Patent Publication Number: US-9833275-B2

Title: Tether tensioning instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/669,909 filed on Nov. 6, 2012, which is a continuation of U.S. application Ser. No. 11/842,371 filed on Aug. 21, 2007 (now U.S. Pat. No. 8,323,294), each of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present application relates to devices and methods for tensioning a tether extending between bone anchors implanted in bone. 
     BACKGROUND 
     Spinal deformities, which include rotation, angulation, and/or curvature of the spine, can result from various disorders, including, for example, scoliosis (abnormal curvature in the coronal plane of the spine), kyphosis (backward curvature of the spine), and spondylolisthesis (forward displacement of a lumbar vertebra). Early techniques for correcting such deformities utilized external devices that apply force to the spine in an attempt to reposition the vertebrae. These devices, however, resulted in severe restriction and in some cases immobility of the patient. Furthermore, current external braces have limited ability to correct the deformed spine and typically only prevent progression of the deformity. Thus, to avoid this need, several rod-based techniques were developed to span across multiple vertebrae and force the vertebrae into a desired orientation. 
     In rod-based techniques, one or more rods are attached to the vertebrae at several fixation sites to progressively correct the spinal deformity. The rods are typically pre-curved intraoperatively to a desired adjusted spinal curvature. Wires as well as bone screws can be used to pull individual vertebra toward the rod. Once the spine has been substantially corrected, the procedure typically requires fusion of the instrumented spinal segments. 
     While several different rod-based systems have been developed, they tend to be cumbersome, requiring complicated surgical procedures with long operating times to achieve correction. Further, intraoperative adjustment of rod-based systems can be difficult and may result in loss of mechanical properties due to multiple bending operations. The rigidity and permanence of rigid rod-based systems can also hinder or prevent growth of the spine and they generally require fusion of many spine levels, drastically reducing the flexibility of the spine. To help remedy some of these issues, a tether and anchor system can be used to correct curvature of the spine using a number of anchors disposed within the spinal bones connected with tethers extending between them. The elasticity of the tethers prevents some of the problems with the rigidity and permanence of the rod-based systems, although the tethers must be tensioned after implantation to achieve the desired force between the anchor to correct the spinal deformities. 
     Accordingly, there remains a need for improved methods and devices for correcting spinal deformities and, in particular, there remains a need for methods and devices for tensioning a tether extending between anchors implanted in bone. 
     SUMMARY 
     Various methods and devices for tensioning a tether are provided. In one embodiment, a tether tensioning device is provided for tensioning a tether extending along a path between at least two bone anchors implanted in adjacent vertebrae and includes a tensioning mechanism adapted to couple to a tether seated across at least two bone anchors. The tensioning mechanism can be adapted to apply a tensioning force to the tether along the path of the tether to move the tether along the path. The device can also include an actuation mechanism movably coupled to the tensioning mechanism such that the actuation mechanism is adapted to effect movement of the tensioning mechanism to control the tensioning force applied to the tether. The tensioning mechanism and the actuation mechanism can be movably coupled to an elongate shaft. In an exemplary embodiment, the path can be a substantially straight path. 
     The tether tensioning mechanism can have a variety of configurations, but in one embodiment the tensioning mechanism can include a wheel rotatably coupled to a distal end of the elongate shaft and adapted to rotate to apply a tensioning force to a tether. The actuation mechanism can include a shaft having a pawl adapted to engage a plurality of teeth formed on the wheel to rotate the wheel. The device can further include a stationary handle coupled to a proximal end of the elongate shaft, and an actuator coupled to the stationary handle and adapted to pivot toward the stationary handle to move the shaft to cause the wheel to rotate. The device can also include a grasping member movably coupled to the elongate shaft and adapted to grasp a tether between the grasping member and the wheel, and optionally a locking mechanism formed on the elongate shaft and adapted to lock the wheel in a fixed position to lock the tether between the grasping member and the wheel. 
     In another embodiment, the tensioning mechanism can be in the form of a lever arm slidably coupled to the elongate shaft and adapted to slide to apply a tensioning force to a tether. The actuation mechanism can include a pusher movably coupled to the elongate shaft and adapted to apply a force to the lever arm to cause the lever arm to slide. A cam surface can be formed on the elongate shaft and it can be positioned to cam the lever arm away from the elongate shaft during sliding movement of the lever arm. The device can also include a grasping member for coupling the lever arm to a tether and it can be adapted to grasp a tether to anchor the tether during tensioning. For example, at least one surface feature can be formed on a distal end of the lever arm and it can be adapted to engage a tether. 
