  as shown (see  FIG. 25 ). Grasper pins  458  and  460  are formed on the ends of deflectable members  452  and  454 , respectively, and are configured for engaging grasper-pin openings  178  of locking plug  170 . 
         [0088]    Collet  470  is provided and is generally cylindrical (see  FIGS. 27-29 ). Collet  470  has grip surface  472  and hollow interior  474 . Grip surface  472  is preferably knurled for enhanced gripping. Threaded portion  476  is provided and configured for threaded engagement with threaded portion  448  of plunger element  440 . Clamping portion  478  having cambered portion  480  is also provided and is configured to urge deflectable members  452  and  454  together when collet  470  is rotated, thus resulting in a clamping force to secure locking-plug  170  to grasper portion  450  of plunger element  440  (see  FIG. 48 ). 
         [0089]    Referring to  FIGS. 30-32 , bone-punch tool  500  is provided. Bone-punch tool  500  comprises first and second elements  510   a  and  510   b  pivotally connected by fastener  502 . First element  510   a  comprises grip portion  512   a , fastener-opening portion  514   a , and punch-pin linkage portion  520   a . Punch pins  522   a  are connected to punch-pin linkage portion  520   a  and protrude outward by depth d 3 , which is preferably about 3 mm. Punch pins  522   a  have ends or tips that are ogival. Second element  510   b  is substantially identical to first element  510   a . Components of bone-punch tool  500  are preferably fabricated from AISI 314L stainless steel. 
         [0090]    Referring to  FIGS. 33-35 , pin-inserter tool  600  is provided. Pin-inserter tool  600  comprises first and second elements  610   a  and  610   b  pivotally connected by fastener  602 . First element  610   a  comprises grip portion  612   a , fastener-opening portion  614   a , and camming portion  616   a . Second element  610   b  is substantially identical to first element  610   a . Components of pin-inserter tool  600  are preferably fabricated from AISI 314L stainless steel. 
         [0091]    Method of Implantation 
         [0092]    To begin, the patient is administered general anesthesia and intubated, then placed in the prone position preferably on either a Jackson table or a radiolucent Wilson frame. After appropriate positioning and padding of the patient&#39;s extremities, the patient&#39;s position may be adjusted to reduce the degree of lumbar lordosis. The patient&#39;s lumbar area to be treated is then given a sterile prep and draped. 
         [0093]    Following appropriate pre-surgery protocol to confirm the patient&#39;s identification and the disc level for treatment, a sterile-draped C-arm is brought into the field and placed in a lateral position. An external marker is used and the surgical level identified. A mark is made on the patient&#39;s skin directly posterior to the appropriate disc level. An approximately 3 cm midline incision is then made with a scalpel centered over the mark. Electrocautery may be used to control bleeding and to dissect through the subcutaneous tissues down to the patient&#39;s lumbar fascia. The disc level is again confirmed preferably by lateral fluoroscopic image. 
         [0094]    Next, the fascia is carefully dissected from each side of the spinous processes of the selected level and taken down to the laminae. The interspinous ligament is then resected and the inferior overhang of the proximal spinous process is trimmed with a rongeur such that it is parallel to the superior edge of the spinous process on the distal vertebra. Trimming is continued until either an appropriate sized ILFD  100  will fit snugly between the spinous processes with moderate force. The size required will depend upon the patient size and anatomy. Preferably, at least two sizes of ILFDs  100  are available, preferably one having heights h 1  equal to 14 mm and or 16 mm. Implant-sizing  200 , with the appropriate sized trial implant  206 , is inserted to test whether an appropriate fit has been achieved. 
         [0095]    Next, decompression procedures are performed. The ligamentum flavum is dissected from the underside of the rostral vertebra. Then, preferably using a Woodson elevator, the median raphe is carefully explored with care not to enter the dural sac. The central portions of the ligamentum flavum are then pulled distally, morselized, and removed with Kerrison rongeurs. If necessary, a laminotomy may be performed in order to complete the decompression of the central spinal canal and to provide appropriate bearing surfaces for the implant. It is preferable that the laminotomy not exceed the extent of the trimming of the spinous processes as it is advantageous that the device be in contact with the laminae due to their superior strength relative to the spinous process. 
         [0096]    While carefully protecting the dural sac, the lateral slip of the ligamentum flavum may be removed. This will allow visualization of the ventral portion of the spondyloapophyseal joint and appropriate bony resection may be performed until the lateral recess is decompressed and the nerve root can be followed out into the neural foramen using preferably a ball tipped Murphy probe. The surgeon then may switch sides and repeat the process on the contralateral side. Following confirmation of decompression using Murphy probes, hemostasis may be achieved. 
