Patent Publication Number: US-11039863-B2

Title: Apparatus and methods for reduction of vertebral bodies in a spine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 14/223,119, filed Mar. 24, 2014, which is a continuation of U.S. patent application Ser. No. 11/567,889, filed Dec. 7, 2006, now U.S. Pat. No. 8,679,128, issue date Mar. 25, 2015, the complete disclosure of which is herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to apparatus and methods used during a spinal surgical procedure. More particularly, the inventive concepts relate to spinal surgical procedure that use apparatus and methods for reducing vertebral bodies. 
     BACKGROUND 
     Modern spine surgery often involves the use of spinal implants to correct or treat various spine disorders or to support the spine. Spinal implants may help, for example, to stabilize the spine, correct deformities of the spine, facilitate fusion, treat spinal fractures, repair annular defects, etc. 
     Spinal implant systems for a lumbar region of the spine may be inserted during a procedure using a posterior spinal approach. Conventional systems and methods for such operations may involve dissecting and retracting soft tissue near or around the surgical site, which may cause trauma to the soft tissue, and extend recovery time. 
     Minimally invasive procedures and systems may reduce recovery time as well as trauma to the soft tissue surrounding a stabilization site. During minimally invasive surgical procedures, often a reduction of one of more vertebrae are indicated. A need exists for reduction apparatus and related methods that provide flexibility of operation, enhanced range of reduction, and adaptability to the patient&#39;s anatomy. 
     SUMMARY 
     The disclosed inventive concepts relate to apparatus and methods for reduction of vertebrae or vertebral bodies. In one exemplary embodiment, an apparatus according to the invention includes a reducer, and an extender coupled releasably to the reducer. The reducer includes a sleeve and a knob. The sleeve has a threaded portion. Similarly, the knob has a threaded portion that is in engagement with the threaded portion of the sleeve to provide reduction of the vertebra or vertebral body. 
     In another exemplary embodiment, a system for reducing a vertebra or vertebral body includes an extender and a reducer. The reducer is releasably coupled to the extender, and is configured to allow incremental reduction of the vertebral body. 
     Yet another exemplary embodiment relates to a method of reducing a vertebra or vertebral body. The method includes moving incrementally one member with respect to a second member. The first member is releasably coupled to the vertebra, which results in the reduction of the vertebra or vertebral body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended drawings illustrate only exemplary embodiments of the invention and therefore should not be considered or construed as limiting its scope. Persons of ordinary skill in the art who have the benefit of the description of the invention appreciate that the disclosed inventive concepts lend themselves to other equally effective embodiments. Unless noted otherwise, in the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks. 
         FIGS. 1A and 1B  show details of how a typical reduction procedure brings into alignment a misaligned vertebra. 
         FIG. 2A  shows a system for a spinal surgical operation that uses a reducer according to an exemplary embodiment of the invention. 
         FIG. 2B  illustrates reduction of a vertebral body by operating the reducer shown in  FIG. 2A . 
         FIG. 3  depicts a reducer according to one exemplary embodiment of the invention. 
         FIG. 4  shows a top view of the locking handles and locking members of the reducer in  FIG. 3 . 
         FIG. 5  illustrates a cross-section of the exemplary reducer illustrated in  FIG. 3 . 
         FIGS. 6-13  depict a plurality of reducers according to exemplary embodiments of the invention. 
         FIG. 14  shows a holding device according to one aspect of the inventive concepts for use with reducers according to the invention. 
         FIGS. 15-19  illustrate a plurality of attachment mechanisms according to exemplary embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed novel concepts relate to apparatus and methods for reducing vertebrae or vertebral bodies during minimally invasive surgical procedures, for example, during a spinal stabilization procedure. Details of minimally invasive surgery are described in detail in U.S. patent application Ser. No. 10/980,675, titled “Instruments and Methods for Reduction of Vertebral Bodies,” filed on Nov. 3, 2004, and incorporated by reference in this application. Briefly, minimally invasive surgery uses apparatus such as guide wires, bone fastener assemblies, extenders, and sleeves, as described in detail in U.S. patent application Ser. No. 10/980,675, referenced above. 
