Patent Publication Number: US-8979862-B2

Title: Rod coercer

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/413,318 filed on Mar. 6, 2012, now U.S. Pat. No. 8,449,549, which is a continuation of U.S. patent application Ser. No. 12/692,212 filed Jan. 22, 2010, now U.S. Pat. No. 8,137,357, which is a continuation-in-part of U.S. patent application Ser. No. 12/357,782 filed Jan. 22, 2009, now U.S. Pat. No. 8,128,629, the entire disclosures of which are expressly incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to instruments for use in surgical applications, and more specifically, to a rod coercer for positioning a rod into a surgical implant during a spinal fixation procedure. 
     2. Related Art 
     In spinal fixation surgery, a rod and a set of vertebral implants (e.g., pedicle screws) are often used to correct spinal deformities. In such procedures, the rod is often bent to a desired shape using an appropriate rod bender. Then, a surgeon installs the implants in selected vertebral bodies along the length of the spine. Each implant usually includes a head which is shaped to receive a portion of the rod. After the implants have been installed, the rod is seated or “reduced” into the head of an implant, using a device which applies force to the rod and the implant, so that the implant and its associated vertebral body, and the rod, are drawn together, and a portion of the rod is seated in the head of the implant. Once the rod has been reduced into the head of the implant, a cap is engaged with (e.g., threaded into) the head of the implant and tightened to retain the rod in the head of the implant. This process may be repeated for each of the remaining implants, as needed, until the rod has been reduced into all of the implants. Once the procedure is complete, the spine conforms to the shape of the rod, to correct the spinal deformity. Thus, it is very important in such procedures to properly reduce a spinal rod into its associated implants. 
     Various devices for reducing a rod into an implant are known. One example is a simple forceps-type apparatus which includes articulating forceps branches and a bifurcated gripping nose which pivotally grips the head of an implant. When the forceps branches are closed and the pivotal grip is established, the device can be pivoted with respect to the implant to contact a rod and to exert force on same using a fulcrum arrangement, so as to reduce the rod into the head of the implant. Other devices include rod reducers having axially-aligned, concentric sleeves that move axially with respect to each other. Such devices include a pistol and trigger grip, as well as a ratchet mechanism interconnected with the trigger to urge one of the sleeves axially relative to another sleeve, causing prongs of the inner sleeve to grip an implant and the outer sleeve to reduce the rod into the implant. Another device includes a forceps-type instrument which grips an implant, and a separate articulating device which attaches to the forceps-type instrument and which pivots to reduce a rod into the implant. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a rod coercer for use in spinal fixation procedures. The rod coercer includes first and second articulating forceps branches, first and second rod contacting arms extending from the first and second forceps branches, and first and second implant gripping arms pivotally interconnected with the first and second forceps branches. The forceps branches can be pivoted away from each other to open the implant gripping arms so that the arms can be positioned about the head of an implant and a rod to be reduced into the implant. The forceps branches can then be pivoted toward each other to clamp the implant gripping arms against the head of the implant, such that the head of the implant is fixedly gripped by the implant gripping arms. Optionally, corresponding locking tabs could be provided on the forceps branches for retaining the forceps branches and the implant gripping arms in a closed and locked position. After clamping the implant with the implant gripping arms, the forceps branches can be pivoted about the implant gripping arms so that the rod contacting arms contact the rod and the implant gripping arms draw the implant and the rod toward each other to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the rod coercer includes pivotally interconnected forceps branches, each of which is divided into upper and lower branch portions which are pivotally interconnected with each other so that the upper branch portion can be pivoted with respect to the lower branch portion. First and second implant gripping arms extend from the lower branch portions of the forceps branches. A rod contacting arm is provided, and is interconnected to an upper branch portion of one of the forceps branches by an upper linkage, and to a lower branch portion of the same forceps branch by a lower linkage. The forceps branches can be pivoted away from each other to open the implant gripping arms so that the arms can be positioned about the head of an implant and a rod to be reduced into the implant. The forceps branches can then be pivoted toward each other to clamp the implant gripping arms against the head of the implant, such that the head of the implant is fixedly engaged by the implant gripping arms. Optionally, corresponding locking tabs could be provided on the forceps branches for retaining the forceps branches and the implant gripping arms in a closed and locked position. After clamping the implant with the implant gripping arms, the upper branch portions can be pivoted with respect to the lower branch portions, so that the rod contacting arm contacts a rod and the implant gripping arms draw the implant and the rod together to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the forceps branches include first and second implant gripping arms which are pivotally interconnected with the branches, and a rod contacting arm coupled by gears to one of the forceps branches. An end of one of the forceps branches is attached to the face of a forceps gear, and an end of the rod contacting arm is attached to the face of an arm gear, such that the arm gear meshes with the forceps gear. The forceps branches can be pivoted away from each other to open the implant gripping arms so that the arms can be positioned about the head of an implant and a rod to be reduced into the implant. The forceps branches can then be pivoted toward each other to clamp the implant gripping arms against the head of the implant, such that the head of the implant is fixedly gripped by the implant gripping arms. Optionally, corresponding locking tabs could be provided on the forceps branches for retaining the forceps branches and the implant gripping arms in a closed and locked position. After clamping the implant with the implant gripping arms, the forceps branches can be pivoted with respect to the implant gripping arms, so that the forceps gear rotates the arm gear to pivot the rod contacting arm downwardly to contact the rod and the implant gripping arms draw the implant toward the rod to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the rod coercer includes first and second articulating handle branches, first and second rod contacting arms extending from the first and second handle branches, and first and second implant gripping arms pivotally interconnected with the first and second handle branches. The handle branches can be pivoted away from each other to open the implant gripping arms so that the arms can be positioned about the head of an implant and a rod to be reduced into the implant. The handle branches can then be pivoted toward each other to clamp the implant gripping arms against the head of the implant, such that the head of the implant is fixedly