Patent Publication Number: US-2023136167-A1

Title: Patient-mounted surgical retractor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/139,434, filed on Sep. 24, 2018. U.S. application Ser. No. 16/139,434 claims the benefit of U.S. Provisional Application Nos. 62/562,055 and 62/562,046, both filed on Sep. 22, 2017. The entire contents of each of these applications are hereby incorporated by reference. 
    
    
     FIELD 
     This disclosure relates generally to surgical instruments, systems, and methods, and more particularly to instruments, systems, and methods for providing access to a surgical site using patient-mounted components. Such instruments, systems, and methods can be used in various procedures, e.g., orthopedic or neurologic surgical procedures such as spinal fusion surgery. 
     BACKGROUND 
     Surgical procedures are used to treat and cure a wide range of diseases, conditions, and injuries. Surgery often requires access to internal tissue through open or minimally invasive surgical procedures. The term “minimally invasive” refers to all types of minimally invasive surgical procedures, including endoscopic, laparoscopic, arthroscopic, natural orifice intraluminal, and natural orifice transluminal procedures. Minimally invasive surgery can have numerous advantages compared to traditional open surgical procedures, including reduced trauma, faster recovery, reduced risk of infection, and reduced scarring. 
     Whether minimally invasive or not, there are a number of surgical procedures in which it can be desirable to form a working channel in a patient to provide access to a surgical site within the patient. One such example is orthopedic or neurologic surgical procedures, including, e.g., spinal fusion procedures where it can be desirable to form a working channel through a patient&#39;s tissue to access their vertebrae and/or the intervertebral discs disposed between adjacent vertebrae. 
     A variety of methods for providing such a working channel are known, including various devices that are anchored to a surgical table upon which a patient is disposed, devices that penetrate tissue without being anchored to any other structure, or devices that anchor to a plurality of anchors implanted in a patient&#39;s bone. In such arrangements, the devices may be inadequately supported, may undesirably move relative to a patient if the patient moves relative to the operating table or some other external structure, or may impede a surgeon or other user in performing some aspect of a procedure. 
     By way of example, in spinal procedures involving operation on a patient&#39;s intervertebral disc disposed between adjacent vertebrae, access to the disc space can be difficult. Prior approaches can involve performing work on intervertebral discs before implanting pedicle screws in the adjacent vertebrae. Surgery on the intervertebral disc, however, can involve removal of portions of bone from the adjacent vertebrae, which can make subsequent implanting of pedicle screws more difficult. Implanting screws before removing vertebral bone can therefore be desirable, but surgeons cannot implant the pedicle screws with receiver heads before performing intervertebral disc work because the receiver heads (and extension posts typically coupled thereto) can block access to the intervertebral disc space. As a result, surgeons often resort to inserting guidewires for the pedicle screws, bending the guidewires away from the intervertebral space to perform disc operations around the guidewires, then implanting the pedicle screws. 
     The advent of modular pedicle screws can allow pedicle anchors to be implanted before performing intervertebral disc operations. This is because modular pedicle screws can include a lower-profile implantable anchor that can be implanted without impeding access to, e.g., an intervertebral disc. A spinal fixation element receiver can be coupled to the anchor after implantation and completion of any intervertebral disc operation. Such anchors can also provide a rigid access point indexed to the patient&#39;s anatomy. 
     Accordingly, there is a need for improved access devices, systems, and methods that can streamline the instrumentation and methodology of various surgical procedures. For example, there is a need for improved access devices, systems, and methods that can utilize anchors implanted in a patient&#39;s anatomy to support surgical instruments. 
     SUMMARY 
     In some embodiments, a patient-mounted surgical retractor is provided that can couple to an implanted anchor by way of, for example, a surgical support or extension that couples to the anchor. The retractor can include one or more tissue manipulating implements that can be configured to interface with tissue. In some embodiments, the retractor can include at least first and second opposed tissue manipulating implements that can be configured to move in a variety of manners, including various combinations of moving and/or pivoting toward and away from one another. For example, a retractor can be provided that can couple to a single implanted pedicle screw or other anchor and provide medial-lateral tissue retraction by moving opposed tissue manipulating implements toward or away from one another. Further, a retractor can be capable of toeing opposed tissue manipulating implements in a medial-lateral direction, e.g., pivoting or moving the tissue manipulating implements such that distal ends thereof move toward to away from one another while a distance between proximal ends thereof remains unchanged. By manipulating tissue in such a manner, the retractor can be used to widen an incision formed in patient&#39;s skin and underlying tissue to provide a working channel to a surgical site, such as a patient&#39;s intervertebral disc space. Such a retractor can advantageously be indexed to a patient via coupling with the implanted anchor and can provide medial-lateral or other tissue retraction while minimizing instrumentation size and complexity. While the systems, devices, and methods described herein can be utilized in a variety of surgical procedures, they can have particular utility in various orthopedic or neurologic surgical procedures, such as spinal operations. 
     In one aspect, a surgical instrument is provided that can include a body configured to couple to an implantable anchor, a first tissue manipulating implement coupled to the body and capable of polyaxial movement relative thereto, and a second tissue manipulating implement coupled to the body and capable of polyaxial movement relative thereto. Moreover, the first and second tissue manipulating implements can be opposed to one another such that they can move any of toward and away from one another. 
     The devices and methods described herein can have a number of additional features and/or variations, all of which are within the scope of the present disclosure. In some embodiments, for example, the instrument can further include an anchor extension extending between the body and the implantable anchor. In some embodiments, the instrument can further include a lock coupled to the body and configured to interface with the anchor extension to selectively lock a position of the body relative to the anchor extension. In certain embodiments, the lock can include a pawl configured to move relative to the body and interface with a ratchet formed on the anchor extension. 
     In some embodiments, each of the first and second tissue manipulating implements can couple to the body via a ball and socket joint. Still further, in some embodiments each of the ball and socket joints can include an expanding member configured to selectively lock the ball and socket joint against movement. 
     The tissue manipulating implements can have a variety of forms. In some embodiments, at least one of the tissue manipulating implements can be a planar blade. In certain embodiments, the tissue manipulating implements can include a first blade and a second blade configured to translate relative to one another to adjust an overall length of the tissue manipulating implement. Moreover, in some embodiments at least one of the tissue manipulating implements can include a distal tip configured to scrape tissue from bone. In other embodiments, at least one of the tissue manipulating implements can include a pointed distal tip. 
     In some embodiments, the instrument can further include an extension post coupled to the body. The extension post can, in some embodiments, pivot relative to the body. The extension post can be utilized to, for example, couple the instrument to an external structure in some embodiments. 
     A variety of movements of the tissue manipulating implements are possible. For example, and as noted above, the implements can be configured to move any of toward and away from one another, for example in medial and lateral directions relative to a patient&#39;s body. In certain embodiments, polyaxial movement of the tissue manipulating implements relative to the body can also include toeing of a distal end of the tissue manipulating implements any of toward and away from one another. For example, a distal end of the tissue manipulating implements can move any of toward and away from one another while a distance between a proximal end of the tissue manipulating implements remains unchanged. 
     In another aspect, a surgical instrument is provided that can include first and second opposed handles pivotably coupled to one another and configured to couple to an implantable anchor, as well as a first tissue manipulating implement coupled to the first handle and a second tissue manipulating implement coupled to the second handle. Moreover, movement of the first and second handles any of toward and away from one another can cause movement of the first and second tissue manipulating implements any of toward and away from one another. 
     As with the system described above, a number of variations and additional features are possible. For example, in some embodiments the instrument can further include an anchor extension extending between the opposed handles and the implantable anchor. In certain embodiments, the instrument can further include a lock coupled to the opposed handles and configured to interface with the anchor extension to selectively lock a position of the opposed handles along a length of the anchor extension. Further, in some embodiments the first and second tissue manipulating implements can be configured to move polyaxially relative to the anchor extension. 
     In some embodiments, the instrument can further include a lock configured to selectively prevent movement of the opposed handles relative to one another. Such a lock can also serve to prevent movement of the tissue manipulating implements relative to one another. 
     The tissue manipulating implements can have a variety of configurations. For example, in some embodiments at least one of the tissue manipulating implements can be a planar blade. In certain embodiments, the tissue manipulating implements can include a first blade and a second blade configured to translate relative to one another to adjust an overall length of the tissue manipulating implement. In other embodiments, at least one of the tissue manipulating implements can include a distal tip configured to scrape tissue from bone. Still further, in some embodiments at least one of the tissue manipulating implements can include a pointed distal tip. 
     In some embodiments, the instrument can further include an extension post coupled to the opposed handles. The extension post can be configured to adjust relative to the opposed handles in certain embodiments. The extension post can be utilized in certain embodiments to couple the instrument to an external structure, such as a surgical table, etc. 
     A variety of movements of the tissue manipulating implements are possible. In some embodiments, for example, the first and second tissue manipulating implements can be configured for toeing movement relative to one another. In such movement, distal ends of the tissue manipulating implements can move any of toward and away from one another by a greater amount than proximal ends of the tissue manipulating implements. 
     In another aspect, a surgical method is provided that can include implanting an anchor in a patient&#39;s bone and coupling an anchor extension to the anchor. The method can further include coupling a retractor assembly to the anchor extension such that first and second tissue manipulating implements of the retractor assembly extend into an incision formed in the patient&#39;s tissue. Further, the method can include moving the first and second implements of the retractor assembly away from one another in a medial-lateral direction to increase a size of the incision formed in the patient&#39;s tissue. 
     In some embodiments, at least one of the first and second tissue manipulating implements can be a planar blade. In certain embodiments, the method can further include scraping tissue from bone using a distal end of at least one of the tissue manipulating implements. For example, a distal end of a planar blade can be utilized for this purpose. 
     In some embodiments, the method can further include toeing the first and second tissue manipulating implements relative to one another such that distal ends of the tissue manipulating implements move any of toward and away from one another by a greater amount than proximal ends of the tissue manipulating implements. 
     In some embodiments, the method can further include adjusting a length of at least one of the tissue manipulating implements. Moreover, in certain embodiments the method can include locking a position of the retractor assembly along a length of the anchor extension. The method can also include locking a position of the anchor extension relative to the anchor in some embodiments. Still further, in some embodiments the method can include locking a position of at least one of the tissue manipulating implements relative to the anchor extension. 