     During minimally invasive surgery, a reduction of one or more vertebral bodies is indicated. As persons of ordinary skill in the art who have the benefit of the description of the invention understand, reduction generally refers to the replacement or realignment of a body part in normal position or restoration of a bodily condition to normal.  FIGS. 1A and 1B  show details of how a typical reduction procedure brings into alignment a misaligned vertebra. 
     More specifically, in  FIG. 1A , vertebral body  90  is out of alignment with the rest of the spine and is to be returned to its original position via a reduction procedure. To do so, the surgeon constructs a “framework” or assembly that will serve as the alignment point. The surgeon constructs the framework with pedicle screws or other suitable fasteners and a rod or elongated member to bridge the “bad” (defective or diseased) segment or vertebra and anchoring to the two “good” (healthy and properly aligned) adjacent segments or vertebrae above and below. 
     The surgeon places fasteners or pedicle screws (collar  112  of the fastener assembly is shown explicitly) into the desired vertebral bodies, including the “bad” segment (labeled  90 ). Once in place, the surgeon locates an elongated member or rod  104  in the adjacent bone fastener assemblies (e.g., screw heads), and fastens it with a closure mechanism (e.g., closure cap). The rod is contoured in a manner that will hold the proper alignment of the segments or vertebrae once the reduction procedure is complete. 
     To aid in the reduction, the surgeon uses one or more extenders. Because elongated member or rod  104  passes through the middle extender (labeled  170 ) in the figure, which is in turn attached to the pedicle screw or fastener of the “bad” segment, the extender serves two purposes. First, the extender acts as a guide for the proper alignment of elongated member or rod  104  into the fastener assembly (e.g., screw head). 
     The extender also serves as a mechanism to “pull up” on the fastener or screw and consequently the vertebral body until elongated member or rod  104  is properly seated within the fastener assembly (e.g., screw head). As described below in more detail, this is done by “pushing” incrementally against elongated member or rod  104  with a hollow shaft or tube (see for example item  188  in  FIGS. 2A and 2B ) while “pulling” up on extender  170  in a manner similar to a tackle being used to hoist up a load. 
     This incremental, controlled relative motion is achieved by reducer (described below in detail). As detailed below, one part of the reducer is releasably coupled to extender  170  via locking member(s), while another part of the reducer (reduction shaft  308 ) is coupled to shaft or tube  188 , which is in turn anchored or coupled to elongated member or rod  104 . 
       FIG. 1B  shows vertebral body  90  in its reduced state. Note that it is completely or substantially aligned with the rest of the spine or adjacent vertebral bodies. At this stage, a closure mechanism is applied that will secure, fasten, or lock elongated member or rod  104  to the bone fastener assembly (e.g., to the screw head), and therefore fix the position of the “bad” or reduced segment or vertebra  90  with respect to the adjacent segments. Bone graft may be applied to aid fusing the segments together while held in place with elongated member or rod  104  and the bone fastener assemblies. 
     Conventional reducers have a number of disadvantages, such as relatively limited range of operation, relative lack of adaptability to the patient&#39;s anatomy (e.g., the patient&#39;s lordotic curve), failing to allow for incremental reduction, and involving manual interaction by the surgeon at all times or substantially all times, etc. 
     As described here in detail, the disclosed reduction apparatus and associated methods overcome those limitations. For example, the disclosed reduction apparatus and related techniques allow incremental reduction without continual surgeon intervention, thus allowing for gradual tissue relaxation, provide relatively extended range of operation or reduction, provide quick-coupling capabilities, and adapt more easily to the patient&#39;s anatomy. 
       FIG. 2A  shows a shows a system  100  for a spinal surgical operation that uses a reducer according to an exemplary embodiment of the invention. System  100  includes bone fastener assembly  102  (e.g., screw, collar, and closure member (e.g., cap)), elongated member  104  (e.g., a rod), extender  170 , sleeve or assembly  186 , and reducer  300 . Some details of system  100  are provided in U.S. patent application Ser. No. 10/980,675, referenced above. 
