Patent Publication Number: US-2005137596-A1

Title: Spinal-column buttress plate assembly and method for attachment

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates generally to medical apparatus and procedures, and more particularly to apparatus and a method which attaches a spinal-column buttress plate to two vertebral bodies of a spinal column of a medical patient.  
      Conventional medical procedures include attaching together (sometimes called fusing) first and second vertebral bodies of a spinal column (such as adjacent first and second cervical vertebral bodies of the cervical column portion of the spinal column) of a medical patient. A spinal-vertebral buttress plate (such as a cervical-vertebral buttress plate) of appropriate length is obtained. The buttress plate is positioned on the anterior side of the first and second vertebral bodies. The buttress plate comes with pre-drilled holes. Using first and second holes, of the positioned buttress plate, which are aligned over the first vertebral body, first and second starter holes are marked and drilled on the anterior cortex of the first vertebral body. Using third and fourth holes, of the positioned buttress plate, which is aligned over the second vertebral body, third and fourth starter holes are marked and drilled on the anterior cortex of the second vertebral body. A first bone screw is inserted in the first hole and a second bone screw is inserted in the second hole of the buttress plate and threaded into the corresponding starter hole in the anterior cortex of the first vertebral body, and a third bone screw is inserted in the third hole and a fourth bone screw is inserted in the fourth hole of the buttress plate and threaded into the corresponding starter hole in the anterior cortex of the second vertebral body. With the four bone screws securing the spinal-column buttress plate to the first and second vertebral bodies, the first and second vertebral bodies are thereby attached together (or fused) preventing their relative movement. Attachment problems arise when the pre-drilled holes of the spinal-column buttress plate are only alignable over a non-optimum area of the first and/or second vertebral body.  
      What is needed is a spinal-column buttress plate assembly (such as a cervical-column buttress plate assembly) and a method for attachment which provides better attachment of the spinal-column (e.g., cervical-column) buttress plate to the first and second vertebral bodies (e.g., the first and second cervical vertebral bodies.  
     SUMMARY OF THE INVENTION  
      A first expression of a preferred embodiment of the invention is for a cervical-column buttress plate assembly for fusing together first and second cervical vertebral bodies of a cervical column of a medical patient. The buttress plate assembly includes a first cervical-vertebral buttress plate, a first screw assembly, and a second screw assembly. The cervical-vertebral buttress plate has an elongated slot with opposing and serrated edges. The first screw assembly includes a first bone screw and a first inner screw. The first bone screw has an internally-threaded hole, has an externally-threaded shaft which is threadably insertable into the first cervical vertebral body of the cervical column of the medical patient and which has an expandable tip, and has an expandable head which is attached to the shaft and which has external teeth. The second screw assembly has a second bone screw and a second inner screw. The second bone screw has an internally-threaded hole, has an externally-threaded shaft which is threadably insertable into the second cervical vertebral body of the cervical column of the medical patient and which has an expandable tip, and has an expandable head which is attached to the shaft and which has external teeth. The first and second inner screws are engageable, respectively, in the internally-threaded holes of the first and second bone screws to expand the tips of the first and second bone screws against the first and second cervical vertebral bodies and to expand the heads of the first and second bone screws to engage the external teeth of the heads of the first and second bone screws against the opposing and serrated edges of the elongated slot of the buttress plate after the elongated slot of the buttress plate has been disposed to enclose the heads of the first and second bone screws after the first and second bone screws have been threadably inserted into the first and second vertebral bodies.  
