Patent Publication Number: US-2021161568-A1

Title: Rod reducer ratchet lock-out mechanism

Description:
CLAIM OF PRIORITY 
     This application is a continuation of U.S. application Ser. No. 16/295,183, filed Mar. 7, 2019, which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/641,500, filed on Mar. 12, 2018, the benefit of priority of which is claimed hereby, and which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates to spinal fusion procedures involving use of rod reduction instruments to assist in securing connecting rods in pedicle screw implants to immobilize one or more vertebrae. 
     BACKGROUND 
     A common surgical procedure to correct deformities in the spine involves stabilizing affected vertebral bodies with interbody implants, pedicle screws and connecting rods. The interbody implants are used to replace disc material between the affected vertebral bodies, and promote boney fusion between the vertebrae. The pedicle screws and connecting rods are used to stabilize the affected portion of the spine to allow fusion to occur. The portion of the procedure involving rod reduction instruments involves implanting pedicle screws bilaterally in affected vertebral bodies and then connecting the pedicle screw implants with stiff, usually metal, connecting rods to secure the vertebrae in a desired orientation. Often a surgeon is attempting to restore some sort of natural curvature or realign a displaced vertebra (spondylosis). It is not uncommon during these procedures for a surgeon to utilize an instrument designed to assist in leveraging a connecting rod into a pedicle screw to restore alignment, these instruments are commonly referred to as rod reduction instruments. Rod reduction may be necessary due to curvature correction or the degree of misalignment (e.g., to pull a vertebra back into alignment). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1A  is an isometric view of a rod reduction instrument, in accordance with an example embodiment. 
         FIG. 1B  is an exploded isometric view of a rod reduction instrument, in accordance with an example embodiment. 
         FIG. 2  is an exploded isometric view of an upper section of a rod reduction instrument, in accordance with an example embodiment. 
         FIGS. 3A-3J  are diagrams and drawings of a ratchet mechanism used in a rod reduction instrument, in accordance an example embodiment. 
         FIG. 4  is an isometric view of a rod reduction instrument, in accordance with an example embodiment. 
         FIG. 5  is an exploded isometric view of an upper section of a rod reduction instrument, in accordance with an example embodiment. 
         FIGS. 6A-6J  are diagrams and drawings of a ratchet mechanism used in a rod reduction instrument, in accordance an example embodiment. 
         FIG. 7  is a flowchart illustrating a method for using a rod reduction instrument, in accordance an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The instrument discussed below can be used to quickly and efficiently reduce connecting rods during spinal fusion procedures utilizing pedicle screws and connecting rods. The inventors have recognized that spinal surgeons need rod reduction instruments that can quickly engage connecting rods, provide mechanical advantage when needed, and have mechanical mechanisms to ensure ease of removal at completion of the procedure. Rod reduction instruments can utilize threaded shafts to provide mechanical advantage to reduce connecting rods through rotation of an instrument handle, such as a t-handle. However, reduction instruments that solely utilize threaded reduction can slow down spinal procedures and require too much manipulation to first engage the rod. Ratchet mechanisms can be utilized to reduce the time and effort to make initial engagement of a connecting rod, but ratchet mechanisms can jam during use and cause difficulties in completing a procedure. In extreme cases, jammed instruments can require cutting the connecting rod and removing the pedicle screw. The current inventors have developed various ratchet lock-out mechanisms for use in rod reduction instruments to solve the problem of jammed instruments and still provide all the benefits of instruments with ratcheting capabilities. 
     Rod reduction instruments are typically provided as part of a fixation system that includes implants (pedicle screws), various length connecting rods, and various instruments for the procedure. The instruments can include tools for pedicle targeting, pedicle preparation, screw insertion, rod and closure top insertion, and manipulation. Manipulation tools include rod reduction instruments, such as rod rockers and reducers. The instruments discussed herein are variations of axial reducers, but the ratchet lock-out mechanisms and techniques could be implemented on other rod reduction instruments utilizing a threaded shaft. Commercial examples of axial reducers include reduction instruments provided by Zimmer Biomet as part of the Vital™ Spinal Fixation System. Commercial examples of rocket reducers include reducers provided by Zimmer Biomet as part of the Polaris™ or Lineum® OCT spinal deformity correction systems. Surgical technique guides from Zimmer Biomet, for systems such as the Vital™ Spinal Fixation System, provide an excellent overview of reduction instrument use and interactions with pedicle screw implants and connecting rods. Accordingly, details regarding how these instruments connect with the implants and operate are not discussed in detail, accept as needed to under the inventive concepts discussed herein. 