     Any of the features or variations described above 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 the avoidance of repetition in this summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an illustration of one embodiment of a surgical instrument assembly according to the teachings provided herein; 
         FIG.  2    is a detail view of a retractor of the assembly of  FIG.  1   ; 
         FIG.  3    is an exploded view of the assembly of  FIG.  1   ; 
         FIG.  4    is an exploded view of the retractor of  FIG.  2   ; 
         FIG.  5    is a partially-transparent detail view of the retractor of  FIG.  2   ; 
         FIG.  6    is a bottom partially-transparent detail view of the retractor of  FIG.  2   ; 
         FIG.  7    is a detail view of tissue manipulating implements of the retractor of  FIG.  2   ; 
         FIG.  8 A  is a perspective view of one embodiment of an actuating instrument according to the teachings provided herein; 
         FIG.  8 B  is an alternative view of the actuating instrument of  FIG.  8 A ; 
         FIG.  9    is a front perspective view of the actuating instrument of  FIG.  8 A  coupled to the surgical assembly of  FIG.  1   ; 
         FIG.  10    is a front perspective view of another embodiment of a surgical instrument assembly according to the teachings provided herein; 
         FIG.  11    is a detail view of a retractor of the assembly of  FIG.  10   ; 
         FIG.  12    is an alternative detail view of the retractor of  FIG.  11   ; 
         FIG.  13    is another detail view of the retractor of  FIG.  11   ; 
         FIG.  14    is still another detail view of the retractor of  FIG.  11   ; 
         FIG.  15    is a detail view of a tissue manipulating implement of the retractor of  FIG.  11   ; 
         FIG.  16    is a detail view of another embodiment of a tissue manipulating implement of the retractor of  FIG.  11   ; 
         FIG.  17    is an exploded view of the tissue manipulating implement of  FIG.  16   ; 
         FIG.  18 A  is a perspective view of an actuating instrument of the assembly of  FIG.  10   ; 
         FIG.  18 B  is an alternative view of the actuating instrument of  FIG.  18 A ; 
         FIG.  19    is a partially-transparent perspective view of the actuating instrument of  FIG.  18 A ; 
         FIG.  20 A  is a front perspective view of one embodiment of a surgical instrument assembly according to the teachings provided herein; 
         FIG.  20 B  is a top perspective view of the assembly of  FIG.  20 A ; 
         FIG.  21    is a detail view of a portion of the assembly of  FIG.  20 A ; 
         FIG.  22 A  is an alternative detail view of the assembly of  FIG.  21   ; 
         FIG.  22 B  is another alternative detail view of the assembly of  FIG.  21   ; 
         FIG.  23 A  is a detail view of one embodiment of a tissue manipulating implement and a driver; 
         FIG.  23 B  is a detail view of the tissue manipulating implement and driver of  FIG.  23 A ; 
         FIG.  24    is a front perspective view of the tissue manipulating implement of  FIG.  23 A  coupling to the assembly of  FIG.  21   ; 
         FIG.  25    is a front perspective view of polyaxial movement of the tissue manipulating implement of  FIG.  23 A  when coupled to the assembly of  FIG.  21   ; 
         FIG.  26    is a front perspective view of adjusting a length of the tissue manipulating implement of  FIG.  23 A ; 
         FIG.  27    is a front perspective view of the driver locking the tissue manipulating implement of  FIG.  23 A ; 
         FIG.  28    is a front perspective view of coupling a second tissue manipulating implement to the assembly of  FIG.  21   ; 
         FIG.  29    is a front perspective view of a driver selectively inducing polyaxial movement of the second tissue manipulating implement of  FIG.  28    and selectively locking against such movement; 
         FIG.  30    is a side perspective view of one embodiment of a surgical instrument according to the teachings provided herein; 
         FIG.  31    is a side perspective view of the instrument of  FIG.  30    coupling to an anchor extension; 
         FIG.  32    is a side perspective view of a plurality of interchangeable tissue manipulating implements that can be coupled to the instrument of  FIG.  30   ; 
         FIG.  33    is a side perspective view of an alternative plurality of interchangeable tissue manipulating implements that can be coupled to the instrument of  FIG.  30   ; 
         FIG.  34 A  is a top view of one embodiment of ranges of motion of tissue manipulating implements and opposed handles of the instrument of  FIG.  30   ; 
         FIG.  34 B  is a side perspective view of the instrument of  FIG.  34 A ; 
         FIG.  35    is a top view of one embodiment of a lock to selectively maintain a position of opposed handles relative to one another; 
         FIG.  36    is a front perspective view of another embodiment of a surgical instrument according to the teachings provided herein; 
         FIG.  37    is a partially transparent bottom perspective view of the instrument of  FIG.  36   ; 
         FIG.  38    is a partially transparent top perspective view of the instrument of  FIG.  36   ; 
         FIG.  39    is an exploded view of the instrument of  FIG.  36   ; 
         FIG.  40    is a front perspective view of one embodiment of a surgical instrument assembly according to the teachings provided herein; 
         FIG.  41    is a front perspective view of a first component of the surgical instrument assembly of  FIG.  40   ; 
         FIG.  42    is a front perspective view of a second component of the surgical instrument assembly of  FIG.  40    coupling with the first component of  FIG.  41   ; 
         FIG.  43    is a front perspective view of a first component of one embodiment of a tissue manipulating implement; 
         FIG.  44    is a front perspective view of a second component of the tissue manipulating implement of  FIG.  43   ; 
         FIG.  45    is a front perspective view of the first component of  FIG.  43    coupling with the second component of  FIG.  44   ; 
         FIG.  46    is a front perspective view of the tissue manipulating implement of  FIGS.  43 - 45    coupling to the assembly of  FIG.  40   ; 
         FIG.  47    is a front perspective view of the assembly of  FIG.  46    illustrating various degrees of freedom of a tissue manipulating implement; 
         FIG.  48    is a detail view of the assembly of  FIG.  46    illustrating one embodiment of a lock to selectively prohibit movement of a tissue manipulating implement; 
         FIG.  49    is a front perspective view of the assembly of  FIG.  47    illustrating removal of a first driver; 
         FIG.  50    is a front perspective view of the assembly of  FIG.  47    illustrating removal of a second driver; 
         FIG.  51    is a detail view illustrating an alternative embodiment of a tissue manipulating implement coupling to the assembly of  FIG.  40   ; 
         FIG.  52    is a detail view illustrating a first step in coupling a tissue manipulating implement to another component of a surgical instrument assembly; 
         FIG.  53    is a detail view illustrating a second step in coupling a tissue manipulating implement to another component of a surgical instrument assembly; 
         FIG.  54    is a detail view illustrating degrees of freedom of a tissue manipulating implement relative to a surgical instrument assembly; 
         FIG.  55    is a detail view illustrating various interchangeable tissue manipulating implements that can be coupled to a surgical instrument assembly; 
         FIG.  56    is a detail view illustrating various degrees of freedom of a tissue manipulating implement of a surgical instrument assembly; 
         FIG.  57    is an alternative view of various degrees of freedom of a tissue manipulating implement of a surgical instrument assembly; 
         FIG.  58    is a front perspective view of one embodiment of a surgical instrument assembly that can perform vertebral distraction; 
         FIG.  59    is a detail view showing a first step in operating the surgical instrument assembly of  FIG.  58   ; 
         FIG.  60    is a detail view showing a second step in operating the surgical instrument assembly of  FIG.  58   ; 
         FIG.  61    is a detail view showing a third step in operating the surgical instrument assembly of  FIG.  58   ; 
         FIG.  62 A  is a side perspective view of one embodiment of a surgical instrument assembly including tissue manipulating implements coupled to polyaxial screw receiver heads; 
         FIG.  62 B  is a top view of the assembly of  FIG.  62 A  including anchor extensions coupled to the polyaxial screws; 
         FIG.  63    is a side perspective view of one embodiment of a method for implanting anchors in a patient&#39;s bone; 
         FIG.  64    is a side perspective view of a plurality of interchangeable tissue manipulating implements that can couple to a polyaxial screw receiver head; 
         FIG.  65    is an alternative, opposite side perspective view of the tissue manipulating implements and polyaxial screw receiver head of  FIG.  64   ; 
         FIG.  66    is a front perspective view of one embodiment of a tissue manipulating implement coupled to a polyaxial screw receiver head; 
         FIG.  67    is a rear perspective view of the tissue manipulating implement and receiver head of  FIG.  66   ; 
         FIG.  68    is a side perspective view of one embodiment of a method for coupling a first tissue manipulating implement and first receiver head to an implanted anchor; 
         FIG.  69    is a side perspective view of one embodiment of a method for coupling a second tissue manipulating implement and second receiver head to an implanted anchor; 
         FIG.  70    is a side perspective view of one embodiment of a method for interfacing the receiver heads with polyaxial lockout posts; 
         FIG.  71 A  is a side perspective view of various degrees of freedom of the polyaxial receiver heads and tissue manipulating implements; 
         FIG.  71 B  is an alternative top view of various degrees of freedom of the polyaxial receiver heads and tissue manipulating implements; 
         FIG.  72    is a side perspective view of one embodiment of a method for removing tissue manipulating implements after use; 
         FIG.  73    is a side perspective view of one embodiment of a spinal distraction instrument according to the teachings provided herein; 
         FIG.  74 A  is a side perspective view of the distraction instrument of  FIG.  73    coupling with other surgical instruments described herein; 
         FIG.  74 B  is a detail view of distal ends of the distraction instrument of  FIG.  73    approaching the other surgical instruments shown in  FIG.  74 A ; 
         FIG.  75    is a side perspective view of the spinal distraction instrument of  FIG.  73    applying a distraction force to the other surgical instruments shown in  FIG.  74 A ; 
         FIG.  76    is a side perspective view of another embodiment of a spinal distraction instrument according to the teachings provided herein; 
         FIG.  77    is a side perspective view of the distraction instrument of  FIG.  76    coupling with other surgical instruments described herein; 
         FIG.  78 A  is a side perspective view of the distraction instrument of  FIG.  76    being actuated; 
         FIG.  78 B  is a side perspective view of the distraction instrument of  FIG.  76    applying a distraction force to the other surgical instruments of  FIG.  77   ; 
         FIG.  79    is a partially transparent perspective view of another embodiment of a retractor; 
         FIG.  80    is a partially transparent detail view of a portion of the retractor of  FIG.  79   ; 
         FIG.  81    is a cross-sectional view of the portion of the retractor shown in  FIG.  80    taken along the line A-A in  FIG.  80   ; 
         FIG.  82    is a partially transparent detail view of a polyaxial locking mechanism of the retractor of  FIG.  79   ; 
         FIG.  83    is a cross-sectional view of the polyaxial locking mechanism of  FIG.  82    taken along the line A-A in  FIG.  82   ; 
         FIG.  84    is a partially transparent perspective view of another embodiment of a retractor; 
         FIG.  85    is a partially transparent detail view of a portion of the retractor of  FIG.  84   ; 
         FIG.  86    is a cross-sectional view of the portion of the retractor shown in  FIG.  85    taken along the line A-A in  FIG.  85   ; 
         FIG.  87    is a cross-sectional view of another embodiment of an actuating instrument; 
         FIG.  88    is a perspective view of another embodiment of an actuating instrument; 
         FIG.  89    is a perspective view of another embodiment of an actuating instrument; 
         FIG.  90    is a perspective view of another embodiment of an actuating instrument; 
         FIG.  91 A  is a side view of another embodiment of an actuating instrument prior to coupling with a tissue manipulating implement; 
         FIG.  91 B  is a side view of the actuating instrument of  FIG.  91 A  coupled to the tissue manipulating implement of  FIG.  91 A ; 
         FIG.  91 C  is a side view of the actuating instrument of  FIG.  91 A  being decoupled from the tissue manipulating implements of  FIG.  91 A ; 
         FIG.  91 D  is a side view of the actuating instrument of  FIG.  91 A  decoupled from the tissue manipulating implement of  FIG.  91 A ; 
         FIG.  92 A  is a detail view of a distal end of the actuating instrument of  FIG.  91 A  and the tissue manipulating implement of  FIG.  91 A ; 
         FIG.  92 B  is a detail view of the portion of the actuating instrument of  FIG.  92 A  coupled to the tissue manipulating implement of  FIG.  92 A ; 
         FIG.  93    is a perspective view of one embodiment of a surgical instrument assembly; 
         FIG.  94    is an exploded view of the components of the surgical instrument assembly of  FIG.  93   ; 
         FIG.  95 A  is a top perspective view of a retractor of the assembly of  FIG.  93   ; 
         FIG.  95 B  is a perspective view of the retractor of  FIG.  95 A ; 
         FIG.  95 C  is a front perspective view of the retractor of  FIG.  95 A ; 
         FIG.  95 D  is a top view of the retractor of  FIG.  95 A ; 
         FIG.  96    is a perspective view of a distraction rack coupler of the assembly of  FIG.  93   ; 
         FIG.  97 A  is a perspective view of a stability handle of the assembly of  FIG.  93    coupling to the retractor of the assembly of the  FIG.  93   ; 
         FIG.  97 B  is a perspective view of the stability handle of the assembly of  FIG.  93    coupled to the retractor of the assembly of  FIG.  93   ; 
         FIG.  97 C  is a perspective view of a light source of the assembly of  FIG.  93    coupled to the stability handle and retractor of the assembly of  FIG.  93   ; 
         FIG.  98    is a side view of the light source of the assembly of  FIG.  93    and various tissue manipulating implements of the assembly of  FIG.  93   ; 
         FIG.  99 A  is a side view of a distal portion of the light source of  FIG.  98    aligned with the various tissue manipulating implements of  FIG.  98   ; 
         FIG.  99 B  is a side view of the distal portion of the light source of  FIG.  98    coupled to the various tissue manipulating implements of  FIG.  98   ; 
         FIG.  99 C  is a perspective view of the various tissue manipulating implements of  FIG.  98   ; 
         FIG.  100 A  is a perspective view of one embodiment of a modular tissue manipulating implement aligned with an arm of the assembly of  FIG.  93   ; 
         FIG.  100 B  is a perspective view of the modular tissue manipulating implement of  FIG.  100 A  coupled to the arm of  FIG.  100 A ; 
         FIG.  101 A  is a top perspective view of one embodiment of a tissue manipulating implement adjuster aligned with an expandable tissue manipulating implement of the assembly of  FIG.  93   ; 
         FIG.  101 B  is a side view of the tissue manipulating implement adjuster and expandable tissue manipulating implement of  FIG.  101 A  aligned with a static tissue manipulating implement of the assembly of  FIG.  93   ; 
         FIG.  101 C  is a side view of the tissue manipulating implement adjuster and expandable tissue manipulating implement of  FIG.  101 A  coupled with the static tissue manipulating implement of  FIG.  101 B ; 
         FIG.  101 D  is a detail view of the tissue manipulating implement adjuster, expandable tissue manipulating implement, and static tissue manipulating implement of  FIG.  101 C ; and 
         FIG.  101 E  is a detail view of the expandable and static tissue manipulating implements of  FIG.  101 D  after decoupling the tissue manipulating implement adjuster. 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices, systems, and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices, systems, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. 
