Patent Publication Number: US-2023157736-A1

Title: Reducer locking mechanisms and methods of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/281,506, filed Nov. 19, 2021. This application also claims the benefit of U.S. Provisional Application No. 63/406,137, filed Sep. 13, 2022. The entire contents of each of these applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     This disclosure relates generally to locking mechanisms for surgical instruments and related methods of use and, more particularly, to locking mechanisms for reducers utilized to approximate two components, e.g., a spinal fixation element and a bone anchor during spine surgery. 
     BACKGROUND 
     Fixation systems can be used in orthopedic surgery or neurosurgery to maintain a desired spatial relationship between multiple bones or bone fragments. For example, in spine surgery, a spinal fixation system can be implanted into a patient to align and/or fix a desired orientation of one or more vertebrae. A typical spinal fixation system can include implants, such as bone anchors, disposed in the vertebrae and a spinal fixation element, such as a rod, that is secured to the implants by closure mechanisms, such as set screws. Implanting the fixation system can involve multiple steps, e.g., surgical site preparation, bone anchor implantation, derotation, rod introduction and reduction, set screw insertion, and others. 
     Rod reduction and set screw management can be a challenging part of posterior spinal fixation procedures and current rod reduction instrumentation has several shortcomings. For example, in some cases handheld reducer instruments can be utilized that employ opposed handles that pivot toward one another to reduce a rod into a receiving portion of a bone anchor or other implant. In order to avoid requiring a user to maintain constant pressure on the opposed handles, such instruments can include a lock to maintain their position. Prior instruments often utilize a lock that includes a large and long ratchet with multiple teeth located at a proximal end of the opposed handles. In such configurations a number of challenges can be present. For example, the long ratchet disposed at a proximal end of the device can be prone to binding due to misalignment between the opposed handles, e.g., due to forces exerted thereon during use. Further, the ratchet can obscure a surgeon or other user&#39;s view, as well as interfere with gripping and actuation of the instrument or introduction of other components to the surgical site. Moreover, the multiple ratchet teeth can make it difficult to determine when the rod is sufficiently reduced to allow for insertion of a bone anchor locking mechanism, such as a set screw. This is because the ratchet lock can engage with one or more teeth before the rod is reduced far enough to allow for set screw insertion. Still further, the ratchet lock can be difficult to disengage, as one or more teeth can catch and prevent continued removal as the opposed handles are separated after use. Finally, ratchet locks using a plurality of teeth can be difficult to manufacture, given the often large number of teeth and need for precision machining. 
     Accordingly, there is a need for improved locking mechanisms for use with reducers that address challenges with work flow, usability, and manufacturing of said devices. 
     SUMMARY 
     Disclosed herein are locking mechanisms and related methods of use for reducer instruments, e.g., handheld acute reducers and others. The locking mechanisms disclosed herein can be located adjacent to a center pivot joint of the reducer, thereby eliminating the use of a large, long ratchet at the proximal end of the instrument near where a surgeon or other user typically grasps the instrument. The locking mechanisms disclosed herein can include a pawl or latch that travels with one instrument handle during actuation from an initial, open position to a closed position. The pawl can fall into a groove formed in an opposing handle such that handles of the reducer can be locked in place relative to one another, at least with regard to movement of the handles away from one another. When falling into the groove, the pawl can create an auditory and/or tactile indication that a sufficient amount of rod reduction has been achieved to allow for set screw or other closure mechanism insertion. After set screw insertion or other locking of the implant is performed, the reducer locking mechanisms disclosed herein can be released by pressing a button coupled to the pawl to clear it of the groove and allow the reducer to return to its initial, open position. 
     In one aspect, a surgical instrument includes a first handle having a proximal grip portion and a distal housing with a lumen extending therethrough. The instrument further includes opposed arms extending distally from the housing that are configured to interface with an implant. The instrument also includes a reducer sleeve disposed around the opposed arms and configured to translate relative thereto, as well as a second handle having a proximal grip portion. The second handle can be pivotably coupled to the housing and the reducer sleeve such that moving the second handle toward the first handle causes distal translation of the reducer sleeve relative to the opposed arms. The instrument further includes a pawl pivotably coupled to the second handle distal to the grip portion. The pawl can be configured to ride over a portion of the housing that includes a groove as the second handle is moved toward the first handle. Further, the pawl can be configured to seat in the groove and maintain a relative position of the first and second handles when the second handle is moved sufficiently toward the first handle. 
     Any of a variety of alternative or additional features can be included and are considered within the scope of the present disclosure. For example, in some embodiments, the instrument can further include a button extending from the pawl and configured to move the pawl clear of the groove when depressed. 
     In certain embodiments, the instrument can further include a spring urging a distal portion of the pawl into the portion of the housing that includes the groove. 
     In some embodiments, the opposed arms can define a tapering slot therebetween having a first distance between the opposed arms at a distal portion of the slot that is greater than a second distance between the opposed arms at a proximal portion of the slot. 
     In certain embodiments, a distal end of at least one of the opposed arms can include a protrusion configured to extend into a recess of the implant. 
     In some embodiments, distal translation of the reducer sleeve relative to the opposed arms can move the opposed arms toward one another. 
     In certain embodiments, the instrument can further include one or more links pivotably coupled to the second handle and the reducer sleeve. 
     In some embodiments, the instrument can further include a biasing element urging the first and second handle away from one another. 
     In certain embodiments, the housing can include at least one protrusion formed thereon that abuts against the second handle at a fully open or a fully closed position of the first and second handles relative to one another. In some embodiments, the at least one protrusion can include a first protrusion that abuts against the second handle at a fully closed position of the first and second handles, and the first protrusion can be separated from the second handle when the pawl is seated in the groove and maintaining a relative position of the first and second handles. 
     In some embodiments, each opposed arm can include a movable portion configured to deflect radially inward relative to the arm. Further, in certain embodiments the reducer sleeve can include a feature formed on an inner surface thereof that is configured to contact the movable portion of each opposed arm. In some embodiments, each movable portion can include an inwardly-extending projection. 
     In another aspect, a surgical method includes positioning opposed arms of a reducer instrument around a portion of an implant, and moving first and second handles of the reducer instrument toward one another until a pawl coupled to the second handle seats within a groove formed in a housing of the first handle to maintain a relative position of the first and second handles. Further, moving the first and second handles of the reducer instrument toward one another can cause a reducer sleeve disposed around the opposed arms to translate distally relative thereto. Still further, distal translation of the reducer sleeve can cause the opposed arms of the reducer instrument to move toward one another and couple with the implant, and also cause a spinal fixation element to translate distally into a receiving portion of the implant. 
     As with the instruments described above, the methods disclosed herein can include any of a variety of additional or alternative steps that are considered within the scope of the present disclosure. For example, in some embodiments, moving the first and second handles of the reducer instrument toward one another can include overcoming a biasing force urging the handles away from one another. 
     In some embodiments, the method can further include locking the spinal fixation element relative to the implant while the reducer instrument maintains a position of the spinal fixation element relative to the implant. In certain embodiments, locking the spinal fixation element relative to the implant can include inserting a set screw through a bore formed in the reducer instrument and coupling the set screw with the implant. In some embodiments, the method can further include reducing the spinal fixation element distally into the receiving portion of the implant using the set screw such that compressive forces between the reducer sleeve and spinal fixation element are reduced. In certain embodiments, the method can further include moving the first and second handles of the reducer instrument toward one another beyond a position at which the pawl seats within the groove of the housing until one of the first and second handles contacts a stop formed on the other handle. In some embodiments, the method can further include depressing a button to move the pawl clear of the groove and allow movement of the first and second handles away from one another. In certain embodiments, the method can further include moving the first and second handles of the reducer instrument away from one another to proximally translate the reducer sleeve relative to the opposed arms and allow the opposed arms to move away from one another and release from the implant. Further, in some embodiments the method can further include repeating the method across a plurality of implants disposed along a patient&#39;s spine. 
     In another aspect, a surgical method includes positioning an instrument in an unlocked configuration, where the instrument includes an implant engagement member, a reduction member having a channel therein for receiving the implant engagement member therethrough, a handle assembly being coupled to the reduction member and receiving the implant engagement member through a bore thereof, and a lock having a pawl disposed outside of a groove formed in the handle assembly. Further, the handle assembly can include a pair of handles pivotably coupled to one another. The method can further include positioning an implant between opposed arms of the implant engagement member, and moving the pair of handles toward one another to position the instrument in a locked configuration. Moreover, moving the pair of handles toward one another distally can advance the reduction member relative to the implant engagement member to reduce a spinal fixation element into a receiving portion of the implant and can move the pawl into the groove of the handle assembly. 
     As with the instruments and methods described above, any of a variety of additional or alternative steps are considered within the scope of the present disclosure. For example, in some embodiments, moving the pair of handles toward one another can include overcoming a biasing force on the pair of handles and causing a linkage disposed between the pair of handles and the reduction member to advance the reduction member distally. 
     In certain embodiments, the method can further include actuating a button coupled to the pawl to disengage the pawl from the groove and allow return of the device from the locked configuration to the unlocked configuration. 
     In some embodiments, the method can further include delivering a set screw to the implant through the bore of the handle assembly. 
     In certain embodiments, distally advancing the reduction member relative to the implant engagement member can deflect movable portions of each of the opposed arms of the implant engagement member radially inward such that the movable portions extend into a recess formed in the implant. 