       FIG. 1A  is an isometric view of a rod reduction instrument  100 , in accordance with an example embodiment. Rod reduction instrument  100  can include inner sleeve  101  and outer housing  110 . The distal end of the inner sleeve  101  can include engagement members  103 , which are adapted to engage a housing on a pedicle screw that receives a connecting rod. The outer housing  110  can include a top sleeve  115  rotationally coupled to a bottom sleeve  111 . The top sleeve  115  can include a tool socket  116  and a ratchet mechanism  120 . The distal end of the bottom sleeve  111  can include a rod engagement  112 , which in this example is a semi-circular cutout in opposing sides of the distal end. In operation, the outer housing  110  translates over the inner shaft  101 , after the inner shaft  101  is coupled to the pedicle screw head via engagement members  103 . 
     The rod reduction instrument  100  is an example of a tower reducer that incorporates the ratchet lock-out mechanism to enable two different reduction modes of operation. First, with the ratchet mechanism operation, the tower reducer operates in a quick on, quick off mode that captures the screw head and engages the rod more quickly. After coupling the engagement members  103  of the inner sleeve  101  to a head of a pedicle screw, the outer housing  110  can slide over the inner sleeve  101  until the rod engagement  112  engages the rod. A T-handle or similar tool can then be attached to the tool socket  116  to rotate the top sleeve  115  causing the outer housing  110  to translate further downward reducing the rod into the head of the pedicle screw. Threaded reduction using the tool socket  116  is accomplished by an engagement feature of the ratchet mechanism  120  engaging a threaded proximal portion of the inner sleeve  101 . In an example, the engagement feature can be a threaded portion of the ratchet mechanism  120 . In other examples, the engagement feature can be an alternative structure, such as small protrusions (numbs) or captured ball bearings. 
     The ratchet mechanism, discussed in greater detail below, can be temporarily disengaged through activation of a button, which allows smooth and quick initial engagement of the connecting rod. In same examples, the button on the ratchet mechanism  120  needs to be activated to allow the outer housing  110  to freely translate over the inner sleeve  101 . In other examples, the ratchet mechanism  120  allows the engagement feature of skip over the threads on the proximal section of the inner sleeve  101  without activation of the button on the ratchet mechanism. 
     In this example, the ratchet mechanism  120  can be shifted into a fixed or threaded mode of operation, locking out the ratchet mechanism. As discussed in detail below, locking out the ratchet mechanism involves forcing an engagement feature of the ratchet mechanism into fixed engagement with a threaded portion of the inner sleeve  101 . In this fixed mode, the reducer operates as a threaded reduction instrument, with no rapid translation of the outer housing  110 . Accordingly, in the fixed mode the outer housing  110  translates based solely on rotation input received through the tool socket  116  (or any rotation of the top sleeve  115  portion of the outer housing  110 ). Shifting the ratchet mechanism  120  of the reduction instrument  100  into fixed mode enables a user to remove the reduction instrument from difficult reduction scenarios, where a ratcheting reduction instrument may not function properly due to high reduction forces. For example, because ratcheting instruments typically rely upon some form of biasing element, such as a coil spring, to keep a threaded member engaged with the threaded inner sleeve, in certain situations the coils spring can fail to keep the threads engaged sufficiently to overcome forces operating on the instrument. In these situations, a ratcheting only instrument may have to be removed through extraordinary measures, such as cutting the connecting rod and removing the pedicle screw. A dual mode ratcheting mechanism with a lock-out capability can avoid such extraordinary measures by providing a mechanism to fix engagement of the engagement feature of the ratchet against the threaded portion of the inner sleeve. In the fixed engagement mode, the reduction instrument can leverage the mechanical advantage of the threads to overcome external forces jamming the instrument. 