     Additionally, to the extent that linear or circular 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. A person skilled in the art will recognize that an equivalent to such linear and circular dimensions can easily be determined for any geometric shape. Further, in the present disclosure, like-numbered components of the embodiments 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 components with which the devices will be used, and the methods and procedures in which the devices will be used. 
       FIGS.  1 - 9    illustrate an exemplary surgical instrument assembly  100  according to the teachings provided herein. The assembly  100  can be used in various surgical procedures, including spinal surgeries such as microsurgical bone resection, spinal decompression, spinal fusion, and the like. In general, the assembly  100  can include a support instrument  102  that couples to an implanted anchor  104 , such as a pedicle or other bone screw. The assembly  100  can further include a retractor  106  coupled to the support instrument  102 . Other components not illustrated here can be included or coupled to the assembly  100 . Such components can include, for example, any of a variety of cameras or visualization systems, and any of a variety of other surgical instruments. 
     An exemplary method of using the assembly  100  of  FIGS.  1 - 9    can include any one or more of the following steps, performed in any of a variety of sequences: a) making an incision in a skin of a patient; b) percutaneously inserting through the incision an implantable anchor, such as a pedicle or other bone screw; c) coupling the support instrument  102  to the implanted anchor (e.g., a pedicle anchor); d) coupling a tissue retractor to the instrument; e) providing medial-lateral retraction of tissue surrounding an incision; f) coupling an optical visualization instrument to the tissue retractor and/or instrument; g) resecting a portion of the superior articular process, and/or performing a microsurgical decompression procedure; h) extracting intervertebral disc material including removing cartilaginous material from the vertebral endplates; i) inserting an interbody device; and j) deploying a mechanism of stabilization to stabilize the intervertebral segment. 
     Returning to  FIGS.  1 - 9   ,  FIG.  1    illustrates one embodiment of a surgical instrument assembly  100  that includes a support instrument  102  coupled to an implantable anchor  104  and a tissue retractor  106 . Further details regarding embodiments of the support instrument  102  can be found in U.S. application Ser. No. 16/139,409, entitled “PATIENT-MOUNTED SURGICAL SUPPORT,” filed on Sep. 24, 2018, and issued as U.S. Pat. No. 10,945,773. Further details regarding embodiments of the implantable anchor  104  can be found in U.S. application Ser. No. 15/208,872, filed on Jul. 13, 2016, entitled “BONE ANCHOR ASSEMBLIES AND RELATED INSTRUMENTATION,” and issued as U.S. Pat. No. 10,463,402. Furthermore, details regarding certain embodiments of retractors that can be used in the surgical assembly  100  can be found below and in U.S. Pat. No. 7,491,168. The entire contents of each of these references are incorporated by reference herein. 
     Generally, the support instrument can include an elongate body  108  with a laterally-extending fork formed at a distal end thereof that can interface with a narrowed neck of the anchor  104 . The fork can include opposed projections that extend laterally from a distal portion of the elongate body and define a U-shaped or otherwise open-ended recess that can be sized to receive a portion of the implantable anchor  104 . For example, the projections can be configured to fit around a proximal portion of a bone anchor that can be part of a modular mono- or poly-axial pedicle screw. Such anchors can include a generally cylindrical distal shank portion with threads for tapping into bone, as well as a narrowed neck proximal of the shank portion and a wider proximal head. The proximal head can be generally spherical or semi-spherical in shape and can be configured to couple with a receiver head before or after implantation in a patient&#39;s bone. The elongate body can also include a lock configured to exert a drag force on the head of the anchor to control polyaxial movement of the instrument  102  relative to the anchor  104 . As shown in  FIG.  3   , the lock can include a lock body  302  that is coupled to the elongate body  108  and translatable relative thereto along a longitudinal axis  304  of the elongate body. The lock body  302  can have a generally elongate shape to facilitate coupling with and translating or sliding along or relative to the elongate body  108 . The lock can be actuated by a lock screw  305  that can cause distal translation of the lock body  302  as the screw is threaded further into the elongate body  108 . The lock body  302  can further include a laterally-extending ring-shaped projection  306  at a distal end thereof that can be configured to contact the proximal head of the anchor  104  and exert a drag force thereon. The ring-shaped projection  306  can define a lumen to maintain access to a drive feature formed on a proximal end of the head of the anchor  104 . This lumen, in combination with the lateral extension of the projection  306  and the fork formed at the distal end of the elongate body  108  can orient the instrument  100  such that a longitudinal axis of the instrument is laterally offset or non-coaxial with a longitudinal axis of the anchor  104 . Such a configuration can allow a driver or other instrument to access the drive feature of the anchor  104  even when the instrument  100  is coupled thereto. This can enable flexibility to implant the anchor  104  any of before and after coupling the instrument  100  thereto. 
     Returning to  FIG.  2   , a more detailed illustration of one embodiment of the tissue retractor  106  is provided. The retractor  106  can include a body  202  that can be configured to couple to the support instrument or anchor extension  102 . First and second tissue manipulating implements  204 ,  206  can be coupled to the body  202  by, for example, rigid arms  208 ,  210 , respectively. Each of the first and second tissue manipulating implements  204 ,  206  can be capable of polyaxial movement relative to the body via a polyaxial joint  212 ,  214 , such as a ball-and-socket joint. Such a joint can allow the tissue manipulating implements  204 ,  206  to move relative to one another in a variety of manners. For example, the implements  204 ,  206  can be pivoted toward or away from one another about an axis extending parallel to a longitudinal axis of a support instrument  102 , (e.g., an axis parallel to the axis  304  in  FIG.  3   ). The implements  204 ,  206  can also be pivoted toward or away from one another about an axis transverse or oblique to, e.g., the axis  304 . For example, the implements  204 ,  206  can be toed relative to one another, wherein distal ends of the implements are moved toward or away from one another by an amount greater than proximal ends of the implements. In some embodiments, toeing can include moving distal ends of the implements away from one another while proximal ends of the implements are either moved toward one another or do not move such that a distance between the proximal ends of the implements remains unchanged. Furthermore, each polyaxial joint  212 ,  214  can include a lock  216 ,  218  that can be used to selectively lock a position of the associated tissue manipulating implement  204 ,  206  or impose a drag force to inhibit movement in the absence of at least a threshold level of force. 
     As noted above, the tissue retractor  106  can be configured to couple to a support instrument or anchor extension  102  and can be configured to slide along a length of such an instrument to adjust a height of the retractor relative to the implanted anchor  104 . As shown in  FIG.  2   , the body  202  of the retractor can include a closed or partially-open lumen or recess  220  configured to receive a portion of the support instrument  102 , such as a generally cylindrical elongate body  108  (see  FIG.  1   ). The retractor  106  can further include a feature to selectively lock a position of the retractor relative to the support instrument  102 , such as a spring-biased protrusion or pawl  222  that can engage a ratchet rack or other series of recesses or other surface features formed on the elongate body  108  of the support instrument. Furthermore, in some embodiments the locking feature  222  can be configured to prevent not only movement along a length of the support instrument  102 , but also rotation thereabout. An actuator  224 , such as the illustrated sliding or translating member, can be included to allow a user to easily withdraw the protrusion  222  against the biasing force of a spring or other biasing element disposed within the body  202  of the retractor  106 . 
     In addition to adjusting a position of the retractor  106  along a length of the support instrument  102 , a length of each of the tissue manipulating implements  204 ,  206  can also be adjusted. For example, in some embodiments the tissue manipulating implements  204 ,  206  can each include an extension  226 ,  228  that can be configured to translate relative to the tissue manipulating implements  204 ,  206 . Proximally or distally translating either extension  226 ,  228  relative to the associated implement  204 ,  206  can change an overall length of the implement and, for example, can allow an implement to reach deeper into tissue even if the retractor  106  is mounted at a greater height above a patient&#39;s skin surface along a more proximal portion of the support instrument elongate body  108 . 
       FIG.  3    illustrates a partially exploded view showing how the retractor  106  can be coupled to the support instrument  102  by sliding the retractor down or distally over a proximal portion of the support instrument. For example, the recess or lumen  220  of the retractor  106  can be aligned with the generally cylindrical elongate body  108  of the support instrument and the retractor can be advanced down or distally along the axis  304 . While advancing the retractor relative to the support instrument, a user can manually retract the spring biased pawl or protrusion  222  using the sliding lever  224  to allow free movement of the retractor relative to the support instrument. When a desired position is reached, the user can release the lever  224  such that the protrusion  222  is advanced into engagement with a complementary recess or other feature formed on the elongate body  108  to maintain the relative positioning of the retractor and support instrument. In other embodiments, the complementary features formed on the elongate body  108  and the protrusion  222  can be formed as a biased ratchet wherein, e.g., distal advancement of the retractor can be achieved without actuating the lever  224 , but proximal withdrawal of the retractor  106  relative to the instrument  102  requires actuating the lever  224  to withdraw the biased protrusion  222 . 
       FIGS.  4 - 7    illustrate the retractor  106  in various exploded and partially transparent views to better explain the interaction of various components thereof. For example, the polyaxial joints  212 ,  214  can be seen in greater detail. Each polyaxial joint  212 ,  214  can include a socket  402 ,  404  formed in the body  202  of the retractor  106 . Each of the arms  208 ,  210  coupled to the tissue manipulating implements  204 ,  206  can have a generally ball-shaped proximal end  406 ,  408  that includes one or more relief slots formed therein such that various portions of the proximal end can deform relative to other portions thereof. A lock  216 ,  218  can be coupled to each arm  208 ,  210  by cooperation between threads  410 ,  412  formed on the lock and threads  414 ,  416  formed on an inner surface of through-holes in the arms  208 ,  210 . Further, a deformable expanding member  418 ,  420  can be formed at a distal end of each lock  216 ,  218 . 
     When assembled, as shown in  FIGS.  5  and  6   , the expanding members  418 ,  420  can be disposed within the generally ball-shaped proximal ends  406 ,  408 . Further, both of these components can be disposed within one of the sockets  402 ,  404  of the body  202 . In use, as the locks  216 ,  218  are rotated relative to the arms  208 ,  210 , they can advance farther into the sockets  402 ,  404  due to the threaded coupling between the arms  208 ,  210  and the locks  216 ,  218 . Advancement of the locks  216 ,  218  into the sockets  402 ,  404  can cause the deformable expanding member  418 ,  420  formed at a distal end of each lock to compress and expand radially outward. As the deformable expanding members  418 ,  420  expands radially, they can urge the various portions of the ball-shaped proximal ends  406 ,  408  of the arms  208 ,  210  into contact with the sidewalls of the sockets  402 ,  404 . This can cause an increase in frictional force between the sockets  402 ,  404  and the ball-shaped proximal ends  406 ,  408  of the arms  208 ,  210 . Further, upon sufficient advancement of the locks  216 ,  218 , the force of the expanding members  418 ,  420  can effectively lock the ball-shaped proximal ends  406 ,  408  in a given position and thereby prevent any movement of the arms  208 ,  210  or tissue manipulating implements  204 ,  206  coupled thereto. 
       FIGS.  4 - 7    also show additional features of the tissue manipulating implements  204 ,  206 , as well as the extensions  226 ,  228  coupled thereto. For example, the tissue manipulating implements  204 ,  206  can each be generally planar blades or surfaces configured to abut against and hold back tissue in order to effectively perform tissue retraction. In other embodiments, however, a variety of other shapes can be utilized, including non-planar blades or surfaces having curvature along any axis. The illustrated implements  204 ,  206  also include arms  702 ,  704  formed along a length thereof that define a recess that can receive an edge of an extension  226 ,  228  to prevent separation of the extension  226 ,  228  and the implement  204 ,  206 . The extensions  226 ,  228  can translate relative to the implements  204 ,  206  and a relative position of the extension and the implement can be maintained by interaction between a ratchet rack  422  formed on each implement  204 ,  206  and a leaf spring  424  with a pawl  426  formed on each extension  226 ,  228 . The pawl  426  and/or teeth or other surface features formed on the ratchet rack  422  can be biased to allow, for example, advancement of the extensions  226 ,  228  relative to the implements  204 ,  206  in one direction while preventing retracting in an opposite direction without urging the pawl  426  against the biasing force of the leaf spring  424 . 