     Spinal anchoring and tensioning systems are also provided, and in one embodiment the system can include first and second bone anchors having a receiver member and a bone-engaging member, and a tether adapted to extend along a path between the receiver members of the first and second bone anchors. A tether tensioning device can be adapted to be positioned adjacent to the receiver member of at least one of the first and second bone anchors and to engage the tether such that the tether tensioning device is effective to apply a tensioning force to the tether along the path to move the tether along the path of the tether. The tether tensioning device can have a variety of configurations, including a wheel adapted to rotate to move the tether along the path, and a lever arm adapted to slide and pivot to move the tether along the path. The tether tensioning device can also include a lumen formed therethrough and adapted to receive a driver for applying a locking mechanism to the receiver member. 
     Methods for applying tension to a tether are also provided, and in one embodiment the method can include grasping a tether extending along a path between first and second bone anchors implanted in adjacent vertebrae, and actuating a tensioning mechanism to apply a tensioning force to the tether along the path of the tether. The path of the tether can be a substantially straight line extending across the first and second bone anchors. The tensioning mechanism can be formed on a tensioning device that is positioned adjacent to one of the first and second bone anchors. The method can also include inserting a driver through a shaft of the tensioning device, and manipulating the driver to lock a locking mechanism to the bone anchor to thereby lock the tether in a fixed position relative to the bone anchor. In one embodiment, grasping the tether can include grasping the tether between the tensioning mechanism and a grasping member adapted to grip the tether and anchor the tether in place. 
     The tensioning mechanism can have a variety of configuration. In one embodiment, the tensioning mechanism can include a wheel, and the wheel can be rotated to apply a tensioning force to the tether. For example, the wheel can be rotated by moving a trigger operatively associated with the wheel. The trigger can be coupled to a shaft and a pawl that rotates the wheel when the trigger is moved. In another embodiment, the tensioning mechanism can include a lever arm slidably and pivotally coupled to a shaft of a tensioning device. Actuating the tensioning mechanism can include sliding and pivoting the lever arm relative to the shaft to push the grasping mechanism along the path of the tether to thereby apply tension to the tether. Applying a tensioning force to the tether can include actuating a pusher movably coupled to the shaft to slide the lever arm relative to the shaft such that the lever arm applies tension to the tether. Grasping the tether can include grasping the tether with a grasping mechanism positioned adjacent to the tensioning mechanism such that movement of the tensioning mechanism is effective to move the grasping mechanism to thereby apply tension to the tether. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments disclosed herein will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of one embodiment of a tether tensioning device shown engaging a tether extending through a bone anchor; 
         FIG. 2  is a side view of the tether tensioning device of  FIG. 1  showing a tensioning mechanism including a wheel and ratchet adapted to tension a tether along its path; 
         FIG. 3  is a side view of the tensioning mechanism of  FIG. 2 ; 
         FIG. 4  is a perspective view of the tensioning mechanism of  FIG. 2 ; 
         FIG. 5  is a perspective view of a grasping member engaging a tether during tensioning of the tether tensioning device of  FIG. 1 ; 
         FIG. 6  is a perspective view of another embodiment of a tether tensioning device having a tensioning mechanism including a lever arm and pusher adapted to tension a tether along its path; 
         FIG. 7  is a side view of the tether tensioning device of  FIG. 6  coupled to a bone anchor having a tether extending therethrough; 
         FIG. 8  is a side view of the tether tensioning device of  FIG. 6  coupled to a bone anchor; and 
         FIG. 9  is a side view of the tether tensioning device of  FIG. 6  coupled to a bone anchor and showing a grasping member engaging a tether during tensioning. 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope. 
     Various exemplary methods and devices are provided for tensioning a tether extending across one or more anchors implanted in bone. In one embodiment, a tensioning mechanism is provided that is adapted to couple to a tether extending along a path between one or more bone anchors implanted in adjacent vertebrae. The tensioning mechanism can be adapted to apply a tensioning force to the tether along the path of the tether as it extends across the bone anchor(s). The path can be, for example, a path extending along and substantially parallel to a patient&#39;s spinal column. The path can, however, have slight departures out of a linear line due to natural curvatures in the spinal column. The path can also be substantially perpendicular to an axis of the device, such that the tensioning mechanism applies tension in a direction perpendicular to an axis of the device. The tensioning mechanism can include an actuation mechanism movably coupled thereto and adapted to effect movement of the tensioning mechanism to control the tensioning force applied to the tether. 