       FIG. 1B  is an exploded isometric view of the rod reduction instrument  100  introduced above. The exploded view provides an introduction to additional elements of an example ratcheting mechanism as well as the overall instrument in accordance with this example. The rod reduction instrument  100  can include an inner sleeve  101 , a threaded proximal portion  102  of the inner sleeve  101 , and a plurality of engagement members  103  (collectively referenced as engagement members  103 ). The rod reduction instrument  100  can also include an outer housing that includes a top sleeve  115  that rotates in reference to a bottom sleeve  111 . The top sleeve  115  is coupled to the bottom sleeve via a thrust washer  118  and retaining ring  119 . In this example, the ratchet mechanism  120  can include a pivot shaft  121 , a locking mechanism  130 , a lever member  140 , and a biasing member  146 . 
       FIG. 2  is an exploded isometric view of an upper section of a rod reduction instrument  100 , in accordance with an example embodiment. In this example, the top sleeve  115  and the ratchet mechanism  120  of the rod reduction instrument  100  are illustrated in additional detail. The ratchet mechanism  120  includes features built into the top sleeve  115 , such as a detent bore  122 , a button opening  123 , a button cutout  124 , pivot shaft bores  125 , slide lock rails  126 , and a transverse shaft opening  127 .  FIG. 2  also illustrates the top sleeve  115  with a tool socket  116  and rotational coupling  117 . The rotational coupling  117  is where the top sleeve  115  is connected to the bottom sleeve  111 . The ratchet mechanism  120  also includes a pivot shaft  121 , a locking mechanism  130 , a lever member  140 , and a biasing member  146 . The locking mechanism  130  can also include a lock detent  136  and a ratchet detent  137 , which operate to retain the locking mechanism  130  is one of the two modes (locked or fixed and ratcheting). The lever member  140  can include a ratchet release button  142 , a pivot  145 , and a bias recess  147 . The pivot  145  can receive the pivot shaft  121 , and is where the lever member  140  rotates or pivots in ratcheting mode. The biasing member  146  operates to bias the lever member  140  into engagement with the threaded proximal portion of the inner sleeve  101 . As illustrated in greater detail in  FIGS. 3A-3J , the biasing member  146  can be a wave washer spring, but can also be a coil spring or other comparable biasing member. In certain examples, an elastic or elastomeric material could be substituted for the wave washer spring. The biasing member needs to allow for sufficient travel to clear threaded on the inner shaft, with provide a balance between thread engagement and ratcheting motion. 
     The locking mechanism  130  slides on the slide lock rails  126  when assembled into the ratchet mechanism  120 . The detent bore  122  is designed to hold a detent ball to engage the lock detent  136  and ratchet detect  137  when locking mechanism  130  slides between fixed mode and ratcheting mode (also referred to as Quick On/Off mode).  100221   FIGS. 3A-3J  are diagrams and drawings of a ratchet mechanism used in a rod reduction instrument, in accordance an example embodiment.  FIG. 3A  is a drawing of a superior surface of an assembled the ratchet mechanism  120 . In this example, the ratchet mechanism  120  can include button opening  123 , button cutout  124 , pivot shaft bores  125 , a locking mechanism  130 , lever member  140 , and ratchet release button  142 . The locking mechanism in this example includes slide lock  132 , which is a U-shaped linear slide that is further illustrated in the following figures. In this example, the lock detent  136  and ratchet detent  137  are shown on opposing arms of the U-shaped slide lock  132 . 
       FIG. 3B  is a drawing of a lateral side of the ratchet mechanism  120 . In this view, the slide lock  132  is illustrated engaged with one of the slide lock rails  126  along a slide recess  133 . The slide lock  132  includes a slide recess  133  along the outbound edge of each arm of the U-shaped structure. Also illustrated in this view is the pivot shaft  121  within the pivot shaft bore  125 . When the ratchet release button  142  of the lever member  140  is activated, the lever member  140  pivots on the pivot shaft  121  and the engagement feature  141  disengages from an threaded portion of the inner shaft  101 . 