      A second expression of a preferred embodiment of the invention is for a spinal-column buttress plate assembly for attaching together first and second vertebral bodies of a spinal column of a medical patient. The buttress plate assembly includes a spinal-vertebral buttress plate, a first screw assembly, and a second screw assembly. The buttress plate has an elongated slot with opposing edges. The first screw assembly includes a first bone screw and a first inner screw. The first bone screw has an internally-threaded hole, has a shaft which is insertable into the first vertebral body of the spinal column of the medical patient, and has an expandable head which is attached to the shaft and which has a first unexpanded state and a first expanded state. The head of the first bone screw is small enough to pass through the elongated slot in the first unexpanded state but not in the first expanded state. The second screw assembly includes a second bone screw and a second inner screw. The second bone screw has an internally-threaded hole, has a shaft which is insertable into the second vertebral body of the spinal column of the medical patient, and has an expandable head which is attached to the shaft and which has a second unexpanded state and a second expanded state. The head of the second bone screw is small enough to pass through the elongated slot in the second unexpanded state but not in the second expanded state. The first and second inner screws are engageable, respectively, in the internally-threaded holes of the first and second bone screws to expand the heads of the first and second bone screws to engage the heads of the first and second bone screws against the opposing edges of the elongated slot of the buttress plate after the elongated slot of the buttress plate has been disposed to enclose the heads of the first and second bone screws after the first and second bone screws have been inserted into the first and second vertebral bodies.  
      An alternate preferred embodiment is identical to the previously-described second expression of the preferred embodiment except that the buttress plate has first and second elongated slots with the first bone screw associated with the first elongated slot and with the second bone screw associated with the second elongated slot.  
      A first expression of a method of the invention is for fusing together first and second vertebral bodies of a spinal column of a medical patient and includes steps a) through h). Step a) includes obtaining first and second bone screws each having an internally-threaded hole, each having a shaft with an expandable tip, and each having an expandable head attached to the shaft and having external teeth. Step b) includes obtaining first and second inner screws engageable, respectively, with the internally-threaded holes of the first and second bone screws to expand the tips and the heads of the first and second bone screws. Step c) includes obtaining a buttress plate having an elongated slot with opposing and serrated edges. Step d) includes inserting the first bone screw into the first vertebral body of the spinal column of the medical patient with the head of the first bone screw protruding above the first vertebral body. Step e) includes inserting the second bone screw into the second vertebral body of the spinal column of the medical patient with the head of the second bone screw protruding above the second vertebral body. Step f) includes placing the buttress plate on the first and second vertebral bodies with the heads of the first and second bone screws disposed in the elongated slot of the buttress plate. Step g) includes threading the first inner screw into the internally-threaded hole of the first bone screw expanding the tip of the first bone screw against the first vertebral body and expanding the head of the first bone screw to engage the external teeth of the head of the first bone screw against the opposing and serrated edges of the elongated slot of the buttress plate. Step h) includes threading the second inner screw into the internally-threaded hole of the second bone screw expanding the tip of the second bone screw against the second vertebral body and expanding the head of the second bone screw to engage the external teeth of the head of the second bone screw against the opposing and serrated edges of the elongated slot of the buttress plate.  
      A second expression of a method of the invention is for attaching together first and second vertebral bodies of a spinal column of a medical patient and includes steps a) through h). Step a) includes obtaining first and second bone screws each having an internally-threaded hole, each having a shaft, and each having an expandable head attached to the shaft. Step b) includes obtaining first and second inner screws engageable, respectively, with the internally-threaded holes of the first and second bone screws to expand the heads of the first and second bone screws. Step c) includes obtaining a buttress plate having an elongated slot with opposing edges. Step d) includes inserting the first bone screw into the first vertebral body of the spinal column of the medical patient with the head of the first bone screw protruding above the first vertebral body. Step e) includes inserting the second bone screw into the second vertebral body of the spinal column of the medical patient with the head of the second bone screw protruding above the second vertebral body. Step f) includes placing the buttress plate on the first and second vertebral bodies with the heads of the first and second bone screws disposed in the elongated slot of the buttress plate. Step g) includes threading the first inner screw into the internally-threaded hole of the first bone screw expanding the head of the first bone screw to engage the head of the first bone screw against the opposing edges of the elongated slot of the buttress plate. Step h) includes threading the second inner screw into the internally-threaded hole of the second bone screw expanding the head of the second bone screw to engage the head of the second bone screw against the opposing edges of the elongated slot of the buttress plate.  
      An alternate second expression of a method of the invention is identical to the previously-described second expression of a method of the invention except that the buttress plate has first and second elongated slots with the first bone screw associated with the first elongated slot and with the second bone screw associated with the second elongated slot.  