       FIGS. 1-2  illustrate one exemplary embodiment of a tether tensioning device  10  that generally includes an elongate shaft  12  extending from a handle  14 . A tensioning mechanism in the form of a rotatable wheel  18  and an actuation mechanism in the form of a pawl  24  are coupled to the elongate shaft  12 . The rotatable wheel  18  can be adapted to engage a tether  16  seated across one or more bone anchors implanted in bone, and the pawl  24  can be adapted to move relative to the elongate shaft  12  and the wheel  18  to effect movement of the rotatable wheel  18  to control a tensioning force applied to the tether  16  by the rotatable wheel  18 . 
     The elongate shaft  12  can have a variety of configurations, and it can be flexible or rigid depending on the intended use. In an exemplary embodiment, the elongate shaft  12  has a length that allows the distal end of the elongate shaft  12  to be positioned adjacent to a tether extending along a spinal column, while the proximal end remains external to the body. This length allows the elongate shaft  12  to extend from the tissue surface to the treatment site, e.g., to a bone anchor implanted in a vertebra. A person skilled in the art will appreciate that the elongate shaft  12  can be made from a variety of biocompatible materials that have properties sufficient to enable the elongate shaft  12  to be inserted into the body. 
     As indicated above, the tensioning mechanism can be in the form of a wheel  18 , shown in more detail in  FIGS. 3-4 , that is rotatably coupled to a distal end of the elongate shaft  12  and that is adapted to rotate to apply a tensioning force to the tether  16 . The wheel  18  can be positioned at a distal end of the elongate shaft  12  in a variety of ways. In the illustrated embodiment, the wheel  18  is housed in a recess formed in the distal end of the elongate shaft  12 . However, in order for the wheel  18  to engage the tether  16  to apply a tensioning force thereto, a distal portion of the wheel  18  can extend distally beyond the distal-most end of the elongate shaft  12 . A person skilled in the art will appreciate that the wheel  18  can be positioned relative to the elongate shaft  12  in any way that allows a portion of the wheel  18  to engage the tether  16 . In addition, the wheel  18  can be coupled to the elongate shaft  12  in a variety of ways. For example, a pivot pin can extend through the wheel  18  and mate to the elongate shaft  12  to allow the wheel  18  to rotate relative to the elongate shaft  12 . A person skilled in the art will appreciate, however, that various other techniques can be used to rotatably couple the wheel  18  and the elongate shaft  12 . The wheel  18  can also include features formed thereon for engaging the tether  16 . For example, the wheel  18  can include a plurality of teeth  20  configured to engage the tether  16 . The teeth  20  can have various shapes and sizes, for example the teeth  20  can be angled to facilitate engagement of the tether  16  as the wheel  18  is rotated. 
     As indicated above, the device  10  can also include an actuation mechanism that is adapted to effect movement of the rotatable wheel  18  to control a tensioning force applied to the tether  16 . In the illustrated embodiment, the actuation mechanism is in the form of a pawl  24  that is movably coupled to a pusher  22 . The pusher  22  is located along a portion of the elongate shaft  12 . For example, it can be located within a longitudinal recess formed along the length of the elongate shaft  12  extending from an actuator adapted to move the pusher  22  to a distal end of the elongate shaft  12 . A person skilled in the art will appreciate that the pusher  22  can be coupled to the elongate shaft  12  in a variety of ways, including movably coupled to an outside portion of the elongate shaft  12 , or being housed in a lumen formed through the elongate shaft  12 . The pusher  22  can also have a variety of configurations. In an exemplary embodiment, the pusher  22  has a length that allows the distal end of the pusher  22  to mate to the pawl  24 , while the proximal end of the pusher  22  is coupled to an actuator, as will be discussed in more detail below. The actuator can be adapted to move the pusher  22  in a longitudinal direction along the elongate shaft  12  between a distal position and a proximal position to cause the pawl  24  to effect rotation of the wheel  18 . As indicated above, the distal end of the pusher  22  can be mated to the pawl  24 . In an exemplary embodiment, the pusher  22  is pivotally mated to the pawl  24  to allow the pawl  24  to move into and out of engagement with the wheel  18 . 