     In another aspect, a surgical method includes positioning opposed arms of a reducer instrument around a portion of an implant, and moving first and second handles of the reducer instrument toward one another until a pawl coupled to the second handle seats within a groove formed in a housing of the first handle to maintain a relative position of the first and second handles. Further, moving the first and second handles of the reducer instrument toward one another can cause a reducer sleeve disposed around the opposed arms to translate distally relative thereto. Moreover, distal translation of the reducer sleeve can cause movable portions of the opposed arms of the reducer instrument to move toward one another and couple with the implant, and also cause a spinal fixation element to translate distally into a receiving portion of the implant. 
     Any of the features or variations described herein can be applied to any particular aspect or embodiment of the present disclosure in a number of different combinations. The absence of explicit recitation of any particular combination is due solely to avoiding unnecessary length or repetition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aspects and embodiments of the present disclosure can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1 A  is a perspective view of one embodiment of a reducer instrument according to the present disclosure; 
         FIG.  1 B  is longitudinal cross-sectional view of the reducer instrument of  FIG.  1 A ; 
         FIG.  1 C  is an exploded view of the reducer instrument of  FIG.  1 A ; 
         FIG.  2    is a perspective view of an implant engagement member of the reducer instrument of  FIG.  1 A ; 
         FIG.  3    is a perspective view of a reduction member of the reducer instrument of  FIG.  1 A ; 
         FIG.  4 A  is a side perspective view of the instrument of  FIG.  1 A  in an initial, open position or unlocked configuration; 
         FIG.  4 B  is a top perspective view of the instrument of  FIG.  4 A ; 
         FIG.  4 C  is a detail view of a distal portion of the instrument of  FIG.  4 A ; 
         FIG.  4 D  is a detail longitudinal cross-sectional view of the distal portion of the instrument of  FIG.  4 A ; 
         FIG.  5 A  is a front perspective view of first and second handles of the instrument of  FIG.  4 A ; 
         FIG.  5 B  is rear perspective view of first and second handles of the instrument of  FIG.  4 A ; 
         FIG.  5 C  is a detail perspective view of a distal portion of the first handle of the instrument of  FIG.  4 A ; 
         FIG.  5 D  is another detail perspective view of the distal portion of the first handle of the instrument of  FIG.  4 A ; 
         FIG.  6 A  is a partially-transparent perspective view of a locking mechanism of the instrument of  FIG.  1 A ; 
         FIG.  6 B  is another partially-transparent perspective view of the locking mechanism of the instrument of  FIG.  1 A ; 
         FIG.  7 A  is a detail perspective view of a pawl of the instrument of  FIG.  1 A ; 
         FIG.  7 B  is another detail perspective view of the pawl of the instrument of  FIG.  1 A ; 
         FIG.  8    is a perspective view of the instrument of  FIG.  1 A  being actuated to move from an open position to a closed position; 
         FIG.  9 A  is a partially-transparent perspective view of a locking mechanism of the instrument of  FIG.  1 A  in a locked position; 
         FIG.  9 B  is another partially-transparent perspective view of the locking mechanism of the instrument of  FIG.  1 A  in a locked position; 
         FIG.  10 A  is a perspective view of one embodiment of set screw insertion according to the present disclosure; 
         FIG.  10 B  is another perspective view of one embodiment of set screw insertion according to the present disclosure; 
         FIG.  10 C  is another perspective view of one embodiment of set screw insertion according to the present disclosure; 
         FIG.  11 A  is a perspective view of one embodiment of locking mechanism release according to the present disclosure; 
         FIG.  11 B  is a detail cross-sectional view of locking mechanism release according to the present disclosure; 
         FIG.  11 C  is another perspective view of one embodiment of locking mechanism release according to the present disclosure; 
         FIG.  11 D  is another detail cross-sectional view of locking mechanism release according to the present disclosure; 
         FIG.  11 E  is another perspective view of one embodiment of locking mechanism release according to the present disclosure; 
         FIG.  12    is a partially-transparent detail view of the locking mechanism of the instrument of  FIG.  1 A  during a further reduction actuation; 
         FIG.  13    is a partially-transparent detail view of the locking mechanism of the instrument of  FIG.  1 A  during release; 
         FIG.  14    is a perspective view of one embodiment of a reducer instrument according to the present disclosure; 
         FIG.  15 A  is a perspective view of a reducer tube of the instrument of  FIG.  14   ; 
         FIG.  15 B  is an exploded view of a reducer tube of the instrument of  FIG.  15 A ; 
         FIG.  16    is a perspective view of one embodiment of a reducer instrument according to the present disclosure; 
         FIG.  17    is a perspective view of an implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  18    is a side perspective view of the implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  19    is a side longitudinal cross-sectional view of the implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  20    is a top perspective view of the implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  21    is a top longitudinal cross-sectional view of the implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  22    is a detail perspective view of a distal portion of the implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  23    is a side perspective longitudinal cross-sectional view of the implant engagement member of the instrument of  FIG.  16   ; 
         FIG.  24    is a perspective view of a reduction member of the instrument of  FIG.  16   ; 
         FIG.  25    is front view of the reduction member of the instrument of  FIG.  16   ; 
         FIG.  26    is a rear view of the reduction member of the instrument of  FIG.  16   ; 
         FIG.  27    is a front perspective view of the reduction member of the instrument of  FIG.  16   ; 
         FIG.  28    is a top longitudinal cross-sectional view of the reduction member of the instrument of  FIG.  16   ; 
         FIG.  29    is a side longitudinal cross-sectional view of the reduction member of the instrument of  FIG.  16   ; 
         FIG.  30    is a perspective view of a distal portion of the instrument of  FIG.  16 A  at a first, proximal-most position relative to the implant engagement member; 
         FIG.  31    is a perspective longitudinal cross-sectional view of a distal portion of the instrument of  FIG.  16 A  at a first, proximal-most position relative to the implant engagement member; 
         FIG.  32    is a perspective view of a distal portion of the instrument of  FIG.  16 A  at a second, more distal position relative to the implant engagement member; 
         FIG.  33    is a perspective longitudinal cross-sectional view of a distal portion of the instrument of  FIG.  16 A  at a second, more distal position relative to the implant engagement member; 
         FIG.  34    is a detail side longitudinal cross-sectional view of a distal portion of the instrument of  FIG.  16 A  at a first, proximal-most position relative to the implant engagement member; 
         FIG.  35    is a detail side longitudinal cross-sectional view of a distal portion of the instrument of  FIG.  16 A  where the reduction member is distally advanced relative to the position of  FIG.  34   ; 
         FIG.  36    is a detail side longitudinal cross-sectional view of a distal portion of the instrument of  FIG.  16 A  where the reduction member is further distally advanced relative to the position of  FIG.  35   ; 
         FIG.  37    is a side perspective view of the instrument of  FIG.  16 A  in a locked configuration; 
         FIG.  38    is a side perspective view of the instrument of  FIG.  16 A  in a final state of distal advancement of the reduction member relative to the implant engagement member; 
         FIG.  39    is a detail perspective view of a distal portion of the instrument of  FIG.  16 A  in a locked configuration; 
         FIG.  40    is a detail perspective view of a distal portion of the instrument of  FIG.  16 A  in a final state of distal advancement of the reduction member relative to the implant engagement member; and 
         FIG.  41    is a side perspective view of the instrument of  FIG.  16 A  being released from a locked configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are locking mechanisms and related methods of use for reducer instruments, e.g., handheld acute reducers and others. The locking mechanisms disclosed herein can be located adjacent to a center pivot joint of the reducer, thereby eliminating the use of a large, long ratchet at the proximal end of the instrument near where a surgeon or other user typically grasps the instrument. The locking mechanisms disclosed herein can include a pawl or latch that travels with one instrument handle during actuation from an initial, open position to a closed position. The pawl can fall into a groove formed in an opposing handle such that handles of the reducer can be locked in place relative to one another, at least with regard to movement of the handles away from one another. When falling into the groove, the pawl can create an auditory and/or tactile indication that a sufficient amount of rod reduction has been achieved to allow for set screw or other closure mechanism insertion. After set screw insertion or other locking of the implant is performed, the reducer locking mechanisms disclosed herein can be released by pressing a button coupled to the pawl to clear it of the groove and allow the reducer to return to its initial, open position. 
     Certain example embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices, systems, and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. The devices, systems, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting embodiments. The features illustrated or described in connection with one embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Additionally, to the extent that linear, circular, or other dimensions are used in the description of the disclosed devices and methods, such dimensions are not intended to limit the types of shapes that can be used in conjunction with such devices and methods. Equivalents to such dimensions can be determined for different geometric shapes, etc. Further, like-numbered components of the embodiments can generally have similar features. Still further, sizes and shapes of the devices, and the components thereof, can depend at least on the anatomy of the subject in which the devices will be used, the size and shape of objects with which the devices will be used, and the methods and procedures in which the devices will be used. 
       FIGS.  1 A- 1 C  illustrate perspective, longitudinal cross-sectional, and exploded views, respectively, of one embodiment of a reducer instrument  100 . The instrument  100  can include an implant engagement member  102 , a reduction member  104 , a handle assembly  106 , and a locking mechanism  108 . The implant engagement member  102  can be used to couple and/or otherwise engage an implant, such as a bone anchor  110 , that is configured to receive a spinal fixation element, such as a spinal rod  112 . The reduction member  104  can be movably coupled to the implant engagement member  102  to reduce the spinal rod  112  into the bone anchor  110  engaged by the implant engagement member  102 . The handle assembly  106  can move the reduction member  104  relative to the implant engagement member  102 , with the locking mechanism  108  locking the device  100  in place once the rod  112  is sufficiently reduced to allow for the insertion of a closure mechanism, such as a set screw, to lock the position of the rod relative to the bone anchor. The instrument  100  can include bores formed therein to allow insertion of additional instruments, e.g., a set screw inserter, therethrough to deliver and install a closure mechanism. 
