Patent Publication Number: US-2015080958-A1

Title: Compression-distraction spinal fixation system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 12/958,304 filed Dec. 1, 2010, which claims the benefit of U.S. Provisional Application Ser. No. 61/292,215, filed on Jan. 5, 2010 and U.S. Provisional Application Ser. No. 61/383,540, filed on Sep. 16, 2010. The disclosure of each of the prior applications is considered part of and is incorporated by reference in the disclosure of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present technology relates to an implant for surgical treatment of the spine, and methods for stabilizing a spine using the implants. More particularly, the present technology provides compression-distraction spinal fixation systems that include screw-rod constructs. 
     BACKGROUND INFORMATION 
     Anterior, posterior and lateral spinal fixation is commonly used for the treatment of degenerative disease, trauma, deformity, and oncological processes. The current state of the art includes the placement of rigid bone screws into the posterior arch, pedicles or vertebral bodies of adjacent spinal segments. These bone screws are then connected to each other by rigid metal rods in order to stabilize the spine and enable progressive bony fusion. Such bone screw-rod constructs have gained prominence due to their superior biomechanical stability relative to alternate fixation techniques, such as wiring, etc., as well as the benefits provided by three column fixation of the spine. Such systems have been made more versatile in recent years with the advent of polyaxial screw head technology, which allows more complex construct placement and screw connections. While current screw-rod systems are ideal for fixating motion segments in the spine in neutral position, certain situations call for the application of compressive or distractive forces in order to improve spinal balance and to aid in spinal fusion. 
     Current screw based spinal fixation systems use smooth, cylindrical metal or ceramic rods to connect screws that are anchored in bony portions of each vertebral level, such as the pedicle, lateral mass, lamina, and/or vertebral body. One example of a currently known screw based spinal fixation system is illustrated in  FIG. 1 . As shown in  FIG. 1 , a bone screw  10  connected to a rod  12 . Rod  12  is cylindrical, and has a smooth outer surface. Bone screw  10  has a screw head  14 , which can have a variable angle head, as shown, or it could be a fixed angle screw. Bone screw  10  includes a threaded shaft  16  attached to the screw head  14 . Bone screw  10  also includes a set screw  18  that is attached to the screw head  14 . Bone screw  10  can be connected to the rod  12  by attaching the bone screw to the desired bony spinal portion, sliding the rod  12  onto the bone screw, and then tightening the set screw  18  to secure the bone screw  10  at a desired location on the rod  12 . 
     After placing this instrumentation, spine surgeons typically apply compressive forces manually between adjacent screws in order to increase lordosis for improved sagittal balance, or to compress upon an interbody graft in order to improve fusion. Alternatively, surgeons may wish to apply distractive forces between adjacent screws in order to improve access to the disc space for discectomy or interbody graft placement, or to affect deformity correction. Due to the smooth, cylindrical rod design, current spinal fixation systems do not provide or allow for the maintenance of compressive or distractive forces. Instead, one surgeon must provide manual compression between two screws while a second surgeon attempts to tighten the rod in place at each fixation point. This technique is both cumbersome and technically challenging. 
     SUMMARY OF THE INVENTION 
     The present technology relates to compression-distraction spinal fixation systems that include screw-rod constructs that include a ratcheting mechanism. 
     In one aspect, a compression-distraction spinal fixation system is provided that includes at least one bone screw, and a toothed rod connected to the at least one bone screw. The at least one bone screw can include a threaded shaft, a screw head, a set screw, and a pawl. The toothed rod can have a plurality of ratchet teeth that receive the pawl of the at least one bone screw. 
     In another aspect, a method of performing compression-distraction spinal fixation is provided that includes attaching a first bone screw to a first bony portion of a patient&#39;s spine, and placing a toothed rod in the screw head of the first bone screw. The first bone screw can include a threaded shaft that attaches the first bone screw to the first bony portion, a screw head, a set screw, and a pawl. The toothed rod can include ratchet teeth. The method can also include orienting the pawl of the first bone screw to engage the ratchet teeth of the toothed rod, and ratcheting the bone screw along the length of the toothed rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Specific examples have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification. 