       FIGS.  8 A- 9    illustrate one embodiment of a driver  800  that can be used to actuate the locks  216 ,  218  of the retractor  106 . As shown in  FIGS.  8 A and  8 B , the driver  800  can include a housing  802  surrounding a driveshaft  804 . The driveshaft  804  can be coupled to a handle  806  at a proximal end thereof and a drive interface  808  at a distal end thereof. The housing can also surround a second stabilizing shaft  810  that can aid in preventing torque applied to the driveshaft  804  from rotating or otherwise moving the retractor  106  and/or support instrument  102  about the implanted anchor  104 , as described below. The drive interface  808  can be configured to abut against a proximal end of one of the locks  216 ,  218 , as shown in  FIG.  9   . Accordingly, the drive interface can include features to aid in transferring torque to the lock, such as a socket including one or more pairs of opposed planar surfaces  812   a,    812   b  that can abut against one or more pairs of opposed planar surfaces formed on a proximal end of the locks  216 ,  218 . 
     In use, as shown in  FIG.  9   , the driver  800  can be positioned such that the drive interface  808  receives a proximal end of one of the locks  216 ,  218 . The stabilizing shaft  810  can be advanced distally to abut against the corresponding arm  208 ,  210  and apply a distally-directed force thereto. In certain embodiments, the arm  208 ,  210  can include a recess formed therein that can receive a distal end of the stabilizing shaft  810 , as described in connection with  FIG.  23 A- 29    below. Torque can then be applied by a user via the handle  806  to actuate the lock  218  and the stabilizing shaft  810  can prevent the torque from rotating the entire retractor assembly  106 . 
     The above described retractor assembly  106 , in combination with the support instrument or anchor extension  102  and implanted anchor  104 , can be used to, for example, widen an incision formed in a patient&#39;s skin and tissue to enable better access to a surgical site. By way of further example, in some embodiments these components can form an assembly that is anchored to a single implanted screw or anchor and provides medial-lateral tissue retraction to increase access for a variety of surgical procedures. Medially and laterally retracting skin and underlying tissue surrounding an incision can provide a wider opening and working channel between the tissue manipulating implements to access the patient&#39;s spine or intervertebral space. In some embodiments, the working channel can extend to encompass an adjacent anchor implanted in an adjacent vertebra. Once the tissue of the incision walls is retracted to form the working channel, any of a variety of surgical procedures can be performed by introducing one or more instruments through the working channel defined by the tissue manipulating implements of the retractor assembly. For example, procedures on the intervertebral disc space, such as disc replacement, discectomy, endplate preparation, fusion cage insertion, bone graft delivery, and the like can be performed by passing instruments or implants through the working channel. 
       FIGS.  10 - 19    illustrate an alternative embodiment of a surgical instrument assembly  1000  that includes a support instrument  1002  coupled to an implantable anchor  104  and a tissue retraction assembly  1006 . Also shown is an alternative embodiment of a driver  1008  that can be used to actuate locks  1010 ,  1012  that can selectively permit or prevent polyaxial movement of opposed tissue manipulating implements  1014 ,  1016  relative to a body  1018  of the retraction assembly  1006 . 
     As shown in  FIGS.  11 - 14   , the surgical instrument assembly  1000  is similar to the assembly  100  described above, including the basic configuration of the support instrument  1002  and the retractor assembly  1006 . The support instrument  1002  has an extended length, as shown in  FIG.  11   , to allow for a greater range of adjustment of the retractor assembly  1006  along the support instrument  1002 . Of course, any of a variety of lengths can be utilized for the support instrument  1002 . Moreover, the tissue manipulating implements  1014 ,  1016  have a different configuration. For example, the implement  1014  is not a planar tissue retracting blade, but instead has a pointed tip that can be useful in contacting bone. 
     Further, and as shown in  FIG.  12   , the tissue retractor assembly  1006  can include a protrusion  1204  extending from the body  1018  that can pivotably couple to an extension post  1206 . The extension post  1206  can pivot relative to the protrusion  1204  and the body  1018  about the axis Pi such that the extension post  1206  can be positioned at a variety of angles relative to the body  1018 . The extension post  1206  can be used to couple the tissue retractor assembly  1006  to an external structure, such as a surgical table, etc. In some embodiments, it can be advantageous to utilize an assembly that is anchored to a patient&#39;s body—and particularly to a single implanted bone screw or other anchor—as opposed to an external structure, such as a surgical table, etc. For example, anchoring relative to a patient&#39;s body can provide an advantage by maintaining a relative position between an access device and a patient even if a patient moves during a procedure. Moreover, it can be advantageous to anchor to a single bone screw or other anchor (e.g., as opposed to constructs that span across multiple implanted anchors), as this can reduce the footprint of instrumentation and can allow greater working space for other implements employed in a procedure. In some embodiments, however, it can be possible to also anchor the instruments and assemblies described herein to an external structure, such as a surgical table, etc. The extension post  1206  can be utilized in some such embodiments. In some embodiments where external fixation is employed, locking a support instrument or anchor extension against movement relative to an implanted anchor can be avoided such that some adjustment relative to an implanted anchor is possible in case of patient movement, etc. 
     As shown in  FIGS.  12  and  14   , the extension post  1206  can be locked at any of variety of angles relative to the body  1018  using a pawl  1402  that can selectively engage with any of a series of recesses  1208  or other complementary surface features formed on an end of the protrusion  1204 . A thumb slide  1210  can be coupled to the pawl  1402  and used to selectively advance the pawl into engagement with one of the recesses  1208  or withdraw it from contact to allow pivoting of the extension post  1206  relative to the protrusion  1204  of the body  1018 . 
       FIGS.  13  and  15 - 17    illustrate various embodiments of tissue manipulating implements, as well as a modular connection mechanism for easily swapping different implements. For example, arms  1302 ,  1304  of the tissue retractor assembly  1006  that are polyaxially coupled to the body  1018  can include slots  1306 ,  1308  formed at distal ends thereof that can receive proximal portions of the tissue manipulating implements  1014 ,  1016 . As shown in  FIG.  15   , for example, the tissue manipulating implement  1014  can include a proximal portion  1502  configured to be received within any one of the slots  1306 ,  1308  of the arms  1302 ,  1304 . The proximal portion  1502  of the arm can include a shape that is complementary to the slots  1306 ,  1308 , including features such as shoulders, ridges, overhangs, arms, etc. that can help prevent unintended separation of the implement  1014  from, e.g., the arm  1302 .  FIG.  15    also illustrates in greater detail one example of a non-planar tissue manipulating implement, including a shaft  1504  extending from the proximal portion  1502  and a laterally extending tapered distal tip  1506 . Such an implement can be useful for contacting a hard surface, such as bone. 
       FIGS.  16  and  17    illustrate various embodiments of planar tissue manipulating implements or blades that can be employed in various embodiments. The implement  1016  of  FIG.  16   , for example, can include a proximal portion  1602  configured to slide into any one of the slots  1306 ,  1308  of the arms  1302 ,  1304  of the tissue retractor assembly  1006 . The implement  1016  can further include a planar body having a plurality of fingers  1604  extending along a length thereof. The fingers  1604  can include distal tips  1606  that extend away from the tissue manipulating implement  1016 . Such features can be used, for example, to scrape tissue away from bone as the tissue manipulating implement  1016  is moved into position at a surgical site. 
       FIG.  17    illustrates a variety of alternative embodiments of generally planar tissue manipulating implements. These can include the implement  1702  having a straight distal edge  1704 , as well as the implement  1706  having a pointed protrusion  1708  formed on a distal edge thereof. The implement  1710  can be configured to mate with an extension, e.g., another embodiment of a planar implement such as the implements  1702 ,  1706 , to provide for an adjustable length tissue manipulating implement. A relative position of the implement  1710  and any extension coupled thereto can be maintained using a ratchet rack  1712  or other series of surface features and a pawl or other protrusion on the extension, as described above. The implement  1710  is also illustrated with a proximal portion  1716  for interfacing with a complementary slot formed on a modular tissue retractor assembly, as described above. Also illustrated is an alternative implement  1714 , which can include a similar proximal portion  1718  for interfacing with a slot on a tissue retractor assembly arm. The implement  1714  can include a plurality of fingers  1720  extending along a length thereof, along with curved distal tips, as described above in connection with the implement  1016 . 
       FIGS.  18 A- 19    illustrate the driver  1008  in greater detail. In some embodiments, the driver  1008  can include a housing  1802  disposed about a driveshaft  1804  that couples to a handle  1806  at a proximal end thereof. A distal end  1812  of the driveshaft  1804  can be configured to interface with a proximal end of a lock  1010 ,  1012  of the tissue retractor assembly  1006  to impart an actuating torque thereto. The driver  1008  can also include a stabilizing shaft  1810  disposed coaxially about the driveshaft  1804  and coupled to the housing  1802  and an interface  1808 . The interface  1808  can include opposed slots or cut-outs  1814 ,  1816  that can receive portions of one of the arms  1302 ,  1304  when the interface is disposed over one of the locks  1010 ,  1012  such that the distal end  1812  of the driveshaft  1804  engages the lock. A user can then counter brace against any tendency of the retractor assembly  1006  to rotate or otherwise move in response to turning the handle  1806  by holding the housing  1802  steady. More particularly, the rigid, non-rotational coupling between the housing  1802 , the stabilizing shaft  1810 , and the interface  1808 , in combination with the interface  1808  being unable to rotate relative to the arms  1302 ,  1304  due to the slots  1814 ,  1816 , can provide effective stabilization when a user holds the base  1802  while turning the handle  1806 . 
       FIGS.  20 A- 29    illustrate still another embodiment of a surgical instrument assembly  2000  including a surgical support instrument  2002  coupled to an anchor  104  and a tissue retractor assembly  2003 . The tissue retractor assembly  2003  is similar to those described above, including first and second opposed tissue manipulating implements  2006 ,  2008  that are polyaxially coupled to a body  2004  that slides along a length of the support instrument  2002 . The tissue manipulating implements  2006 ,  2008  are illustrated as curved bodies with at least the implement  2006  including an extension  2010  to adjust a length thereof. Further, the extension  2010  can include a plurality of fingers  2012  extending from a distal end thereof that can be used, for example, to scrape tissue from bone as the implement  2006  and extension  2010  is positioned at a surgical site. As with embodiments described above, the polyaxial joints  2014 ,  2016  can be selectively lockable to introduce a drag force when moving the tissue manipulating implements  2006 ,  2008  or to completely prevent their movement relative to the body  2004  of the retractor assembly  2003 . 
     As shown in the figures, the tissue retractor assembly  2003  can slidingly couple to the support instrument  2002  via a slot  2020  formed in the body  2004  that can receive a complementary-shaped ridge or protrusion  2022  formed along a length of the support instrument  2002 . For example, the body  2004  of the tissue retractor assembly  2003  can be aligned over the support instrument  2002  and advanced downward or distally such that the ridge  2022  is received within the slot  2020 , as shown in  FIG.  21   . In order to allow free sliding of the support instrument  2002  and the retractor assembly  2003 , a lock lever  2018  can be moved about a pivot axis to clear a pawl  2202  from a ratchet rack  2204  formed on the support instrument  2002 , as shown in  FIG.  22 A . When a desired position of the retractor assembly  2004  relative to the support instrument  2002  is reached (e.g., a height aligned with a skin surface of a patient or at some desired distance above the skin surface), the lock lever  2018  can be moved to engage the pawl  2202  with the ratchet rack  2204 , thereby locking the two components relative to one another, as shown in  FIG.  22 B . Of course, in various embodiments the lock lever  2018  can be biased and/or the pawl and ratchet rack can have complementary shapes that allow for movement in one direction, e.g., downward or distally along a length of the support instrument  2002 , while resisting movement in an opposite direction. 
     As shown in  FIGS.  23 A- 29   , tissue manipulating implements can be modularly coupled to the tissue retractor assembly  2003 . For example, a driver  2300  can be coupled to a proximal end of the tissue manipulating implement  2006  as shown in  FIGS.  23 A and  23 B . Note that a distal end of a driveshaft  2302  of the driver  2300  can interface with a lock  2306  of the tissue manipulating implement  2006 , and a distal end of a stabilizing shaft  2304  can be received within a recess  2308  formed in a proximal portion of the implement  2006 , such as a connecting arm that couples to the lock  2306 . With the implement  2006  coupled to the driver  2300 , the driver can position the implement such that a ball-shaped distal portion of the lock  2306  is received within a socket formed in the body  2004  of the tissue retractor assembly  2003 , as shown in  FIGS.  24  and  25   . The tissue manipulating implement  2006  can be moved polyaxially relative to the body  2004 , support instrument  2002 , and anchor  104  using the driver  2300  or direct manipulation by the user. Such polyaxial movement is illustrated by arrows  2502  in  FIG.  25   . Further, a length of the tissue manipulating implement  2006  can be adjusted by translating the extension  2010  relative thereto in a proximal or distal direction, as indicated by arrows  2602  in  FIG.  26   . 