gripped by the implant gripping arms. Means for releasably locking the handle branches are provided for retaining the handle branches and the implant gripping arms in a closed and locked position. The means for releasably locking could include a ratcheting assembly having a hinged, toothed lever extending from one handle branch to engage an angled pawl on the second handle branch. After clamping the implant with the implant gripping arms, the handle branches can be pivoted about the implant gripping arms so that the rod contacting arms contact the rod and the implant gripping arms draw the implant and the rod toward each other to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the rod coercer includes a single handle having first and second implant gripping arms connected by a bridge and pivotally attached to the handle. Each implant gripping arm includes a spring-loaded locking lever for gripping sides of an implant. Springs bias protrusions on ends of the locking levers so that the protrusions extend through apertures in the implant gripping arms and into corresponding recesses in the implant to fixedly engage the implant. The levers can be pressed inward to disengage the protrusions from the recesses of the implant, to allow for removal of the rod coercer from the implant. Optionally, the levers can be L-shaped. After fixedly engaging the implant with the spring-loaded locking mechanism and implant gripping arms, the handle can be pivoted with respect to the implant gripping arms, so that the rod contacting arm contacts a rod and the implant gripping arms draw the implant and the rod together to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the rod coercer includes an adjustable rod contacting arm which can be adjusted to a desired angle with respect to the handles of the coercer. An implant gripping arm assembly (e.g., two implant gripping arms) is provided at ends of the handles, is pivotally connected thereto, and is positionable about the head of an implant and secured thereto. The rod contacting arm can then by adjusted to the desired angle using an adjustment assembly associated with the rod contacting arm. The adjustment assembly could include a screw, or threaded shaft, pivotally attached at one end to the handle and extending through a threaded aperture of the rod contacting arm. The adjustment assembly could also include a partial gear attached to the handle and in mechanical communication with a worm gear positioned within the rod contacting arm. Rotation of the worm gear, by a key or other device, alters the angle of the rod contacting arm. When the rod contacting arm is positioned at a desired angle, the handles can then be pivoted with respect to the implant gripping arms, so that the handle pivots the rod contacting arm downwardly to contact the rod and the implant gripping arms draw the implant toward the rod to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the rod coercer includes pivotally interconnected handle branches, each of which is divided into upper and lower branch portions which are pivotally interconnected with each other so that the upper branch portion can be pivoted with respect to the lower branch portion, an implant gripping assembly extending from the lower branch portions of the handle branches, and a rod contacting arm slidably and pivotally coupled to the upper branch portion by a first joint and slidably coupled to the lower branch by a second joint. The handle branches can be pivoted away from each other to open the implant griping arms so that the arms can be positioned about the head of an implant and a rod to be reduced into the implant. The handle branches can then be pivoted toward each other to clamp the implant gripping arms of the implant gripping assembly against the head of the implant, such that the head of the implant is fixedly engaged by the implant gripping arms. After engaging the implant with the implant gripping assembly, the upper branch portions can be pivoted with respect to the lower branch portions, causing the rod contacting arm to contact a rod and the implant gripping arms to draw the implant and the rod together to reduce the rod into the head of the implant. 
     In another embodiment of the present invention, the implant gripping arms of the rod coercer of the present invention are secured to each other by a flexible retainer. Pivoting the arms towards each other causes the flexible retainer to flex upwardly so that the implant may be gripped properly without interference from arch. Urging the gripping arms away from each other causes the retainer to flex. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features of the invention will be apparent from the following Detailed Description of the Invention, taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing the rod coercer of the present invention; 
         FIG. 2  is a partial perspective view showing the rod coercer of  FIG. 1  in greater detail; 
         FIG. 3  is a partial front view showing the rod coercer of  FIG. 1  in greater detail; 
         FIGS. 4A-4C  are side views showing operation of the rod coercer of  FIG. 1  to reduce a surgical rod into the head of an implant; 
         FIGS. 5A-5C  are rear and side views of another embodiment of the rod coercer of the present invention, which includes pivotable upper and lower forceps branches and a rod contacting arm interconnected therewith; 
         FIGS. 6A-6C  are partial rear, perspective, and side views of another embodiment of the rod coercer of the present invention, which includes pivotable implant gripping arms and a geared rod contacting arm; 
         FIG. 7  is a perspective view showing another embodiment of the rod coercer of the present invention, wherein integral rollers are provided at ends of the rod contacting arms and a retainer interconnects the implant gripping arms to maintain the arms in facing relationship; 
         FIG. 8  is a perspective view of a cannula that can be used with the rod coercer of the present invention; 
         FIG. 9  is a perspective view showing the rod coercer of the present invention, wherein releasable locking means are provided on the handles of the rod coercer; 
         FIGS. 10A-11D  are perspective, side, and cross-sectional views showing another embodiment of the rod coercer of the present invention which includes a single handle and spring-loaded implant gripping levers for releasably locking the rod coercer to an implant; 
         FIGS. 12A-13B  are side and cross-sectional views of another embodiment of the rod coercer of the present invention in greater detail, wherein an adjustable rod contacting arm assembly is provided; 
         FIGS. 14A-14B  are side views showing another embodiment of the rod coercer of the present invention, which includes pivotable upper and lower forceps branches and a rod contacting arm slidably coupled therewith by first and second slidable joints; and 
         FIGS. 15A-15C  are partial perspective and front views showing another embodiment of the rod coercer of the present invention in greater detail, wherein a flexible retainer interconnects the implant gripping arms to maintain the arms in facing relationship. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a rod coercer for use in spinal fixation procedures. The rod coercer includes handle branches which can be pivoted along a first arc (i.e., about a first axis) to fixedly grip the head of an implant, and which can be pivoted along a second arc (i.e., about a second axis) to reduce a rod into the head of the implant. By the terms “coerce” and “reduce,” it is meant the seating of a rod into a surgical implant through a mechanical application of force, such that the implant and the rod are drawn together and the rod is seated into the head of the implant. 