     During minimally invasive surgery, extender  170  allows the surgeon to manipulate bone fastener assembly  102  and to couple fastener  108  to vertebra  90 . A distal end of an extender  170  couples to bone fastener assembly  102  and allows the surgeon to manipulate assembly  102 . In the embodiment shown, extender  170  couples to collar  112  of assembly  102 . 
     After a bone fastener assembly is coupled to extender  170 , a driver may be coupled to a bone fastener of the bone fastener assembly. The driver may be used to insert the bone fastener into vertebral bone, such as vertebra  90 . 
     Elongated member  104  allows the surgeon to accomplish a desired goal, for example, stabilize the spine, maintain the natural spacing between vertebrae, etc., as persons of ordinary skill in the art who have the benefit of the description of the invention understand. After bone fastener assemblies are installed and an elongated member is placed in the bone fastener assemblies, closure members may be secured to the bone fastener assemblies. 
     When a closure member is threaded on a bone fastener assembly, a counter torque wrench may be used to inhibit the application of torque to the spine of the patient. A counter torque wrench may hold an extender that is coupled to a collar. The counter torque wrench allows the application of an appropriate or desired amount of torque, for example, to shear off the tool portion of a closure member. 
     In some embodiments, a counter torque wrench may inhibit application of torque to a patient during tightening of a closure member and/or during shearing of a tool portion of the closure member by applying a force to an elongated member to counter the force applied to a bone fastener assembly by rotation of the closure member. 
     The counter torque wrench may take a variety of forms. For example, it may constitute a sleeve that includes hollow shaft or tube  188 . Hollow shaft  188  may be inserted through an opening in the body over extender  170  and advanced toward the patient&#39;s spine. 
     Handle  190  of sleeve or assembly  186  may have of various shapes or designs, as desired. In some embodiments, a shape of handle  190  may facilitate gripping of sleeve or assembly  186  or hollow tube  188 . Handle  190  may include a cut-out portion to facilitate gripping and/or to reduce the weight of the sleeve. In certain embodiments, a shape of handle  190  may be tapered toward hollow shaft  188  to reduce interference and/or increase visibility of a surgical site. 
     In the embodiment shown, handle  190  includes lock button or mechanism  191 . During normal operation, lock mechanism  191  locks or holds the position of handle  190  with respect to sleeve or assembly  186  or hollow shaft  188 . By pulling back lock button  191 , the surgeon may “flip” handle  190  around (i.e., move it along the path shown by arrows labeled A) in order to reduce interference with the (patient&#39;s body and/or increase visibility of the surgical site. 
     In some embodiments, reducing one or more vertebral bodies to the shape of an elongated member (e.g., a contoured elongated member) or to a desired position may be indicated. Reduction of a vertebral body during a spinal stabilization procedure may include forcing or moving the vertebral body into a position determined by the contour of the elongated member used in the spinal stabilization system or by other indicia. 
     During a spinal stabilization or implant procedure, a first portion of an elongated member may be seated in a collar of a first bone fastener assembly that is coupled to a first vertebra. A closure member may be coupled to the collar and the elongated member to seat the elongated member fully in the collar and to fix the position of the elongated member relative to the first bone fastener assembly. 
     A second portion of the elongated member may be positioned adjacent to a collar of a second bone fastener assembly that is coupled to a second vertebra. The position of the second vertebra and/or the shape of the elongated member, however, may inhibit the second portion of the elongated member from being fully seated in the collar of the second bone fastener assembly. 
     A reducer may be coupled to the elongated member and to the collar of the second bone fastener assembly (e.g., via extender  170 ). The reducer may be used to reduce the vertebral body, e.g., fully seat the second portion of the elongated member in the collar of the second bone fastener assembly. 