      A third expression of a method of the invention is for attaching together first and second vertebral bodies of a spinal column of a medical patient and includes steps a) through e). Step a) includes obtaining first and second bone screws. Step b) includes obtaining a buttress plate. Step c) includes inserting the first bone screw into the first vertebral body of the spinal column of the medical patient. Step d) includes inserting the second bone screw into the second vertebral body of the spinal column of the medical patient. Step e) includes attaching the buttress plate to the first and second bone screws after performing steps a) through d).  
      Several benefits and advantages are derived from the invention. The apparatus and method of the invention allows a physician to choose an optimum location for the first bone screw on the first vertebral body (e.g., on the first cervical vertebral body) and to choose an optimum location for the second bone screw on the second vertebral body (e.g., on the second cervical vertebral body) for maximum attachment strength and mechanical stability. This is accomplished by first installing the bone screws on the vertebral bodies and then securing the buttress plate to the installed bone screws. In comparison, the prior art forces the physician to use pre-drilled holes in the buttress plate which often provide less than optimum attachment locations (providing less attachment strength and less mechanical stability) for the bone screws to be installed in the vertebral bodies. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic, top planar view a preferred embodiment of the buttress plate assembly of the invention (showing a buttress plate and three screw assemblies) attached to three vertebral bodies of a spinal column of a medical patient;  
       FIG. 2  is a cross-sectional view of the buttress plate assembly and one of the vertebral bodies of  FIG. 1  taken along lines  2 - 2  in  FIG. 1 ;  
       FIG. 3  is a schematic, top planar view of the buttress plate portion of the buttress plate assembly of  FIGS. 1 and 2 ;  
       FIG. 4  is a cross-sectional view of the buttress plate of  FIG. 3  taken along lines  4 - 4  in  FIG. 3 ;  
       FIG. 5  is a front elevational view of a bone screw portion of a first screw assembly of  FIGS. 1 and 2 ;  
       FIG. 6  is a top planar view of the bone screw of  FIG. 5 ;  
       FIG. 7  is a side elevational view of the bone screw of  FIG. 5 ;  
       FIG. 8  is a front elevational view of an inner screw portion of the first screw assembly of FIGS.  1  and;  
       FIG. 9  is a schematic, top planar view of an alternate preferred embodiment of a buttress plate showing multiple elongated slots having various orientations. 
    
    
     DETAILED DESCRIPTION  
      A preferred embodiment of the invention, shown in  FIGS. 1-8 , is for a spinal-column buttress plate assembly  10  for attaching together first and second vertebral bodies  12  and  14  of a spinal column  16  of a medical patient  18  (only a portion of the spinal column of whom is shown in  FIG. 1 ). Preferably, the spinal column  16  is a cervical column, the first and second vertebral bodies  12  and  14  are first and second cervical vertebral bodies, the spinal-column buttress plate assembly  10  is a cervical-column buttress plate assembly, and the spinal-column buttress plate assembly  10  is for fusing together the first and second cervical vertebral bodies of the cervical column of the medical patient. Preferably, the cervical-column buttress plate assembly is an anterior cervical-column buttress plate assembly. In other medical procedures, the first and second vertebral bodies  12  and  14  are vertebral bodies of an upper back portion and/or a lower back portion of the spinal column. Preferably the medical patient is a person, although the buttress plate assembly  10  of the invention is applicable to animals having spinal columns with vertebral bodies. It is noted that the terminology “first (or second) vertebral body” means a vertebral body (also known as a vertebral level) and is not limited to a specific vertebral body medically known as the first (or second) vertebral body or level.  
      The spinal-column buttress plate assembly  10  of  FIGS. 1-8  includes a spinal-vertebral buttress plate  20 , a first screw assembly  22 , and a second screw assembly  24 . Preferably, the spinal-vertebral buttress plate  20  is a cervical-vertebral buttress plate. The buttress plate  20  has an elongated (and preferably longitudinal) slot  26  with opposing edges  28  and  30 , and preferably the opposing edges  28  and  30  are opposing and serrated edges. In a preferred construction, the buttress plate  20  comprises (and preferably consists essentially of, and more preferably consists of) titanium or a titanium alloy.  