         FIG. 1  illustrates one example of a prior art screw-rod construct. 
         FIG. 2  illustrates one example of a screw-rod construct of the present technology. 
         FIG. 3  illustrates an exploded view of the example of  FIG. 2 . 
         FIG. 4  illustrates a screw of the example of  FIG. 2  in a first orientation. 
         FIG. 5  illustrates a screw of the example of  FIG. 2  in a second, or reversed, orientation. 
         FIG. 6  illustrates a screw of the example of  FIG. 2  in a sectioned view with an enlarged region to illustrate the ratchet and pawl mechanism. 
         FIG. 7  illustrates a second example of a screw-rod construct of the present technology in a first orientation. 
         FIG. 8  illustrates a screw of the example of  FIG. 7  in a second, or reversed, orientation. 
         FIG. 9  illustrates a third example of a screw-rod construct of the present technology in a first orientation. 
         FIG. 10  illustrates a screw of the example of  FIG. 9  in a second, or reversed, orientation. 
         FIG. 11  illustrates an exploded view of a screw of the example of  FIG. 9 . 
         FIG. 12  illustrates a fourth example of a screw-rod construct of the present technology in a first orientation. 
         FIG. 13  illustrates a screw of the example of  FIG. 12  in a second, or reversed, orientation. 
         FIG. 14  illustrates a fifth example of a screw-rod construct of the present technology in a first orientation. 
         FIG. 15  shows an exploded view of the screw of the example of  FIG. 14 . 
         FIG. 16  illustrates a cross sectional view of the screw of the example of  FIG. 14 . 
         FIG. 17  illustrates a sixth example of a screw-rod construct of the present technology in a first orientation. 
         FIG. 18  illustrates an exploded view of the screw of the example of  FIG. 17 . 
         FIG. 19  illustrates a sectioned view of one example of teeth on a rod of the present technology having triangular ratchet teeth cut into the rod. 
         FIG. 20  illustrates a sectioned view of a second example of teeth on a rod of the present technology having sawtooth ratchet teeth cut into the rod. 
         FIG. 21  illustrates a sectioned view of a third example of teeth on a rod of the present technology having spaced ratchet teeth cut into the rod. 
         FIG. 22  illustrates a sectioned view of a fourth example of teeth on a rod of the present technology having square ratchet teeth cut into the rod. 
         FIG. 23  illustrates a sectioned view of a fifth example of teeth on a rod of the present technology having a helical coil sintered, welded, soldered, bonded or otherwise attached to the rod. 
         FIG. 24  illustrates a sectioned view of a sixth example of teeth on a rod of the present technology having helical threads cut into the rod. 
         FIG. 25  illustrates a perspective view of one example of a rod of the present technology having ratchet teeth cut straight across the rod. 
         FIG. 26  illustrates a sectioned view of the example of a rod illustrated in  FIG. 25 . 
         FIG. 27  illustrates a perspective view of a second example of a rod of the present technology having ratchet teeth cut radially on the rod. 
         FIG. 28  illustrates a sectioned view of the example of a rod illustrated in  FIG. 27 . 
         FIG. 29  illustrates a seventh example of a screw-rod construct of the present technology. 
         FIG. 30  illustrates a sectioned view of the screw-rod construct illustrated in  FIG. 29 . 
         FIG. 31  illustrates an eighth example of a screw-rod construct of the present technology. 
         FIG. 32  illustrates an exploded view of the screw-rod construct illustrated in  FIG. 31 . 
         FIG. 33  illustrates a sectioned view of the screw-rod construct illustrated in  FIG. 31 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present technology relates to compression-distraction spinal fixation systems that include screw-rod constructs. More particularly, the present technology provides a rod and screws that incorporate a ratchet and pawl mechanism for imposition of compression and distraction forces on the spinal column Preferably, compression-distraction spinal fixation systems described herein can allow a single surgeon the ability to apply compressive or distractive forces as desired between adjacent spinal levels in a seamless and efficient manner. By employing the unique ratcheting mechanism provided in compression-distraction spinal fixation systems of the present technology, which in at least some examples can integrate into existing bone-screw rod technology, regional forces can be maintained segmentally or across the entirety of a given spinal construct, avoiding the cumbersome technique of compression/distraction that is inherent to traditional screw-rod systems. Combining improvements in maintenance of regional forces with ease of application and use, the compression-distraction spinal fixation systems of the present technology can add to a spine surgeon&#39;s armamentarium in the treatment of complex spinal disease. 