     While the reducer holds the second portion of the elongated member seated in the collar of the second bone fastener assembly, driver  101  may be used to secure a closure member (e.g., cap or other suitable item) to the collar to fix the position of the elongated member relative to the collar. Radiological imaging or fluoroscopy may be used to determine when the reducer has fully seated the second portion of the elongated member in the collar of the second bone fastener assembly. 
     Reducers may be used during a minimally invasive surgical procedure or during procedures where access to an elongated member and working room are restricted. During a minimally invasive procedure or a procedure with limited access and/or limited working room, a reducer may be used to pull an extender coupled to a bone fastener assembly of a spinal implant or stabilization system upward (e.g., away from the spine) to seat the elongated member in a collar of the bone fastener assembly. Movement of a reducer may be achieved by, but is not limited to being achieved by, use of threading, cam action, linkage arms, or a combination thereof, as described below. 
     In some embodiments, a reducer may be used with one or more other instruments to achieve reduction of a vertebral body coupled to a spinal stabilization system.  FIG. 2A  depicts an embodiment of reducer  300  that may be used in combination with extender  170  and sleeve or assembly  186 , including hollow shaft  188 . 
     The reducer may be used to seat elongated member  104  in collar  112  of bone fastener assembly  102  when the bone fastener assembly is coupled to a vertebra. The reducer is designed to couple to extender  170  and pull it upward while pushing elongated member  104  into collar  112 . 
     Without loss of generality, in one embodiment, reduction of vertebral body  90  is accomplished by moving vertebral body  90  coupled to bone fastener assembly  102  relative to elongated member  104  in such a manner that the elongated member  104  is captured within collar  112  of bone fastener assembly  102 , thus holding vertebral body  90  in desired position. The reduction is accomplished by inducing relative motion of elongated member  104  with respect to collar  112  coupled to vertebral body  90  via assembly  102  or vice versa. 
     An apparatus for inducing relative motion is reducer  300  with engaging tabs  306  and reduction sleeve  308  that moves with respect to engaging tabs  306 . Engaging tabs  306  are coupled to extender  170 , which in turn is coupled to vertebral body  90  via assembly  102 . Reduction sleeve  308  is coupled to hollow shaft  188 , which in turn is coupled to elongated member  104 . By manipulating reduction sleeve  308  with respect to engaging tabs  306 , shaft  188  moves relative to extender  170 . As a consequent, elongated member  104  moves relative to collar  112  of assembly  102 , which is coupled to vertebral body  90 . 
     Note that the reduction apparatus uses shaft  188  and the extender  170  in order to “reach” through a small incision into the patient and manipulate elongated member  104  with respect to vertebral body  90 .  FIG. 2B  shows elongated member  104  seated into collar  112  of assembly  102  as a result of operating reducer  300  (i.e., as a result of the reduction of vertebra or vertebral body  90 , as described below in detail). 
       FIG. 3  shows a reducer according to one exemplary embodiment of the invention. Reducer  300  includes knob or handle  302 , locking handles  304 , locking or engaging members or tabs  306 , reduction sleeve  308 , and bore  310 . 
       FIG. 4  shows a top view of locking handles  304  and locking members  306 . Locking handles  304  include or couple to a biasing mechanism, e.g., springs to facilitate engagement of locking members  306  to extender  170 . Depressing locking handles  304  causes locking members  306  to withdraw from openings in reduction sleeve  308 . Releasing locking handles  304 , however, causes locking members  306  to return to their original positions in the openings. 
       FIG. 5  shows a cross-section of reducer  300 . Note that an inner portion or surface of knob  302  includes threads  312 . An outer portion or surface of reduction sleeve  308  includes threads  314 , which are complementary to threads  312  of knob  302 . 
     Once assembled, the threads of knob  302  engage the threads of reduction sleeve  308 . By rotating knob  302  along the arrows labeled “B,” one may cause the coupled or engaged threads of knob  302  and reduction sleeve  308  to cause sleeve  308  to move up or down or vertically, as the arrow labeled “C” shows. The movement of sleeve  308  may in turn cause the corresponding motion of other apparatus or items coupled to it. 