       FIG. 1  is a perspective view showing the rod coercer  10  of the present invention. The rod coercer  10  includes right and left forceps branches  12 ,  14  which are pivotally interconnected at a pivot point  16  (e.g., by a pin extending through and pivotally interconnecting the branches  12 ,  14 , or any other suitable type of pivotable interconnection). The branches  12 ,  14  include finger loops  18 ,  20  for receiving an operator&#39;s fingers. Optionally, corresponding locking tabs  22  (which included mating inner surfaces having teeth) could be provided for maintaining the branches  12 ,  14  in a closed and locked arrangement. Rod contacting arms  24 ,  26 , which contact a rod to reduce it into an implant, are provided at the ends of the branches  12 ,  14 . Implant gripping arms  28 ,  30  are pivotally interconnected with the branches  12 ,  14 . The implant gripping arms  28 ,  30  fixedly grip an implant  50  (which could be a screw (e.g., pedicle screw), hook, or any other suitable implant which is configured to receive a rod), while the arms  24 ,  26  pivot with respect to the arms  28 ,  30  to reduce a rod into the implant  50 . 
     To grip the implant  50 , the forceps branches  12 ,  14  are pivoted away from each other about a first axis (in the direction shown by arrow A), which causes both the implant gripping arm  28  to move away from the implant gripping arm  30 , and consequently, the arms  24 ,  26  similarly move away from each other. The arms  28 ,  30  are then positioned about opposite sides of the implant  50 , as well as about a rod (not shown in  FIG. 1 ) to be reduced into the implant  50 . The forceps branches  12 ,  14  are then urged toward each other in the direction shown by arrow A, by an operator&#39;s fingers applying force to the branches  12 ,  14 , so that the arms  28 ,  30  fixedly clamp the implant  50  and, consequently, the arms  24 ,  26  are brought together. The arms  28 ,  30  each have inner surfaces which could be cylindrical in shape or could have any other shape configured to match the shape of the implant  50 . The inner surfaces contact the sides of the implant  50  and are held in a fixed position against the implant  50  when the arms  28 ,  30  are clamped against the implant  50 . The locking tabs  22 , if provided, maintains the forceps branches  12 ,  14  and the arms  28 ,  30  in a locked configuration, such that the arms  28 ,  30  remain clamped against the implant  50  when the operator releases his or her grip on the rod coercer  10 . Advantageously, this frees the surgeon&#39;s hand to perform other tasks (if desired or necessary) prior to reduction of a rod, as discussed below. When the arms  28 ,  30  are clamped against the implant  50 , the forceps branches  12 ,  14  can pivot with respect to the arms  28 ,  30 , in the direction shown by arrow B. As discussed below, this motion allows for reduction of a rod into the implant  50 . Thus, the rod coercer  10  can be pivoted in a first direction (i.e., about a first axis) to fixedly grip the implant  50 , and can be pivoted in a second direction (i.e., about a second axis) generally transverse to the first direction to reduce a rod into the implant  50 . 
       FIG. 2  is a partial perspective view showing the rod coercer  10  in greater detail. As mentioned above, the arms  28 ,  30  are pivotally interconnected with the branches  12 ,  14 . Such a pivotable interconnection could be provided by a first pin  32  inserted through the arm  30  and the branch  12 , and a second pin  34  inserted through the arm  28  and the branch  14 , as well as any other suitable type of pivotable interconnection between the arms  28 ,  30  and the branches  12 ,  14 , such as screws having smooth (pin-like) portions on the shafts thereof about which the arms  28 , rotate. The arms  28 ,  30  clamp opposite sides of the head  52  of the implant  50 , and optionally include shoulders  36 ,  38 . The space between the arms  28 ,  30  allows for insertion of a threaded cap, which could be threaded into the head  52  of the implant  50  to lock a rod to the implant  50 , as well as an instrument for tightening such a cap. 