     Compression-distraction spinal fixation systems of the present technology are more particularly described in the following examples with reference to the accompanying drawings, and are intended as illustrative only. Referring to the drawings, like numbers indicate like parts throughout the views. Compression-distraction spinal fixation systems of the present technology include a toothed rod and at least one bone screw of the present technology. In some examples, compression-distraction spinal fixation systems of the present technology include a toothed rod, at least one bone screw of the present technology, and at least one conventional bone screw. In other examples, compression-distraction spinal fixation systems of the present technology include a toothed rod, a first bone screw of the present technology, and a second bone screw of the present technology. 
     As used in the description herein, and throughout the claims that follow, the meaning of “ratcheting the bone screw along the length of the toothed rod” means that the position of the bone screw is changed with respect to its original position along the length of the toothed rod due to movement of the bone screw, movement of the rod, or movement of both the bone screw and the rod. As used in the description herein, and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
     The rods of compression-distraction spinal fixation systems of the present technology include ratchet teeth, which are preferably evenly spaced along a portion of the length of the rod, preferably along the entire length or substantially the entire length of the rod. Placing evenly spaced ratchet teeth along the length of the rod can allow the rod to be cut and contoured as desired in the operating room. In some examples, precut and precontoured rods can be provided, such as for example, for short segment constructs typically spanning 2, 3, and 4 vertebral levels. The ratchet teeth can cover at least a portion of the outer surface, or circumference, of the rod, including but not limited to, the entire circumference of the rod, half the circumference of the rod, one third of the circumference of the rod, one quarter of the circumference of the rod, or any other suitable portion of the circumference of the rod. The ratchet teeth can be formed as depressions in a toothed rod, or as protrusions that extend from the toothed rod. Toothed rods of the present technology can be made from any suitable material, including but not limited to a biocompatible metal, such as titanium, titanium alloy, stainless steel or cobalt chromium; a biocompatible polymer, such as PEEK; a composite material such as carbon fiber; or a biocompatible metal coated with another biocompatible metal or biocompatible polymer. In at least some examples, the inner diameter of the toothed rods, which is the diameter of the rod not including the height of the ratchet teeth, can be the same as the diameters that are currently used with known smooth rods, which can provide the same mechanical strength as currently known rods. 
     Bone screws of the present technology can also be made from any suitable material, including but not limited to a biocompatible metal, such as titanium, titanium alloy, stainless steel or cobalt chrome; a biocompatible polymer, such as PEEK; a composite material such as carbon fiber; or a combination of these. Bone screws of the present technology include a pawl that can engage the teeth on the toothed rod to provide a ratcheting mechanism. The pawl engages at least one ratchet tooth at a location on the toothed rod, and can allow unidirectional ratcheting of the bone screw on the rod to maintain either a compressive or distractive force as desired. In some examples, pawls are flexible, while in others they are rigid. Some of the examples described herein include reversible pawls, meaning that the pawl can be adjusted to allow ratcheting in either direction along the length of the toothed rod, depending on the orientation of the pawl. In other examples, however, pawls that are not reversible, and that provide ratcheting in only a single direction, are also provided. Bone screws of the present technology can also include a shaft, such as a threaded shaft, that can be used to attach the bone screw to a desired bony portion of the spine. Bone screws of the present technology can further include a screw head, and a set screw. 
       FIGS. 2 through 6  illustrate one example of a screw-rod construct  100  of the present technology that includes a toothed rod  102  having ratchet teeth  104 , a first bone screw  106  of the present technology and a second bone screw  108  of the present technology. In an alternative example, either bone screw  106  or bone screw  108  could be replaced with a conventional bone screw, such as bone screw  10  illustrated in  FIG. 1 . In the illustrated example of  FIG. 2 , each bone screw includes a threaded shaft  110 , a screw head  112 , a set screw  114 , and a pawl  116 . The set screw  114  of each bone screw includes a retaining ring  118 , which retains the pawl  116  on the set screw  114 . The pawl  116  is preferably flexible, and includes a bend  120  and a blade  122 . 