     In some embodiments, a user can employ the driver  2300  coupled to the tissue manipulating implement  2006  in place of a cobb or other surgical instrument for separating muscle or other tissue from bone. For example, a user could utilize the plurality of fingers or teeth  2012  at a distal end of the tissue manipulating implement or blade  2006  to scrape tissue from bone prior to coupling the implement to the body  2004 . In still other embodiments, the implement  2006  can be utilized in a similar manner after coupling to the body  2004 , but adjusting a position of retractor assembly  2003  and polyaxially moving the implement  2006  to separate tissue from bone. 
     When a desired position of the tissue manipulating implement  2006  is achieved, a user can rotate a handle of the driver  2300  as shown at arrow  2702  in  FIG.  27    to actuate the lock  2306  as described above and set a position of the implement  2006 . The driver  2300  can be decoupled from the implement  2006 , coupled to the opposing implement  2008 , and the process can be repeated, including polyaxial positioning of the implement, as shown by arrows  2902  in  FIG.  29   , and selective locking against polyaxial movement by actuating the driver, as shown by arrow  2904  of  FIG.  29   . 
     In the embodiments described above, movement of the tissue manipulating implements any of toward and away from one another, e.g., to accomplish tissue retraction, can be accomplished using, for example, a driver coupled to the tissue manipulating implement or direct manipulating by a user.  FIGS.  30 - 39    illustrate alternative embodiments that utilize a forceps or plier-like design including a pair of opposed handles that can control movement of opposed tissue manipulating implements relative to one another. 
     Turning to  FIG.  30   , for example, a surgical instrument assembly  3000  is illustrated that includes a support instrument  3002 , similar to the instruments described above. A tissue retractor  3004  is coupled to the support instrument  3002  and includes first and second tissue manipulating implements  3006 ,  3008 . The retractor  3004  also includes first and second handles  3010 ,  3012  disposed on an opposite side of the support instrument  3002  from the tissue manipulating implements  3006 ,  3008 . The retractor  3004  can be coupled to the support instrument  3002  in a manner that permits the retractor to move polyaxially relative to the support instrument, as shown by arrows  3014 . As explained in more detail below, movement of the opposed handles  3010 ,  3012  toward or away from one another can cause corresponding movement of the tissue manipulating implements  3006 ,  3008  toward or away from one another. In some embodiments, the handles  3010 ,  3012  can be biased toward to the illustrated open configuration by a spring  3016  or other biasing element. In some embodiments, an open configuration of the handles can correspond to a closed configuration of the tissue manipulating implements  3006 ,  3008  wherein the implements are near to one another. In such an embodiment, urging the handles  3010 ,  3012  toward one another against the biasing force of the spring  3016  can cause the tissue manipulating implements  3006 ,  3008  to pivot away from one another, e.g., to retract tissue forming the walls of an incision. Also shown in  FIG.  30    is a lock  3018  that can be used to selectively maintain a position of the opposed handles  3010 ,  3012  (and thus the opposed tissue manipulating implements  3006 ,  3008 ) relative to one another. 
       FIG.  31    illustrates one embodiment of a method for coupling the retractor  3004  to the support instrument  3002 . The retractor  3004  can include a joint  3102  having a lumen  3103  formed therethrough that can be sized to receive a proximal portion of the support instrument  3002 . The joint  3102  can also include a locking element  3104 , such as a spring-biased locking pin, protrusion, or other feature, that can engage a complementary recess or other feature formed in the support instrument  3002  to selectively lock a position of the retractor  3004  along a length of the support instrument. The joint  3102  can include a ball-shaped distal portion  3106  that can be seated within a socket  3108  of the retractor  3004 , thereby providing for polyaxial movement of the tissue manipulating implements and the opposed handles relative to the joint  3102  and the support instrument  3002  coupled thereto. The polyaxial movement can be selectively locked in a variety of manners. For example, in some embodiments movement of the opposed handles  3010 ,  3012  can squeeze the ball-shaped distal portion  3106  of the joint  3102 , thereby locking the retractor  3004  against movement relative to the joint  3102  and support instrument  3002 . In other embodiments, however, a separately engageable locking mechanism for polyaxial movement can be included. 
       FIG.  32    illustrates an alternative embodiment in which a retractor  3200  with opposed actuating handles  3202 ,  3204  can be configured for modular connection with any of a plurality of tissue manipulating implements  3206 ,  3208 . For example, a distal portion of the retractor  3200  can include recesses  3210 ,  3212  that can be configured to receive proximal ends of any of the various tissue manipulating implements  3206 ,  3208 . Any of a variety of retention mechanisms can be utilized to secure the tissue manipulating implements  3206 ,  3208  to the retractor  3200 , including locking pins, clips, magnets, etc. As described above, the various tissue manipulating implements  3206 ,  3208  can have any of a variety of shapes and sizes, and can be configured to retract soft tissue, scrape or separate soft tissue from bone, contact bone, etc. 
       FIG.  33    illustrates another embodiment of a retractor  3300  that includes opposed tissue manipulating implements  3302 ,  3304  and opposed actuating handles  3301 ,  3303 . The tissue manipulating implements  3302 ,  3304  can be configured to couple with any of a variety of extensions  3306  to provide adjustable length to the implements  3302 ,  3304 . As described above, a relative position between an implement and an extension coupled thereto can be maintained in a variety of manners. For example, the extension  3306  can include a ratchet rack  3308  or other series of surface features formed thereon that can be engaged by a pawl, protrusion, or other surface feature formed on the tissue manipulating implement  3302 ,  3304 . 
       FIGS.  34 A- 35    illustrate operation of the above-described retractor  3004  in greater detail. As shown in  FIGS.  34 A and  34 B , moving the opposed handles  3010 ,  3012  toward one another in the direction of arrows  3402 ,  3404  can cause corresponding movement of the opposed tissue manipulating implements  3006 ,  3008  away from one another in the direction of arrows  3406 ,  3408 . Accordingly, a user squeezing the opposed handles  3010 ,  3012  toward one another can cause the tissue manipulating implements  3006 ,  3008  to move apart, thereby retracting tissue abutting outer surfaces of the tissue manipulating implements. The lock  3018  can be engaged to maintain a position of the handles  3010 ,  3012  close to one another against the bias force of the spring  3016  or any compressive force applied to the tissue manipulating implements by retracted tissue. 
     When a user wishes to release any retracted tissue, the lock  3018  can be released by moving it in the direction of arrow  3502  shown in  FIG.  35   . This can allow the opposed handles  3010 ,  3012  to move in the direction of arrows  3504 ,  3506  away from one another. Such movement can cause corresponding movement of the tissue manipulating implements  3006 ,  3008  toward one another in the direction of arrows  3508 ,  3510 . Such movement can return retracted tissue to its original position and return the tissue manipulating implements to a more streamlined configuration that can be used to insertion into, or withdrawal from, an incision. 
       FIGS.  36 - 39    illustrate an alternative embodiment of a retractor  3600  including opposed tissue manipulating implements  3602 ,  3604  and actuating handles  3606 ,  3608 . The retractor  3600  can have a slightly different configuration from the retractor  3004  described above and can provide for additional movements of the tissue manipulating implements relative to one another. For example, in the illustrated embodiment the retractor  3600  can move the tissue manipulating implements  3602 ,  3604  any of toward and away from one another by corresponding movement of the actuating handles  3606 ,  3608 , but can also allow for toeing of the tissue manipulating implements relative to one another using the rotating actuators  3624 ,  3626 . 
     As can be seen in the partially transparent views of  FIGS.  37  and  38   , the rotating actuators  3624 ,  3626  can include threads that mesh with gears  3704 ,  3804  to transfer rotation of the actuators into transverse rotation of the arms  3706 ,  3707  that couple to the tissue manipulating implements  3602 ,  3604  via slots  3806 ,  3807 , as described above. Rotation of the arms  3706 ,  3707  can cause the coupled tissue manipulating implements  3602 ,  3604  to toe relative to one another such that distal ends thereof move any of toward and away from one another to a greater degree than proximal ends thereof such that the opposed tissue manipulating implements no longer extend parallel to one another. 
     In addition to toeing movement, the tissue manipulating implements  3602 ,  3604  can be moved any of toward and away from one another by movement of the opposed handles  3606 ,  3608 . Each handle and associated tissue manipulating implement can pivot relative to a central body  3610 . Further, a rotating lock  3612 ,  3614  can be provided to selectively lock a position of each handle and tissue manipulating implement relative to the body  3610 . Further, a proximal portion of each handle  3606 ,  3608  can be pivoted relative to a distal portion thereof in order to, for example, reduce a footprint of the retractor  3600  when the handles are not in use or to angle the handles around surrounding instrumentation. A ratchet  3616 ,  3618  or other series of recesses or surface features can be formed around a curved proximal surface of a distal portion of each handle  3606 ,  3608  and the proximal portion of each handle can be pivotably coupled thereto. A pawl  3710  or other similar component in each arm can be biased by a spring  3712  to interface with the ratchet  3616 ,  3618 . Moreover, a sliding lever  3620 ,  3622  can be coupled to the pawl in each handle to allow a user to selectively draw the pawl away from the ratchet and permit pivoting movement of the proximal portion of each handle relative to a distal portion thereof 
     The retractor  3600  can be polyaxially coupled to a support instrument in a manner similar to the retractor  3004  described above. For example, a support coupler  3630  can be coupled to the body  3610  using a selectively lockable polyaxial joint  3628 , e.g., a joint similar to the ball-and-socket locking joints described herein. The support coupler  3630  can include lumen or recess  3703  configured to couple with an elongate body of a support instrument, as well as a spring biased movable pawl or protrusion  3702  that can engage a complementary recess or other feature formed along a length of the support instrument to selectively lock a position of the retractor  3600  relative to the support instrument. In some embodiments, a lever  3705  can be provided to aid a user in selectively disengaging the locking feature  3702  to allow free sliding movement of the retractor  3600  relative to a support instrument. In addition to locking the support coupler  3630  at a desired position along a length of a support instrument using the protrusion  3702 , the polyaxial joint  3628  can be selectively locked to prevent movement of the tissue manipulating implements  3602 ,  3604  and handles  3606 ,  3608  relative to the support coupler  3630 . As with other embodiments described herein, any of a variety of modular tissue manipulating implements  3602 ,  3604 ,  3902  can be utilized with the retractor  3600 . 
       FIGS.  40 - 61    illustrate still other embodiments of a tissue retractor assembly based on a concept of a modular scaffold that can be added to as desired and coupled to a support instrument that is coupled to a single implantable anchor. For example,  FIG.  40    illustrates one example of such a retractor assembly  4000  that includes a base  4004  coupled to a support instrument  4002  that is coupled to an implantable anchor, such as a bone screw. The base  4004  can be selectively locked at a desired position along a length of the support instrument  4002  using, for example, a pivoting lever  4018  having a pawl or locking pin coupled to one end thereof that can engage a complementary feature on the support instrument  4002 . A first tissue manipulating implement  4006  can be coupled to the base  4004  and a second tissue manipulating implement  4008  can be coupled to an opposite side of the base such that the two tissue manipulating implements are disposed opposite one another. A position of the tissue manipulating implement  4006  can be adjusted along a lateral adjustment shaft  4007  extending therefrom to allow the implement  4006  to translate toward or away from the opposed implement  4008 . The implement  4006  can also be rotated relative to the implement  4008  and locked at a desired position using a lock  4010 . The second implement  4008  can be coupled to an extension shaft  4009  extending from the base  4004 . The implement can be positioned along a length of the shaft  4009  and rotated thereabout to a desired position, then a locking screw  4012  can be used to prevent further movement of the implement  4008  relative to the base  4004 . As with the embodiments described above, a number of additional features are possible, including, for example, the use of an extension  4016  to adjust a length of either of the first and second tissue manipulating implements  4006 ,  4008 . 
       FIGS.  41 - 50    illustrate one embodiment of a method for constructing the tissue retractor assembly  4000  shown in  FIG.  40   . As shown in  FIG.  41   , for example, the base  4004  can be coupled to the support instrument  4002  by passing the base down or distally in the direction of arrows  4102  such that a proximal portion of the support instrument  4002  is received within a lumen formed in the base. The lock  4018  can be utilized to set a desired position of the base  4004  along a length of the support instrument  4002 . As shown in  FIG.  42   , the tissue manipulating implement  4008  can then be coupled to the shaft  4009  that extends from one side of the base  4004 . The implement  4008  can be translated along a length of the shaft  4009  in the direction of arrows  4202 , as well as rotated about the shaft. When a desired positon is reached, the locking screw  4012  can be rotated in the direction of arrow  4204  to lock a position of the implement  4008  relative to the shaft  4009 . 