     During minimally invasive surgery, reducer  300  couples to other surgical apparatus in order to reduce a vertebral body. For example, in one embodiment, reducer  300  couples to extender  170  (see above) via locking members  306 . More specifically, by depressing locking handles  304 , the surgeon causes locking members  306  to withdraw or move in an outward direction (away from sleeve  308 ). The surgeon then couples reducer  300  to extender  170  (e.g., by placing reduction sleeve  308  over or inside extender  170 , as desired) and releases locking handles  304 , as described above. 
     Once reducer  300  has coupled to extender  170 , the surgeon may turn knob  302  in a desired direction and by a desired amount. As described above, the turning of knob  302  causes shaft  188  moves relative to extender  170 . As noted, extender  170  is coupled to the bone fastener assembly  102  (see  FIGS. 2A and 2B ). Consequently, elongated member  104  moves relative to collar  112  of assembly  102 , which is coupled to vertebral body  90 , hence causing reduction of vertebral body  90 . 
     By using relatively fine thread pitches, one may allow the surgeon to fine-tune the reduction of the vertebral bodies, as desired. For example, the surgeon may accomplish the reduction through relatively small or incremental steps. This approach provides the benefit of allowing the affected tissue to relax and helps to reduce trauma. 
     Furthermore, under normal circumstances, the surgeon need not continually manipulate reducer  300 . Put another way, the surgeon may activate reducer  300  by a desired amount (by turning knob  302  in a desired direction and by a desired amount). Once the surgeon finishes manipulating reducer  300 , it maintains the desired or final reduction. 
       FIG. 6  shows a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer in  FIG. 6  includes knob  302  and body  320 . Body  320  couples to extender  170  through any suitable or desired mechanism, such as locking members  306 . 
     Body  320  has a threaded portion  320 A that engages a complementary threaded portion  302 A of knob  302 . Body  320  couples to extender  170 . Turning knob  302  clockwise or counterclockwise causes body  320  and, hence, extender  170  to move up or down relative to hollow shaft  188 . As a result, by turning knob  302  in a desired direction and by a desired amount, the surgeon can reduce the corresponding vertebral body. 
       FIG. 7  shows a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer includes knob  302 , upper body  322 , and lower body  324 . Upper body  322  couples to extender  170  through any suitable or desired mechanism, such as locking members  306 . (Note that, alternatively, or in addition, lower body  324  may couple to extender  170 , as desired, and as persons of ordinary skill in the art who have the benefit of the description of the invention understand.) 
     Upper body  322  has a threaded portion  322 A that engages a complementary threaded portion  302 A of knob  302 . Similarly, lower body  324  has a threaded portion  324 A that couples to threaded portion  302 A of knob  302 . Threaded portion  322 A and threaded portion  324 A have opposite thread directions. For example, in the embodiment shown, threaded portion  322 A has right-hand threads, whereas threaded portion  324 A has left-hand threads. 
     Of course, as persons of ordinary skill in the art, who have the benefit of the description of the invention understand, one may use other arrangements of threads. For example, in one embodiment, threaded portion  322 A may have left-hand threads and threaded portion  324 A has right-hand threads. 
     Turning knob  302  clockwise or counterclockwise causes upper body  322  and lower body  324  to move in opposite directions. As extender  170  couples to upper body  322  (or lower body  324 , as desired), movement of upper body  322  (or lower body  324 ) causes extender  170  to move up or down relative to hollow tube  188 . As a result, by turning knob  302  in a desired direction and by a desired amount, the surgeon can reduce the corresponding vertebral body. 
       FIG. 8  shows a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer includes knob  302  and body  320 . Body  320  couples to extender  170  through any suitable or desired mechanism, such as locking members  306 . 