     When the toothed rod  102  is slidably connected to the first bone screw  106  and the second bone screw  108 . The blade  122  of each pawl  116  of each bone screw engages at least one tooth of the ratchet teeth  104  on toothed rod  102 . The first bone screw  106  can be ratcheted along the toothed rod  102  in the direction indicated by arrow A, but the engagement of the blade  122  of the first bone screw  106  with the ratchet teeth  104  of the toothed rod  102  can prevent movement of the first bone screw  106  in the opposite direction. Likewise, the second bone screw  108  can be ratcheted along the toothed rod  102  in the direction indicated by arrow B, but the engagement of the blade  122  of the second bone screw  108  with the ratchet teeth  104  of the toothed rod  102  can prevent movement of the second bone screw  108  in the opposite direction. 
       FIG. 3  shows an exploded view of the first bone screw  106 , which further illustrates the attachment of the pawl  116  to the set screw  114 . As illustrated, the retaining ring  118  is a circular, flexible piece of material with a cut portion  124  to allow expansion of the diameter of the retaining ring  118 . The set screw  114  has a circular boss  128  that includes a retaining ring groove  130 , and a threaded portion  132 . The pawl  116  has a circular bore  126  that communicates with the circular boss  128  on the set screw  114 . The pawl  116  slides over the circular boss  128  and the retaining ring  118  is captured in a retaining ring groove  130  to attach the pawl  116  to the set screw  114  without restraining the rotation of the pawl  116 . 
     In use, first bone screw  106  can be inserted into a bony portion of a patient&#39;s spine, such as the posterior arch, pedicle, or vertebral body of a vertebra. Then, toothed rod  102  can be placed into a recess  134  in screw head  112 . The set screw  114  can be threaded into the screw head  112  until there is significant engagement of the pawl  116  with the ratchet teeth  104  of the toothed rod  102 . Distracting or compressing forces, depending on the orientation of the pawl  116 , can then be used to slide the first bone screw  106 , and therefore the vertebra to which it is attached, relative to toothed rod  102 . 
       FIG. 4  illustrates that rotation of the pawl  116  in the direction of the arrow C can reverse the direction of travel of first bone screw  106  by changing to the orientation shown in  FIG. 5 . The pawl  116  is rotatable from a first position, as shown in  FIG. 4 , to a second position, as shown in  FIG. 5 , that is about  180 ° from the first position. The pawl  116  can include a locking boss  136 , which can prevent inadvertent rotation of the pawl  116 . The locking boss  136  can allow rotation of the pawl  116  when the set screw  114  is loosened an amount sufficient for the locking boss  136  to clear the screw head  112 . After the first bone screw  106  has been moved along toothed rod  102  to a desired location, the set screw  114  can be tightened to rigidly secure the screw head  112  to the toothed rod  102 .  FIG. 6  shows a sectioned view of the first bone screw  106  with an enlargement to further illustrate the elements of the first bone screw  106  as described above. 
       FIGS. 7 and 8  illustrate a second example of a screw-rod construct of the present technology. Screw-rod construct  200  as shown in  FIGS. 7 and 8  includes a toothed rod  202  having ratchet teeth  204 , and a bone screw  206 . The bone screw  206  has a threaded shaft  208 , a screw head  210 , a set screw  212 , and a pawl  214 . The pawl  214  can be rotatably mounted to a side of the screw head  210  by a fastener  216 , such as a pin. The pawl  214  includes a bend  218  and a blade  220 . The blade  220  of the pawl  214  engages the ratchet teeth  204  of the toothed rod  202 . Rotation of the pawl  214  from a first position, as shown in  FIG. 7 , to a second position, as shown in  FIG. 8 , that is about 180° from the first position, can reverse the direction of travel of the bone screw  206  along the length of the toothed rod  202 . 