       FIGS. 3C-3D  are cutaway views of the ratchet mechanism  120  and associated portions of the inner sleeve  101 . In these views, the following ratchet mechanism  120  details are depicted, pivot shaft  121 , button opening  123 , button cutout  124 , slide lock  132 , lever member  140 , and biasing member  146 . In this example, the slide lock  132  includes the transverse shaft  138 , which is the structure of the locking mechanism  130  that locks out the ratcheting action of the lever member  140 . In these views, the lever member  140  is illustrated as including an engagement feature  141  on an inferior side of the proximal portion. The cutaway demonstrates how the engagement feature  141  engages the proximal threaded portion  102  of inner sleeve  101 . In this example, the engagement feature  141  is a plurality of partial threads that correspond to the proximal threaded portion  102  of the inner sleeve  101 . The cutaway also illustrates how the biasing member  146  biases the engagement feature  141  into engagement with the proximal threaded portion  102 . The lever member  140  also includes a locking surface  143  and a ratchet cavity  144 , which are positioned below the transverse shaft  138  of the slide lock  132 . In ratcheting mode, the slide lock  132  is positioned as shown and the transverse shaft  138  is opposite the ratchet cavity  144 , which provides clearance for the lever member  140  to pivot without interference from the transverse shaft  138 . However, in the fixed (or locked) mode, the slide lock  132  is shifted proximally, and the transverse shaft  138  is positioned opposite the locking surface  143 . In the fixed mode, the lever member  140  is prevented from pivoting due to engagement between the transverse shaft  138  and the locking surface  143 . 
       FIGS. 3E-3J  are various drawings providing additional detailed views of the locking mechanism  130 , the lever member  140 , and parts of the ratchet mechanism  120 .  FIG. 3E  is an isometric view of the pivot shaft  121 , locking mechanism  130 , and lever member  140 . In this view, the U-shaped structure of the slide lock  132  is depicted with the slide recesses  133  along the ends of each arm.  FIG. 3F  is a superior surface view of the locking mechanism  130  and lever member  140 .  FIG. 3G  is an inferior surface view of the locking mechanism  130  and lever member  140 . In this view, the engagement feature  141  of the lever member  140  is shown including at least three angled threads in the thread pattern. In other examples, a different thread pattern can be utilized and the engagement feature  141  can have more or fewer threads. In other examples, the engagement feature  141  can include a series of protrusions positioned to engage the threaded proximal portion  102 . In yet other examples, the engagement feature  141  can include one or more captured ball bearings positioned to engage the threads in the threaded proximal portion  102 , in this example the threads in the threaded proximal portion  102  may be structured to accept the ball bearings. This view also includes detent balls  134  and detent springs  135 , which assist in holding slide lock  132  in the fixed or ratcheting position.  FIG. 3H  is a lateral view drawing of the locking mechanism  130  and lever member  140 .  FIG. 3I  is an axial view along a longitudinal axis of the rod reduction instrument of the locking mechanism  130  and the lever member  140 . This view depicts the U-shaped structure of the slide lock  132  with the c-shaped slide recesses  133  on the outbound end of each leg of the U. The view also depicts the curve of the engagement feature  141  on the inferior side of the proximal portion of the lever member  140 . Opposite the engagement feature  141  is the biasing member  146 , which is held in place by an inferior surface of the slide lock  132 .  FIG. 3J  is a cutaway perspective view of the locking mechanism  130  and lever member  140  providing a slightly different perspective on the elements discussed above. 
       FIG. 4  is an isometric view of a rod reduction instrument  200 , in accordance with an example embodiment. The rod reduction instrument  200  is similar to rod reduction instrument  100  discussed above, but includes a different ratchet lock-out mechanism. The following discussion will primarily focus on the differences in the ratchet mechanism  220 , as the rest of the functionality of the rod reduction instrument  200  is comparable to that of rod reduction instrument  100 . As illustrated in  FIG. 4 , the rod reduction instrument  200  can include an inner shaft  201 , engagement members  203 , an outer housing  210 , and a ratchet mechanism  220 . The outer housing  210  can include a bottom sleeve  211  and a top sleeve  215 . The top sleeve  215  can include a tool socket  216 , which can be used to receive a handle to introduce rotation to the top sleeve  215 . The top sleeve  215  can rotate in reference to the bottom sleeve  211  around the rotational coupling  217 . The bottom sleeve  211  includes a rod engagement  212  on a distal end. 