      The first screw assembly  22  includes a first bone screw  32  and a first inner screw  34  having threads which are preferably tapered. The first bone screw  32  has an internally-threaded hole  36  which preferably is a through hole coaxially aligned with the longitudinal axis of the first bone screw  32  (not to be confused with the longitudinal axis of the buttress plate). The first bone screw  32  also has a shaft  38  which is insertable into the first vertebral body  12  of the spinal column  16  of the medical patient  18 . Preferably, the shaft  38  is an externally-threaded shaft which is threadably insertable into the first vertebral body  12 . It is noted that the terminology “bone screw” includes any elongated member, threaded or non-threaded, which is securable within a bone. Typically, a starter hole is made by an awl, and the first bone screw  32  is inserted into the starter hole. The first bone screw  32  additional has an expandable head  40  attached to the shaft  38 . The expandable head  40  has a first unexpanded state and a first expanded state. The head  40  of the first bone screw  32  is small enough to pass through the elongated slot  26  in the first unexpanded state but not in the first expanded state. In one design, the head  40  has a longitudinal slit  42  which allows head expansion. Preferably, the shaft  38  has an expandable tip  44 . In one design, the tip  44  has a longitudinal slit  46  which allows tip expansion. Preferably, the expandable head  40  has external teeth  48 .  
      The second screw assembly  24 , shown in  FIG. 1 , is substantially identical to the first screw assembly  22  shown in detail in  FIGS. 2 and 5 - 8 , and therefore details of the second screw assembly  24  are not separately shown. The second screw assembly  24  includes a second bone screw substantially identical to the first bone screw  32  and a second inner screw substantially identical to the first inner screw  34 . The second bone screw has an internally-threaded hole which preferably is a through hole coaxially aligned with the longitudinal axis of the second bone screw (not to be confused with the longitudinal axis of the buttress plate). The second bone screw also has a shaft which is insertable into the second vertebral body  14  of the spinal column  16  of the medical patient  18 . Preferably, the shaft is an externally-threaded shaft which is threadably insertable into the second vertebral body  14 . It is noted that the terminology “bone screw” includes any elongated member, threaded or non-threaded, which is securable within a bone. Typically, a starter hole is made by an awl, and the second bone screw is inserted into the starter hole. The second bone screw additional has an expandable head attached to the shaft. The expandable head has a second unexpanded state and a second expanded state. The head of the second bone screw is small enough to pass through the elongated slot in the second unexpanded state but not in the second expanded state. In one design, the head has a longitudinal slit which allows head expansion. Preferably, the shaft has an expandable tip. In one design, the tip has a longitudinal slit which allows tip expansion. Preferably, the expandable head has external teeth.  
      The first and second inner screws  34  are engageable, respectively, in the internally-threaded holes  36  of the first and second bone screws  32  to expand the heads  40  of the first and second bone screws  32  to engage the heads  40  of the first and second bone screws  32  against the opposing edges  28  and  30  of the buttress plate  20  after the elongated slot  26  of the buttress plate has been disposed to enclose the heads  40  of the first and second bone screws  32  after the first and second bone screws  32  have been inserted into the first and second vertebral bodies  12  and  14 . Preferably, the first and second inner screws  34  are engageable, respectively, in the internally-threaded holes  36  of the first and second bone screws  32  to expand the tips  44  of the first and second bone screws against the first and second cervical vertebral bodies and to expand the heads  40  of the first and second bone screws to engage the external teeth  48  of the heads of the first and second bone screws against the opposing and serrated edges of the buttress plate  20  after the elongated slot of the buttress plate has been disposed to enclose the heads of the first and second bone screws after the first and second bone screws have been threadably inserted into the first and second vertebral bodies. In one example, the heads  40  have different textured outer surfaces (instead of the preferred longitudinally-extending external teeth) and the opposing edges  28  and  30  have different textured surfaces (instead of the preferred serrations) to have the heads better grip the opposing edges.  