       FIGS. 9 through 11  illustrate a third example of a screw-rod construct of the present technology, with  FIG. 11  showing an exploded view. Screw-rod construct  300  as shown in  FIGS. 9 through 11  includes a toothed rod  302  having ratchet teeth  304 , and a bone screw  306 . The bone screw  306  has a threaded shaft  308 , a screw head  310  having a pawl receiving groove  318 , a set screw  312 , and a pawl  314 . The pawl  314  is a clip-on pawl that can be connected to the screw head  310  by being received by the pawl receiving groove  318  of the screw head  310 . Pawl  318  can include a cut  316  that allows expansion of the diameter of the pawl  314  to facilitate installation of the pawl  314  onto the pawl receiving groove  318  of the screw head  310 . The pawl  314  can include a spring portion  320  and a blade  322 . The blade  322  engages the ratchet teeth  304  of the toothed rod  302 . The spring portion  320  can provide flexibility to the pawl  314  to allow the blade  322  to slide over the ratchet teeth  304  of the toothed rod  302  when the bone screw  306  is ratcheted along the length of the toothed rod  302 . Rotation of the pawl  314  from a first position, as shown in  FIG. 9 , to a second position, as shown in  FIG. 10 , that is about 180° from the first position, can reverse the direction of travel of the bone screw  306  along the length of the toothed rod  302 . 
       FIGS. 12 and 13  illustrate a fourth example of a screw-rod construct of the present technology. Screw-rod construct  400  as shown includes a toothed rod  402  having ratchet teeth  404 , and a bone screw  406 . The bone screw  406  has a threaded shaft  408 , a screw head  410 , a set screw  412 , and a sliding pawl  414 . The sliding pawl  414  can be slidably attached to the screw head  410  with a fastener  416 , such as a pin. The pawl  414  can also include a fastener groove  420 , and the fastener can extend through the fastener groove to slidably attach the pawl  414  to the screw head  410 . The screw head  410  can include a pawl receiving groove  418  on a side of the screw head  310 , and sliding pawl  414  can be slidably received in the pawl receiving groove  418 . The pawl can further include a first blade  422  at one first end, and a second blade  422  (not shown) at the opposite end. The first blade  422  can engage the ratchet teeth  404  of the toothed rod  402  when the slidable pawl is in a first position, as shown in  FIG. 12 , allowing the bone screw to ratchet along the length of the toothed rod in one direction. The second blade  422 , which can be a mirror image of the first blade  422 , can engage the ratchet teeth  404  of the toothed rod  402  when the slidable pawl is in a second position, as shown in  FIG. 13 , allowing the bone screw to ratchet along the length of the toothed rod in the opposite direction. 
       FIGS. 14 through 16  illustrate a fifth example of a screw-rod construct of the present technology, with  FIG. 15  being an exploded view and  FIG. 16  being a cross-sectional view. Screw-rod construct  500  includes a toothed rod  502  having ratchet teeth  504 , and a bone screw  506 . The bone screw  506  has a threaded shaft  508 , a screw head  510 , a set screw  512 , and a pawl  514 . The pawl  514  can be a raised boss on the bottom surface of the set screw  512  that engages the ratchet teeth  504  of the toothed rod  502 . A leaf spring  516  can be positioned under the rod receiving groove  518  of the screw head  510 , and can provide an upward force on the toothed rod  502  to ensure engagement of the ratchet teeth  504  and the pawl  514 . When horizontal force is exerted in the direction of arrow D, the leaf spring  516  can deflect out of the way and allow ratcheting of the bone screw  506  along the length of the toothed rod  502 . 