     While various implants and spinal fixation elements can be used,  FIGS.  1 A- 1 C  illustrate an example embodiment of a bone anchor  110  that can be used with the rod reduction devices disclosed herein. As shown, the bone anchor  110  includes a threaded shank  114  and a rod-receiving head  116 . The threaded shank  114  can be configured to be threaded into bone and the rod-receiving head  116  can be configured to receive a spinal fixation element, such as the spinal rod  112 . In the illustrated embodiment, the rod-receiving head  116  includes opposed arms that define a u-shaped receiving portion for seating the spinal rod  112 . The rod-receiving head  116  can also include mating features formed thereon to facilitate mating with the implant engagement member  102 . While various mating features can be used, in one embodiment the rod-receiving head  116  can include one or more recesses (e.g., blind bores, through-bores, grooves, notches, thread forms, etc.) formed in a proximal portion thereof for receiving one or more projections (e.g., pins, nubs, broken or continuous ridges, hooks, thread forms, etc.) formed on the implant engagement member  102 , as discussed in more detail below. In certain embodiments, any of a variety of complementary features can be utilized in any configuration (e.g., protrusions or other male features formed on the bone anchor with complementary recesses or female features formed on the instrument, etc.). Other implants can also be used, including, for example, hooks, plates, staples, etc. 
     The implant engagement member  102  can be configured to engage at least a portion of the bone anchor  110 . For example, as shown in  FIG.  2   , the implant engagement member  102  can include a proximal portion having an elongate substantially cylindrical portion  115  defining a lumen  117 . The lumen  117  extending through the implant engagement member  102  can have any number of openings and its cross-section does not need to form a complete or continuous closed structure, such as an uninterrupted circle, at any point along the length of the implant engagement member  102 . For example, as shown, the implant engagement member  102  can include one or more cutouts or slots  118  that extend proximally from the distal end  102   d . The rod slot  118  can form a pair of opposed arms  120 ,  122  at the distal end of the implant engagement member  102  that can be configured to engage and couple with the bone anchor  110 . The opposed arms  120 ,  122  can extend generally parallel to one another or can be obliquely angled to one another. As shown in  FIG.  1 B , the opposed arms in the illustrated embodiment diverge from one another to create an outer circumference that increases in a proximal-to-distal direction along a longitudinal axis A 1  of the instrument. This configuration can result in a tapering slot  118  and the arms having a first distance D 1  therebetween at a distal portion of the slot that is greater than a second distance D 2  between the opposed arms at a proximal portion of the slot. Further, the arms  120 ,  122  can be configured to move relative to one another, e.g., elastically deform toward or away from one another in response to forces imparted by a reducer sleeve translating along a length of the implant engagement member  102 , as described in more detail below. For example, the opposed arms  120 ,  122  can be configured to flex, e.g., in a radial direction, between a first, relaxed position that facilitates advancement of the arms  120 ,  122  longitudinally over the rod-receiving head  116 , and a second, compressed position wherein the arms  120 ,  122  are moved toward one another to a position in which the arms  120 ,  122  provide a radially compressive force onto the rod-receiving head  116 , thereby coupling the bone anchor  110  to the instrument  100 . In some embodiments, the arms can be configured such that they clear a bone anchor receiving head  116  when in the first, relaxed configuration such that the instrument can be distally advanced over a proximal portion of the receiver head without needing to impart large axial forces to deflect the arms over the head, as is required with many prior devices. 
     The opposed arms  120 ,  122  can also include various features to facilitate mating to the bone anchor  110 . For example, one or more of the opposed arms  120 ,  122  can include at least one mating element  124  disposed on an inner surface thereof. By way of a non-limiting example, the mating element can be in the form of at least one projection that is configured to extend into at least one recess formed in the rod-receiving head  116 , as noted above. The size, shape, and number of mating elements  124  formed on each arm  120 ,  122  can vary depending on the configuration of the bone anchor  110  and the type of connection desired. In other embodiments, rather than having opposed arms  120 ,  122 , the implant engagement member  102  can include any number of arms, or can have other configurations for engaging the bone anchor  110 . 
       FIGS.  4 C and  4 D  illustrate a distal portion of the instrument  100  in greater detail, including the mating elements  124 . The mating element  124  can be a protrusion, such as a pin, nub, or a ridge extending across a width of the arm, that can be configured to be received within a slot or other recess formed in a proximal outer surface portion of a bone anchor receiver member to facilitate coupling between the components. In embodiments that include a ridge or other elongate protrusion, it can extend across an entire width of the arm or, in some embodiments, can extend across only a portion of a width of the arm or include one or more breaks along its length. Example bone anchors having such features are described in U.S. Pat. No. 7,179,261, the entire contents of which are incorporated by reference herein. Other engagement feature configurations are possible as well, including reversing the above-described configuration such that a protrusion formed on a bone anchor is received in a recess formed in the distal portion of the arms  120 ,  122 . 
     In some embodiments, the mating element  124  can be disposed proximal to a distal-most end of the arm&#39;s distal portion and an inner surface of the arm distal to the engagement feature can be configured to facilitate alignment and coupling of the instrument with a bone anchor. For example, an internal surface  402  of the arm can have a shape or profile that is complementary to an outer surface of the bone anchor in order to facilitate coupling even in the event there is some amount of misalignment, whether that be, e.g., lateral or rotational misalignment along an axis of a rod, rotational misalignment along a longitudinal axis of the instrument  100 , etc. In some embodiments, for example, the inner surface  402  can include a tapered profile complementary to an outer surface of opposed arms of a polyaxial bone anchor receiver head. In some instances, the inner surface  402  can include a conical tapering profile that is complementary to the conical tapering profile of a receiver member. Such an arrangement can allow for some pivoting misalignment between the receiver head and the instrument  100  that can be corrected as the instrument is advanced distally relative to the receiver head. In other embodiments, however, the profile can be flat without any tapering. Even in such a configuration, the additional extension of the distal portion of the arm beyond the engagement feature  402  can facilitate alignment and coupling between the instrument  100  and a bone anchor receiver member. 
     Further, the inner surface  402  can include sidewalls  404  extending outward from the inner surface  402  at lateral ends thereof. The sidewalls  404  can similarly include a tapering profile to aid alignment with a receiver member of a bone anchor, e.g., by self-correcting for rotational misalignment about the longitudinal axis of the instrument as the instrument is advanced distally relative to the bone anchor. In some embodiments, the opposed, inward-facing surfaces of each sidewall  404  can have a planar tapering profile that can be complementary to a planar tapering profile of abutting surfaces on a bone anchor receiver member. The various tapered surfaces can accommodate misalignment when coupling the instrument  100  to a bone anchor such that advancement of the instrument over the bone anchor forces the two components into proper alignment just prior to positive engagement of the arms  120 ,  122  with the anchor to simplify attachment of the instrument  100  to the anchor. As noted, the receiver member can include one or more complementary tapering profiles to the tapered surfaces provided on the outer sleeve. Further details on features of the anchor that can be utilized with the instruments disclosed herein can be found in U.S. Pat. Nos. 10,039,578 and 10,299,839, as well as U.S. Provisional Appl. No. 63/157,362, entitled “Multi-Feature Polyaxial Screw,” and U.S. Provisional Appl. No. 63/157,395, entitled “Sequential Reducer and Modular Derotation Tube,” both of which were filed on Mar. 5, 2021. The entire contents of each of these applications are incorporated by reference herein. 
     The rod slot  118  can be sized to receive the spinal rod  112  therethrough. For example, in some embodiments, the spinal rod  112  can be placed within the rod slot  118  at the proximal end  102   p  of the implant engagement member  102  and translated distally by the reduction member  104 , as described below. The rod slot  118  can be sized to receive a spinal rod  112  of various diameters and, in some embodiments, the tapering width of the slot can allow for misalignment between the implant engagement member  102  and the bone anchor  110 . As noted above, the rod slot  118  can taper proximally such that a distance between the arms  120 ,  122  at the distal end  102   d  is larger than a distance between the arms  120 ,  122  at a proximal portion of the slot. In some embodiments, the rod slot  118  can include an enlarged opening  126  along a distal portion of the implant engagement member  102  that is wider than the remainder of the rod slot  118  to further allow for situations in which the spinal rod  112  exhibits rotational and/or lateral misalignment about the longitudinal axis A 1  relative to the rod-receiving head  116  and instrument  100  coupled thereto. 
     Returning to  FIG.  3   , one embodiment of the reduction member  104  is illustrated. The reduction member  104  can be a reducer sleeve having a cylindrical sidewall  128  with a proximal end  104   p  and a distal end  104   d  that defines a channel or lumen  130  therebetween. The channel  130  can be configured to receive the implant engagement member  102  therethrough such that the reduction member  104  is disposed around the opposed arms  120 ,  122 . As noted above, the distal end  104   d  of the reduction member  104  can be configured to abut against the rod  112  when it extends between the opposed arms  120 ,  122  of the implant engagement member  102 . The reduction member  104  can have one or more openings  132  formed in the sidewall  128  thereof. One or more of the openings  132  can align with the slot  118  formed in the implant engagement member  102  to allow instrumentation and/or other devices to pass through the reduction member  104  and the implant engagement member  102  if necessary. In addition, the openings  132  can facilitate cleaning and sterilization of the device, permit visualization through the reduction member  104  during use to allow a surgeon to view the bone anchor, rod, closure mechanism, or other components or anatomy that might otherwise be blocked from view. 
     The proximal end  104   p  of the reduction member  104  can be coupled to the handle assembly  106  for axially translating the reduction member  104  proximally and/or distally with respect to the implant engagement member  102 . For example, the reduction member  104  can include a pair of arms  134 ,  136  extending proximally therefrom. Each arm  134 ,  136  can include an opening  138 ,  140  for receiving a pin therethrough to enable pivotable coupling with other components. 