       FIG. 5  is an exploded isometric view of an upper section (top sleeve  215 ) of the rod reduction instrument  200 , in accordance with an example embodiment. In this example, the ratchet mechanism  220  includes pivot shaft  221 , button opening  223 , button cutout  224 , pivot shaft bores  225 , ratchet cover  226 , locking mechanism  230 , and lever member  240 . The lever member  240  is similar to the lever member  140 , and includes a threaded inferior surface on a proximal portion and a ratchet release button  242  on a superior surface of a distal portion. The lever member  240  receives the pivot shaft  221  between the proximal portion and distal portion. On a superior surface of the proximal portion of the lever member  240  there is a bias recess  247  adapted to receive a biasing member  246 . In this example, the locking mechanism  230  includes a slide lock  232  in the form of a stepped cylindrical shaft. The slide lock  232  includes a large diameter section  233 , a small diameter section  234 , a locking ring  235 , and a biasing member  236 . As assembled, the slide lock  232  is located within a slide lock bore  237  (labeled in  FIG. 6J ), with the locking ring  235  securing the slide lock  232  shaft within the bore  237 . 
     In this example, the lever member  240  and the biasing member  246  are dropped into the ratchet mechanism  220  through an opening in the superior surface, then the ratchet cover  226  is slid into position over the opening to provide an engagement surface for the biasing member  246  to operate against. In an example, edges of the ratchet cover  226  slide into recesses in the opening in the superior surface of the ratchet mechanism  220 . Once the lever member  240  is in position, the pivot shaft  221  can be inserted to retain the lever member  240 , while allowing the lever member  240  to pivot. 
       FIGS. 6A-6J  are diagrams and drawings of the ratchet mechanism  220  used in a rod reduction instrument  200 , in accordance an example embodiment.  FIGS. 6A and 6B  are cutaway illustrations of the ratchet mechanism  220  as well as depictions of portions of inner shaft  201 , top sleeve  215 , and bottom sleeve  211 . In this example, the thrust washer  218  and retaining ring  219  are illustrated in reference to top sleeve  215  and bottom sleeve  211 . Inner shaft  201  includes proximal threaded portion  202 , which engages with the engagement feature  241  of the lever member  240 . The biasing member  246  is illustrated urging the lever member  240  to pivot on pivot shaft  221  and engage the threaded proximal portion  202  of inner shaft  201 . The locking surface  243  is also illustrated in these cutaway views. The locking surface  243  on the lever member  240  is a semi-circular recess along a lateral inferior surface under a portion of the ratchet release button  242 . As illustrated in other figures, the large diameter  233  of the slide lock  232  can be shifted laterally into engagement with the locking surface  243  to prevent the lever member  240  from pivoting and forcing the engagement feature  241  into fixed engagement with the threaded proximal portion  202  of inner shaft  201 . With the slide lock  232  engaged, the rod reduction instrument  200  operates through rotation of the top sleeve  215  only. The cutaway views also illustrate the structure of the button opening  223  and the button cutout  224 . The button opening  223  is an opening in the ratchet mechanism  220  that conforms to the outline of the ratchet release button  242  of the lever member  240 , while the button cutout  224  is a recessed portion around the ratchet release button  242 . In some examples, the button cutout  224  can include curved sidewalls, and in other examples the sidewalls can be straight but angled. 
       FIG. 6C-6I  are various drawings providing additional detailed views of the locking mechanism  230  and lever member  240  parts of the ratchet mechanism  220 .  FIG. 6C  is an isometric view of the pivot shaft  221 , locking mechanism  230 , and lever member  240 . In this example, the pivot  245  of lever member  240  is identified as the bore in the lever member  240  receiving the pivot shaft  221 . Other features of the lever member  240  illustrated in this example include engagement feature  241 , ratchet release button  242 , locking surface  243 , bias recess  247 , and the bias member  246 . This example illustrates the relationship between the locking surface  243  on the lever member  240  and the large diameter section  233  of the stepped cylindrical slide lock  232 . While not specifically identified with a reference number, the slide lock  232  includes an enlarged lateral end that operates as a button for activation of the slide lock  232  of the locking mechanism  230 . 