       FIGS. 17 and 18  illustrate a sixth example of a screw-rod construct of the present technology, with  FIG. 18  being an exploded view. Screw-rod construct  600  includes a toothed rod  602  having ratchet teeth  604 , and a bone screw  606 . The bone screw  606  has a threaded shaft  608 , a screw head  610 , a set screw  612 , and a pawl  614 . The pawl  614  is attached to a frame  616  that has a recess  618 . The recess  618  attaches to the screw head  610 , and can be lowered over the screw head  610  into alignment with the toothed rod  602  so that the pawl  614  engages the ratchet teeth  602  of the toothed rod  602 . The pawl  614  can be is attached to the frame  616  with a fastener  620 , such as a pin, that extends through a bore  624  in the frame  618  and can be rigidly attached to the pawl  614  due to press fit of the fastener  620  into a pawl hole  626  in the pawl  616 . As illustrated, the fastener  620  can have a hexagonal head  622 . A spring  628  can be attached to the frame  618  by a spring fastener  630 , and can exert an inward force on the pawl  614  to maintain engagement of the pawl  614  with the ratchet teeth  602 . To disengage the pawl  614  from the ratchet teeth  602 , an operator can rotate the hexagonal head  622  of the fastener  618  clockwise. 
       FIGS. 19 through 24  illustrate examples of ratchet teeth that can be formed on a toothed rod  700  of the present technology. The ratchet teeth can be formed on the toothed rod  700  in any suitable manner, such as by being cut, pressed, rolled, forged, molded or otherwise formed. In one example, toothed rod  700  having ratchet teeth can be fabricted in a molding operation such as MIM (Metal Injection Molding). In other examples, ratchet teeth can be formed by waterjet cutting, EDM (Electrical Discharge Machining), etching, or ECM (Electrochemical Machining).  FIG. 19  shows toothed rod  700  having triangular teeth  702 .  FIG. 20  shows toothed rod  700  having saw teeth  704 .  FIG. 21  shows toothed rod  700  having triangular teeth  706  in a staggered pattern, wherein the ratchet teeth  706  are separated by an offset R.  FIG. 22  shows toothed rod  700  having squared teeth  708 .  FIG. 23  shows toothed rod  700  having ratchet teeth formed by a helical piece of material  710  that is wrapped around and secured to the toothed rod  700 . The helical piece of material  710  can be secured to the toothed rod in any suitable manner, including, for example, being sintered, welded, soldered, or bonded.  FIG. 24  toothed rod  700  having ratchet teeth formed by helical threads  712 . Helical threads  712  can be formed in any suitable manner, including being cut into toothed rod  700 , or being formed by a thread rolling operation which could increase the fatigue life of toothed rod  700 . 
       FIGS. 25 and 26  illustrate toothed rod  700  having triangular teeth  714  formed straight, meaning on a linear path, across an outer surface of the toothed rod  700 .  FIGS. 26 and 27  illustrate toothed rod  700  having triangular teeth  714  formed radially, meaning on a non-linear, arcuate path, across an outer surface of the toothed rod  700 . 
       FIGS. 29 and 30  illustrate a seventh example of a screw-rod construct of the present technology, with  FIG. 30  being sectioned view. Screw-rod construct  800  includes a toothed rod  802  having ratchet teeth  804 , and a bone screw  806 . The bone screw  806  has a threaded shaft  808 , a screw head  810 , a set screw  812 , and a pawl  814 . The pawl  814  is a toggle pawl located in a side of the screw head  810 . The toggle pawl  814  is housed within a recess  816  in the side of the screw head  810 . The toggle pawl  814  is attached to the screw head  810 , preferably at the center of the toggle pawl  814 , by a fastener  818 , such as a pin. The toggle pawl  814  can rotate about the fastener, from a first position, as shown in  FIG. 30 , to a second position that has an orientation opposite that of the first position, thus allowing the bone screw  806  to be ratcheted along the length of the toothed rod  802  in a first or second direction, respectively. The toggle pawl  814  can be spring-loaded, or can have sufficient friction to allow it to be rotated from the first position to the second position by manual force exerted by an operator. 