         [0097]    Referring to  FIGS. 36-52 , a preferred method  700  of implanting ILFD  100  in a spine  10  (see  FIG. 1 ) of a patient using implant-sizing tool  200  (discussed above), implant-grasper tool  300 , locking-plug inserter tool  400 , bone-punch tool  500 , and pin-inserter  600  is described. For clarity, spine  10  is shown only in  FIG. 37  and omitted from  FIGS. 38-52 . 
         [0098]    The appropriately sized implant body  110  is selected. Then, it is grasped using implant-grasper tool  300  and locking mechanism  390  is engaged (step  702 ). Using implant-grasper tool  300  having grasped implant-body  110 , implant body  110  is positioned between the patient&#39;s spinous processes  16  and  20  and at the appropriate depth so that ventral surface  112   f  of implant body  110  is between the patient&#39;s laminae (step  704 ). When implant body  110  is oriented correctly, orientation indicator  120  on implant body  110  indicates the direction of the patient&#39;s head as shown by arrow  30  ( FIG. 37 ). Preferably, direct vision and lateral fluoroscopy are used to ensure that implant body  110  is at the appropriate depth, with ventral surface  112   f  firmly between the laminae but without any contact with, or compression of, the dural sac. 
         [0099]    Preferably, the surgeon positions himself on the side of the patient so that his dominant hand is caudal to the operative site. He then stabilizes implant-grasper tool  300  with his non-dominant hand and uses his dominant hand to insert bone-punch tool  500  (step  706   a ) and makes starter holes in the spinous process (step  706   b ). Fixation-pin assemblies  130  and  150  are then inserted one at a time (steps  708   a ,  708   b ,  714   a , and  714   b ) and pressed into place using pin-inserter tool  600  (steps  712   a ,  712   b ,  716   a , and  716   b ). Fixation-pin assemblies  130  and  150  may be inserted in either order. 
         [0100]    Next, locking plug  170  is inserted partially into implant body  110  (step  718 ). Then, preferably, breakaway portions  132   b  and  152   b  of fixation-pin assemblies  130  and  150 , respectively, are bent until failure at breakoff notches  136  and  156  (step  720 ). Alternatively, breakaway portions  132   b  and  152   b  may be cut off. Breakoff notches  136  and  156  may be discarded (step  722 ). 
         [0101]    Locking-plug inserter tool  400  is inserted into implant-grasper tool  300 . This is done by first inserting handle element  410  of locking-plug inserter tool  400  through slot  306  of implant-grasper tool  300 , then rotating locking-plug inserter tool  400  such that pivot-point engagement portion  418  engages fulcrum  310  (see  FIG. 47 ). Alternatively, plunger element  440  may be initially disassembled from handle element  410  and fastened to handle element  410  once properly inserted into implant-grasper tool  300 . Once grasper pins  458  and  460  of locking-plug inserter tool  400  engage grasper-pin openings  178  of locking plug  170  (see  FIGS. 12 and 25 ), collet element  470  is rotated, thus securing locking plug  170  (steps  724  and  726 ). Upward torque is then applied to grip portion  414  (step  728   a ), thereby causing locking plug  170  to be fully inserted into implant body  110  (step  728   b ). Collet element  470  is rotated in reverse (step  730   a ), thereby releasing locking plug  170  (step  730   b ). Locking-plug inserter tool  400  is removed. Lastly, grasper-lock mechanism  390  is disengaged (step  732   a ), handles  322  and  352  are urged apart (step  732   b ), implant body  110  is released (step  732   c ), and implant-grasper tool  300  is removed. 
         [0102]    Finally, x-rays may be taken for medical records. After checking that adequate hemostasis is maintained, the incision is closed preferably by using number 1 Vicryl in the lumbar fascia, 2-O Vicryl in the subcutaneous tissues and subcuticular 3-O Vicryl V-Loc suture for the skin. A Dermabond dressing is preferably then applied, and the patient is transferred to the post anesthetic recovery unit. 
         [0103]    If more than one disc level is to be done during the same operation, the above procedure may be repeated. 
       Alternate Embodiment 
       [0104]    A second embodiment of certain tooling is provided in  FIGS. 53-77  in accordance with principles of the present invention. These second embodiments are used with implant body  110 , fixation-pin assemblies  130  and  150 , implant-sizing tool  200 , bone-punch tool  500 , and pin-inserter tool  600 . 
         [0105]    Turning to  FIGS. 53-59 , a second embodiment  800  of an implant-grasper tool is provided in accordance with the present invention. Implant-grasper tool  800  comprises: first element  820  pivotally connected to second element  850  by fastener  802 ; horn  806 ; and grasper portion  814 . Components of implant-grasper tool  800  are preferably fabricated from AISI 314L stainless steel. 