       FIG. 6D  is an inferior side view of the pivot shaft  221 , locking mechanism  230 , and lever member  240 . In this example, the engagement feature  241  of the lever member  240  is illustrated as including at least three threads running at a shallow angle transverse to a longitudinal axis of the lever member  240 . In some example, more or fewer threads can be included on the engagement feature  241 . The small diameter section  234  of the slide lock  232  stepped cylindrical shaft is shown within a recess in the inferior side of the ratchet release button  242  portion of the lever member  240 . The lock biasing member  236  is illustrated in position to bias the slide lock  232  into an unlocked position. 
       FIG. 6E  is a superior side view of the pivot shaft  221 , locking mechanism  230 , and lever member  240 .  FIG. 6F  is a lateral side view of the pivot shaft  221 , locking mechanism  230 , and lever member  240 . In this view, the engagement feature  241  is illustrated as including four partial threads to engage the threaded proximal portion  202  of the inner shaft  201 . 
       FIG. 6G  is a medial side view of the pivot shaft  211 , locking mechanism  230 , and lever member  240 . In this view, the U-shaped slide lock recess  248  in the inferior side of the ratchet release button  242  portion of the lever member  240  is shown in relationship to the small diameter section  234  and lock biasing member  236  of the slide lock  232 . The slide lock recess  248  provides sufficient clearance to allow the lever member  240  to pivot around pivot shaft  221  with the ratchet release button  242  is activated, or when ratcheting as the outer housing  210  slides over the inner shaft  201 .  FIGS. 6G and 6I  are distal and proximal views, respectively, along the longitudinal axis of the rod reduction instrument  200 .  FIG. 6  depicts the curved structure of the inferior surface of the engagement feature  241  of the lever member  240 . The engagement feature  241  is curved to match the outer curvature of the inner shaft  201 . 
       FIG. 6J  is a transverse cutaway view of the ratchet mechanism  220 , top sleeve  215 , and inner shaft  201 . The cutway runs through the stepped cylindrical shaft of the slide lock  232 . As illustrated, the locking ring  235  retains the slide lock  232  within the slide lock bore  237  by engaging a cylindrical recess enlarging a section of the slide lock bore  237 . The cutaway also illustrates how the large diameter section  233  can engage the locking surface  243  on the lever member  240  when the button of the slide lock  232  is pushed in compressing the lock biasing member  236 . 
       FIG. 7  is a flowchart illustrating a method  700  for using a rod reduction instrument, such as rod reduction instrument  100  or  200  discussed above. The method  700  illustrates a common set of operations utilizing one of the rod reduction instruments discussed above. However, the method  700  does not cover all possible uses of the instruments, the operations discussed can be done in a different sequence, operations could be repeated or omitted, as fits the particular scenario of use. In this example, the method  700  can include operations such as: coupling to a pedicle screw at  710 , selecting Quick On/Off mode at  720 , sliding the outer housing into engage with a connecting rod at  730 , optionally attaching a T-handle at  740 , reducing the connecting rod at  750 , insert closure into pedicle screw at  760 , remove rod reduction instrument at  770 . 
     The method  700  can begin at  710  the mode of operation of the instrument being selected. In this example, the Quick On/Off (or ratcheting) mode can be selected by shifting the slide lock, such as slide lock  132 , into the Quick On/Off (distal) position. As discussed above, with the instrument in the Quick On/Off mode, the ratchet mechanism is free to ratchet. In other words, the engagement feature  141  of the lever member  140  is not fixed into engagement of the threaded proximal portion  102  of the inner sleeve  101 . In another example, the user may choose to engage the threaded operation mode by shifting the slide lock into the Fixed (proximal) position. The operations discussed in method  700  are depicted in a common order of operation, but many of the operations can be shifted into other positions in the method or repeated. For example, the mode of operation can be switched at any point during the procedure. 