       FIG. 3  is a partial front view showing the rod coercer  10  in greater detail. The arms  24 ,  26  could include curved surfaces  40 ,  42  which could be shaped to receive the rod. This facilitates a proper interface between the arms  24 ,  26  as they bear against a rod during reduction of the rod into the implant  50 . The shape of the curved surfaces  40 ,  42  could be varied to accommodate the geometry of the rod. It is noted that the arms  24 ,  26  need not extend at an angle to the branches  12 ,  14 . Indeed, the arms  24 ,  26  could be parallel to the branches  12 ,  14 . Additionally, the shapes and angles of the arms  24 ,  26  could be modified so that the arms  24 ,  26  can contact the rod at any desired location. It is also noted that a single arm could be provided for contacting the rod to reduce it into an implant. 
     The shoulders  36 ,  38 , if provided, abut opposed upright walls  54 ,  56  of the head  52  of the implant  50  when the arms  28 ,  30  are clamped against the walls  54 ,  56  of the head  52 . The shoulders  36 ,  38  help to prevent the rod coercer  10  from moving with respect to the implant  50  when the head  52  is clamped by the arms  28 ,  30 . It is noted that the arms  28 ,  30  and walls  54 ,  56  could include complementary mechanical engagements (e.g., in the form of protrusions and corresponding recesses, etc.) which prevent movement between the arms  28 ,  30  and the implant  50  when the head  52  is clamped by the arms  28 ,  30 . Such a protrusion is shown in  FIG. 6B , discussed below, and could be provided in any desired geometry. The walls  54 ,  56  define a channel  58  into which a surgical rod is reduced by the arms  24 ,  26 . 
       FIGS. 4A-4C  are side views showing operation of the rod coercer  10  to reduce a surgical rod  60  into the head  52  of the rod  50 . First, as shown in  FIG. 4A , the arms  28 ,  30  of the rod coercer  10  are clamped against the head  52  of the implant  50  in the manner discussed above, such that the rod  60  is positioned between the arms  28 ,  30  and the arms  24 ,  26  are positioned above the rod  60 . As can be seen, the implant gripping arms  28 ,  30  and the rod contacting arms  24 ,  26  define a first angle with respect to each other. Then, as shown in  FIG. 4B , the forceps branches  12 ,  14  are pivoted in the direction shown by arrow B. This causes the arms  24 ,  26  to move downwardly in the direction shown by arrow C, so that the arms  24 ,  26  contact and exert force against the rod  60 . As can be seen, when the branches  12 ,  14  are pivoted, a second angle (different than the first angle shown in  FIG. 4A ) is defined between the implant gripping arms  28 ,  30  and the rod contacting arms  24 ,  26 . The implant  50  (and an anatomical structure, such as a vertebral body, in which the implant  50  is installed) is then moved upwardly toward the rod  60 , as shown by arrow D. It is noted that the rod  60  could also be moved downwardly toward the implant  50 , i.e., in a direction opposite the direction shown by arrow D. Thus, the arms  24 ,  26  operate as levers for moving the implant  50 . Finally, as shown in  FIG. 4C , the branches  12 ,  14  are further pivoted in the direction of arrow B, so that the arms  24 ,  26  are urged to a final position against the rod  60 . In this position, the rod  60  is reduced into the head  52  of the implant  50 , and a threaded cap or other type of locking device can be installed into the head  52  of the implant  50  to lock the rod  60  in position in the head  52 . Once the rod is locked with respect to the implant  50  using a suitable locking device, the rod coercer  10  can be removed from the implant  50  by pivoting the forceps branches  12 ,  14  away from each other. 
       FIGS. 5A-5C  are rear and side views of another embodiment of the rod coercer of the present invention, indicated generally at  100 . The rod coercer  100  includes forceps branches  112 ,  114  which are pivotally interconnected and which can be pivoted with respect to each other, in the direction shown by arrow E. The branch  112  is divided into upper and lower branch portions  112   a ,  112   b  which pivot with respect to each other, and the branch  114  is divided into upper and lower branch portions  114   a ,  114   b  which pivot with respect to each other. Implant gripping arms  128 ,  130  are provided at the ends of the lower branch portions  112   b ,  114   b  for gripping opposite sides of the head  52  of the implant  50 , and finger loops  118 ,  120  are provided at opposite ends of the branches  112 ,  114  for receiving an operator&#39;s fingers. The gripping arms  128 ,  130  can be brought together to clamp the head  52  of the implant  50  by urging the branches  112 ,  114  together in the direction of arrow E. Corresponding locking tabs  122  could be provided to lock the branches  112 ,  114  together, which locks the gripping arms  128 ,  130  against the head  52  of the implant  50 . Upper and lower linkages  132   a ,  132   b  link a rod contacting arm  124  to the upper and lower branch portions  114   a ,  114   b  of the forceps branch  114 . Of course, the linkages  132   a ,  132   b  could be attached to the upper and lower branch portions  112   a ,  112   b  of the forceps branch  112 . 
     As shown in  FIG. 5B , an upper end of the rod contacting arm  124  is pivotally interconnected to the upper branch portion  114   a  by the linkage  132   a , such that the linkage  132   a  is fixedly attached at one end to the upper branch portion  114   a  and pivotally attached at an opposite end to the rod contacting arm  124 . The lower end of the rod contacting arm  124  is linked to the lower branch portion  114   b  by the linkage  132   b , such that the linkage  132   b  is pivotally attached at one end to the lower branch portion  114   b  and pivotally attached at an opposite end to the rod contacting arm  124 . A curved surface  134  could be provided at the bottom of the rod contacting arm  124 , which could be shaped to match the shape of the rod  60 . 