     Body  320  has a threaded portion  320 A that engages a complementary threaded portion  302 A of knob  302 . Turning knob  302  clockwise or counterclockwise causes knob  302  to move relative to body  320 . Note, however, that turning knob  302  does not change its position relative to extender  170 . As extender  170  couples to knob  302 , movement of knob  302  causes extender  170  to move up or down relative to hollow tube  188 . Thus, by turning knob  302  in a desired direction and by a desired amount, the surgeon can reduce the corresponding vertebral body. 
       FIG. 9  illustrates a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer includes two progressively inclined members or wedges  350  and  352 . Progressively inclined wedge  350  couples to extender  170  (via, for example, coupling members not shown explicitly). Progressively inclined wedge  352  couples to hollow shaft  188 . 
     By turning progressively inclined wedge  350  in a desired direction and by a desired amount, while holding progressively inclined wedge  352  stationary (or vice-versa), the surgeon can cause movement of extender  172  and hence reduce the corresponding vertebral body. Note that one may use a variety of implementations of the reducer, as persons of ordinary skill in the art who have the benefit of the description of the invention understand. For example, one may use progressively inclined wedges  350  and  352  that include steps (rather than a continuously inclining profile) of desired size or height, as desired. Using stepped wedges would allow incremental reduction in discrete amounts or steps. 
       FIG. 10  depicts a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer includes a “z lever” configuration or assembly. Specifically, the reducer includes base  364  coupled to hollow shaft  188 , and body  320  coupled to extender  170  (e.g., through locking members  306 ), lever bar  360 , and truss  362 . 
     Lever bar  360  couples at joint  367  to truss  362 . Truss  362  couples to base  364  at joint. Lever bar  360  forms a lever, with a fulcrum at joint  366 . The surgeon may lift lever bar  360 , thus exerting downward force on truss  362  through joint  367 . Truss  362  in turn exerts downward pressure on base  364  and hence on hollow tube  188 . Lifting lever bar  360  also causes the lifting of body  320  and thus extender  170 . Consequently, by lifting lever bar  362  by a desired amount, the surgeon can reduce the corresponding vertebral body. 
       FIG. 11  shows a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer includes base  372  coupled to hollow tube  188 , and body  320  coupled to extender  170 . 
     The reducer further includes bolt or screw  370 , whose threads engage with threaded portion  320 A of body  320 . An end of screw or bolt  370  couples to base  372 . Slide pin  374  couples a portion of body  320  (opposite or distal end from screw or bolt  370  in the embodiment shown in  FIG. 11 ) to base  372 . Slide pin  374  provides stability to the mechanism and facilitates movement of body  320  with respect to base  372 . 
     The surgeon may turn screw or bolt  370 , which causes body  320  to move closer to (or farther from, depending on the type of threads of screw or bolt  370  and threaded portion  320 A) base  372 . Because extender  170  couples to body  320 , movement of body  320  causes reduction of the corresponding vertebral body. 
       FIG. 12  illustrates a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . The reducer includes a “scissor jack” configuration or assembly. Specifically, the reducer includes base  382  coupled to hollow shaft  188 , and body  320  coupled to extender  170  (e.g., through locking members  306 ), lever bar  386 , screw or bolt  380 , and lever bar  388 . 
     Lever bar  386  and lever bar  388  couple to each other at joint  390 A. Lever bar  386  couples to body  320  at joint  390 B and to base  382  at joint  390 D. Similarly, lever bar  388  couples to body  320  at joint  390 C and to body  382  at joint  390 E. By turning screw or bolt  380 , the surgeon causes the location of joint  390 C to move through slot  320 A and the location of joint  390 D to move through slot  382 A, thus lifting body  320  with respect to base  380 . 
     As noted, body  320  and base  380  couple, respectively, to extender  170  and to hollow shaft  188 . Thus, the lifting of body  320  causes the lifting of extender  170  and therefore reduction of the corresponding vertebral body. 
       FIG. 13  shows a cross-section of another reducer according to an exemplary embodiment of the invention, coupled to extender  170  and hollow shaft  188 . Generally speaking, the reducer includes an offset cam (locking member  306 ) assembly. 
