Patent Abstract:
The pedicle screw extension system may include a removable cannulated extension provided to a pedicle screw tulip head. The cannulated extension may permit percutaneous implantation of pedicle screws followed by rod placement that may be guided by slots running along the length of the extension. The cannulation may allow for passage and attachment of secondary instruments, such as for example: a screw driving device, a rod measuring device, and a set screw driving device. The screw extension may also include secondary device attachment features allowing the rod to be pushed down in a screw tulip head and for extension removal as needed.

Full Description:
PRIORITY 
     This application is a divisional of U.S. patent application Ser. No. 13/665,545, filed on Oct. 31, 2012, which claims the benefit of U.S. Provisional Application No. 61/553,714, filed on Oct. 31, 2011, and both of which are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present invention generally relates to a pedicle screw extension system. More particularly, the present invention relates to a cannulated extension to a pedicle screw tulip head. The cannulated extension permits percutaneous implantation of pedicle screws followed by rod placement that is guided by slots running along the length of the extension. 
     BACKGROUND 
     Many systems exist for placing screws and other hardware into bone. However, there continues to be a need for a screw placement system that reliably and securely delivers the screws and facilitates screw removal when necessary. Further, there exists a need for an easy to use, reliable screw extension system that permits percutaneous implantation of pedicle screws. 
     SUMMARY 
     According to one aspect of the present invention, the pedicle screw extension system may include a removable cannulated extension provided to a pedicle screw tulip head. In one embodiment, the cannulated extension may permit percutaneous implantation of pedicle screws followed by rod placement that may be guided by slots running along the length of the extension. In an embodiment, the cannulation may allow for passage and attachment of secondary instruments, such as for example: a screw driving device, a rod measuring device, and a set screw driving device. In another embodiment, the screw extension may also provide secondary device attachment features allowing the rod to be pushed down in a screw tulip head and for extension removal as needed. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. It is understood that the features mentioned hereinbefore and those to be commented on hereinafter may be used not only in the specified combinations, but also in other combinations or in isolation, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 2  is a cross-sectional view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 3  is a cross-sectional view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 4  is a cross-sectional view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 5  is a perspective exploded view of a pedicle screw extension system according to certain embodiments. 
         FIG. 6  is a perspective exploded view of a pedicle screw extension system according to certain embodiments. 
         FIG. 7  is a perspective exploded view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 8  is a cross-sectional view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 9  is a perspective view of a portion of a pedicle screw extension system according to certain embodiments. 
         FIG. 10  is a cross-section end view of a portion of a pedicle screw extension system according to certain embodiments. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular example embodiments described. On the contrary, the invention is to cover all modifications, equivalents, combinations and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     In the following descriptions, the present invention will be explained with reference to example embodiments thereof. However, these embodiments are not intended to limit the present invention to any specific example, embodiment, environment, applications or particular implementations described in these embodiments. Therefore, description of these embodiments is only for purpose of illustration rather than to limit the present invention. It should be appreciated that, in the following embodiments and the attached drawings, elements unrelated to the present invention are omitted from depiction; and dimensional relationships among individual elements in the attached drawings are illustrated only for ease of understanding, but not to limit the actual scale. 
     In an embodiment as can be seen in  FIGS. 1-4 , the screw extension  10  may attach to and/or lock onto a screw tulip head  12  by a unique hinged capture locking mechanism  14 .  FIG. 2  depicts the locking mechanism  14  in an open position.  FIG. 3  depicts the locking mechanism  14  in a partially closed position grasping a screw  12 .  FIG. 4  depicts the locking mechanism  14  in a fully closed position having the screw  12  fully secured. This hinged locking mechanism  14  pivots locally which provides for extremely strong holding power. In one embodiment, the locking mechanism  14  may be comprised of small distal hinged locking doors that may be constrained for maximum open and closed angular positions utilizing designed interferences to the door opening. According to one aspect, the locking mechanism  14  may float in its angular constrained range of motion. In an embodiment, the locking mechanism  14  may include radiused interference bars  16   a  and  16   b  on its distal end. The locking mechanism  14  may further include closing platforms  18   a  and  18   b , adjacent to the interference bar, that may be timed to the spacing of mating geometries on a screw tulip head  12 . 
     As shown in  FIGS. 1-4 , in one embodiment, a screw tulip head  12  may be loaded into a distal pocket  20  thus constraining lateral movement of extension arms. According to one aspect, as an implant/screw  12  is placed into a pocket  20  on the distal end of the extension  10 , locking doors may be displaced to an open angular position as the implant slides past a radiused interference bar  16   a  or  16   b  of the locking door. In an embodiment, a proximal surface of a screw tulip head  12  may contact a closing platform  18   a  or  18   b  of the locking door such that the door closes as the tulip head  12  is seated in the final loaded position within the screw extension  10 . 