       FIGS.  4 A- 4 D  illustrate the instrument  100  in its initial, open position or unlocked configuration. In this configuration, the implant engagement member  102  can receive the bone anchor  110  between the arms  120 ,  122 . The handle assembly  106  can be utilized to move the device  100  between the initial, unlocked position and a locked position or locked configuration. The handle assembly  106  can include a first handle  142  and a second handle  144  that are pivotably coupled to one another. As shown, the first handle  142  can be a stationary handle that remains substantially stationary while the second handle  144  pivots relative thereto, though it will be appreciated that, in some embodiments, the first handle  142  can pivot relative to the second handle  144 , which is stationary, and/or the first and second arms can each move relative to one another. The first handle  142  can be pivotably coupled to the second handle  144  using a pivot pin  148  or a similar mating element inserted through a pair of openings (see  FIGS.  5 C- 5 D ) formed in a housing  146  defined by the first arm  142 . The pin  148  can extend through each of the openings along an axis A 2  that is substantially transverse to the longitudinal axis A 1 . 
     The first handle  142  and the second handle  144  can each include a grip or grasping portion  150 ,  152  along a proximal portion thereof. For example, the grip portions  150 ,  152  can be positioned to facilitate grip of a hand of a user placed thereon. The grip portions  150 ,  152  can include features that assist in the comfort and ease of use of the instrument  100 . Any number of features can be included to provide such comfort and ease of use. For example, the handles  142 ,  144  can include surface features to facilitate engagement, such as recesses or protrusions to engage with a user&#39;s fingers, finger loops, etc. In some embodiments, different materials can be utilized for form the grip portions  150 ,  152 , or some portion thereof. For example, in some embodiments a silicone overmold or grip portion of a different material can be coupled to the handles  142 ,  144 . The exploded view of  FIG.  1 C  shows grip portions  150 ,  152  separated from the remainder of the handles  142 ,  144 . It should be noted, however, that a user can grasp the handle  142 ,  144  itself directly, and in such cases the proximal portions of the handles can be the grip portions  150 ,  152 . 
     A distal portion of the first handle  142  includes the housing  146  that includes a bore  154  configured to receive the proximal end of the implant engagement member  102 . For example, a diameter D 4  of the bore  154  can be larger than an outer diameter D 3  of the implant engagement member  102  such that the implant engagement member  102  can be disposed within the bore  154 . In this configuration, the lumen  117  of the implant engagement member  102  can be in communication with the bore  104  such that various devices and/or instruments, e.g., set screw inserters, etc., can be inserted therethrough to access the bone anchor  110 . 
     The housing  146  of the first handle  142  can include a pair of prongs  158 ,  160  that extend from the housing to define a recess  162  therebetween, as shown in  FIGS.  5 A- 5 D . The pivot pin  148  can be received within an opening in each prong  158 ,  160  to mate the first handle  142  to the second handle  144 . The openings in the prongs  158 ,  160  can align with corresponding openings in a distal portion of the second handle  144  such that the pivot pin  148  received therethrough can allow the second handle  144  to pivot relative to the first handle  142 . 
     The instrument  100  can include a torsion spring  164  or another biasing element to bias proximal ends of the first and second handles  142 ,  144  away from one another. For example, the torsion spring  164  can be disposed around the pivot pin  148  to bias the handles  142 ,  144  toward the open configuration. As shown, the torsion spring  164  can be disposed around a portion of the pivot pin  148  within the recess  162  defined between the prongs  158 ,  160  to bias the first and second handles  142 ,  144  apart into the open position. 
     A distal portion of the second handle  144  can include a forked extension  166  having two arms  168 ,  170 . The illustrated forked extension  166  of the second handle  144  begins at a mid-portion and extends distally. The arms  168 ,  170  of the forked extension can be spaced to receive the housing  146  of the first handle  142  and the reduction member  104  therebetween. As shown, the second handle  144  can also house the locking mechanism  108 , as discussed further below. 
     Each of the arms  168 ,  170  of the forked extension  166  can be coupled to a linkage member  172 ,  174 . As shown, the arms  166 ,  168  of the forked extension define recesses  176 ,  178  that can receive an extension  180  formed at one end of the linkage members  172 ,  174 . Pins  182  can couple the components and allow pivoting between the distal end of the second handle  144  and the linkage members  172 ,  174 . The linkage members  172 ,  174  can also define recesses  184 ,  185  on an opposite end thereof for coupling to the arms  134 ,  136  of the reduction member  104 . For example, as shown, each arm  134 ,  136  of the reduction member  104  can be received in the recesses  184 ,  185  of the linkage members  172 ,  174 . As noted above, pins  187  (see  FIGS.  1 C and  4 A ) can be received within the openings  138 ,  140  in the arms  134 ,  136  to couple the linkage members  172 ,  174  and allow pivoting of the linkage members  172 ,  174  relative to the reduction member  104 . 
       FIGS.  6 A- 6 B  illustrate the locking mechanism  108  of the instrument  100  in greater detail. The locking mechanism  108  can be located adjacent to the housing  146  of the first handle  142  distal to the proximal grip portion  150 . Positioning the locking mechanism in this location can avoid the need for a locking mechanism near a proximal end of the handles that can interfere with a surgeon or other user&#39;s grasping the device, visualizing components or anatomy beyond the device, or introducing additional instrumentation through the device or adjacent thereto. 
     As shown, the locking mechanism  108  can include a pawl or latch  186  that locks the instrument  100  in the closed position or locked configuration. The pawl  186  can interact with a groove  188  formed in the housing  146  of the first handle  142  to lock the first and second handles  142 ,  144  against movement away from one another. As shown, the pawl  186  can be coupled to the second arm  144  while the groove  188  can be formed in the housing  146  of the first arm  142 , though it will be appreciated that the location of the pawl  186  and the groove  188  can be reversed or otherwise modified. A button  190  can be coupled to and extend from the pawl  186  such that the button protrudes from an outer surface of the second handle  144  to facilitate user movement of the pawl. For example, the pawl  186  can be pivotably coupled to the second handle  144  with a distal end that is configured to seat within the groove  188  and a proximal end coupled to the button  190 . To unlock the instrument  100 , a user can depress the button  190 , thereby causing the pawl  186  to pivot in a manner that draws the distal end of the pawl away from and clear of the groove  188 . With the pawl  186  clear of the groove  188 , the first and second handles  142 ,  144  can pivot such that proximal ends of the handles move away from one another. This can be accomplished manually by a user or via the bias force provided by the spring  164 . 
       FIGS.  7 A- 7 B  illustrate the pawl  186  in greater detail. As shown, the pawl  186  can include a body  192  having one or more extensions formed thereon. For example, the pawl  186  can include a distal extension  194  that is configured to engage the groove  188 , as discussed above, to lock the orientation of the pawl  186  with respect to the first handle  142 . The pawl  186  can include a series of bores formed therein. As shown, a transverse bore  196  can pass through the body  192  to couple the pawl  186  to the second arm  144 . The transverse bore  196  can receive a pawl pin  198  therethrough for coupling the pawl  186  to the second handle  144  when the transverse bore  196  aligns with a corresponding opening in the second handle  144 . Coupling of the pawl  186  with the second handle  144  is shown in  FIGS.  1 B,  5 A,  5 B,  6 A, and  6 B , among others. 
     A proximal end  186   p  of the pawl  186  can include a series of openings in the superior and inferior surfaces thereof. For example, a bore  200  in the inferior surface can be configured to receive a coil spring  202  therein. The spring  202  can abut an interior surface of the second handle  144  to bias the proximal end  186   p  of the pawl  186  away from the second handle  144  and urge a distal end  186   d  of the pawl toward the housing  146  of the first handle  142 . This can cause the pawl  186  to ride along a surface of the housing  146  during actuation of the device and fall into the groove  188  when the pawl and groove are correctly aligned. 
     The superior surface can include a threaded bore  204  for receiving the button  190 . The button  190  can include a proximal head  206  and a threaded distal end  208  that threads into the threaded bore  204  such that the proximal head  206  extends above an outer surface of the second handle  144 . The threaded bore  204  can align with a slot  210  formed in the second handle  144 , as shown in  FIG.  5 A , such that the slot  210  is in communication with the threaded bore  204 . Alignment between the slot  210  and the threaded bore  204  allows the proximal head  206  of the button  190  to extend through and out of the slot  210  to be pressed by a user during operation of the instrument  100 . Moreover, the proximal head  206  can be larger than a size of the slot  210  to provide a large surface area for actuation of the button  190  during unlocking. 
     Returning to  FIGS.  6 A- 6 B , the instrument  100  is illustrated in the unlocked configuration. As shown, the implant engagement member  102  is disposed over the bone anchor  110  while the reduction member  104  is in a proximal position spaced from the bone anchor  110 . The pawl  186  is resting on an outer surface of the prong  158  of the housing  146  of the first handle  142  distal to the groove  188 . The linkage members  172 ,  174  are disposed at an oblique angle with respect to the longitudinal axis A 1  of the instrument  100 . 