         [0106]    First element  820  comprises handle  822 , handle linkage  824 , fastener opening  826 , lock-mechanism opening  828  (optional), and lower portion  830 . Horn protrusion  832  is formed at the medial end of lower portion  830  and is connected to grasper linkage  834 . Grasper detent  836  is formed at the distal end of grasper linkage  834 . Grasper plate  838  is connected to the distal end of grasper linkage  834  as shown and has grasper flange  840 . Grasper pins  842  are formed on one side of grasper plate  838  and are configured to mate with grasper-pin openings  178  on implant body  110  (see  FIG. 4 ). 
         [0107]    Second element  850  comprises handle  852 , handle linkage  854 , fastener opening  856 , and lower portion  860 . Horn protrusion  862  is formed at the medial end of lower portion  860  and is connected to grasper linkage  864 . Grasper plate  868  is connected to the distal end of grasper linkage  864  as shown and has grasper flange  870 . Grasper pins  872  are formed on one side of grasper plate  868  and are configured to mate with grasper-pin openings  178  on implant body  110  (see  FIG. 4 ). First grasper bar  876  is connected to the lower portion of grasper linkage  864  and grasper plate  868  as shown. Second grasper bar  878  is connected to grasper plate  868  and grasper flange  870  as shown. Grasper bars  876  and  878  protrude in parallel towards grasper plate  868  when implant-grasper tool  800  is in the closed position (see  FIG. 53 ). 
         [0108]    Optional, locking mechanism  890  is connected to first element  820  at opening  828  by fastener  804  and is used to secure implant-grasper tool  800  in the closed position. Locking mechanism  890  comprises upper portion  892 , lateral portion  894 , and locking portion  896 . Fastener opening  898  is formed in lateral portion  894 . In yet other embodiments, locking mechanism may be connected to second element  850  instead of first element  820 . Alternatively, other means for locking implant-grasper tool  800  in the closed position may be used. 
         [0109]    Referring to  FIGS. 60-62 , a second embodiment  900  of a locking plug in accordance with the present invention is provided. Locking plug  900  comprises plug body  902  having rounded-insertion surface  904 . Catch  906  is formed on one surface of plug body  902 . Grasper opening  920  is provided in plug body  902  in the side opposite rounded-insertion surface  904 . A rectangular, alignment slot  922  is provided in grasper opening  920 . A threaded, extraction slot  924  is also provided as shown. Optionally, guide channel  926  is also provided. Grasper opening  920  is configured for receiving tip  1070  of locking-plug inserter  1000  (shown in  FIGS. 63-69 ) and also threaded tip  1184  of extractor nut  1180  (shown in  FIG. 77 ). In other embodiments, a non-threaded extraction slot is provided, which may be used with a self-tapping extraction nut. Preferably, locking plug  900  is 2 mm wide, 13 mm deep, and 6 mm high (for use with a 14 mm height implant body) or 8 mm high (for use with a 16 mm height implant body). Locking plug  900  is preferably fabricated from polyetheretherketone (PEEK). 
         [0110]    Referring to  FIGS. 63-69 , a second embodiment  1000  of a locking-plug inserter tool is provided. Locking-plug inserter tool  1000  comprises inserter housing  1010  in slidable engagement with inserter plunger  1050 . Components of locking-plug inserter  1000  are preferably fabricated from AISI 314L stainless steel. 
         [0111]    Inserter housing  1010  comprises body  1012 . Body  1012  is generally cylindrical having hollow interior  1020  configured for housing body  1052  of inserter plunger  1050  (see  FIG. 68 ). Seat  1014 , preferably concave, is provided at a first end of body  1012  and is configured for mating with horn  806  of inserter-grasper tool  800  (see  FIG. 79 ). Assembly channel  1024  is provided in the end distal to seat  1014  and is configured for allowing trigger  1060  of inserter plunger  1050  (see  FIG. 68 ) to slide through when plunger  1050  is inserted into body  1012  to fully assemble locking-plug inserter  1000 . Plug-insertion channel  1022  is provided in body  1012  and is configured to provide sufficient travel, preferably 11 mm, for inserter plunger  1050  to fully insert locking plug  900  into implant body  110  during implantation as discussed below. Trigger  1016  is provided and is circumferentially offset from plug-insertion channel  1022  as shown in  FIG. 66 . 
         [0112]    Inserter plunger  1050  comprises body  1052 , trigger  1060 , and inserter tip  1070 . Stops  1062  and  1064  are provided and are configured for engagement with ends of plug-insertion channel  1022  and are configured to allow passage through assembly channel  1024  during assembly of locking-plug inserter  1000 . Alignment portion  1072  of inserter tip  1070  is provided and is configured for aligned engagement with alignment slot  922  of locking plug  900 . Guide portion  1074  of inserter tip  1070  is provided and is configured for engagement with guide channel  926  of locking plug  900 . 