      In a preferred construction, the buttress plate  20  includes claws (i.e., bone claws)  50  engageable with the first and second vertebral bodies  12  and  14 . The claws  50  provide the buttress plate  20  with a better grip on the first and second vertebral bodies  12  and  14 . The bone claws are located along the prominent edges of the inferior side of the buttress plate  20 . In an example, the first bone screw  32  includes first means  52  for trapping the first inner screw  34  when the first inner screw  34  is fully engaged in the internally-threaded hole  36  of the first bone screw  32 , and wherein the second bone screw includes second means for trapping the second inner screw when the second inner screw is fully engaged in the internally-threaded hole of the second bone screw. This will prevent the first inner screw  34  from backing out of the first bone screw  32 . Preferably, the second means is substantially identical to the first means  52 , and the first means includes a lip  54  which is attached to, or a monolithic portion of, the shaft  38 . Other means include conventional anti-rotation features employed with, or on, conventional bolts and screws, as is known to those skilled in the art. For example, in one variation (not shown), a screw cap (which either is separate from or attached to the first inner screw) further secures the first inner screw to the first bone screw preventing screw back out. In a preferred design, the head  40  of the first bone screw  32  has a substantially rectangular shape, and the head of the second bone screw has a substantially rectangular shape. This will provide a better grip for the expansion of the head  40  against the opposing edges  28  and  30 .  
      The spinal-column buttress plate assembly  10  of  FIG. 1  includes a third screw assembly  56 , substantially identical to the first screw assembly  22 , whereby the spinal-vertebral buttress plate  20  is also attached to a third vertebral body  58  of the spinal column  16 . Different buttress plates may span two or more vertebral bodies depending on the needs of a particular medical application. Preferably, the buttress plate  20  is narrow-waisted over soft tissue regions  60  between the vertebral bodies  12 ,  14 , and  58 , as seen in  FIG. 1 . Each narrow-waisted region of the buttress plate  20  provides a bend zone for inter-operative modification, as can be appreciated by the artisan. Preferably, there is one bone screw for each involved vertebral level (i.e., body).  
      An alternate embodiment of the buttress plate  62  is shown in  FIG. 9  as including a first elongated slot  64 , a second elongated slot  66 , and additional elongated slots  68  and  70 . Here, the head  40  of the first bone screw  32  is small enough to pass through the first elongated slot  64  in the first unexpanded state but not in the first expanded state, and the head of the second bone screw is small enough to pass through the second elongated slot  66  in the second unexpanded state but not in the second expanded state. The first elongated slot  64  is disposed to enclose the head  40  of the first bone screw  32 , and the second elongated slot  66  is disposed to enclose the head of the second bone screw after the first bone screw  32  has been inserted into the first vertebral body  12  and the second bone screw has been inserted into the second vertebral body  14 . It is noted that the first and second elongated slots  64  and  66  are horizontal slots, but that other applications require that the bone screws be engaged in longitudinal or oblique elongated slots  68  and  70  or in any combination of arbitrarily-aligned elongated slots and/or arbitrarily-located holes.  
      An example of a buttress plate  20  for cervical use is a buttress plate having rounded edges, having a length sufficient to span the required number of vertebral bodies to be fused, having a thickness of substantially 3 mm, having a width of substantially 18 mm over a vertebral body, having a width of substantially 10 mm over a soft tissue region, having a slot substantially 25 mm long and 4 mm wide with a substantially 1 mm wide and 1 mm deep chamfered perimeter extension. The chamfered perimeter extension allows the first inner screw  34  to sit flush with the surface of the buttress plate  20 , as seen in  FIG. 2 . An example of a first bone screw  32  is a bone screw having a length of between substantially 12 and 16 mm, having a diameter of substantially 5 mm which will be positioned perpendicular to the anterior cortex and along the cephalo-caudal midline of each involved vertebral body. A typical use is to install the buttress plate after a graft to a soft tissue region so that the installed buttress plate provides intervertebral graft stabilization and fixation of the anterior cervical column. Preferably, a conventional-design adjustable-depth driver is used to insert the first bone screw  32  which prevents the first bone screw  32  from being driven beyond the proper depth into the first vertebral body  12 . Preferably, the buttress plate  20  has an overall lordotic curve in the widthwise direction to match the curve of a vertebral body.  