       FIG.  8    illustrates actuation of the instrument  100  to move from the open position to the closed position. Actuation of the instrument  100  includes exerting a force to move the first and second handles  142 ,  144  toward one another, e.g., by pivoting a proximal end of the second handle  144  toward the proximal end of the first handle  142 . As noted above, in the illustrated embodiment, the second handle  144  functions as an actuator that can be moved toward the first handle  142 . For example, as shown, the second handle  144  can rotate or pivot clockwise towards the second handle  144  in the view of  FIG.  8    about the pivot pin  148 . The application of force to the proximal portions of the handles  142 ,  144  to effect this movement can overcome the force from the spring  164  that urges the proximal ends of the arms away from one another. Such movement causes the distal portion  142   d  of the second handle  144  to move toward the longitudinal axis A 1  such that the distal portion  142   d  of the second handle  144  extends closer to parallel to the implant engagement member  102 . It will be appreciated that the distal portion  144   d  of the second handle  144  can, in some embodiments, cross beyond the longitudinal axis A 1  depending on a shape thereof. Clockwise movement of the second arm  144  can move the distal extension  194  of the pawl  186  in tandem and clockwise along the outer surface of the prong  158  of the housing  146  of the first handle  142  toward—and ultimately into—the groove  188 . In some embodiments, when the distal extension  194  enters the groove  188 , the locking mechanism  108  is in the locked position and the reduction member  104  is in a distal position having reduced the spinal rod  112  into the receiving portion of the bone anchor  110 . In some embodiments, when the pawl  186  enters the groove  188 , the pawl can create an auditory and/or tactile indication such that a user can know they have achieved a desired level of spinal rod reduction, e.g., sufficient to introduce a set screw or other closure mechanism successfully. Engagement of the pawl  186  and groove  188  can be superior to, e.g., prior ratchet locking mechanisms because there is a one-step confirmation that the device  100  is in a locked position where set screw insertion or other implant locking/closure can be performed successfully. Prior ratchet locking mechanisms can require stepping through engagement with a plurality of ratchet teeth to reach a closed configuration where set screw insertion is possible. This can be time-consuming, provide inadequate feedback to a user (e.g., it can be unclear how many ratchet steps are needed to achieve desired reduction), can result in inadvertent locking of the ratchet mechanism prior to achieving desired reduction, etc. 
     Moving the first and second handles  142 ,  144  together can slide the reducer sleeve or reduction member  104  relative to the opposed arms of the implant engagement member  102 . The reducer sleeve can contact the spinal rod  112  disposed between the opposed arms and urge it distally into the receiving portion of the bone anchor  110 . For example, rotating the second arm  144  relative to the first arm  142  can pivot the linkage members  172 ,  174  from being obliquely angled with respect to the longitudinal axis A 1  to being closer to parallel to the axis. In an example embodiment, pivoting the linkage members  172 ,  174  can move the reduction member  104  parallel to the longitudinal axis A 1  to reduce the spinal rod  112  into the bone anchor  110 . In particular, the reduction member  104  can be moved between a first position in which the reduction member  104  is either disengaged with the spinal rod  112  or is in contact with the rod at a location proximal to the bone anchor  110 , and a second position in which the reduction member  104  is in contact with the spinal rod  112  and the rod  112  is disposed in the receiving portion of the bone screw  100 . 
     Advancing the reducer sleeve  104  from the first position shown in  FIG.  6 B  to the second position shown in  FIG.  8    can also be effective to lock the opposed arms  120 ,  122  in a fixed position relative to the bone screw  100 . This can secure the instrument  100  relative to the bone anchor  110  and ensure the two components do not become decoupled until a user desires and releases the pawl lock. In this sense, the instrument  100  can provide for simultaneous locking of the instrument relative to the bone anchor  110  and reduction of the spinal rod  112  into the receiving portion of the bone anchor via one actuation movement of the first and second handles  142 ,  144  toward one another. This can be advantageous in situations where the instrument  100  is used to repeatedly couple with various bone anchors implanted along a patient&#39;s spine and reduce a rod into each anchor. In such a situation, the ability to couple the instrument  100  with a bone anchor without needing to apply large axial forces, e.g., because the opposed arms  120 ,  122  are biased toward a relaxed position that easily receives a bone anchor therebetween, can be desirable. This configuration can also facilitate easier release of the instrument  100  from the bone anchor, as releasing the pawl lock and allowing the handles  142 ,  144  to move away from one another can result in moving the opposed arms  120 ,  122  away from one another in a manner that releases the instrument  100  from the bone anchor  110  and allows separation of the two components without the need for large axial forces. 
       FIGS.  9 A- 9 B  illustrate the locking mechanism  108  in the locked position. As shown, the distal extension  194  of the pawl  186  rests within the groove  188 . In this locked configuration, the linkage members  172 ,  174  are pivoted into a position that is closer to parallel to the central longitudinal axis A 1 , while the reducer sleeve has been distally advanced along the opposed arms to reduce a spinal rod in contact with a distal end thereof. 
       FIGS.  10 A- 10 C  illustrate an example embodiment of a set screw insertion procedure that can be used with the instrument  100  described herein. Set screws can be inserted into the bone anchor once the spinal rod has been sufficiently reduced such that a set screw can engage with threads formed on an interior proximal surface of the receiving portion of the bone anchor  110 . A set screw inserter  300  having a set screw  302  disposed on a distal end  300   d  thereof can be introduced through the bore  154  in the instrument  100  for securing the set screw  302  to the bone anchor  110 . As shown, the set screw inserter  300  can advance distally through the bore  154  in the housing  146  of the first handle  142  and the lumen  117  of the implant engagement member  102  until the set screw  102  is disposed within the rod-receiving head  116  of the bone anchor  110 . Once the set screw inserter  300  is advanced to a position in which the set screw  302  engages with the rod-receiving head  116 , a torque applied to a handle  304  of the set screw inserter  300  can tighten the set screw  302  to the rod-receiving head  116 , as shown in  FIG.  10 B . The set screw inserter  300  can be rotated until the set screw  302  is sufficiently tightened to the bone anchor  110  to hold the reduced spinal rod  112  in place. Once sufficiently tightened, the set screw inserter  300  can be removed from the device  100 , as shown in  FIG.  10 C . 
     In some embodiments, the instrument  100  can be configured to provide for the reduction of multiple diameter spinal fixation rods, e.g., 5.5 mm and 6 mm diameter rods, while providing sufficient reduction to allow a set screw or other locking element to engage a receiving portion of a bone anchor (e.g., threads of a set screw to engage with threads formed on a proximal surface of a bone anchor receiver member) and prevent excessive reduction that can create tension and inhibit easy decoupling of the instrument from the receiver member after the set screw or other locking element is installed. 
       FIGS.  11 A- 11 E  illustrate releasing of the locking mechanism  108  to move the instrument  100  from the locked position to the unlocked position. As shown, the button  190  can be pressed to unlock the instrument  100  by releasing the pawl  186  from the groove  188 . For example, pressing the button  190  can exert a force onto the proximal end  186   p  of the pawl  186  to counter the force of the spring  202 , thereby pivoting the pawl  186  about the pawl pin  198  to disengage the distal extension  194  from the groove  188  in the prong  158 , as shown in  FIG.  11 B . Once the distal extension  194  is clear of the groove  188 , the torsion spring  164  disposed in the joint region  146  can urge the handles  142 ,  144  apart. For example, the second handle  144  can rotate about the pivot pin  148  in a counterclockwise direction (in the view of  FIG.  11 B ) away from the first handle  142 . As shown, rotation of the second handle  144  can pivot the linkage members  172 ,  174  counterclockwise to move the reduction member  104  proximally relative to the implant engagement member  102  and out of the engagement with the spinal rod  112 . The force exerted by the torsion spring  164  can cause the pawl  186  to rotate in a counterclockwise direction and slide distally along the prong  158  to return the locking mechanism  108  to its unlocked position, as shown in  FIG.  11 D . The instrument  100  can be proximally withdrawn from the bone anchor  110  leaving the reduced spinal rod  112  locked within the bone anchor by the set screw or other closure mechanism, as shown in  FIG.  11 E . The instrument  100  can then be coupled to another bone anchor for repeating the above-described procedure. Indeed, in some methods the reducer instruments disclosed herein are repeatedly utilized to reduce a rod into a plurality of bone anchors implanted along a patient&#39;s spine. The use of locking mechanism  108  in place of the prior long ratchet with multiple teeth disposed at a proximal end of the instrument can facilitate improved decoupling from the bone anchor, as prior ratchets can undesirably reengage during decoupling as the ratchet catch or pawl passes each successive ratchet tooth. Replacing the prior ratchet bar lock with the locking mechanism disclosed herein can eliminate this and promote easy-on and easy-off coupling and decoupling of the instrument  100  with the bone anchor. 
     In some embodiments, the first and second handles  142 ,  144  can be moved beyond a point at which the pawl  186  engages with the groove  188 . As noted above, when the locking mechanism  108  enters the locked position, the pawl  186  can create an auditory and/or tactile indication that the spinal rod  112  has been reduced into the fastener. In some embodiments, the auditory and/or tactile indication can occur prior to the spinal rod  112  being fully reduced, e.g., into a bottom seating surface of the receiving portion of the bone anchor. The rod  112  need only be reduced far enough to allow a set screw to engage with threads formed at a proximal end of the bone anchor receiving portion. This can allow the set screw  302  to be inserted through the instrument  100  to perform final reduction and locking of the rod relative to the bone anchor. Such a configuration can reduce the tension present between the instrument and the bone anchor and facilitate easier decoupling of the instrument  100  from the bone anchor  110 . 
     The instrument  100 , however, can be actuated beyond the above-noted position where the pawl  186  sits within the groove  188 . That is, a user can move the first and second handles  142 ,  144  closer to one another in a manner that urges the pawl  186  proximally away from the groove  188  and further advances the reducer sleeve  104  distally. A user can make use of this feature to, for example, release tension that may be on the pawl  186  and allow an easier release of the pawl  186  from the groove  188  when the button  190  is depressed. Alternatively or in addition, a user might utilize this feature to aid in set screw insertion and tightening to help reduce the rod a final degree with regard to the bone anchor. 