     The upper and lower branch portions  112   a ,  114   a  and  112   b ,  114   b  are pivotally interconnected by a pivotable interconnection  136  provided in each branch  112 ,  114 , which allows the upper branch portions  112   a ,  114   a  to pivot with respect to the lower branch portions  112   b ,  114   b , as shown by arrow F in  FIG. 5C . Such movement causes the rod contacting arm  124  to move downwardly in the general direction indicated by arrow G, so that the rod contacting arm  124  contacts the rod  60 . This causes the implant  50  (and an anatomical structure in which it is installed, such as a vertebral body) to be drawn upwardly toward the rod  60 , so as to reduce the rod  60  into the head  52  of the implant  50 . It is also noted that the rod contacting arm could cause the rod  60  to move downwardly toward the implant  50  to reduce the rod  60  into the head  52  of the implant  50 . 
       FIGS. 6A-6C  are partial rear, perspective, and side views of another embodiment of the rod coercer of the present invention, indicated generally at  200 . As shown in  FIG. 6A , the rod coercer  200  includes branches  212 ,  214  which are pivotally interconnected via pivotable interconnection  216  and which can be pivoted with respect to each other, in the direction of arrow H. Upper ends of the branches  212 ,  214  could include finger loops and, optionally, locking tabs, such as the finger loops and locking tabs shown in the previous embodiments. Implant gripping arms  226 ,  228  are provided for gripping opposite sides of the head  52  of the implant  50 , and can be brought together to clamp the head  52  of the implant  50  by urging the branches  212 ,  214  together in the direction of arrow H. 
     As shown in  FIG. 6B , the implant gripping arms  226 ,  228  are pivotally interconnected with the branches  212 ,  214  via joints  230 ,  232 . The joint  230  is formed by a collar  250  attached to an end of the branch  212 , which pivots about a pin  252  extending through the upper portion of the gripping arm  226 . The joint  232  links a rod contacting arm  234  to the forceps branch  214 . The branch  214  is attached to a face of a forceps gear  242 , and the rod contacting arm  234  is attached to the face of an arm gear  240 , both of which gears  240 ,  242  intermesh. The gears  240 ,  242  rotate about pins  244 ,  246  inserted into an upper end of the implant gripping arm  228 . Thus, both the forceps branch  214  and the rod contacting arm  234  pivot at adjacent pivot points in joint  232 . 
     Optionally, protrusions  248  could be provided on the rod contacting arms  226 ,  228  for insertion into corresponding recesses formed on an implant. The geometry of such protrusions could be varied as desired. Also, the rod contacting arm  234  could be bent (as shown in  FIG. 6B ) or provided in any desired shape or geometry. Additionally, a curved surface  236 , shaped to match the shape of a rod, could be provided on the rod contacting arm  234 . 
     As shown in  FIG. 6C , when the branches  212 ,  214  are pivoted in the direction of arrow I, the forceps gear  242  rotates. This causes the arm gear  240  to rotate, which causes the rod contacting arm  234  to pivot in the direction of arrow J, so that the surface  236  contacts the rod  60 . This causes the implant  50  (and an anatomical structure (e.g., a vertebral body) into which the implant  50  is installed) to be drawn upwardly toward rod  60  by the implant gripping arms  228 ,  230 , as indicated by arrow K, so that the rod is reduced into the head  52  of the screw  50 . It is noted that the rod  60  could also be urged downwardly toward the screw  50  to reduce the rod  60  into the head  52  of the screw  50 . 
       FIG. 7  is a perspective view showing another embodiment of the present invention, which is similar in construction to the rod coercer shown in  FIGS. 1-4C . In this embodiment, integral rollers  352 ,  354  are provided on ends of the rod contacting arms  324 ,  326 , which roll along a rod as it is reduced. The rollers  352 ,  354  reduce friction between the rod and the arms  324 ,  326 , thereby reducing the amount of force required to reduce a rod. Also provided is a flexible retainer  356  interconnecting the implant gripping arms  328 ,  330 . The retainer  356  allows the arms  328 ,  330  to be maintained in facing relationship with each other as they are pivoted with respect to forceps branches  312 ,  314 . Also, the retainer  356  stretches (as shown by arrow L) so that the arms  328 ,  330  can be spread apart by manipulating the forceps branches  312 ,  314 . As such, the retainer  356  does not interfere with operation of the rod coercer. The rollers  352 ,  354  could be provided on the rod contacting arms of each of the embodiments of the rod coercer disclosed herein, and the flexible member  356  could be provided for interconnecting the implant gripping arms of each embodiment of the rod coercer disclosed herein. 
       FIG. 8  is a perspective view showing a cannula (guide tube)  400  which could be utilized with each embodiment of the rod coercer of the present invention. The cannula  400  could be positioned between the implant gripping arms of the present invention to guide a set screw and an associated tightening tool for locking a rod into an implant. The shape and size of the cannula  400  could be modified as desired without departing from the spirit or scope of the present invention. It is also noted that the cannula  400  could be threadably, frictionally, or otherwise engaged with the implant gripping arms of the present invention (e.g., using corresponding interlocking protrusions/recesses to lock the cannula  400  to the arms). 