      A first preferred method of the invention is for fusing together first and second vertebral bodies  12  and  14  of a spinal column  16  of a medical patient  18 , and the method includes steps a) through h). Step a) includes obtaining first and second bone screws  32  each having an internally-threaded hole  36 , each having a shaft  38  with an expandable tip  44 , and each having an expandable head  40  attached to the shaft  38  and having external teeth  48 . Step b) includes obtaining first and second inner screws  34  engageable, respectively, with the internally-threaded holes  36  of the first and second bone screws  32  to expand the tips  44  and the heads  40  of the first and second bone screws  32 . Step c) includes obtaining a buttress plate  20  having an elongated slot  26  with opposing and serrated edges. Step d) includes inserting the first bone screw  32  into the first vertebral body  12  of the spinal column  16  of the medical patient  18  with the head  40  of the first bone screw  32  protruding above the first vertebral body  12 . Step e) includes inserting the second bone screw into the second vertebral body  14  of the spinal column of the medical patient with the head of the second bone screw protruding above the second vertebral body. Step f) includes placing the buttress plate  20  on the first and second vertebral bodies  12  and  14  (with or without an intervening layer of something else) with the heads  40  of the first and second bone screws  32  disposed in the elongated slot  26  of the buttress plate  20 . Step g) includes threading the first inner screw  34  into the internally-threaded hole  36  of the first bone screw  32  expanding the tip  44  of the first bone screw  32  against the first vertebral body  12  and expanding the head  40  of the first bone screw  32  to engage the external teeth  48  of the head  40  of the first bone screw  32  against the opposing and serrated edges of the elongated slot  26  of the buttress plate  20 . Step h) includes threading the second inner screw into the internally-threaded hole of the second bone screw expanding the tip of the second bone screw against the second vertebral body  14  and expanding the head of the second bone screw to engage the external teeth of the head of the second bone screw against the opposing and serrated edges of the buttress plate.  
      A second preferred method of the invention is for attaching together first and second vertebral bodies  12  and  14  of a spinal column  16  of a medical patient  18 , and the method includes steps a) through h) Step a) includes obtaining first and second bone screws  32  each having an internally-threaded hole  36 , each having a shaft  38 , and each having an expandable head  40  attached to the shaft  38 . Step b) includes obtaining first and second inner screws  34  engageable, respectively, with the internally-threaded holes  36  of the first and second bone screws  32  to expand the heads  40  of the first and second bone screws. Step c) includes obtaining a buttress plate  20  having an elongated slot  26  with opposing edges  28  and  30 . Step d) includes inserting the first bone screw  32  into the first vertebral body  12  of the spinal column  16  of the medical patient  18  with the head  40  of the first bone screw  32  protruding above the first vertebral body  12 . Step e) includes inserting the second bone screw into the second vertebral body  14  of the spinal column of the medical patient with the head of the second bone screw protruding above the second vertebral body. Step f) includes placing the buttress plate  20  on the first and second vertebral bodies  12  and  14  (with or without an intervening layer of something else) with the heads  40  of the first and second bone screws  32  disposed in the elongated slot  26  of the buttress plate  20 . Step g) includes threading the first inner screw  34  into the internally-threaded hole  36  of the first bone screw  32  expanding the head  40  of the first bone screw  32  to engage the head  40  of the first bone screw  32  against the opposing edges  28  and  30  of the elongated slot  26  of the buttress plate  20 . Step h) includes threading the second inner screw into the internally-threaded hole of the second bone screw expanding the head of the second bone screw to engage the head of the second bone screw against the opposing edges of the elongated slot of the buttress plate.  
      In an alternate method, the buttress plate  62  has first and second elongated slots  64  and  66 , and step f) places the buttress plate  62  so that the first bone screw  32  is disposed in the first elongated slot  64  and the second bone screw is disposed in the second elongated slot  66 .  