       FIG.  12    illustrates an example embodiment of such a configuration where force is exerted onto the first and second handles  142 ,  144  to move them past the point in which the distal extension  194  of the pawl  186  falls into the groove  188 . In this configuration, the distance between the arms  142 ,  144  is smaller than in the above-described closed position, with the distal extension  194  of the pawl  186  continuing to travel clockwise around the prong  158  of the housing  146  such that a gap  212  forms between the distal extension  194  and a wall of the groove  188 . The additional movement of the handles  142 ,  144  in this configuration can push the reduction member  104  distally to further reduce the rod  112  into the bone anchor  100 , as noted above. Rotation of the handles  142 ,  144  can continue until the reduction member  104  cannot translate further with respect to the implant engagement member  102  and/or when an ancillary stop for preventing further movement of the handles  142 ,  144  relative to one another is reached. For example, in some embodiments the housing  146  can include one or more protrusions formed thereon that can be configured to interfere with the second handle  144  and prevent further movement therebetween in a given direction. For example, the housing  146  can include a first protrusion or stop  214  formed thereon that can contact and interfere with the second handle  144  at a fully advanced position (as shown in  FIG.  12   ) and prevent any further movement of the second handle  144  toward the first handle  142 . In some embodiments, the instrument  100  can include a further protrusion or stop  215  configured to contact and interfere with the second handle  144  at a fully retracted position (as shown in  FIG.  4 A ) and prevent any further movement of the second handle  144  away from the first handle  142 . 
       FIG.  13    illustrates the locking mechanism  108  being released from the fully advanced configuration described above. Releasing the pawl  186  from this position is similar to the steps discussed with respect to  FIGS.  11 A- 11 E . As described above, actuating the button  190  can disengage the distal extension of the pawl from the outer surface of the housing to clear the groove  188 , thereby allowing movement of the handles  142 ,  144  away from one another. As noted above, a user can move the instrument  100  to this fully advanced configuration in order to release any tension or force between the pawl  186  and groove  188  to facilitate easier release of the pawl via depression of the button  190 . 
       FIG.  14    illustrates another embodiment of a reducer instrument  1400  according to the present disclosure. The instrument  1400  is a biplanar reducer configured to effect movement of a spinal rod in two dimension, e.g., axially along a longitudinal axis A 2  of the instrument and laterally along an axis transverse to the longitudinal axis A 2 . This can be accomplished using first and second handles  1402 ,  1404  that include distally extending arms or jaws  1406 ,  1408  that can pivot toward or away from one another in combination with movement of the proximal portions of the handles toward or away from one another. Such movement can allow the capture of a rod between the distally extending arms  1406 ,  1408  and lateral reduction thereof as the arms move toward one another. Axial reduction can be accomplished utilizing a reducer tube  1410  having a threaded portion that is received within a threaded bore formed in a housing  1412  of the first handle  1402 . A rod-engaging tip  1414  can be rotatably coupled to the reducer tube  1410  and extends into the space between the distally extending arms  1406 ,  1408 . The rod-engaging tip  1414  can be translated distally without rotating as the reducer tube  1410  is rotated such that the threaded portion moves into the threaded bore of the housing  1412 . 
       FIGS.  15 A and  15 B  illustrate additional views of the reducer tube  1410  and rod-engaging tip  1414 . The reducer tube  1410  is rotatably coupled to the rod-engaging tip  1414 , i.e., the two components can rotate relative to one another but are prevented from axially translating relative to one another. The rod-engaging tip  1414  can include opposed extensions  1502  formed at a distal end thereof that can be sized and shaped to contact a spinal fixation element, such as a rod, during an axial reduction maneuver. The extensions  1502  can also be configured to extend into a U-shaped gaps formed between opposed arms of a bone anchor receiver member, such that the rod-engaging tip  1502  can axially reduce a rod into the receiver member without interfering with delivery of a set screw or other locking element. Also to facilitate delivery of a set screw or other locking element, the rod-engaging tip  1414  and reducer tube  1410  can define an inner lumen  1504 . 
     The rod-engaging tip  1414  can also include one or more openings  1506  formed in a sidewall to facilitate viewing into the lumen  1504 . This can be useful to facilitate visualizing placement of a set screw or locking element delivered through the lumen  1504 , as described in more detail below. 
     The rod-engaging tip  1414  can also include a groove  1508  or other recess formed in an outer surface thereof and extending at least partially along a length thereof. The groove  1508  can receive a protrusion formed on the surface of the bore of the housing  1412  in order to prevent relative axial rotation between the tip  1414  and the arms  1406 ,  1408 . 
     As noted above, the reducer tube  1410  and rod-engaging tip  1414  can be rotatably coupled in a manner that permits relative rotation while preventing relative axial translation between the components. This can be accomplished using pins  1510  disposed through bores formed in the reducer tube  1410  and extending into an interior of the reducer tube. The pins can be received within a groove  1512  formed in a proximal end of the rod-engaging tip  1414 . In addition, a thrust washer  1514  can be disposed between a proximal end of the rod-engaging tip  1414  and a shoulder formed on an interior surface of the reducer tube  1410 . 
     The reducer tube  1410  can include a threaded outer surface portion  1516  configured to interface with threads formed on the surface of the bore of the housing  1412 . A depth stop  1518  can be formed on the reducer tube  1410  at a position proximal to the threads  1516 . The depth stop  1518  can be configured to contact a proximal portion of the housing  1412  in order to limit the distal advancement of the reducer tube  1410  and rod-engaging tip  1414  relative to the first and second arms  1406 ,  1408 . This depth can be configured to allow for the reduction of multiple diameter spinal fixation rods, e.g., 5.5 mm and 6 mm diameter rods, while providing sufficient reduction to allow a set screw or other locking element to engage a receiver member (e.g., threads of a set screw to engage with threads formed on a proximal surface of a receiver member) and prevent excessive reduction that can create tension and inhibit easy decoupling of the instrument from the receiver member after the set screw or other locking element is installed. For example, in some embodiments the depth stop can be positioned to provide about 6.5 mm of clearance between a distal end of the rod-engaging tip  1414  and the base of a bone anchor receiver member rod slot at maximum axial reduction when the depth stop  1518  contacts the housing  1412 . Such a configuration can allow using the device with both 5.5 mm and 6 mm rods with the benefits noted above. The depth stop  1518  can have a variety of forms, including any of a variety of protrusions formed on an outer surface of the reducer tube  1410  around part of or an entirety of its circumference. In the illustrated embodiment, the depth stop  1518  is a shoulder formed around a circumference (i.e., an entire perimeter) of the reducer tube  1410 . 
     An intermediate portion  1520  can extend proximally from the depth stop  1518  to a drive feature  1522  formed on a proximal end of the reducer tube  1410 . The intermediate portion  1520  can have a variety of shapes, diameters, and lengths. In the illustrated embodiment, the intermediate portion  1520  has a generally cylindrical shape. The drive feature  1522  formed at a proximal end of the reducer tube  1410  can allow for modular coupling of a driver handle, powered driver, or other torque application implement to the reducer tube  1410  in order to effect rotation of the tube and axial reduction of a spinal fixation element. The drive feature  1522  can also permit access to the lumen  1504  therethrough. The drive feature  1522  can have a variety of forms and sizes. In some embodiments, the drive feature  1522  can include one or more flats to facilitate the application of torque thereto. In the illustrated embodiment, the drive feature  1522  is a hex feature having six flat portions disposed around a circumference of the reducer tube  1410 . Further, in the illustrated embodiment an outer diameter of the depth stop  1518  can be greater than an outer diameter of any other portion of the reducer tube  1410 . Utilizing a lower profile drive feature  1522  can reduce the footprint of the instrument  1400  while still allowing a larger driver handle (e.g., a T-handle, powered driver, etc.) to be coupled to the instrument when needed. 
     The instrument  1400  can utilize a similar set of handles, housing, biasing element, and locking mechanism  108  as the instrument  100  described above. Accordingly, detail descriptions of these elements are not repeated here. The locking mechanisms described herein can provide the similar advantages to the instrument  1400 . For example, a single actuation of the handles  1402 ,  1404  toward one another can simultaneously provide lateral reduction and secure coupling to a bone anchor and a user can be provided with clear feedback of sufficient lateral reduction and implant coupling when, e.g., the pawl falls into the groove of the locking mechanism. Subsequent rotation of the reducer tube  1410  can then effect axial reduction and a similar set screw inserter can be inserted through the reducer tube  1410  to deliver a set screw or other closure mechanism to the implant for final reduction and locking. Further details on biplanar forceps reducers that can be utilized in connection with the features described in the present disclosure can be found in U.S. application Ser. No. 17/522,164, entitled “Biplanar Forceps Reducers and Methods of Use,” filed Nov. 9, 2021. The entire contents of this application are incorporated by reference herein. 
       FIGS.  16 - 38    illustrate another embodiment of a reducer instrument  1600  according to the present disclosure. The instrument  1600  can be similar to the instrument  100  discussed above, except as explained in further detail below. For example, the instrument  1600  can include an alternative embodiment of an implant engagement member  1602  and a reduction member  1604 . The proximal portion of the instrument  1600 , however, can be the same as the instrument  100 . 
       FIG.  17    illustrates the implant engagement member  1602  in greater detail. The implant engagement member  1602  can be similar to the earlier described implant engagement member  102  in certain respects, but also can have notable differences in the manner in which it is configured to engage an implant. For example, the implant engagement member  1602  can have opposed arms  1720 ,  1722  that are rigidly positioned relative to one another and do not flex toward or away from one another, as with the arms  120 ,  122  described above. The spacing of the arms  1720 ,  1722  can be configured to allow passage of a rod-receiving head  116  therebetween, with various internal surfaces of the arms  1720 ,  1722  contacting counterpart surfaces of the rod-receiving head  116  in a manner similar to that described with respect to the inner surfaces  402  and  404  above. 