     The reducer includes body  390  coupled to hollow shaft  188  and disk  392  coupled to extender  170 . Disk  392  couples to one end of shaft  394 , which passes through a bore or opening in body  390 . Another end of shaft  394  couples to handle or member  396 . Note that, rather than separate pieces (e.g., disk  392 , shaft  394 , and member  396 ), one may integrate or combine one or more of the components shown in  FIG. 13 . As merely one example, one may combine shaft  396  and disk  392  as one component. 
     Crank or handle  398  couples to member  396  and assists in turning shaft  394  and, hence, disk  392 . Disk  392  couples to extender  170  via locking member  306  (e.g., a cam). Locking member  306  has an offset location with respect to shaft  394 . Thus, turning shaft  394  causes the lifting of extender  170  and, hence, the reduction of the corresponding vertebral body. 
     Another aspect of the invention relates to holding devices suitable for use with reducers according to various embodiments of the invention.  FIG. 14  shows a cross section of an exemplary embodiment of a holding device. One may use the holder in conjunction or in combination with a reducer (e.g., the reducers in  FIGS. 9, 10, and 13 ) in order to hold extender  170  in place (i.e., keep steady or hold constant the degree or amount of reduction). 
     The holder includes base  402  coupled to hollow shaft  188  and body  404  coupled to extender  170 . Columns or bars  408 A and  408 B coupled body  404  to base  402 . Body  404  may move along the length of columns  408 A and  408 B. Columns  408 A and  408 B have ratcheting teeth  410 A and  410 B, respectively. Ratcheting teeth  410 A and  410 B allow upward movement of body  404 , but prevent its downward movement. Thus, the holder allows the surgeon to maintain a desired degree or amount of reduction once it is achieved. 
     The holder further includes release handles or members  406 A and  406 B. By activating or operating release handles  406 A and  406 B, the surgeon can cause the release of the ratcheting teeth  410 A and  410 B, respectively, thus allowing movement of body  404  with respect to base  402 . 
     One may use a variety of mechanisms to couple the reducers according to the invention with extender  170 , as persons of ordinary skill in the art who have the benefit of the description of the invention understand. As one specific case, one may couple the reducer to the extender in a releasable manner, such that the surgeon need not reverse some of the reduction procedure steps in order to decouple or release the reducer from the extender. The following description provides some examples of releasable coupling mechanisms that may be used with the reduction apparatus described above. 
       FIG. 15  shows a cross-section of an attachment mechanism according to an exemplary embodiment of the invention. The attachment mechanism includes locking members  306 A and  306 B, and screw or bolt  420 . Locking members  306 A and  306 B couple to extender  170 , for example, through notches or other mechanisms in extender  170 . Locking member  306 A is stationary (e.g., part of the body of a reducer), but locking member  306 B may move in response to force applied to it. 
     More specifically, by turning screw or bolt  420 , one may cause it to contact and exert force against locking member  306 B. Force applied against locking member  306 B causes it to engage extender  170  and couple to it. Thus, by using the attachment mechanism, one may securely couple the reducer or other desired apparatus to extender  170  in order to perform the reduction procedure. 
       FIG. 16  shows a cross-section of other attachment mechanisms according to an exemplary embodiment of the invention. The apparatus shown in  FIG. 16  illustrates two locking mechanisms. The locking mechanisms may be included within housing or member  432 , for example, the body of a reducer. 
     One locking mechanism includes locking member  306 A. Locking member  306 A couples to housing  432  via a joint or hinge  434 . Hinge  434  allows locking member  306 A to swing or flip down. In this position, locking member  306 A engages and couples to extender  170 . Hinge  434  also allows locking member  306 A to swing or flip up. In this position, locking member  306 A disengages or uncouples from extender  170 . 
     The second locking mechanism in  FIG. 16  includes locking member  306 B and biasing member or spring  430 . Locking member  306 B may slide within housing  432 . When it slides towards extender  170 , locking member  306 B engages and couples to extender  170 . Conversely, when it slides away from extender  170 , locking member  306 B disengages and uncouples from extender  170 . 
