Minimally invasive screw extension assembly

Abstract

A screw extension assembly for use in minimally invasive spinal surgery, the assembly has an inner slotted shaft and an outer shaft, a rod reducer and a removable nut. The combination when assembled is configured to move a spinal fixation rod into a slotted rod receiving spinal implant where it is seated and affixed thereto. The screw extension assembly further has a locking knob rotationally coupled to a proximal end of the outer shaft, wherein the inner shaft has one or more cam grooves and the locking knob has a pin extending into and guided by said cam groove causing the outer shaft to translate longitudinally upon rotation of the locking knob relative to the inner shaft toward an engaged position locking the deflectable legs in the coupled position to the slotted rod receiving implant.

What is claimed is: 
     
         1 . A screw extension assembly for use in minimally invasive spinal surgery, the assembly comprising:
 an inner slotted shaft, the inner slotted shaft being an elongated hollow tubular shaft having a proximal end, a distal end and a slotted distal end portion having a pair of slots open through the distal end defining a pair of deflectable leg extensions, each leg extension having a projection configured to engage a groove on an outer surface of a slotted rod receiving implant thereby coupling the inner shaft to the slotted rod receiving implant adjacent slots at the distal end of the leg extensions having a plurality longitudinal edges keyed to abut proximal walls of the slotted rod receiving implant to prevent rotation;   an outer shaft configured to receive and pass over the inner shaft; the outer shaft having a pair of slots open through a distal end with longitudinal rails adjacent edges of each slot of the outer shaft to slide along each edge of the slots of the leg extensions of the inner shaft along at least a portion of the slots; and   wherein the outer shaft, when moved inwardly toward the distal end of the inner shaft into an engaged position, locks the deflectable legs in a coupled position to the grooves of the slotted rod receiving implant.   
     
     
         2 . The screw extension assembly of  claim 1  wherein the outer shaft at the distal end has two or more prongs extending from the distal end, the two or more prongs when the outer shaft is moved engages an inner side of the slotted rod receiving implant in the engaged position. 
     
     
         3 . The screw extension assembly of  claim 1  wherein a proximal portion adjacent the proximal end of the inner shaft has a threaded portion. 
     
     
         4 . The screw extension assembly of  claim 3  wherein the threads of the threaded portion have longitudinal extending grooves aligned to receive the longitudinal rails of the outer shaft. 
     
     
         5 . The screw extension assembly of  claim 4  wherein the grooves are aligned with the edges of the slots forming a keyed pathway allowing the longitudinal rails to slide relative to the inner shaft toward the distal end on assembly. 
     
     
         6 . The screw extension assembly of  claim 1  further comprises a locking knob rotationally coupled to a proximal end of the outer shaft, wherein the inner shaft has one or more cam grooves and the locking knob has a pin extending into and guided by said cam groove causing the outer shaft to translate longitudinally upon rotation of the locking knob relative to the inner shaft toward an engaged position locking the deflectable legs in the coupled position to the slotted rod receiving implant. 
     
     
         7 . The screw extension assembly of  claim 1  wherein the one or more cam grooves has a cam over pocket feature in a distal end of the cam groove, the cam over pocket locks the locking knob at or past the engaged position. 
     
     
         8 . The screw extension assembly of  claim 1  wherein the cam over pocket at the distal end of the cam groove rotationally moves the locking knob in the absence of forward longitudinal translation of the outer shaft to the inner shaft at the locked position. 
     
     
         9 . The screw extension assembly of  claim 1  wherein the pair of slots in the inner shaft and the pair of slots in the outer shaft are aligned to pass rods therethrough. 
     
     
         10 . The screw extension assembly of  claim 6  further comprises:
 a rod reducer, the rod reducer being a hollow tube with a distal end to push a rod received in the aligned slots of the assembly when the rod reducer is placed over the inner and outer shaft. 
 
     
     
         11 . The screw extension assembly of  claim 10  further comprises:
 a nut having female threads for engaging the threaded proximal end of the inner shaft and wherein the nut when tightened abuts a proximal end of the reducer and pushes the reducer inwardly to move a rod received in the aligned slots of the assembly into the slotted rod receiving implant. 
 
     
     
         12 . The screw extension assembly of  claim 11  wherein the threads of the proximal end of the inner shaft has a pitch sufficient to allow the nut to auto-rotate, solely due to the weight of the nut, to abut the proximal end of the reducer and further rotation pushes the reducer inwardly to seat a rod in a rod seating position. 
     
     
         13 . The screw extension assembly of  claim 11  wherein the nut is removable and separate from the outer shaft. 
     
     
         14 . The screw extension assembly of  claim 11  wherein the outer shaft has flats in the proximal portion and the locking knob has flats configured to align with the flats of the outer shaft when the locking knob is rotated to a locked position allowing the reducer with complimentary internal flats to non-rotationally move relative to the assembly as the nut pushes the reducer. 
     