     The device can also optionally include a biasing element, such as a spring  31 , positioned within the shaft  12  and abutting against the pawl  24 . When the pusher  22  is in the distal position, the spring  31  can bias the pawl  24  into engagement with a tooth  20  formed on the wheel  18 . As the pusher  22  is moved into the proximal position using the actuator, the pawl  24  will pull the engaged tooth  20  on the wheel  18  in a proximal direction, thereby rotating the wheel  18 . This rotation of the wheel  18  causes a tensioning force to be applied to the tether  16  along its path to tension the tether  16  relative to at least one bone anchor  33  implanted in the spine. When the pusher  22  is returned to the distal position, the pawl  24  will pivot out of engagement with the teeth  20 , thereby compressing the spring  31 . This allows the pawl  24  to slide over the teeth  20  of the wheel  18  and into engagement with an adjacent tooth  20 . The pusher  22  can then be moved proximally once again to rotate the wheel  18  to apply additional tension to the tether. A person skilled in the art will appreciate that any components adapted to rotate the wheel to tension the tether can be used in place of the actuation mechanism described above. For example, a cable can be wound around the wheel and pulling on the cable can be effective to rotate the wheel  18  to apply a tensioning force to the tether  16 . 
     In order to facilitate engagement of the tether  16  by the wheel  18 , the distal end of the elongate shaft  12  can include a grasping member  32  disposed thereon and adapted to grasp the tether  16  between the grasping member  32  and the wheel  18 . The grasping member  32  can have any size and shape to facilitate grasping of the tether  16 , but in the embodiment shown in  FIGS. 1-5 , it is in the form of an elongate foot extending from the distal end of the elongate shaft  12  and positioned substantially transverse, e.g., perpendicular, to the elongate shaft  12  and a distance from the wheel  18  sufficient to allow the tether  16  to slide between the grasping member  32  and the wheel  18 . The grasping member  32  can also be movable between a first position in which the tether  16  is not engaged between the grasping member  32  and the wheel, and a second position in which the tether  16  is engaged between the grasping member  32  and the wheel. The grasping member  32  can be coupled to or formed on a moveable shaft (not shown) that is disposed along or within a lumen formed in the elongate shaft  12 . A proximal end of the movable shaft can be coupled to a grasping actuator  34  that can be adapted to effect vertical movement of the grasping member  32  to allow the grasping member  32  to grasp the tether  16  with the wheel  18 . For example, the grasping actuator  34  can move the grasping member  32  between a first unlocked position in which the grasping member  32  is located a distance distally from the wheel  18  to allow the tether  16  to slide between the grasping member  32  and the wheel  18 , and a second locked position in which the grasping member  32  is moved proximally towards the wheel  18  to allow the grasping member  32  to grasp the tether  16  therebetween. 
     The tensioning mechanism can also include features to prevent the wheel from back-spinning as tension is being applied. In one embodiment, the tensioning mechanism can include a locking mechanism  26  disposed on a distal end of the elongate shaft  12 . The locking mechanism  26  can be sized to extend between two adjacent teeth  20  formed on the wheel  18 , and it can be shaped to allow the wheel  18  to spin in one direction to apply a tensioning force to the tether  16 , while preventing the wheel  18  from spinning in the opposite direction to maintain the tensioning force applied to the tether  16 . For example, the locking mechanism  26  can be a triangular member having a first side coupled to the elongate shaft  12 , a second side having an angle that corresponds to the angle between the two adjacent teeth  20 , and a third side substantially perpendicular to the first side that is effective to block rotation of the teeth in one direction. A person skilled in the art will appreciate that any mechanism can be used in conjunction with the wheel  18  that can prevent back-spinning of the wheel during the application of tension to the tether  16 . 
     As previously discussed, the elongate shaft  12  extends from the handle  14  which can have any shape and size, but is preferably adapted to facilitate grasping and manipulation of the device  10 . In the illustrated embodiment, as shown in  FIGS. 1-2 , the handle  14  includes a stationary member  28  and a actuator  30  pivotally coupled to the stationary member  28 . As discussed above, a distal end of the actuator  30  can be coupled to a proximal end of the pusher  22 . The actuator  30  can be adapted to pivot toward the stationary member  28  to pull the pusher  22  in a proximal direction to cause the wheel  18  to rotate and apply a tensioning force to the tether  16 . A person skilled in the art that any mechanism can be used to move the pusher  22  along the elongate shaft  12 . Moreover, a person skilled in the art will appreciate that either of the stationary member  28  or the actuator  30  can be movable, or both of the stationary member  28  and the actuator  30  can be movable. 