     Each of the opposed arms  1720 ,  1722 , however, can include a movable portion  1702 ,  1704  formed therein and configured to selectively latch onto a portion of the rod-receiving head  116  and lock its position relative to the implant engagement member  1602 . The movable portions  1702 ,  1704  can be formed in a variety of manners, including, in some embodiments, by forming a nested cantilevered spring arm with a living hinge coupling the movable portion of the arm to the more rigid portion of the arm. This can be accomplished in a number of manners, including, for example, by partially cutting free the spring arm portion such that natural elastic deformation of the material combines with the geometry of the cut to permit the desired range of motion. In other embodiments, however, the movable portions  1702  can be formed from separate components coupled to the implant engagement member  1602  in a variety of manners. For example, the nested spring arm movable portions and implant engagement member can be formed from a welded multi-piece assembly of component parts. 
       FIGS.  18 - 21    illustrate side and top perspective and longitudinal cross-sectional views of the implant engagement member  1602 . These views illustrate that each movable portion  1702 ,  1704  includes a narrowed portion  1902  at a proximal end thereof to form the living hinge, a thickened portion distal thereto, and an inwardly-extending protrusion  1906  that can be configured to extend into a groove or other recess formed in an outer surface of the rod-receiving head  116  in order to couple to the head of the implant engagement member  1602 . 
       FIGS.  22  and  23    illustrate the distal end geometry of the implant engagement member  1602  in greater detail. As noted above, the opposed arms  1720 ,  1722  can include internal surfaces  2202  and  2204  that are similar to surfaces  402  and  404  described above and can be configured to interface with complementary-shaped and -dimensioned surfaces on a rod receiving head  116  to facilitate coupling the two components in a desired orientation and with a high degree of rigidity to prevent relative movement between the two components when coupled. 
     As can be seen in these figures and especially in the detail view of  FIG.  23   , a resting position of each movable portion  1702 ,  1704  is such that an outer surface thereof remains in alignment with an outer surface of the corresponding arm  1720 ,  1722  (e.g., the movable portion is not recessed below an outer surface defined by the arm and also does not protrude from such an outer surface). Similarly, on the interior side of each movable portion  1702 ,  1704 , the projection  1906  has a resting position where it does not interfere with passage of a rod-receiving head  116  into or out of the space between the opposed arms  1720 ,  1722 . In other words, to help retain a rod-receiving head  116  to the implant engagement member  1602 , the movable portions  1702 ,  1704  must be moved radially inward from their resting positions, as explained in more detail below. 
     Another feature of the distal end geometry of the implant engagement member  1602  is that the rigid arms  1720 ,  1722  can serve as a guard to prevent any hard or soft tissue from interfering with the movement of the portions  1702 ,  1704 . This can be an issue with certain reducers that utilize inwardly deflecting arms or other components to grasp an implant, such as a rod-receiving head  116 . Tissue surrounding the instrument can interfere with the outward movement of the arms and the release of the instrument from the implant. With the illustrated instrument  1600 , however, the movable portions  1702 ,  1704  have an outer surface aligned with the outer surface of the rigid implant engagement member arms  1720 ,  1722  when in an open or released state. This means the rigid arms  1720 ,  1722  can serve as a guard to maintain tissue spacing during use and a clear path for the inward and outward deflection of the movable portions  1702 ,  1704 . This can ensure a more reliable latch and release of the instrument  1600  to the rod-receiving head  116 . 
     To this end, in some embodiments the inwardly-extending protrusion  1906  of each movable portion  1702 ,  1704  can also be formed with a positive draft that does not include an undercut surface. In the embodiment of  FIG.  23   , for example, the protrusion  1906  is shown with a generally triangular cross-sectional shape where the apex  2302  of the triangle is disposed between the endpoints  2304 ,  2306  of its base. This can allow more reliable engagement and release of the protrusion with a groove or other recess formed in a rod-receiving head  116  and avoid binding of the components upon release, for example. 
       FIGS.  24 - 29    illustrate the reduction member  1604 , which is similar to the reduction member  104  (e.g., the rear view of  FIG.  26    is the same for each) but includes certain modifications to interface with the movable portions  1702 ,  1704  and control their actuation in the manner described above. In particular, a distal portion of the reduction member  1604  includes channels or recesses  2402  formed along an internal surface thereof extending proximally from the distal end. In the illustrated embodiment, two parallel channels  2402  extend to create a central ridge  2404  extending therebetween. The feature is repeated on opposite sides of the inner surface of the reduction member  1604  to align with the movable portions  1702 ,  1704  disposed on opposed arms  1720 ,  1722  of the implant engagement member  1602 . 
       FIGS.  30  and  31    show perspective and longitudinal cross-sectional views of the reduction member  1604  disposed over the implant engagement member  1602  at a first, proximal-most position of the reduction member relative to the implant engagement member. In this position, an outer diameter of the implant engagement member  1602  is similar to the inner diameter of the reduction member  1604 , so the movable portions  1702 ,  1704  of each opposed arm  1720 ,  1722  remain in their resting position. In such a configuration, a rod-receiving head  116  can be passed freely into and out of the space between the opposed arms  1720 ,  1722 . 
       FIGS.  32  and  33    show perspective and longitudinal cross-sectional views of the reduction member  1604  disposed over the implant engagement member  1602  at a second, more distal position of the reduction member relative to the implant engagement member (e.g., as would be achieved when a user begins squeezing the handles  142 ,  144  toward one another to actuate the device). As the reduction member  1604  begins translating distally over the implant engagement member  1602 , it travels over an area having an increased outer diameter. The increased outer diameter of the opposed arms  1720 ,  1722  can be received within the channels  2402  formed in the inner surface of the reduction member  1604  to allow continued distal movement, but the ridges  2404  formed between the channels  2402  contact the movable portions  1702 ,  1704  and begin deflecting them radially inward toward a longitudinal axis of the instrument. If a rod-receiving head  116  is disposed between the opposed arms  1720 ,  1722 , the radially inward movement of the movable portions  1702 ,  1704  can cause the projections  1906  to extend into a groove or other recess formed in the rod-receiving head  116  and securely prevent separation of the head  116  from the implant engagement member  1602 . 
     Further, the implant engagement member  1602  and its movable portions  1702 ,  1704  can have particular geometry to facilitate desired movement of the portions  1702 ,  1704  as the reduction member  1604  is advanced distally. The detail longitudinal cross-sectional view of  FIG.  34    illustrates that the movable portion  1704  includes a first outer portion  3402   a  that increases outer diameter in a distal direction at a first, steeper angle and a second outer portion  3402   b  that increases outer diameter in a distal direction at a second, flatter angle (while not shown in the detail view of the figure, the following description can be similar for the movable portion  1702  that is opposite the illustrated movable portion  1704 ). When the reduction member  1604  is withdrawn proximally, as shown in  FIGS.  30 ,  31 , and  34   , the ridge  2404  does not deflect the movable portion  1704  radially inward and a rod  3404  and/or rod-receiving head  116  can be passed into the space between the arms  1720 ,  1722  of the rod engagement member  1602 . 
     As shown in the detail view of  FIG.  35   , advancing the reduction member  1604  distally relative to the implant engagement member  1602  causes the ridge  2404  to initially contact the first outer portion  3402   a . This contact can produce a rapid inward deflection of the movable portion  1704  such that the protrusion  1906  engages with the rod-receiving head  116  or other implant. For example, by the time the reduction member  1604  contacts the rod  3404 , the movable portion  1704  can be completely engaged with the implant  116 . 
     As shown in  FIGS.  35  and  36   , as the reduction member  1604  continues to advance relative to the implant engagement member  1602  and reduce the rod  3404 , the ridge  2404  rides over the second outer portion  3402   b  having a flatter angle than the first outer portion  3402   a . The shape of the second outer portion  3402   b  can prevent further inward deflection of the movable portion  1704  during rod reduction. 
       FIGS.  37 - 40    illustrate further states of distal advancement of the reduction member  1604  relative to the implant engagement member  1602 .  FIGS.  37  and  39   , for example, illustrate the instrument  1600  in a locked configuration similar to that shown in  FIGS.  9 A- 9 C , as well as the detail view of  FIG.  36   . In this configuration, the reduction member  1604  has been advanced distally along the implant engagement member  1602  to reduce a spinal rod in contact with a distal end thereof and the locking mechanism  108  has been engaged to maintain a position of the instrument. 
       FIGS.  38  and  40    illustrate a final state of distal advancement of the reduction member  1604  relative to the implant engagement member  1602 . In these figures, the reduction member  1604  is advanced distally to a maximum extent relative to the implant engagement member  1602 . This configuration is similar to that shown in  FIG.  12    and described above, and can be utilized to release tension that may be on the lock mechanism pawl and allow an easier release of the pawl from its groove when the release button  190  is depressed. Alternatively or in addition, a user can utilize this feature to aid in set screw insertion and tightening to help reduce the rod a final degree with regard to the bone anchor. 
       FIG.  41    illustrates actuation of the release button  190  that can release the lock mechanism and allow the instrument  1600  to move from the configuration shown in  FIG.  41    to the open configuration shown in  FIG.  16    wherein the reduction member  1604  is withdrawn proximally relative to the implant engagement member  1602 . Upon withdrawal of the reduction member  1604  proximally, the movable portions  1702 ,  1704  will return to their resting positions as shown in  FIG.  23   , which will clear the inwardly-extending protrusions  1906  from any groove or other recess formed in a rod-receiving head  116  disposed between the opposed arms  1720 ,  1722 , thereby allowing the head to be separated from the instrument  1600  and another head loaded for coupling. 