     The tissue manipulating implement  4006  and its extension  4016  can be assembled in a different manner. As shown in  FIG.  43   , for example, the tissue manipulating implement  4006  and the lateral adjustment shaft  4007  extending therefrom can be coupled to an insertion instrument  4302  by advancing the instrument in the direction of the arrow  4304  such that a distal end of the instrument interfaces with (e.g. receives, extends into, or otherwise couples with) a mating post  4306  coupled to the shaft  4007 . Separately, a second instrument  4402  can couple to the extension  4016  by advancing a distal end of the instrument in the direction of arrow  4404 , as shown in  FIG.  44   . The implement  4006  and extension  4016  can be joined together by sliding the extension  4016  in the direction of arrow  4502  in  FIG.  45    to create the tissue manipulating implement assembly  4500 . 
       FIG.  46    illustrates one embodiment of a method for coupling the tissue manipulating implement assembly  4500  to the base  4004 . Specifically, the lateral adjustment shaft  4007  of the assembly  4500  can be inserted through a through-hole  4602  formed in a rotating portion  4604  of the base  4004 . As the shaft  4007  is inserted into the through-hole  4602 , a ridge  4606  formed along a distal portion of the instrument  4302  can urge the lock  4010  against a biasing force away from the rotating portion  4604  of the base  4004 , thereby freeing motion of the rotating portion relative to the base  4004 . Accordingly, once inserted as shown in  FIG.  47   , a position of the tissue manipulating implement  4006  can be adjusted in multiple dimensions by moving the assembly  4500  relative to the base  4004  in the direction of any of the arrows  4702 ,  4704 ,  4706  in  FIG.  47   . 
     Once a desired position of the implement  4006  is achieved, the instrument  4302  can be rotated in the direction of arrow  4804  in  FIG.  48    to cause the ridge  4606  to move out of engagement with the lock  4010 . The lock  4010  can then be urged into contact with the rotating portion  4604  of the base  4004  by a biasing force, thereby preventing further rotation of the portion  4604  relative to the base  4004 . In some embodiments, the lock  4010  can also be configured to lock the lateral adjustment shaft  4007  against translation through the through-hole  4602 , such that the lock  4010  can set a lateral position of the implement  4006  as well as an angle of rotation relative to the base  4004 . In other embodiments, however, a separate lock can be employed to selectively permit or prevent translation of the shaft  4007  (and implement  4006  coupled thereto) through the through-hole  4602 . 
     As shown in  FIG.  49   , the instrument  4302  can be separated from the implement  4006  by pressing a release button  4902  to free a distal end of the instrument from the mating post  4306  and withdrawing the instrument in the direction of arrow  4904 . The instrument  4402  can be separated from the extension  4016  by, for example, depressing a release button  5001  in the direction of arrow  5002  and withdrawing the instrument  4402  in the direction of arrow  5004 . 
       FIGS.  51 - 54    illustrate an alternative embodiment of a retractor assembly  5100  in which a support instrument  5002  coupled to an implantable anchor can be coupled to a modular scaffold base  5004  that includes a ball-and-socket polyaxial joint  5005  to permit polyaxial movement of a tissue manipulating implement  5006  relative to the base. As with embodiments described above, the tissue manipulating implement  5006  can include an extension  5016  coupled thereto that can translate relative to the implement to adjust an overall length thereof. A desired position of the extension  5016  relative to the implement  5006  can be maintained using a ratchet rack  5008  and spring pawl  5010  or other similar cooperating components. 
       FIGS.  52 - 54    illustrate one embodiment of a method for constructing the modular scaffold retractor assembly  5100 . As described above, a modular scaffold base  5004  can be coupled to a support instrument  5002  that is itself coupled to an implantable anchor. The tissue manipulating implement  5006 , which can include a ball-shaped proximal portion  5204  configured to be received within a socket  5202  formed in the base  5004 , can be coupled to an instrument  5206 . Further, the extension  5016 , which can be coupled to another instrument  5304 , can be slidably coupled to the implement  5006  as shown by arrow  5208  in  FIG.  52   . The instruments  5206  and  5304  can then be used to guide the implement  5006  and extension  5016  toward the base  5004  in the direction of arrow  5302  to seat the ball-shaped portion  5204  in the socket  5202 , as shown in  FIG.  53   . The tissue manipulating implement  5006  can then be moved polyaxially relative to the base  5004 , as shown by the arrows  5402  in  FIG.  54   . Further, a position of the extension  5016  relative to the implement  5006  can be adjusted by moving the extension in the direction of arrows  5406  using instrument  5304 . Once a desired position is achieved, the polyaxially joint  5004  can be locked using the instrument  5206 , a position of the extension  5016  relative to the implement  5006  can be locked, and both instruments  5206 , 5304  can be separated from the retractor assembly  5100 . 
       FIGS.  55 - 57    illustrate alternative embodiments for coupling the tissue manipulating implement  4008  that is disposed opposite the tissue manipulating implement  4006 . For example, the retractor  5500  of  FIG.  55    includes a base  5504  that can couple to a support instrument  5502  and can include a modular coupling  5506  that can be used to couple any of a variety of tissue manipulating implements  5508  to the base. For example, the modular coupling  5506  can include a protrusion extending from the base and each of the modular tissue manipulating implements  5508  can include a complementary-shaped recess  5510  formed therein to permit coupling with the base  5504 . As described above, a number of variations on this type of coupling are also possible. 
     The retractor assembly  5600  of  FIG.  56    is similar to the retractor  4000  of  FIG.  40    and employs a shaft  5606  that extends from a base  5604  that is coupled to a support instrument  5602 . The tissue manipulating implement  5608  is coupled to the shaft  5606  by a link  5610  that can be selectively tightened about the shaft  5606  by a locking screw  5612 . Accordingly, when the screw  5612  is appropriately loosened, the implement  5608  and link  5610  can be translated along the shaft  5606  in the direction of arrows  5614  and/or rotated about the shaft until the locking screw  5612  is rotated in the direction of arrows  5616  to a sufficient degree to prevent movement between the link  5610  and the shaft  5606 . 
     The retractor assembly  5700  of  FIG.  57    illustrates still another embodiment in which a base  5704  coupled to a support instrument  5702  includes a shaft  5706  extending therefrom that includes a ratchet rack, gear teeth, or other series of surface features formed thereon. A tissue manipulating implement  5708  can include a proximal portion  5710  disposed around the shaft  5706  and can include an actuator  5712 , such as a gear, etc. Rotation of the actuator  5712  in the direction of arrow  5716  can cause the tissue manipulating implement  5708  to advance laterally along the shaft  5706  in the direction of the arrow  5714 . Such advancement can be utilized, for example, to retract tissue abutting against the tissue manipulating implement  5708 . 
     In some embodiments, a modular scaffold-based tissue retractor assembly can be further expanded to perform other operations, including, for example, vertebral distraction.  FIGS.  58 - 61    illustrate one embodiment of a tissue retractor assembly  5800  that can be used for such a purpose. As shown in  FIG.  58   , the retractor assembly  5800  can include a base  5804  coupled to a support instrument  5802  that is coupled to an implanted anchor (not shown). As in the embodiments described above, the base  5804  can include a shaft  5806  extending from one end thereof for coupling with a tissue manipulating implement (not shown), as well as a socket  5808  for coupling with a second tissue manipulating implement (not shown). 
     Also coupled to the base  5804  is a distraction rack  5810 , which can secure to the base  5804  using a lock  5817 , such as a spring-biased locking pin or pawl. A post  5812  is coupled to the distraction rack  5810  and a screw extension receiver  5814  is coupled to the post. The post  5812  can be translated along a length of the distraction rack  5810  in the direction of arrows  5820  using a rotating actuator  5816  that can be coupled to, e.g., a gear that interfaces with gear teeth or other surface features formed along a length of the distraction rack. The screw extension receiver  5814  can be translated along the post  5812  in the direction of arrows  5822 , rotated about the post in the direction of arrows  5824 , and rotating about an axis transverse to the post in the direction of arrows  5826 . Further, a cam  5818  or other lock can be included to lock any or all of the above-listed degrees of freedom of the receiver  5814 . 
     An exemplary method of using the assembly  5800  for distraction is illustrated in  FIGS.  59 - 61   . As shown in  FIG.  59   , the method can include coupling the distraction rack  5810 , post  5812 , and receiver  5814  to the scaffold base  5804  that is coupled to a support instrument  5802 . The support instrument  5802  can be coupled to an implantable anchor, such as a pedicle screw implanted in a patient&#39;s first vertebra. The support instrument can be locked to the anchor such that there is no relative movement between these two components. Similarly, the base  5804  can be locked against movement relative to the support instrument  5802 . Further, the receiver  5814  can be positioned and locked against movement such that it is aligned with a second implantable anchor implanted in an adjacent vertebra of the patient. 
       FIG.  60    illustrates insertion of a shank extension instrument  6002  through the receiver  5814  to engage and lock on to the second implantable anchor. Once all components are locked to create a rigid construct, the actuator  5816  can be rotated in the direction of arrow  6102  to advance the post  5812  and receiver  5814  along the distraction rack  5810  in the direction of arrow  6104 . Because the construct is locked against movement relative to each of the implanted anchors, movement of the post  5812  and receiver  5814  can cause corresponding movement of the shank extension  6002  and second implanted anchor, thereby distracting the adjacent vertebra and urging them away from one another. 
       FIGS.  62 A- 72    illustrate still other embodiments wherein tissue manipulating implements are coupled to polyaxial receiver heads that are coupled to implantable anchors. In such embodiments, the above described support instruments and tissue retractor assemblies can be eliminated, as tissue retraction can be accomplished using the tissue manipulating implements coupled directly to polyaxial receiver heads. Indeed, embodiments of receiver heads often include extension tabs to aid in various procedures that are broken off or otherwise removed from the receiver heads prior to finishing a procedure. Such tabs could serve as a mounting location for tissue manipulating implements to perform tissue retraction. 
       FIGS.  62 A and  62 B  illustrate one embodiment of an assembly  6200  that can include a first anchor  6202  and a second anchor  6204  that each can be coupled to a polyaxial receiver head  6206 ,  6208 . Further, a first tissue manipulating implement  6210  can be coupled to the receiver head  6206  and a second tissue manipulating implement  6212  can be coupled to the receiver head  6208 . The tissue manipulating implements can be arranged in a variety of manners but, in one embodiment in which the anchors  6202 ,  6204  are implanted along or parallel to a patient&#39;s spine or midline axis, the implement  6210  can be configured to perform lateral tissue retraction and the implement  6212  can be configured to perform medial tissue retraction. 
     An exemplary method for using the assembly  6200  described above is illustrated in  FIGS.  63 - 72   . As shown in  FIG.  63   , for example, the anchors  6202 ,  6204  can be implanted in a patient&#39;s vertebrae using extension tubes  6302 ,  6304  and drivers  6306 ,  6308 . Following implantation, the drivers  6306 ,  6308  can be removed. Further, markings  6310  formed on the extensions  6302 ,  6304  can be utilized to measure a depth of tissue from the one surface that require retraction to facilitate further operations. 
     Appropriately sized tissue manipulating implements  6210  and  6212  can be selected for each of the receiver heads  6206 ,  6208 , as shown in  FIGS.  64  and  65   . As noted above, any of a variety of sizes and shapes of tissue manipulation implements can be interchanged as desired based on factors such as depth of tissue, type of tissue, etc. After selecting appropriate tissue manipulation implements  6210 ,  6212 , the implements can be coupled to the receiver heads  6206 ,  6208  that are to be coupled to the implanted anchors  6202 ,  6204 . For example, a first tissue manipulation implement  6210  can be coupled to an extension tab  6704  of a receiver head  6206  using a locking screw  6702  and a second tissue manipulation implement  6212  can be coupled to an extension tab  6606  of a receiver head  6208  by turning a locking screw  6602  in the direction of arrow  6604 , as shown in  FIGS.  66  and  67   . 