       FIG. 9  is a perspective view showing another embodiment of the rod coercer of the present invention, indicated generally at  500 . The rod coercer  500  includes right and left handle branches  512 ,  514  which are pivotally interconnected at a point  516  (e.g., by a pin extending through and pivotally interconnecting the branches  512 ,  514 , or any other suitable type of pivotable interconnection). The branches  512 ,  514  include means for releasably locking the branches  512 ,  514  in a closed and locked position, such as a ratchet mechanism comprising a pivotable toothed lever  522  rotating about a hinge  525  on one handle and a pawl  523  located on the opposite handle. Rod contacting arms  524 ,  526 , which contact a rod to reduce it into an implant, are provided at the ends of the branches  512 ,  514 . Implant gripping arms  528 ,  530  are pivotally interconnected with the branches  512 ,  514 . The implant gripping arms  528 ,  530  fixedly grip an implant  50  (which could be a screw (e.g., pedicle screw), hook, or any other suitable implant which is configured to receive a rod), while the rod contacting arms  524 ,  526  pivot with respect to the implant gripping arms  528 ,  530  to reduce a rod into the implant  50 . 
     To grip the implant  50 , the handle branches  512 ,  514  are pivoted away from each other about a first axis (in the direction shown by arrow M), which causes the implant gripping arm  528  to move away from the implant gripping arm  530 , and consequently, the arms  524 ,  526  similarly move away from each other. The arms  528 ,  530  are then positioned about opposite sides of the implant  50 , as well as about a rod (not shown in  FIG. 9 ) to be reduced into the implant  50 . The handle branches  512 ,  514  are then urged toward each other in the direction shown by arrow M, by an operator&#39;s hand applying force to the branches  512 ,  514 , so that the arms  528 ,  530  fixedly clamp the implant  50  and, consequently, the arms  524 ,  526  are brought together. The gripping arms  528 ,  530  each have inner surfaces which could be cylindrical in shape or could have any other shape configured to grip or hold the implant  50 . The inner surfaces contact the sides of the implant  50  and are held in a fixed position against the implant  50  when the arms  528 ,  530  are clamped against the implant  50 . When the arms  528 ,  530  are clamped against the implant  50 , the handle branches  512 ,  514  can pivot with respect to the arms  528 ,  530 , in the direction shown by arrow N. As discussed herein, this motion (similar to the motion shown by arrow B in FIGS.  1  and  4 B- 4 C) allows for reduction of a rod into the implant  50 . 
     To utilize the ratchet mechanism, as the branches  512 ,  514  are urged together, the pawl  523  moves with respect to the teeth of the lever  522  until the branches  512 ,  514  stop moving and the pawl  523  settles against one of the teeth of the lever  522 . The teeth of the lever  522  are shaped such that after the branches  512 ,  514  are urged together, the teeth retain the pawl  523  in a fixed position, thereby locking the branches  512 ,  514  together. This locks of the handles  512 ,  514  in position as the implant gripping arms  528 ,  530  hold the implant  50 . The coercer  500  can be released from the implant  50  by pivoting the lever  522  upwardly, so that the pawl  523  disengages from the lever  522 . 
     It is noted that the ratchet mechanism shown in  FIG. 9  could be substituted with any other suitable means for releasably locking the handle branches  512 ,  514 , such as a screw that releasably locks the handle branches  512 ,  514 , or any other suitable type of interconnection. 
       FIGS. 10A-11D  are perspective, side, and cross-sectional views showing another embodiment of the rod coercer of the present invention, indicated generally at  600 , having a single handle  612  and spring-loaded implant gripping levers  631 ,  633 . As shown in  FIGS. 10A-10B , the rod coercer  600  includes a single handle  612  which is pivotally interconnected with an implant gripping assembly  620  at a pivot point  614  via a pin  616 , allowing the assembly  620  to be pivoted in the direction shown by arrow O. One end of the handle  612  includes a rod contacting arm  624  and a curved rod-contacting surface  626 . Spring-loaded implant gripping levers  631 ,  633  are provided on implant gripping arms  628 ,  630 , which are attached to extension arms  618 ,  622 . The gripping arms  628 ,  630  are affixed to each other by a bridge  620  which connects the extension arms  618 ,  622 . 
     As shown in  FIG. 10C , the spring-loaded locking levers  631 ,  633  are connected to the implant gripping arms  628 ,  630  by hinges  636 ,  638 . Springs  644 ,  646  bias upper ends  632 ,  634  of the levers  631 ,  633  away from the arms  628 ,  630 , forcing projections  640 ,  642  through apertures  648 ,  650  in the arms  628 ,  630 , and causing the projections  640 ,  642  to engage recesses  51  in the head  52  of the implant  50  to lock the arms  628 ,  630  in position on sides of the implant  50 . To engage the arms  628 ,  630  with the implant  50 , the upper ends  632 ,  634  of the locking levers  631 ,  633  are first pressed in the direction shown by arrows Q. This causes the protrusions  640 ,  642  to retract from the apertures  648 ,  650 , as shown by arrows R. Then, the arms  628 ,  630  are positioned about the head  52  of the implant  50 , and the implant gripping levers  632 ,  634  are released by the operator. The springs  646 ,  648  urge the protrusions  640 ,  642  through the apertures  648 ,  650  and into the recesses  51 , thereby fixedly engaging the arms  628 ,  630  (and, thus, the rod coercer  600 ) to the implant  50 . To disengage the coercer  600  from the implant  50  (after rod reduction), the upper ends  632 ,  634  of the levers  631 ,  633  are depressed, resulting in the disengagement of the projections  640 ,  642  from the recesses  51  in the direction shown by arrows R. Optionally, the protrusions  640 ,  642  may be angled or rounded so that the implant gripping arms  628 ,  630  can be pushed directly on to the implant head  52  to obviate the need to depress the upper ends  632 ,  634 . 