     At  720 , the method  700  can continue by coupling the rod reduction instrument to a head of a pedicle screw. For example, engagement members  203  of the rod reduction instrument  100  can be placed into engagement with the head of a pedicle screw. Prior to engaging the pedicle screw, a ratchet release button  142  can be engaged and the inner shaft  101  fully extended into a fully open position. In an example, the instrument can include four separate engagement members that engage four vertical slots on the screw head. In other examples, the instrument may only include two engagement members that engage either arm of the U-shaped pedicle screw head. 
     Once the head of the pedicle screw is engaged, the method  700  can continue with the instrument free to engage the connecting rod at  730 . In this example, the outer housing  110  can slide over the inner sleeve  201  to quickly engage the connecting rod through ratcheting. If the instrument were in the Fixed mode, rotational input to the top sleeve  115  would be necessary to translate the outer housing  110  over the inner sleeve  101  to engage the connecting rod. 
     With the connecting rod engaged, the method  700  can optionally continue at  740  with attachment of a T-handle on the tool socket  116  of the top sleeve  115 . At  750 , the method  700  can continue with the instrument being manipulated to reduce the connecting rod into the head of the pedicle screw. Instrument manipulation can include rotation of the T-handle (or top sleeve  115  if no extra torque is needed), which causes translation of the outer housing  110 . Optionally, the instrument can be shifted into Fixed mode, if rod reduction is particular difficult to ensure that the ratchet mechanism  120  does not disengage during threaded reduction. 
     Once the rod is fully reduced into the pedicle screw, the method  700  can continue at  760  with a closure being inserted into the head of the pedicle screw to secure the rod in place. The instrument includes a central cylindrical passage to allow the closure to be inserted without removing the rod reduction instrument. Once the rod is secure, the method  700  can continue at  770  with removal of the reduction instrument from the head of the pedicle screw. 
     The instrument removal operation  770  can optionally include operations such as: selecting a mode at  772 , rotating the instrument input at  774 , activating the ratchet release button  776 , and disengaging the pedicle screw at  778 . In certain examples, the ratchet mechanism  120  in the Quick On/Off mode may not be able to release the tension on the rod reduction instrument  100 . In such a scenario, the instrument can be shifted into Fixed mode through manipulation of the slide lock  132  into the proximal position. In fixed mode, the top sleeve  215  can be rotated at  774  to release tension on the outer housing  110  from engagement with the connecting rod. Once the tension is released, the mode can be shifted back to the Quick On/Off mode, and the ratchet release ratchet release button  142  can be activated at  776 . Activating the ratchet release ratchet release button  142  allows the outer housing  110  to slide in reference to the inner sleeve  101  to open the instrument. Once the instrument is open, the engagement members  103  can be disengaged from the pedicle screw head at  778 . 
     VARIOUS NOTES &amp; EXAMPLES 
     Each of these non-limiting examples may stand on its own, or may be combined in various permutations or combinations with one or more of the other examples. 
     Example 1 describes subject matter that can include a rod reduction instrument. In this example, the rod reduction instrument can include an inner shaft, an outer housing, and ratchet mechanism. The inner shaft can include a threaded proximal portion and a distal end, the distal end including a plurality of engagement members adapted to receive a housing of a pedicle screw. The outer housing can be slidably received over at least a portion of the inner shaft. The outer housing can also include a top sleeve and a bottom sleeve. In this example, the top sleeve can include the ratchet mechanism to selectively engage the threaded proximal portion of the inner shaft, and a distal end of the bottom sleeve adapted to engage a connecting rod. The ratchet mechanism can be disposed along the top sleeve of the outer housing. In this example, the ratchet mechanism can include an engagement feature to selectively engage the threaded proximal portion of the inner shaft, and a locking mechanism to selectively lock the engagement feature of the ratchet mechanism against the threaded proximal portion of the inner shaft. 
     In Example 2, the subject matter of Example 1 can optionally include the top sleeve being rotatably coupled to the bottom sleeve and adapted to translate rotational input into linear translation of the outer housing relative to the inner shaft. 