     The receiver heads  6206 ,  6208  with tissue manipulating implements  6210 ,  6212  coupled thereto can then be coupled to the implanted anchors  6202 ,  6204  and the extension posts  6302 ,  6304  can be removed, as shown in  FIGS.  68  and  69   . Polyaxial lockout posts  7002 ,  7004  can then be inserted as shown in  FIG.  70    to provide levers for manipulating the orientation of the receiver heads  6206 ,  6208  and tissue manipulating implements  6210 ,  6212  coupled thereto. For example, a user can grasp the lockout posts  7002 ,  7004  to move the receiver heads  6206 ,  6208  and tissue manipulation implements  6210 ,  6212  polyaxially relative to the implanted anchors  6202 ,  6204 , as shown by arrows  7102 ,  7104  in  FIG.  71 A . Such movement can also include moving lateral and medial tissue manipulation implements  6210 ,  6212  away from one another to perform medial-lateral tissue retraction, as shown by arrows  7110 ,  7112  in  FIG.  71 B . When a desired position is reached (e.g., including desired tissue retraction), the lockout posts  7002 ,  7004  can be rotated in the direction of arrows  7106 ,  7108  in  FIGS.  71 A and  71 B  to lock the receiver heads  6206 ,  6208  and tissue manipulation implements coupled thereto against movement relative to the implanted anchors  6202 ,  6204 . 
     Following completion of a spinal procedure, extension tabs of polyaxial screw receiver heads are often broken off or otherwise removed to leave a lower profile implant in the patient. As shown in  FIG.  72   , in some embodiments the tissue manipulation implements  6210 ,  6212  coupled to the extension tabs  6606 ,  6704  can be utilized to break the extension tabs free from the receiver heads  6206 ,  6208 . For example, a proximal portion of the tissue manipulation implements  6210 ,  6212  can be grasped and bent in the direction of arrows  7202 ,  7204  to break the tissue manipulation implements and extension tabs coupled thereto away from the receiver heads. 
       FIGS.  73 - 78 B  illustrate various embodiments of instruments for distracting adjacent vertebrae and their use with the support instruments and retractor assemblies described herein. For example,  FIG.  73    illustrates one embodiment of a distractor  7300  that includes a rack  7302  and two interfaces  7304 ,  7306  for coupling with any of an anchor or an instrument coupled to an anchor. The interface  7304  can be anchored to one end of the rack  7302  and the interface  7306  can be coupled to the rack  7302  via a pawl, cog, gear, or other feature that can interface with a series of teeth, recesses, or other features formed along a length of the rack. A thumbwheel  7308  can be coupled to the cog or gear to control movement of the interface  7306  along the rack  7302 . 
     As shown in  FIGS.  74 A- 75   , the interfaces  7304 ,  7306  can be coupled to anchors implanted in adjacent vertebrae and the thumbwheel  7308  can be rotated to distract the vertebrae by moving the interfaces away from one another along the rack  7302 . In the illustrated embodiment, the interfaces can couple to the anchors implanted in the adjacent vertebrae via an extension tower and/or support instrument as described herein that can be coupled to the implanted anchors and locked against movement relative thereto. Accordingly, as shown in  FIGS.  74 B and  75   , the interface  7304  can couple to a proximal end of an extension tower  7402  that is coupled to an anchor  7404  implanted in a first vertebra and the interface  7306  can couple to a proximal end of a support instrument  7406  that is coupled to a second anchor  7408  implanted in a second vertebra. As shown in  FIG.  74 B , the interfaces  7304 ,  7306  can include distal ends configured to couple with features formed on proximal ends of the extension tower  7402  and support instrument  7406 . Also note that a retractor assembly  7410  is coupled to the support instrument  7406  to provide, e.g., medial-lateral tissue retraction during the procedure. 
     Once the distraction instrument  7300  is coupled to the anchors  7404 ,  7408  implanted in adjacent vertebrae via the extension tower  7402  and support instrument  7406 , and the tower and support instrument are locked against movement relative to the anchors, the thumbwheel  7308  or other distraction actuator can be rotated as shown by arrow  7502  in  FIG.  75   . This can cause the interface  7306  to move away from interface  7304  along the rack  7302 , thereby causing corresponding distraction of the anchors  7404 ,  7408  and the adjacent vertebrae they are implanted into, as shown by arrows  7504 ,  7506 . 
     In an alternative embodiment illustrated in  FIGS.  76 - 78 B , a forceps-like distractor  7602  can be utilized instead of the distractor  7300  described above. Furthermore, the distractor  7602  can include interfaces  7702 ,  7704  that can be configured to abut against the extension tower  7402  and support instrument  7406  laterally at a position along a length thereof, rather than interfacing with a proximal end thereof, as described above. The method of operation can be similar to that described above, wherein the extension tower  7402  and support instrument  7406  can be locked to prevent movement relative to the implanted anchors  7404 ,  7408 . The interfaces  7702 ,  7704  can then be inserted into the working channel provided between the opposed tissue manipulating implements of the retractor assembly  7410  and opposed handles  7802 ,  7804  of the distractor  7602  can be urged toward one another, as shown by the arrows  7806 ,  7808  of FIG.  78 A. This can cause the interfaces  7702 ,  7704  to move apart from one another, contact the tower  7402  and support instrument  7406 , and urge the two components away from one another, as shown by arrows  7810 ,  7812  of  FIG.  78 B . Given the rigid implantation of the anchors  7404 ,  7408  in adjacent vertebrae (not shown), the vertebrae can be drawn away from one another in the same manner. 
       FIGS.  79 - 101 E  illustrate further embodiments of surgical instrument assemblies. For example,  FIGS.  79 - 81    illustrate an embodiment of a surgical retractor  7900  that includes alternative mechanisms for controlling movement of retractor arms, and tissue manipulating implements coupled thereto. The retractor  7900  can be configured to couple to a support instrument, such as the instrument  102  described above, in a similar manner as the retractor  106  described above, e.g., using a recess  7902  and a spring-biased protrusion or pawl  7904 . Rather than the fixed polyaxial joints  212 ,  214 , however, the retractor  7900  can include polyaxial joints  7906 ,  7908  that are configured to translate toward or away from the recess  7902  using, e.g., a lead screw mechanism. In such a configuration, the joints  7906 ,  7908 , as well as any tissue manipulating implements coupled thereto, can be moved toward or away from one another (e.g., medially or laterally relative to a patient) to increase or decrease a space between tissue manipulating implements. 
     In the illustrated embodiment, each joint  7906 ,  7908  is threadedly coupled to a respective rod  7910 ,  7912  such that rotation of the rod effects translation of the respective joint along a length of the rod. A gear  7914 ,  7916  disposed about each respective rod  7910 ,  7912  can interact with a drive gear  7918 ,  7920  that is coupled to or formed integrally with a drive feature  7922 ,  7924 . A user can rotate the drive feature  7922 ,  7924  to cause translation of the respective joint  7906 ,  7908  along a length of the retractor body  7926 . In the illustrated embodiment, positions of each joint  7906 ,  7908  can be controlled independently of one another using the two drive features  7922 ,  7924 . The above-described joint translation mechanisms are shown in greater detail in the partially-transparent detail view of  FIG.  80    and the cross-sectional detail view of  FIG.  81   . 
     The joints  7906 ,  7908  of the retractor  7900  also include an alternative embodiment of a polyaxial movement mechanism.  FIG.  82   , for example, illustrates a partially transparent detail view of the joint  7906 . The joint can include an arm  8202  having a ball  8204  (that can be incompressible) formed at one end thereof and an opposite end configured for attachment to a tissue manipulating implement (e.g., either directly or through another arm or other linkage). The ball  8204  can be captured between a base  8206  and a cap  8208  such that the ball cannot be removed or passed through a hole  8210  formed in the cap. The joint mechanism can be biased to lock the ball  8202  from moving relative to the base  8206  and cap  8208 , and a release button  8212  can be configured to free the ball when depressed inward toward the base and cap. Such an arrangement can provide an advantage in that actuation of a single button or lever can control locking of the ball  8204  and arm  8202 . Further, the button  8212  can be biased such that no actuation is needed to tighten or lock the ball and a single input from a user (e.g., inward depression of the button) can selectively free the ball for polyaxial movement. 
     The cross-sectional view of  FIG.  83    illustrates one embodiment of a mechanism for effecting the behavior of the button  8212  and joint  7906  described above. A compression member  8302  can be disposed within a recess formed by the base  8206  and cap  8208  and includes a surface that is complementary to the ball  8204 . The compression member  8302  can be configured to translate up and down in the plane of the figure and can be biased upward in the plane of the figure by a biasing element  8304 , such as a spring, Belleville washer, etc. The button  8212  can be coupled to a tongue  8306  having an angled end  8308  that engages a ramp  8310  formed on the compression member  8302 . As the button  8212  is depressed into the base  8206  (i.e., to the right in the plane of the figure) the angled surfaces  8308 ,  8310  can interact to cause the compression member  8302  to move away from the ball  8204  (i.e., down in the plane of the figure), thereby freeing the ball to articulate relative to the compression member, cap, and base of the joint  7906 . Upon release of the button  8212 , the biasing element  8304  will urge the compression member  8302  toward the ball  8204 , thereby locking its position relative thereto and causing the button  8212  to move outward from the base  8206  to its starting position. 
       FIGS.  84 - 86    illustrate another embodiment of a retractor  8400  that is similar to the retractor  7900  but utilizes a single drive feature  8402  to move both joints  8404 ,  8406  toward or away from a center thereof. Each joint  8404 ,  8406  includes a threaded shaft extending therefrom (only the shaft  8405  extending from joint  8406  is shown in the figure). These threaded shafts are received within threaded sockets  8407 ,  8409  that are coupled to gears  8410 ,  8412 . The gears  8410 ,  8412  mesh with gear  8408  that is coupled to the single drive feature  8402  such that turning the drive feature can cause rotation of the sockets  8407 ,  8409  and translation of the joints  8404 ,  8406  relative to the retractor body  8414 . One advantage of the movement mechanisms of the retractors  7900  and  8400  is that there is no need for a separate mechanism to control positional lockout of the joints or to control directionality of the movement of any attachments coupled thereto. The lead screw mechanisms can effectively hold the joints in place when not being actuated and movement direction can be changed by reversing direction of rotation of the drive feature(s). 
       FIGS.  87 - 92 B  illustrate various embodiments of actuating instruments or drivers that can be used with the retractors and surgical assemblies described herein.  FIG.  87    illustrates one embodiment of an actuating instrument  8700  that can be used to lockout a polyaxial joint, such as the joint  212  of the retractor  106  described above. The instrument can function similarly to the driver  1008  described above to rotate the lock  216  of the joint  212 , for example. Similar to the driver  1008 , the driver  8700  can include a driveshaft  8702  with a distal end configured to be received within a drive feature of the lock  216 , and the driveshaft can be disposed within a stabilizing shaft  8704  having a distal end interface  8706  with slots that can receive a portion of the retractor body to provide counterrotating torque when the driveshaft  8702  is rotated. A housing  8708  toward a proximal end of the instrument can include a trigger  8710  that can be depressed to rotate the driveshaft  8702 , thereby promoting one-handed use of the instrument  8700 . In particular, pulling the trigger  8710  toward the housing  8708  can cause a pawl  8712  to engage a rack  8714  and advance the rack distally relative to the housing  8708  while locking its rotational position. A pin  8716  coupled to the rack  8714  and received within a spiral groove  8718  formed in the driveshaft  8702  can advance distally with the rack. Distal advancement of the rack without rotation can cause rotation of the driveshaft  8702  as the pin rides distally within the spiral groove  8718 . Once fully depressed, the trigger  8710  can be released and a biasing element  8719  can urge the trigger away from the housing  8708 . This can withdraw the pawl  8712  from the rack  8714 , thereby freeing its rotational position and allowing it to return proximally in response to force from the biasing element  8720 . As a result, on the return (i.e., proximal-moving) stroke of the rack, the rack can rotate about the stationary driveshaft  8702  and return to a proximal-most position where the trigger can be depressed again to rotate the driveshaft during an advancing (i.e., distal-moving) stroke of the rack. Accordingly, a user can rapidly rotate the driveshaft  8702  by repeatedly depressing and releasing the trigger  8710 . This can be especially helpful for initial coarse adjustment or tensioning of the driveshaft  8702 . Additional fine adjustment or tensioning can be accomplished by directly rotating a proximal end of the driveshaft  8702  that can protrude proximally from the housing  8708 . 
       FIGS.  88 - 92 B  illustrate various embodiments of instruments that can be used to couple tissue manipulating implements to a retractor body.  FIG.  88   , for example, illustrates one embodiment of an instrument  8800  that can be utilized with one hand to couple to a tissue manipulating implement, position the implement relative to a retractor using a polyaxial joint coupled thereto, lockout the position of the implement via the polyaxial joint, and decouple therefrom. In the illustrated embodiment, a tissue manipulating implement  8802  is coupled to an arm  8804  and an expandable ball  8806  that can be received within a socket in a retractor body, as described above. This assembly is in turn coupled to the actuating instrument  8800  to allow a user to couple the tissue manipulating implement assembly to a retractor and polyaxially move it into a desired position. Once in position, the user can rotate the knob  8808  to expand the ball  8806  and lock the position of the tissue manipulating implement relative to the retractor body (as shown by arrow  8809 ). Once positioned and locked, the user can depress the button  8810  (as shown by arrow  8811 ) to detach the instrument  8800  from the tissue manipulating implement assembly. Also shown in the figure is that the instrument  8800  includes a smooth distal stem  8812  that can be grasped by a user&#39;s second hand when additional force is needed, e.g., when cobbing or using the tissue manipulating implement to scrape or separate tissue from bone, etc. 