     Optionally, the spring-loaded implant gripping levers can be L-shaped, as shown in  FIGS. 11A-D . As shown therein, the rod coercer  600  includes a single handle  712  which is pivotally interconnected with an implant gripping assembly  720  at a pivot point  714  via a pin  716 , allowing the assembly  720  to be pivoted in the direction shown by arrow S. One end of the handle  712  includes a rod contacting arm  724  and a curved rod-contacting surface  726 . L-shaped, spring-loaded implant gripping levers  731 ,  733  are provided on implant gripping arms  728 ,  730 , which are attached to extension arms  718 ,  722 . The gripping arms  728 ,  730  are affixed to each other by a bridge  720  which connects the extension arms  718 ,  722 . 
     As shown in  FIG. 11D , the spring-loaded locking levers  731 ,  733  are interconnected to the implant gripping arms  728 ,  730  by hinges  778 ,  779 . Springs  780 ,  782  bias ends  784 ,  786  of the levers  731 ,  733  away from the arms  728 ,  730 , forcing projections  770 ,  774  through apertures  772 ,  776  in the arms  728 ,  730 , and causing the projections  770 ,  774  to engage recesses in the head of an implant (see, e.g., implant  50  discussed above) to lock the arms  728 ,  730  in position on sides of the implant. To engage the arms  728 ,  730  with the implant, the ends  784 ,  786  of the levers  731 ,  733  are first pressed in the direction shown by arrows T. This causes the protrusions  770 ,  774  to retract from the apertures  772 ,  776 , as shown by arrows U. Then, the arms  728 ,  730  are positioned about the head of the implant, and the ends  784 ,  786  of the implant gripping levers  731 ,  733  are released by the operator. The springs  780 ,  782  urge the protrusions  770 ,  774  through the apertures  772 ,  776  and into the recesses, thereby fixedly engaging the arms  728 ,  730  (and, thus, the rod coercer  600 ) to the implant  50 . To disengage the coercer  600  from the implant  50  (after rod reduction), the ends  784 ,  786  of the levers  731 ,  733  are depressed, resulting in the disengagement of the protrusions  770 ,  774  from the recesses in the direction shown by arrows U. Optionally, the protrusions  770 ,  774  may be angled or rounded so that the implant gripping arms  728 ,  730  can be pushed directly on to the implant head to obviate the need to depress the ends  784 ,  786 . 
       FIGS. 12A-12B  are side views of another embodiment of the rod coercer of the present invention, indicated generally at  800 , which includes a rod contacting arm having an adjustable angle with respect to a handle. The rod coercer  800  includes a handle  812  which is pivotally interconnected with an implant gripping assembly  828  at a pivot point  816  and can be pivoted in the direction shown by arrow W. The implant gripping assembly  828  could include any of the implant gripping arm configurations (and associated levers, protrusions, hinges, etc.) disclosed herein, or it could even include a single, cylindrical sleeve with internal, spring-loaded protrusions which permit the assembly  828  to be pushed onto the head of the screw  50  and releasably coupled thereto. Located on handle  812  are two more pivot points  834 ,  838 . The first pivot point  834  is connected to a linkage  844  and associated knob  830 . The knob  830  includes a threaded shaft  832  and a terminal end  842  rotatably captured within the linkage  844 . The threaded shaft  832  is threadably engaged with a threaded aperture  840  in an upper portion  836  of rod contacting arm  824 . The second pivot point  838  is connected to the rod contacting arm  824 , which includes a curved surface  826  to accommodate the geometry of a rod to be reduced. 
     As shown in  FIG. 12B , the threaded shaft  832  remains in permanent mechanical communication with threaded orifice  840  of the adjustment arm  836 . Rotation of the knob  830  (as shown by arrow X in  FIG. 12A ) causes mechanical interaction between the threaded shaft  832  and the threaded orifice  840 , resulting in movement of the upper portion  836  of the rod contacting arm  824  along the threaded shaft  832 , as shown by arrow Y of  FIG. 12A . This movement can be in either direction, depending on clockwise or counter-clockwise rotation of the knob  830 . This movement results in movement of rod contacting arm  824 , along the direction shown by arrow V of  FIG. 12A . Such movement allows the rod contacting arm  824  to be adjusted to a desired location and angle, whereupon the handle  812  can then be rotated downward in the general direction indicated by arrow W to bring rod contacting arm  824  in contact with the rod  60 . This causes the implant  50  and the rod  60  to be drawn together, so as to reduce the rod  60  into the head  52  of the implant  50 . It is also noted that the rod contacting arm could cause the rod  60  to move downwardly toward the implant  50  to reduce the rod  60  into the head  52  of the implant  50 . 