     Various devices disclosed herein can be constructed from any of a variety of known materials. Example materials include those which are suitable for use in surgical applications, including metals such as stainless steel, titanium, nickel, cobalt-chromium, or alloys and combinations thereof, polymers such as PEEK, ceramics, carbon fiber, and so forth. Further, various methods of manufacturing can be utilized, including 3D printing or other additive manufacturing techniques, as well as more conventional manufacturing techniques, including molding, stamping, casting, machining, etc. 
     Various devices and methods disclosed herein can be used in minimally-invasive surgery and/or open surgery. While various devices and methods disclosed herein are generally described in the context of surgery on a human patient, the methods and devices disclosed herein can be used in any of a variety of surgical procedures with any human or animal subject, or in non-surgical procedures. 
     Various devices or components disclosed herein can be designed to be disposed of after a single use, or they can be designed to be used multiple times. In either case, however, various devices or components can be reconditioned for reuse after at least one use. Reconditioning can include any combination of the steps of disassembly, followed by cleaning or replacement of particular pieces, and subsequent reassembly. In particular, a device or component can be disassembled, and any number of the particular pieces or parts thereof can be selectively replaced or removed in any combination. Upon cleaning and/or replacement of particular parts, the device or component can be reassembled for subsequent use either at a reconditioning facility, or by a surgical team immediately prior to a surgical procedure. Reconditioning of a device or component can utilize a variety of techniques for disassembly, cleaning/replacement, and reassembly. Use of such techniques, and the resulting reconditioned device, are all within the scope of the present disclosure. 
     Various devices or components described herein can be processed before use in a surgical procedure. First, a new or used device or component can be obtained and, if necessary, cleaned. The device or component can then be sterilized. In one sterilization technique, the device or component can be placed in a closed and sealed container, such as a plastic or TYVEK bag. The container and its contents can then be placed in a field of radiation that can penetrate the container, such as gamma radiation, x-rays, or high-energy electrons. The radiation can kill bacteria on the device or component and in the container. The sterilized device or component can then be stored in the sterile container. The sealed container can keep the device or component sterile until it is opened in the medical facility. Other forms of sterilization are also possible, including beta or other forms of radiation, ethylene oxide, steam, or a liquid bath (e.g., cold soak). Certain forms of sterilization may be better suited to use with different devices or components, or portions thereof, due to the materials utilized, the presence of electrical components, etc. 
     In this disclosure, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B,” “one or more of A and B,” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” is intended to mean, “based at least in part on,” such that an un-recited feature or element is also permissible. 
     Further features and advantages based on the above-described embodiments are possible and within the scope of the present disclosure. Accordingly, the disclosure is not to be limited by what has been particularly shown and described. All publications and references cited herein are expressly incorporated herein by reference in their entirety, except for any definitions, subject matter disclaimers or disavowals, and except to the extent that the incorporated material is inconsistent with the express disclosure herein, in which case the language in this disclosure controls. 
     Examples of the above-described embodiments can include the following:
         1. A surgical instrument, comprising:
           a first handle having a proximal grip portion and a distal housing with a lumen extending therethrough;   opposed arms extending distally from the housing that are configured to interface with an implant;   a reducer sleeve disposed around the opposed arms and configured to translate relative thereto;   a second handle having a proximal grip portion, the second handle being pivotably coupled to the housing and the reducer sleeve such that moving the second handle toward the first handle causes distal translation of the reducer sleeve relative to the opposed arms;   a pawl pivotably coupled to the second handle distal to the grip portion, the pawl being configured to ride over a portion of the housing that includes a groove as the second handle is moved toward the first handle;   wherein the pawl is configured to seat in the groove and maintain a relative position of the first and second handles when the second handle is moved sufficiently toward the first handle.   
           2. The instrument of claim  1 , further comprising a button extending from the pawl and configured to move the pawl clear of the groove when depressed.   3. The instrument of any of claims  1  to  2 , further comprising a spring urging a distal portion of the pawl into the portion of the housing that includes the groove.   4. The instrument of any of claims  1  to  4 , wherein the opposed arms define a tapering slot therebetween having a first distance between the opposed arms at a distal portion of the slot that is greater than a second distance between the opposed arms at a proximal portion of the slot.   5. The instrument of any of claims  1  to  4 , wherein a distal end of at least one of the opposed arms includes a protrusion configured to extend into a recess of the implant.   6. The instrument of any of claims  1  to  5 , wherein distal translation of the reducer sleeve relative to the opposed arms moves the opposed arms toward one another.   7. The instrument of any of claims  1  to  6 , further comprising one or more links pivotably coupled to the second handle and the reducer sleeve.   8. The instrument of any of claims  1  to  7 , further comprising a biasing element urging the first and second handle away from one another.   9. The instrument of any of claims  1  to  8 , wherein the housing includes at least one protrusion formed thereon that abuts against the second handle at a fully open or a fully closed position of the first and second handles relative to one another.   10. The instrument of claim  9 , wherein the at least one protrusion includes a first protrusion that abuts against the second handle at a fully closed position of the first and second handles, and wherein the first protrusion is separated from the second handle when the pawl is seated in the groove and maintaining a relative position of the first and second handles.   11. A surgical method, comprising:
           positioning opposed arms of a reducer instrument around a portion of an implant;   moving first and second handles of the reducer instrument toward one another until a pawl coupled to the second handle seats within a groove formed in a housing of the first handle to maintain a relative position of the first and second handles;   wherein moving the first and second handles of the reducer instrument toward one another causes a reducer sleeve disposed around the opposed arms to translate distally relative thereto;   wherein distal translation of the reducer sleeve causes the opposed arms of the reducer instrument to move toward one another and couple with the implant, and also causes a spinal fixation element to translate distally into a receiving portion of the implant.   
           12. The method of claim  11 , wherein moving the first and second handles of the reducer instrument toward one another includes overcoming a biasing force urging the handles away from one another.   13. The method of any of claims  11  to  12 , further comprising locking the spinal fixation element relative to the implant while the reducer instrument maintains a position of the spinal fixation element relative to the implant.   14. The method of claim  13 , wherein locking the spinal fixation element relative to the implant includes inserting a set screw through a bore formed in the reducer instrument and coupling the set screw with the implant.   15. The method of claim  14 , further comprising further reducing the spinal fixation element distally into the receiving portion of the implant using the set screw such that compressive forces between the reducer sleeve and spinal fixation element are reduced.   16. The method of any of claims  11  to  15 , further comprising moving the first and second handles of the reducer instrument toward one another beyond a position at which the pawl seats within the groove of the housing until one of the first and second handles contacts a stop formed on the other handle.   17. The method of any of claims  11  to  16 , further comprising depressing a button to move the pawl clear of the groove and allow movement of the first and second handles away from one another.   18. The method of claim  17 , further comprising moving the first and second handles of the reducer instrument away from one another to proximally translate the reducer sleeve relative to the opposed arms and allow the opposed arms to move away from one another and release from the implant.   19. The method of claim  18 , further comprising repeating the method across a plurality of implants disposed along a patient&#39;s spine.   20. A surgical method, comprising:
           positioning an instrument in an unlocked configuration, the instrument having an implant engagement member, a reduction member having a channel therein for receiving the implant engagement member therethrough, a handle assembly being coupled to the reduction member and receiving the implant engagement member through a bore thereof, and a lock having a pawl disposed outside of a groove formed in the handle assembly, the handle assembly including a pair of handles pivotably coupled to one another;   positioning an implant between opposed arms of the implant engagement member; and   moving the pair of handles toward one another to position the instrument in a locked configuration;   wherein moving the pair of handles toward one another distally advances the reduction member relative to the implant engagement member to reduce a spinal fixation element into a receiving portion of the implant and moves the pawl into the groove of the handle assembly.   
           21. The method of claim  20 , wherein moving the pair of handles toward one another includes overcoming a biasing force on the pair of handles and causing a linkage disposed between the pair of handles and the reduction member to advance the reduction member distally.   22. The method of any of claims  20  to  21 , further comprising actuating a button coupled to the pawl to disengage the pawl from the groove and allow return of the device from the locked configuration to the unlocked configuration.   23. The method of any of claims  20  to  22 , further comprising delivering a set screw to the implant through the bore of the handle assembly.   24. The instrument of any of claims  1  to  10 , wherein each opposed arm includes a movable portion configured to deflect radially inward relative to the arm.   25. The instrument of claim  24 , wherein the reducer sleeve includes a feature formed on an inner surface thereof that is configured to contact the movable portion of each opposed arm.   26. The instrument of any of claims  24  to  25 , wherein each movable portion includes an inwardly-extending projection.   27. The method of any of claims  20  to  23 , wherein distally advancing the reduction member relative to the implant engagement member deflects movable portions of each of the opposed arms of the implant engagement member radially inward such that the movable portions extend into a recess formed in the implant.   28. A surgical method, comprising:
           positioning opposed arms of a reducer instrument around a portion of an implant;   moving first and second handles of the reducer instrument toward one another until a pawl coupled to the second handle seats within a groove formed in a housing of the first handle to maintain a relative position of the first and second handles;   wherein moving the first and second handles of the reducer instrument toward one another causes a reducer sleeve disposed around the opposed arms to translate distally relative thereto;   wherein distal translation of the reducer sleeve causes movable portions of the opposed arms of the reducer instrument to move toward one another and couple with the implant, and also causes a spinal fixation element to translate distally into a receiving portion of the implant.