     Spring  430  exerts some force against locking member  306 B, which causes it to slide towards and couple to extender  170 . When one desires to uncouple extender  170  from locking member  306 B, one may slide away or push back locking member  306 B from extender  170 . 
       FIG. 17  depicts a cross-section of an attachment mechanism according to an exemplary embodiment of the invention. The attachment mechanism in  FIG. 17  constitutes an “iris type” of mechanism, and includes locking members  306 , ring  440 , and handle or lever  444 . 
     Turning handle  444  causes movement of locking members  306 . More specifically, turning handle  444  in one direction (e.g., clockwise) causes locking members  306  to move towards each other, and thus engage and couple to extender  170 . Turning handle  444  in the opposite direction (e.g., counterclockwise), however, causes locking members  306  to move away from each other, and thus disengage and uncouple from extender  170 . 
       FIG. 18  depicts a cross-section of an attachment mechanism according to an exemplary embodiment of the invention. The attachment mechanism in  FIG. 18  includes locking members  306 , housing  460  (e.g., body or other part of a reducer), shaft  450 , and handle  454 . 
     Handle  454  couples to shaft  450  via hinge or joint  452 . Engaging handle  454 , e.g., by pulling it towards shaft  450 , causes locking members  306  to move in one direction, for example, towards each other. As a result, locking members  306  engage with and couple to extender  170 . 
     Disengaging handle  454 , e.g., by pulling it away from shaft  450 , causes locking members  306  to move in the opposite direction, for example, away each other. As a result, locking members  306  disengage and uncouple from extender  170 . 
     Note that one may include in the apparatus shown in  FIG. 18  mechanisms for holding handle  454  in a desired position, as desired, and as persons of ordinary skill in the art who have the benefit of the description of the invention understand. Examples of such mechanisms include ratchets, holding clamps, etc. 
       FIG. 19  depicts a cross-section of an attachment mechanism according to an exemplary embodiment of the invention. The attachment mechanism in  FIG. 19  constitutes a “collet type includes locking members  306 , sleeves  472 , and engaging members  474 .  FIG. 19  shows one attachment mechanism in the locked position (the right side of  FIG. 19 ), and another attachment mechanism in the unlocked position (left side of  FIG. 19 ). 
     Each of locking members  306  may move around a respective joint or hinge  474 . Generally, moving sleeves  472  causes engaging members  472  to contact locking members  306 , form a collar or collet around them, and cause them to move. Movement of locking members  306  may cause them to engage and couple to extender  170 , or to disengage and uncouple from extender  170 . Note that the apparatus in  FIG. 19  allows the surgeon to couple either side of the reducer to extender  170  independently of the other side. 
     As described, several embodiments of reducers according to the inventive concepts use threaded mechanisms or portions. By using a desired thread type and/or pitch, one may provide reducers with desired characteristics, as persons of ordinary skill in the art who have the benefit of the description of the invention understand. 
     For example, by using a relatively fine thread pitch, one may produce a reducer that causes a relatively small amount of reduction for a given amount of activation of the reducer (e.g., turning knob  302  in  FIG. 3 ), and vice-versa. As noted, by using relatively fine thread pitches, one may allow the surgeon to fine-tune the reduction of the vertebral bodies with a relatively high degree of precision. 
     Furthermore, by varying the size or length of the threaded portion, one may produce reducers with desired characteristics. For example, a relatively long or large threaded portion would allow a relatively large reduction of the vertebral body, and vice-versa. This property allows reducers according to the inventive concepts to overcome the limited range of conventional reducers. 
     Various modifications and alternative embodiments of the invention in addition to those described here will be apparent to persons of ordinary skill in the art who have the benefit of the description of the invention. Accordingly, the manner of carrying out the invention as shown and described are to be construed as illustrative only. 
     Persons skilled in the art may make various changes in the shape, size, number, and/or arrangement of parts without departing from the scope of the invention described in this document. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described here, or use certain features of the invention independently of the use of other features, without departing from the scope of the invention.