       FIGS. 6-10  illustrate another embodiment of a device for applying tension to a tether extending across anchors implanted in bone. The device  100  is similar in configuration to device  10  described above, and has an elongate shaft  112  extending from a handle  114  and having a tensioning mechanism and an actuation mechanism coupled thereto. In the embodiment shown in  FIGS. 6-10 , the tensioning mechanism includes a lever arm  118  that is slidably coupled to a distal portion of the elongate shaft  112  and that is adapted to slide to apply a tensioning force to a tether  116  along the path of the tether  116 . 
     The lever arm  118  can have a variety of configurations, but in one embodiment as shown in  FIGS. 6-9 , it has a substantially hemi-cylindrical shape to allow the lever arm  118  to be received around a portion of the shaft  112 . The lever arm  118  can be coupled to the elongate shaft  112  in a variety of ways. In the illustrated embodiment, the lever arm  118  is pivotally and slidably coupled to a distal portion of the elongate shaft  112  to allow the lever arm  118  to move distally and outwardly relative to the shaft  112 . In particular, the proximal end  118   a  of the lever arm  118  can include pins (only one pin  118   p  is shown) formed on an opposed inner surfaces thereof that extend into corresponding cam recesses (only one recess  120  is shown) formed in opposed sides of the elongate shaft  112 . The cam recesses  120  can be in the form of shaped slots that receive the pins and guide the pins along the cam recesses  120  to guide movement of the lever arm  118 . For example, the cam recesses  120  can be adapted to guide movement of the lever arm  118  in a distal and outward direction relative to the elongate shaft  112 . This allows the distal end  118   b  of the lever arm  118  to slide substantially parallel along the path of the tether  116  to tension the tether  116  along its path. Various techniques for moving the lever arm  118  in such a way as to apply the tensioning force along the path of the tether  116  will be discussed in more detail below. 
     In order to further facilitate movement of the lever arm  118  outwardly away from the elongate shaft  112 , the distal end  112   b  of the elongate shaft  112  can include a cam surface  113  formed thereon. In particular, as shown in  FIGS. 6-9 , the distal end  112   b  of the elongate shaft  112  can include opposed arms extending outward from the longitudinal axis of the shaft  112  such that each arm defines the cam surface  113  on the top portion thereof. The cam surface  113  can slope downwardly, and the lever arm  118  can include a corresponding downwardly sloping surface  119  formed thereon that abuts against the cam surface  113 . As a result, when the lever arm  118  is moved distally, the surface  119  on the lever arm  118  will abut against the cam surface  113  on the shaft  112 . The cam surface  113  will thus force the distal end  118   b  of the lever arm  118  to move outwardly away from the distal end  112   b  of the elongate shaft  112 , thereby allowing the lever arm  118  to move a tether along its path. 
     In order to engage a tether to move the tether  116  along its path, the lever arm  118  can also include one or more surface features or other engagement mechanisms on the distal end  118   b  thereof. For example, the distal end  118   b  of the lever arm  118  can include one or more protrusions or teeth formed thereon and adapted to pierce a portion of the tether  116  to temporarily couple the lever arm  118  to the tether  116  to anchor the tether  116  during tensioning. Alternatively or in addition, the tether  116  could have a surface featured formed thereon, such as a raised button, to form a surface for the lever arm  118  to push against to apply a tensioning force to the tether  116 . In another embodiment, a grasping member  132 , shown in  FIG. 8 , can be positioned at a location adjacent to a bone anchor through which the tether  116  extends and can be used to grasp the tether  116  to anchor it during tensioning. In particular,  FIG. 8  illustrates the grasping member  132  engaging the tether  116  adjacent to the lever arm  118 . This will allow the lever arm  118  to push against the grasping member  132 , and thereby move the tether  116 . A person skilled in the art will appreciate that any technique or device known in the art can be used to facilitate anchoring of the tether  116  during application of the tensioning force. 