      In the first and second preferred methods of the invention, preferably, the first and second vertebral bodies  12  and  14  are adjacent first and second vertebral bodies of the spinal column such as adjacent first and second cervical vertebral bodies of the spinal column. In these two methods, preferably step d) inserts the first bone screw  32  into the anterior cortex of the first (e.g., cervical) vertebral body  12 , and step e) inserts the second bone screw into the anterior cortex of the second (e.g., cervical) vertebral body. Also in these two methods, preferably step d) inserts the first bone screw  32  into the first (e.g., cervical) vertebral body  12  along the midline of the first (e.g., cervical) vertebral body  12 , and wherein step e) inserts the second bone screw into the second (e.g., cervical) vertebral body  14  along the midline of the second (e.g., cervical) vertebral body. It is preferred in these two methods that the buttress plate  20  has claws  50 , and that step f) includes tamping down the buttress plate  20  to engage the claws  50  into the anterior cortex of the first and second (e.g., cervical) vertebral bodies  12  and  14 .  
      A third preferred method of the invention is for attaching together first and second vertebral bodies  12  and  14  of a spinal column  16  of a medical patient  18 , and the method includes steps a) through e). Step a) includes obtaining first and second bone screws each having a shaft. Step b) includes obtaining a buttress plate. Step c) includes inserting the first bone screw into the first vertebral body of the spinal column of the medical patient. Step d) includes inserting the second bone screw into the second vertebral body of the spinal column of the medical patient. Step e) includes attaching the buttress plate to the first and second bone screws after performing steps a) through d).  
      In an example of a medical procedure utilizing a preferred method of the invention, the anterior cervical-column buttress plate is installed following a graft placement to a soft tissue region. The anterior aspect of a vertebral body is prepared by removing soft tissue and prominent osteophytes. The midline portion of the vertebral body is identified, and an optimum site for screw placement is determined. An awl is used to breach the anterior cortex with an awl guide used to ensure that the awl is driven perpendicular to the anterior cortex. A bone screw of appropriate length is selected and then is driven into the starter hole to the proper depth using the adjustable-depth driver giving care to place the bone screw perpendicular to the anterior cortex in both the lateral and transverse planes. These steps are repeated for all vertebral bodies to be plated. A malleable template is used to determine the appropriate plate length and curvature. A buttress plate is selected which is the smallest plate which allows the elongated slot to engage the heads of the bone screws and allows the claws to engage the anterior cortex. Following plate selection, the buttress plate is positioned with the elongated slot(s) over the heads of the bone screws and lightly tamped down onto the anterior cortex. This allows the claws to engage the bone. An inner screw of corresponding length is then placed into an installed bone screw. As the tip of the inner screw advances towards the tip of the bone screw, the tip of the bone screw expands, thus increasing the purchase of the screw against the vertebral body. As the tapered threads of the inner screw advance down the shaft of the bone screw, the head of the bone screw expands. This causes the external teeth of the head of the bone screw to engage the serrations of the opposing edges of the elongated slot of the buttress plate. The final turn of the inner screw will seat the screw flush with the buttress plate and will recess the top thread of the inner screw below a lip in the shaft of the bone screw. These steps are repeated until the last inner screw is in place.  
      Several benefits and advantages are derived from the invention. The apparatus and method of the invention allows a physician to choose an optimum location for the first bone screw on the first vertebral body (e.g., on the first cervical vertebral body) and to choose an optimum location for the second bone screw on the second vertebral body (e.g., on the second cervical vertebral body) for maximum attachment strength and mechanical stability. This is accomplished by first installing the bone screws on the vertebral bodies and then securing the buttress plate to the installed bone screws. In comparison, the prior art forces the physician to use pre-drilled holes in the buttress plate which often provide less than optimum attachment locations (providing less attachment strength and less mechanical stability) for the bone screws to be installed in the vertebral bodies.  
      The foregoing description of several expressions of a preferred embodiment of the invention and several methods of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise forms and processes disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.