     In Example 3, the subject matter of Example 2 can optionally include the engagement feature of the ratchet mechanism engaging the threaded proximal portion of the inner shaft, upon receiving rotational input from the top sleeve, to linearly translate the outer shaft along a longitudinal axis in relation to the inner shaft. 
     In Example 4, the subject matter of any one of Examples 1 to 3 can optionally include the ratchet mechanism having a lever member including a proximal end and a distal end separated by a pivot. 
     In Example 5, the subject matter of Example 4 can optionally include the engagement feature of the proximal end of the lever member being adapted to selectively engage the threaded proximal portion of the inner shaft. 
     In Example 6, the subject matter of any one of Examples 4 and 5 can optionally include the distal end of the lever member having a button exposed on an external surface of the ratchet mechanism. 
     In Example 7, the subject matter of any one of Examples 4 to 6 can optionally include the pivot having a pivot shaft extending into opposing side walls of the locking mechanism, which enables rotational movement of the lever member about the pivot shaft. 
     In Example 8, the subject matter of Example 7 can optionally include the engagement feature on the proximal portion of the lever member selectively engaging the threaded proximal surface of the inner shaft through the rotational movement of the lever member. 
     In Example 9, the subject matter of Example 8 can optionally include the ratchet mechanism having a biasing member positioned against a superior surface of the proximal portion of the lever member opposite the engagement feature to bias the engagement feature against the threaded proximal surface of the inner shaft. 
     In Example 10, the subject matter of any one of Examples 4 to 9 can optionally include the locking mechanism having a slide lock disposed on an external surface of the ratchet mechanism adapted to lock the locking mechanism in a first position and unlock the locking mechanism in a second position. 
     In example 11, the subject matter of Example 10 can optionally include the slide lock being a U-shaped linear slide slidably engage along opposing sides of the ratchet mechanism, the slide lock translates along a longitudinal axis of the rod reduction instrument between the first position and the second position. 
     In Example 12, the subject matter of Example 11 can optionally include the slide lock including a transverse shaft projecting from an inferior surface of the slide lock towards the longitudinal axis to engage a locking surface on the lever member. 
     In Example 13, the subject matter of Example 12 can optionally include the slide lock being in the first position so the transverse shaft engages the locking surface to prevent the lever member from pivoting the engagement feature of the lever member away from the threaded proximal portion of the inner shaft. 
     In Example 14, the subject matter of Example 12 can optionally include the slide lock being in the second position so the inferior shaft is positioned over a cavity in the lever member allowing the lever member to pivot freely within the ratchet mechanism. 
     In Example 15, the subject matter of Example 10 can optionally include the slide lock being a stepped cylindrical shaft positioned transverse the lever member and disposed within a bore extending across a portion of a width of the ratchet mechanism. 
     In Example 16, the subject matter of Example 15 can optionally include the stepped cylindrical shaft including a large diameter section coupled to a small diameter section, the large diameter section engageable with a locking surface on the lever member to prevent pivoting of the lever member within the ratchet mechanism. 
     In Example 17, the subject matter of any one of Examples 15 or 16 can optionally include the slide lock translating within the bore between the first position and the second position. 
     In Example 18, the subject matter of Example 17 can optionally include the slide lock being in the first position where a portion of a larger diameter section of the stepped cylindrical shaft engages a locking surface on the lever member to lock-out the ratchet mechanism. 
     In Example 19, the subject matter of any one of Examples 15 to 18 can optionally include the locking mechanism including a biasing element disposed within the bore to bias the stepped cylindrical shaft into a particular position, such as the second position. 
     In Example 20, the subject matter of any one of Examples 15 to 19 can optionally include the stepped cylindrical shaft being biased into a second position where the lever member within the ratchet mechanism is free to pivot the engagement feature away from the threaded proximal portion of the inner shaft allowing the outer shaft to translate distally over the inner shaft towards the pedicle screw without rotational input. 
     In Example 21, the subject matter of any one of Examples 1 to 20 can optionally include the engagement feature being selected from a group of structures including: threads, numbs, cylindrical protrusions, square or rectangular protrusions, and one or more captured ball bearings. 
     The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein. 
     In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls. 
     In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. 
     The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R § 1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.