     In order to apply a tensioning force to the tether  116 , the lever arm  118  can be actuated using an actuation mechanism. In the illustrated embodiment, the actuation mechanism is in the form of a pusher  122  that is movably coupled to the elongate shaft  112  to apply a force to the lever arm  118  to cause the lever arm  118  to slide and apply the tensioning force to the tether  116 . The pusher  122  can have a variety of configuration, but in an exemplary embodiment the pusher  112  is in the form of an elongate member that extends along or through a portion of the elongate shaft  112  and that includes a distal end (not shown) that is pivotally mated to the proximal end  118   a  of the lever arm  118 , and a proximal end  122   a  that is mated to an actuator  130 , which will be discussed in more detail below. Actuation of the actuator  130  can be effective to cause the pusher  122  to move longitudinally along the shaft  112  to a distal position in which the pusher  122  pushes against the lever arm  118 , causing the lever arm  118  to slide distally and outward to apply a tensioning force to the tether  116 . 
     The pusher  122  can be moved using an actuator  130  coupled to the elongate shaft  112 . In the illustrated embodiment, the actuator  130  is part of a handle assembly  114  formed on the proximal end  112  of the shaft. The handle assembly  114  can have any shape and size, but it is preferably adapted to facilitate grasping and manipulation of the device  100 . In the illustrated embodiment, as shown in  FIGS. 6-7 , the handle assembly  114  includes a stationary portion  128  formed on and extending proximally from the elongate shaft  112  for a user to hold the handle of the device  100 , and the actuator  130  which is coupled to the stationary portion  128  and is adapted to allow a user to control the tensioning of the tether  116 . In an exemplary embodiment, the actuator  130  is pivotally coupled to the stationary portion  128  and to the proximal en  112   a  of the pusher  122 . Pivotal movement of the actuator  130  toward the stationary portion  128  can be effective to move the pusher  122  in a distal direction to cause the lever arm  118  to move and slide along the tether  116  to apply a tensioning force thereto. A person skilled in the art that any mechanism can be used to move the pusher  122  to apply tensioning force to the tether  116 . 
     Various exemplary methods for tensioning a tether are also provided. While the methods are described in connection with devices  10  and  100 , a person skilled in the art will appreciate that any device can be used. In an exemplary embodiment, the device  10 ,  100  can be inserted through tissue, or through an access port disposed in tissue, so that the handle can extend from the tissue or port on the outside, and the distal end of the device  10 ,  100  can be positioned adjacent to a bone anchor. The device  10 ,  100  can be positioned adjacent to a tether  16 ,  116  extending between bone anchors to be tensioning. For example, the device  10 ,  100  can be removably mated directly to the bone anchor, or it can be positioned against a side of the bone anchor, or spaced apart from the bone anchor. The tether  16 ,  116  can be grasped to anchor the tether in place during tensioning, such as with the grasping member  32 ,  132  of  FIG. 2  or  FIG. 7 . Once the tether  16 ,  116  is anchored in place, a force can be applied to the actuator  30 ,  130  of device  10 ,  100  to move it toward the stationary member  28 ,  128  and thereby cause a tensioning force to be applied to the tether  16 ,  116 . For example, the wheel  18  of device  10  will rotate to push or pull the tether  16  away from the anchor to apply the tensioning force thereto. With device  100 , the lever arm  118  will slide to push the tether  116  away from the anchor to apply the tensioning force thereto. In an exemplary embodiment, the tether  16 ,  116  is tensioned along its path as it extends longitudinally along the spinal column. This applies the tension in such as a way as to push or pull on the tether  16 ,  116  without substantially bending the tether  16 ,  116 . The proper tension can be applied to the tether  16 ,  116 , and after the tether  16 ,  116  has been locked in the bone anchor to retain the tension thereon, the device  10 ,  100  can be removed and the tether  16 ,  116  can be released from the grasping member  32 ,  132 . In one embodiment, the tether can be locked between adjacent bone anchors by applying a locking mechanism, such as a set screw, to each bone anchor. A person skilled in the art will appreciate that any mechanism can be used to lock the tensioned tether  16 ,  116  between adjacent bone anchors. 
     A person skilled in the art will appreciate that the various methods and devices disclosed herein can be formed from a variety of materials. Moreover, particular components can be implantable and in such embodiments the components can be formed from various biocompatible materials known in the art. Exemplary biocompatible materials include, by way of non-limiting example, composite plastic materials, biocompatible metals and alloys such as stainless steel, titanium, titanium alloys and cobalt-chromium alloys, and any other material that is biologically compatible and non-toxic to the human body. 
     One skilled in the art will appreciate further features and advantages based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.