     In yet another embodiment shown in  FIGS. 1-4 , the locking doors may include a cylindrical channels  22   a  and  22   b  perpendicular to an angular pivot point such that when the locking door is closed the cylindrical channel  22   a  or  22   b  may be oriented along the axis of the screw extension  10 . According to one aspect, the screw extension  10  system may employ locking bars  24   a  and  24   b  that are driven along the axis of the screw extension  10  into the cylindrical channels  22   a  and  22   b  of the locking doors precluding any angular motion of the locking doors which then restricts linear motion of the screw tulip head  12 , thus locking the screw/implant  12  onto the screw extension  10 , much like a dead bolt style lock. In yet another embodiment, lock bars  24   a  and  24   b  may be withdrawn out of the lock doors allowing the lock doors to freely swing through their angular pathway. According to one embodiment, pulling a screw tulip head  12  out of a distal screw extension  10  pocket  20  may cause the radius lock bar  24   a  and  24   b  features to ramp out of a mating pocket on the screw tulip head  12 , such that the tulip head  12  is freed for removal. Nearly no force is required to load or unload a screw tulip head  12 . 
     Locking mechanism  14  may include a rounded detent which allows a screw head  12  to roll out in the unlocked state. Locking mechanism  14  may pivotally roll out of the locked position due to the linear motion of implant  12  removal. Cylindrical lock bars  24   a  and  24   b  may rest in cylindrical seats on locking mechanisms  14  giving holding strength. Lock bars  24   a  and  24   b  may be actuated by rotational movement of a turn knob and/or wheel  26 . The lock knob  26  may be a rotary threaded device that drives the lock rods  24   a  and  24   b  linearly. The threads on the lock knob  26  produce linear motion from rotation. 
     As can be seen in  FIG. 5 , a rotating motion may drive a male wedge  28  linearly to open a stationary split female wedge  30  to mate with the male wedge  28  which drives the hex  32  apart causing interference between the hex  32  of the set screw placer and the hex of the screw resulting in extreme frictional holding force. 
     According to an embodiment as can be seen in  FIGS. 6-7 , locking bars  24   a  and  24   b  may be coupled together by a cylindrical ring  34  concentric to the screw extension  10  which only moves in a linear motion along the axis of the screw extension  10 . Lock rods  24   a  and  24   b  and rotating lock knob  26  may be coupled such that the rods  24   a  and  24   b  may be driven forward and backward. In one embodiment, the locking bar ring  34  may be driven linearly by a rotating threaded locking wheel and/or knob which may be coupled to a locking bar ring. The locking bar ring  34  may include an intermediary floating ring  36  having male groove protrusions which may engage female groove cuts in both the locking bar ring and locking wheel. 
     As shown in  FIGS. 6-7 , in one embodiment, a stop ring  38  may be nested between a locking wheel and a locking bar ring  34  and entrapped by a coupling ring. According to one aspect, the stop ring  38  may be a spiral wrapped ring or a split half moon ring pair. In an embodiment, the stop ring  38  may be positioned distally forward of a male thread  40  on the screw extension  10  providing a proximal stop  42 . According to one aspect, a distal stop wall  44  may be designed into the screw extension  10 . In one embodiment, clockwise lock wheel  26  rotation may drive the lock bars  24   a  and  24   b  distally into cylindrical lock door channels  22   a  and  22   b  until a stop wall  44  is reached. Counter clockwise lock wheel  26  rotation may withdraw lock bars  24   a  and  24   b  out of the door channels  22   a  and  22   b  until the stop ring  38  precludes proximal linear motion by abutting to the distal end of the male threads  40  on the screw extension  10 . Extension  10  is elf contained and requires no secondary tools to load and unload screws  12 . 
     According to one aspect, the screw extension  10  system may employ secondary devices for pushing a rod down the extension system and seating the rods into a screw tulip head  12  both internally and externally of the cannulated extension. Additional secondary devices may be used for removing the screw extension from the screw tulip head. 
     In one embodiment of the present invention, the screw extension  10  may include novel features on its proximal end as shown in  FIGS. 8-10 . According to one embodiment, the screw extension  10  may include a slot  46  configured for secondary device radial alignment with respect to the extension&#39;s  10  longitudinal axis. In yet another embodiment, the screw extension  10  may include spherical recessed cuts (dimples)  48   a - d . In one embodiment, the screw extension  10  may include 4 dimples  48   a - d . According to one aspect, the dimples  48   a - d  may provide engagement locations and bearing surfaces for interlocking secondary devices to the extension  10 . Dimples  48   a - d  may be utilized to increase the force bearing contact surface with engaging spherical balls of a secondary device. The spherical recessed cuts  48   a - d  provide an increased surface area for bearing force versus a traditional 360 degree spherical groove. 
     As can be seen in  FIGS. 8-10 , according to one embodiment, secondary devices may utilize primary housings having radial cylinders  50   a  and  50   b  perpendicular to the axis of the screw extension  10  and/or housing and floating ball bearings  52   a  and  52   b  matched to the radial positions of the dimples  48   a - d  in the extension. A secondary housing  54  may contain a radial groove which when aligned with the cylinders  50   a  and  50   b  may allow the balls  52   a  and  52   b  to float out from the central cylinder. When misaligned, the balls  52   a  and  52   b  may be forced into the path of the central cylinder and then into the matching dimples  48   a - d  of the extension  10  such that the devices are locked together preventing radial and linear movement. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is, therefore, desired that the present embodiment be considered in all respects as illustrative and not restrictive. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.

Technology Classification (CPC): 0