       FIG.  89    illustrates another embodiment of an actuating instrument  8900 . The instrument  8900  is similar to the instrument  8800 , but includes a differently oriented lockout actuator and detachment actuator. The illustrated embodiment includes a thumbwheel  8902  oriented to rotate about an axis perpendicular to a longitudinal axis of the instrument  8900  (as shown by arrow  8901 ), rather than the parallel rotation axis orientation of the instrument  8800 . Further, separating the instrument  8900  from the tissue manipulating implement assembly can be accomplished by pulling back a sheath and separating the instrument (as shown by arrow  8903 ). The instrument  8900  similarly includes a smooth distal stem  8904  to facilitate an extra hand when, e.g., cobbing during a surgical procedure. 
       FIG.  90    illustrates still another embodiment of an actuating instrument  9000 . The instrument is similar to the above-described instruments but utilizes a lever  9002  at a proximal end thereof to control lockout of polyaxial movement of the tissue manipulating implement assembly relative to the retractor body. In particular, a user can depress the lever  9002  in the direction of arrow  9001  to lockout polyaxial movement by expanding the ball  8806  within the socket of the retractor. A detent can signal maximum lockout and detachment of the instrument from the tissue manipulating implement assembly can be achieved by pressing the lever beyond the detent in the direction of arrow  9003  by a distance  9005 . The instrument  9000  similarly includes a smooth distal stem  9004  to facilitate an extra hand when, e.g., cobbing during a surgical procedure. 
       FIGS.  91 A- 91 D  illustrate coupling and decoupling of another embodiment of an actuating instrument  9100  to a tissue manipulating implement assembly  9102  that includes a tissue manipulating implement  9104  coupled to an arm  9106  and an expandable ball  9108 . To begin, a user can depress the button  9110  at the proximal end of the instrument  9100  in the direction of arrow  9111  to put the instrument in a “load” configuration, as shown in  FIG.  91 A . The user can then press the instrument  9100  onto the tissue manipulating implement assembly  9102  to couple the two components. This coupling will cause the button  9110  to pop up or proximally, as shown by arrow  9113  in  FIG.  91 B . The user can then manipulate the position of the assembly  9102  using the instrument  9100  and, once a desired position is reached, the user can expand the ball  9108  to lock the position of the assembly  9102  relative to the retractor body using the thumbwheel  9112 . Once positioned and locked, the instrument  9100  can be detached from the assembly  9102  by again pressing the button  9110 , as shown by the arrow  9115  in  FIG.  91 C . Doing so will decouple the instrument from the assembly, as shown in  FIG.  91 D . 
     The instrument  9100  can advantageously be utilized entirely single-handedly by a user, who need only grab the instrument and manipulate the button  9110  and thumbwheel  9112  with their thumb. Further, the instrument  9100  can include a castellated feature  9202  formed on a distal end thereof that can be complementary to a castellated feature  9204  formed on a proximal end of the assembly  9102  to allow a user to couple the two components at a variety of rotational orientations relative to one another. 
       FIGS.  93 - 101 E  illustrate one embodiment of a surgical retractor system  9300  according to the teachings provided herein. The system can be used to facilitate retraction of skin, muscle, and other soft tissue to access, for example, various portions of a patient&#39;s spine. Further, the system can include a retractor and other components docked via support instruments to a patient&#39;s body via, e.g., vertebrae, and as a result can be utilized to perform various procedures, including vertebral distraction, etc. 
     As shown by the assembled system of  FIG.  93    and the disassembled view of  FIG.  94   , the system  9300  can include one or more support instruments  9302  coupled to screws implanted in a patient&#39;s vertebrae, a retractor  9304  coupled to a support instrument, one or more tissue manipulating implements  9306  coupled to the retractor, a stability handle  9308  with light source  9310  coupled to the retractor  9304 , a distraction module  9312  coupled to another support instrument  9302  from the retractor  9304 , and a distraction rack  9314  coupled to the retractor  9304  and the distraction module  9312  to perform distraction, e.g., between adjacent vertebrae. Also shown in  FIG.  94    is the above-described actuating instrument  9100  that can be used to couple the tissue manipulating implements  9306  to the retractor  9304  and control positioning/locking thereof, as well as a tissue manipulating implement adjuster  9402  that can be utilized to adjust a position, depth, etc. of an expandable tissue manipulating implement, as described herein. 
       FIGS.  95 A- 95 D  illustrate various views of the retractor  9304 , which is similar to the other retractor embodiments described herein. For example, the retractor  9304  includes a post  9502  that can be utilized to attach various components thereto, e.g., the stability handle  9308  or a mount coupled to a surgical table, etc. The retractor  9304  also includes a socket  9504  to receive a post on the distraction rack  9314 . Further, the retractor  9304  includes drive features  9506 ,  9508  to independently control translation of tissue manipulating implement sockets  9510 ,  9512  that can receive expandable balls of tissue manipulating implement assemblies, as described above. Finally, the retractor  9304  includes a recess  9514  and locking feature  9516  for adjusting a position of the retractor along a length of a support instrument received within the recess. 
       FIG.  96    illustrates the distraction module  9312  in greater detail. The distraction module includes a recess  9602  and locking feature  9604  similar to the retractor module  9304  to allow the distraction module to be coupled to and adjusted along a length of a support instrument received within the recess. The distraction module also includes a socket  9606  to receive a post formed on the distraction rack  9314 . 
       FIGS.  97 A- 97 C  illustrate the stability handle  9308  coupled to the retractor  9304  via the post  9502 . For example, the stability handle can be slid onto the post  9502  in the direction of arrow  9701  in  FIG.  97 A  to reach the configuration shown in  FIG.  97 B . The stability handle can be used for added stabilization during tissue manipulating implement positioning, for example. The handle can be utilized alone or, in some embodiments, a light source  9310  can be placed within a recess formed in the stability handle  9308  if additional lighting is desired at the surgical site, as shown in  FIG.  97 C . 
       FIG.  98    illustrates the light source  9310  in greater detail. The light source  9310  can, in some embodiments, include a battery or other power source and a light source. In some embodiments, the light source and battery can be disposed in a housing with optical fibers  9802  or other light guides carrying light therefrom. In other embodiments, light sources, such as light emitting diodes, can be disposed separate from a housing containing a battery or other power source and wires  9802  can carry electrical power to the light sources disposed at a distal end of each wire  9802 . Further, the leads or optical fibers  9802  can be configured to dock within recesses formed in the various types of tissue manipulating implements that can be coupled to the retractor  9304 .  FIGS.  99 A- 99 C  illustrate various tissue manipulating implements  9306  having recesses  9902  formed therein that are configured to receive leads or optical fibers  9802 . Further, and as shown in  FIG.  99 C , the tissue manipulating implements  9306  can include angled, reflective facets  9904  to direct light into an operative corridor for optimal distribution. 
       FIGS.  100 A and  100 B  illustrate a modular attachment mechanism for a tissue manipulating implement  10002  and an arm assembly  10004  that includes an expandable ball  10006  that can be received within a socket  9510 ,  9512  of the retractor  9304 . In the illustrated embodiment, the arm assembly  10004  includes a protrusion  10008  that can be received within a slot  10010  formed in the tissue manipulating implement  10002 . Further, a translating locking feature  10012  on the arm assembly  10004  can selectively lock the tissue manipulating implement to the arm assembly. As shown in  FIG.  100 A , coupling a tissue manipulating implement to an arm assembly can include sliding the locking feature  10012  in the direction of arrow  10013  to withdraw the locking pawl  10014  and then sliding the tissue manipulating implement  10002  in the direction of arrow  10015  to position the protrusion  10008  within the slot  10010 . Note that while the figure and arrow  10015  indicate a bottom loading configuration in which the implement  10002  is moved upward in the direction of arrow  10015  from below the arm assembly  10004  to couple the two components, a reverse top loading operation is also possible. In such a configuration, the implement  10002  can be lowered onto the protrusion  10008  of the arm assembly  10004  from above. After positioning the two components relative to one another, the locking feature  10012  can be released (in embodiments where it is biased) or slid in an opposite direction into position where the locking pawl  10014  is seated in a detent (not shown) of the tissue manipulating implement to prevent separation of the two components. Decoupling the two components can be accomplished by reversing this procedure.  FIG.  100 B  illustrates the two components coupled and locked to one another. 
       FIGS.  101 A- 101 E  illustrate use of the tissue manipulating implement adjuster  9402  that can be utilized to adjust a position, depth, etc. of an expandable tissue manipulating implement  10102 . As shown in  FIG.  101 A , the adjuster  9402  can be coupled to an adjustable or expandable tissue manipulating implement  10102  by aligning dovetail protrusions  10104  with a complementary slot  10106  formed on the implement  10102  and inserting a distal end of the adjuster into the slot  10106 . With the expandable implement coupled to the adjuster, a user can depress the button  10108  in the direction of arrow  10109  to retract a spring or other connecting mechanism that can lock the expandable implement to a static tissue manipulating implement  10110  (e.g., as described above with regard to adjustable depth tissue manipulating implements). While depressing the button  10108 , the user can slide the expandable implement  10102  along the static implement  10110  to achieve a desired height and then release the button  10108  to lock a position of the expandable implement  10102  relative to the static implement  10110 , as shown in  FIG.  101 C and  101 D . The blade adjuster can then be removed by withdrawing the dovetail protrusions  10104  from the slot  10106  to leave the locked assembly of expandable and static tissue manipulating implements, as shown in  FIG.  101 E . 
     In combination with the above-described distraction, any of a variety of surgical procedures can be performed utilizing the working channel provided by the support instrument  7406  and retractor assembly  7410  (or any of the other embodiments of such components described herein). For example, a user can perform a spinal fusion cage insertion procedure via the working channel between the opposed tissue manipulating implements of the retractor assembly  7410 . Other exemplary procedures can include disc replacement, discectomy, endplate preparation, bone graft delivery, and the like. 
     It should be noted that any ordering of method steps expressed or implied in the description above or in the accompanying drawings is not to be construed as limiting the disclosed methods to performing the steps in that order. Rather, the various steps of each of the methods disclosed herein can be performed in any of a variety of sequences. In addition, as the described methods are merely exemplary embodiments, various other methods that include additional steps or include fewer steps are also within the scope of the present disclosure. 
     The instruments disclosed herein can be constructed from any of a variety of known materials. Exemplary 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. The various components of the instruments disclosed herein can have varying degrees of rigidity or flexibility, as appropriate for their use. Device sizes can also vary greatly, depending on the intended use and surgical site anatomy. Furthermore, particular components can be formed from a different material than other components. One or more components or portions of the instrument can be formed from a radiopaque material to facilitate visualization under fluoroscopy and other imaging techniques, or from a radiolucent material so as not to interfere with visualization of other structures. Exemplary radiolucent materials include carbon fiber and high-strength polymers. 
     The devices and methods disclosed herein can be used in minimally-invasive surgery and/or open surgery. While the devices and methods disclosed herein are generally described in the context of spinal surgery on a human patient, it will be appreciated that 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. 
     The devices 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, the device can be reconditioned for reuse after at least one use. Reconditioning can include any combination of the steps of disassembly of the device, followed by cleaning or replacement of particular pieces, and subsequent reassembly. In particular, the device can be disassembled, and any number of the particular pieces or parts of the device can be selectively replaced or removed in any combination. Upon cleaning and/or replacement of particular parts, the device can be reassembled for subsequent use either at a reconditioning facility, or by a surgical team immediately prior to a surgical procedure. Those skilled in the art will appreciate that reconditioning of a device 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 application. 
     The devices described herein can be processed before use in a surgical procedure. First, a new or used instrument can be obtained and, if necessary, cleaned. The instrument can then be sterilized. In one sterilization technique, the instrument 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 instrument and in the container. The sterilized instrument can then be stored in the sterile container. The sealed container can keep the instrument sterile until it is opened in the medical facility. Other forms of sterilization known in the art are also possible. This can include 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 portions of the device due to the materials utilized, the presence of electrical components, etc. 
     One skilled in the art will appreciate further features and advantages based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described. All publications and references cited herein are expressly incorporated herein by reference in their entirety.