     
         15 . A kit for use in minimally invasive spinal surgery, the kit comprising:
 a slotted rod receiving implant, the rod receiving implant having a proximal slotted rod holding element and a threaded bone fastener extending distal from the rod holding element;   an inner slotted shaft, the inner slotted shaft being an elongated hollow tubular shaft having a proximal end, a distal end and a slotted distal end portion having a pair of slots open through the distal end defining a pair of deflectable leg extensions, each leg extension having a projection configured to engage a groove on an outer surface of the slotted rod receiving implant thereby coupling the inner shaft to the slotted rod receiving implant adjacent slots at the distal end of the leg extensions having a plurality longitudinal edges keyed to abut proximal walls of the slotted rod receiving implant to prevent rotation;   an outer shaft configured to receive and pass over the inner shaft; the outer shaft having a pair of slots open through a distal end with longitudinal rails adjacent edges of each slot of the outer shaft to slide along each edge of the slots of the leg extensions of the inner shaft along at least a portion of the slots; and   wherein the outer shaft when moved inwardly relative to translate toward the distal end of the inner shaft into an engaged position locks the deflectable legs in a coupled position to the grooves of the slotted rod receiving implant.   
     
     
         16 . The kit of  claim 15  wherein the proximal slotted rod holding element has the grooves for attachment to the deflectable legs of the inner shaft. 
     
     
         17 . The kit of  claim 15  further comprises:
 a threaded set screw for attachment to internal threads of the rod holding element configured to hold a rod when tightened and a fastener driver tool to pass through the inner shaft to fasten and tighten the set screw. 
 
     
     
         18 . The kit of  claim 15  further comprises:
 a rod reducer, the rod reducer having a distal end for pushing a rod and an opposing proximal end. 
 
     
     
         19 . The kit of  claim 18  wherein the outer shaft and the rod reducer have complimentary flats extending longitudinally allowing the rod reducer to translate, but not rotate, relative to the outer shaft. 
     
     
         20 . The kit of  claim 19  wherein a proximal portion adjacent the proximal end of the inner shaft has a threaded portion;
 and the kit further comprises; 
 a nut for engaging the threads of the proximal end of the inner shaft and to abut at the proximal end of the rod reducer, the handle when tightened pushes a rod into a seated position in the rod receiving element. 
 
     
     
         21 . The kit of  claim 20  wherein the threads of the threaded portion of the inner shaft have longitudinal extending grooves aligned to receive the longitudinal rails of the outer shaft. 
     
     
         22 . The kit of  claim 21  wherein the grooves are aligned with the edges of the slots to allow the longitudinal rails to slide relative to the inner shaft toward the distal end on assembly. 
     
     
         23 . The kit of  claim 15  further comprises:
 a locking knob rotationally coupled to a proximal end of the outer shaft wherein the inner shaft has one or more cam grooves and the locking knob is pinned to said cam groove causing the outer shaft to translate longitudinally upon rotation of the locking knob relative to the inner shaft toward an engaged position locking the deflectable legs in the coupled position to the slotted rod receiving implant. 
 
     
     
         24 . The kit of  claim 23  wherein the one or more cam grooves has a cam over pocket feature in an end of the cam groove, the cam over pocket locks the locking knob at or past the engaged position. 
     
     
         25 . The kit of  claim 24  wherein the cam over pocket at the end of the cam groove rotationally moves the locking knob in the absence of forward longitudinal translation of the outer shaft to the inner shaft at the locked position. 
     
     
         26 . The kit of  claim 25  wherein the inner shaft and outer shaft have aligned slots to pass rods therethrough. 
     
     
         27 . The kit of  claim 26  further comprises a rod reducer, the rod reducer being a hollow tube with a distal end to push a rod when placed over the inner and outer shaft. 
     
     
         28 . The kit of  claim 27  further comprises a nut having female threads for engaging the threaded proximal end of the inner shaft and wherein the nut when tightened pushes the reducer inwardly to move a rod into the slotted rod receiving implant wherein the nut is removable and separate from the outer shaft. 
     
     
         29 . The kit of  claim 28  wherein the threads of the proximal end of the inner shaft has a pitch sufficient to allow the nut to auto-rotate, solely due to the weight of the nut, to abut the proximal end of the reducer and further rotation pushes the reducer inwardly to a rod seating position. 
     
     
         30 . The kit of  claim 29  wherein the outer shaft has flats in the proximal portion and the locking knob has flats configured to align with the flats of the outer shaft when the locking knob is rotated to the locked position allowing the reducer with complimentary internal flats to non-rotationally move relative to the assembly as the nut pushes the reducer.