     Previously described are pawls which flex or rotate, however it should be understood that a pawl may also translate linearly away from toothed rod and return to contact with toothed rod under the action of a spring such as a helical spring, a leaf spring, a machined spring, or any elastic resilient material.  FIGS. 31 through 33  illustrate one example of a screw-rod construct of the present technology having such a linearly translating pawl, with  FIG. 32  being an exploded view, and  FIG. 33  being a sectioned view. Screw-rod construct  900  includes a toothed rod  902  having ratchet teeth  904 , and a bone screw  906 . The bone screw  906  has a threaded shaft  908 , a screw head  910 , a set screw  912 , and a pawl  914 . The pawl  914  is attached to a side of the screw head  910 , and can be located in a screw head bore  922  that has a keyway  924 . The pawl  914  is a plunger pawl, having teeth  916 , a blind hole  926 , a helical cut  918 , and an anti-rotation boss  920 . Helical cut  918  allows plunger pawl  914  to compress like a helical spring. In lieu of helical cut  918 , plunger pawl  914  could incorporate a wire wound helical spring, a leaf spring or other resilient material. The anti-rotation boss  920  of the plunger pawl  914  can align with the keyway  924  of the screw head  910  to maintain alignment of plunger pawl  914  with the ratchet teeth  904  of the toothed rod  902 . As the bone screw  900  is ratcheted along the length of the toothed rod  902 , the helical spring  918  can compress and extend to so that plunger pawl  914  maintains contact with toothed rod  902  and allows motion in one direction only. 
     Screw-rod constructs including at least one bone screw of the present technology and at least one rod of the present technology can allow compressive or distractive forces to be applied sequentially across each level of a given construct as desired. 
     In at least one example, the application of compressive or distractive forces can be accomplished by first attaching at least one bone screw of the present technology to at least one desired bony portion of a patient&#39;s spine. In one example a first bone screw can be attached to a first bony portion of a patient&#39;s spine, and a second bone screw can be attached to a second bony portion of a patient&#39;s spine. At least one of the bone screws, or both, can have a pawl. The toothed rod of the present technology can be optionally shaped by an operator, such as a surgeon, and can be attached to each bone screw. In some examples, the toothed rod can be attached to each bone screw by placing the toothed rod in the screw head of the first bone screw and in the screw head of the second bone screw, and then placing a first set screw on the screw head of the first screw and a second set screw on the screw head of the second screw to maintain the toothed rod in the screw head of each bone screw. The pawl of the at least one bone screw having a pawl can be oriented to engage the ratchet teeth of the toothed rod. In some examples, the pawl can be oriented to engage the ratchet teeth of the toothed rod in a first position or a second position, for the application of either distractive or compressive forces as desired. The bone screw having a pawl, or at least one of the bone screws having a pawl, can then be ratcheted along the length of the toothed rod to apply the desired amount of distractive or compressive force. Once the desired amount of distractive or compressive force is achieved, each set screw can be tightened to maintain each bone screw in a fixed position relative to the toothed rod. The distractive or compressive force can be maintained temporarily or permanently. 
     The distractive or compressive force can be used to alter the distance between bony portions of a patient&#39;s spine. For example, the distance between spinal vertebrae of a patient can be altered by attaching a first bone screw to a first spinal vertebra and attaching a second bone screw to a second spinal vertebra, wherein at least the first bone screw has a pawl. A toothed rod can then be attached to the first and second bone screws, and the pawl of the first bone screw can be oriented to engage the ratchet teeth of the toothed rod. The method can then include altering the distance between the first vertebra and the second vertebra. The distance between the first vertebra and the second vertebra can be altered by ratcheting the first bone screw a desired amount along the length of the toothed rod to apply an amount of distractive or compressive force sufficient to obtain the desired altered distance between the first vertebra and the second vertebra. The altered distance can then be maintained, temporarily or permanently, by the pawl engaging the ratchet teeth of the toothed rod. 
     EXAMPLE 
     A screw-rod construct of the present technology was made in accordance with the example illustrated in  FIGS. 2-6 . The toothed rod had triangular ratchet teeth formed by cutting grooves having a 90° angle along the length of the toothed rod. The grooves were cut about 0.75 mm apart, and were cut radially in an arc that was about 60°. The toothed rod had an inner diameter of about 5.5 mm, and was made from Grade 23 Titanium alloy (Ti6Al4V-ELI). The pawl was also made of Grade 23 Titanium alloy (Ti6A14V-ELI), and was about 0.016 inches (0.4mm) thick. The blade of the pawl was about 5 mm wide. 
     From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.