       FIGS. 13A-13B  are side views of another embodiment of the rod coercer of the present invention in greater detail, indicated generally at  900 , which includes an adjustable rod contacting arm. The rod coercer  900  includes a handle  912  which is pivotally interconnected with an implant gripping assembly  928  at a pivot point  916  and can be pivoted in the direction shown by arrow Z. Located on the handle  912  is a second pivot point  938 . The second pivot point  938  allows for the rotation of the adjustable rod contacting arm  924  in the general direction show by arrow AA through a fixed partial gear  940  and a worm gear  944 . 
     The angle of the adjustable rod contacting arm  924  can be adjusted by rotating a worm gear  944  provided in the rod contacting arm  924 , as shown in  FIG. 13B . The partial gear  940  includes teeth  942  in mechanical communication with helical grooves of the worm gear  944  of the contacting arm  924 . The worm gear  944  is connected to the contacting arm  924  by a spindle  946  which allows for rotation of the gear. Of course, any other suitable way of capturing the gear  944  within the rod contacting arm  924  could be provided. Rotation of the gear  944  is achieved using a key  952  which can be inserted through an aperture  950  of the contacting arm  924  and turned. This causes the grooves of the worm gear to move along the teeth of the fixed gear  940 , resulting in the movement of the rod contacting arm  924  along the fixed gear  940 , as shown by arrow AA. This allows the arm  924  to be moved to a desired angle, whereupon the handle  912  can then be rotated downward, in the general direction indicated by arrow Z, to bring the rod contacting arm  924  in contact with the rod  60 . This causes the implant  50  and the rod  60  to be drawn together, so as to reduce the rod  60  into the head  52  of the implant  50 . 
       FIGS. 14A-14B  are side views showing operation of another embodiment of the rod coercer of the present invention in greater detail, indicated generally at  1000 , which includes a rod contacting arm slidably coupled to the coercer by first and second joints. The rod coercer  1000  includes upper handle branches  1012   a ,  1014   a  which are pivotally interconnected with lower handle branches  1012   b ,  1014   b  by pivotable interconnections  1036 . An implant gripping assembly  1028  is provided at the ends of the lower handle branches  1012   b ,  1014   b  for gripping the head  52  of the implant  50 . First and second joints  1032 ,  1046  interconnect arm  1024  to the upper and lower branch portions  1014   a ,  1014   b , and allow the arm  1024  to slide. Of course, the joints  1032 ,  1046  could be attached to the upper and lower branch portions  1012   a ,  1012   b . The arrangement of the upper and lower branch portions is similar to the upper and lower branch portions discussed above in connection with  FIGS. 5A-5C . 
     As shown in  FIG. 14A , the joint  1032  includes a bracket  1034  attached to one end of the upper branch portion  1014   a . The bracket  1034  includes a pin  1035  which travels along a slot  1032  formed at an upper end of the rod contacting arm  1024 , and allows for translation and pivoting of the bracket  1034  and pin  1035  with respect to the slot  1033 . The lower end of the rod contacting arm  1024  is linked to the lower branch portion  1014   b  by the joint  1046 . The joint  1046  includes a projection  1046  which is attached to, or formed with, the lower branch portion  1014   b , and which includes an aperture  1038  for receiving the contacting arm  1024 . The rod contacting arm  1024  translates upwardly and downwardly within the aperture  1038 , thereby allowing for slidable coupling of the arm  1024  and the branch  1012   b . A curved surface  1026  could be provided at the bottom of the rod contacting arm  1024 , which could be shaped to accommodate the rod  60 . 
     As mentioned above, the upper and lower branch portions  1012   a ,  1014   a  and  1012   b ,  1014   b  are pivotally interconnected by a pivotable interconnection  1036 . This allows the upper branch portions  1012   a ,  1014   a  to pivot with respect to the lower branch portions  1012   b ,  1014   b , as shown by arrow BB in  FIG. 14B . Such movement causes the bracket  1034  and pin  1035  to move along the slot  1033 , resulting in the movement of rod contacting arm  1024  downwardly in the general direction indicated by arrow CC, so that the rod contacting arm  1024  contacts the rod  60 . This causes the implant  50  and the rod  60  to be drawn together, so as to reduce the rod  60  into the head  52  of the implant  50 . 
       FIGS. 15A-15C  are partial perspective and front views showing operation of another embodiment of the rod coercer of the present invention, which is similar in construction to the rod coercer shown in  FIG. 9  and is generally indicated at  1100 . In this embodiment, a flexible retainer  1140  is provided which interconnects the implant gripping arms  1128 ,  1130 . The retainer  1140  allows the arms  1128 ,  1130  to be maintained in a facing relationship with each other as they are pivoted about pivot point  1116 , as well as when one of the arms  1128 ,  1130  is moved. 
     As shown in  FIG. 15B , when the arms  1128 ,  1130  are in a closed arrangement, the retainer  1140  is generally arched. When the arms  1128 ,  1130  are pivoted in the direction of arrow DD, as shown in  FIG. 15C , the retainer  1140  flexes while maintaining the arms  1128 ,  1130  in facing relationship. 
     Having thus described the invention in detail, it is to be understood that the foregoing description is not intended to limit the spirit or scope thereof. What is desired to be protected is set forth in the following claims.