         [0113]    Referring to  FIGS. 70-77 , locking-plug extractor tool  1100  is provided. Locking-plug extractor tool  1100  comprises: extractor body  1110 , extractor cam  1140 , bobbin  1170 , and extractor nut  1180 . Extractor body  1110  is pivotally connected to extractor cam  1140 . Extractor nut  1180  is concentrically within bobbin  1170 , and both are in a camming relationship with extractor cam  1140 . Components of locking-plug extractor  1100  are preferably fabricated from AISI 314L stainless steel. 
         [0114]    Referring more particularly to  FIGS. 71-73 , extractor body  1110  comprises handle  1112  and brace frame  1114 . Fastener opening  1114  is provided for receiving fastener  1102 . Extractor opening  1118  is provided and is configured for receiving bobbin  1170 . 
         [0115]    Referring more particularly to  FIGS. 74-75 , extractor cam  1140  comprises handle  1142  and cam head  1144 . Camming surface  1146  is provided on cam head  1144 . Fastener opening  1148  is provided for receiving fastener  1102 . 
         [0116]    Referring more particularly to  FIG. 76 , bobbin  1170  is provided. Bobbin  1170  comprises cylindrical body  1172  having hollow interior  1174 . Hollow interior  1174  is configured for receiving body  1182  of extractor nut  1180  (see  FIG. 77 ). Bobbin head  1176  is also provided and is configured for engagement with camming surface  1146  of extractor cam  1140  and also is configured for engagement with extractor-nut head  1186  of extractor nut  1180 . 
         [0117]    Referring more particularly to  FIG. 77 , extractor nut  1180  is provided. Extractor nut  1180  comprises cylindrical body  1182  having threaded tip  1184 . Threaded tip  1184  is configured for engaging extraction slot  924  of locking plug  900  (see  FIG. 61 ). Extractor-nut head  1186  is configured for engagement with bobbin head  1176  of bobbin  1170 . 
         [0118]    Method of Implantation Using Second Embodiment 
         [0119]    Referring to  FIGS. 78-81 , a preferred method  1200  of implanting ILFD  100  using locking plug  900  (instead of  170 ) in a spine  10  (see  FIG. 1 ) of a patient using implant-sizing tool  200  (discussed above), implant-grasper tool  800 , locking-plug inserter tool  1000 , bone-punch tool  500 , and pin-inserter  600  is described. For clarity, spine  10  is omitted. Method  1200  is substantially the same as described above and shown in  FIGS. 36-52 , except as described below. 
         [0120]    In method  1200 , assembly and placement of implant body  110 , fixation-pin assemblies  130  and  150 , locking plug  900  as shown in  FIG. 78 , and preceding steps, are substantially the same as described above and shown in  FIGS. 36-44 . Next, locking-plug inserter tool  1000  is positioned so that concave seat  1014  engages horn  806  (step  1202 ). Trigger  1060  is then depressed until inserter tip  1070  addresses grasper opening  920  of locking plug  900  (step  1204 ) and then fully depressed until stop  1064  reaches the end of channel  1022 , at which point locking plug  900  will be fully inserted (steps  1208  and  1210 ). Trigger  1060  is then raised (step  1212 ) and locking-plug inserter tool  1000  is removed (step  1214 ). Breakaway portions  132   b  and  152   b  of fixation-pin assemblies  130  and  150  may be removed now or, alternatively, have been removed after partial insertion of locking plug  900  (see  FIG. 45 ). Lastly, implant-grasper tool  800  may be removed as shown in  FIG. 52  and described above and all remaining steps may be performed. 
         [0121]    Method of Extraction 
         [0122]    Referring to  FIGS. 82-84 , a preferred method  1300  of extracting locking plug  900  from implant body  110  is provided. For clarity, spine  10  is omitted. The surgical steps are substantially the same as described above. 
         [0123]    First, locking-plug extractor tool  1100  is positioned over implant body  110  such that threaded tip  1184  of extractor nut  1180  is proximate to grasper opening  920  of locking plug  900  (step  1302 ). Next, wing  1188  is rotated such that threaded tip  1184  engages extraction slot  924  of grasper opening  920  (step  1304 ). Then, handle  1142  of extractor cam  1140  is raised (step  1306 ). This creates a camming action that urges bobbin  1170  upwards and extractor nut  1180  upwards, thereby partially extracting locking plug  900  from implant body  110 . Lastly, locking-plug extractor tool  1100  and locking plug  900  are removed and the ILFD may be disassembled and removed. 
         [0124]    While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.