System and method for spinal implant placement

Abstract

A posterior spinal fusion system may include a plurality of cannulas that mate with cages polyaxially coupled to pedicle screws. The cannulas maintain access to the pedicle screws to facilitate percutaneous insertion of a fusion rod into engagement with the cages. Each cannula has a pair of blades that may be held together by an abutment member that at least partially encircles the blades. Each abutment member abuts the skin to define a variable subcutaneous length of the corresponding cannula. Each abutment members is also lockably removable from the corresponding blades to enable the blades to pivot with respect to the connecting element to a position in which they can be withdrawn from the connecting element. The blades of each cannula are spaced apart to provide first and second slots of each cannula, through which the fusion rod can be percutaneously inserted.

The invention claimed is: 
     
       1. A system for providing access to a spine of a patient, the system comprising:
 a first connecting element implantable in a first vertebra of a spine; and   a first cannula adapted to receive at least a portion of a spinal fusion rod therealong, the first cannula comprising:
 a first blade; and 
 a second blade discrete from the first blade; 
   wherein the first and second blades are configured to be assembled together substantially parallel to each other and mated with the first connecting element, without being directly connected to one another, in order to provide the first cannula such that the first cannula has a distal end terminating at the connecting element, whereby the first cannula provides access to the spine when the first connecting element is implanted in the first vertebra of the spine; and   wherein the first and second blades are independently detachable from the first connecting element such that the first and second blades are independently removable from the patient.   
     
     
       2. The system of  claim 1 , wherein the connecting element comprises a pedicle screw implantable in a pedicle of the first vertebra, and a cage polyaxially movable with respect to the pedicle screw. 
     
     
       3. The system of  claim 1 , wherein the first and second blades are configured to be disassembled from one another without removing the distal end from within the patient. 
     
     
       4. The system of  claim 3 , wherein each of the first and second blades comprises a locked configuration, in which the blade is secured to the connecting element, and an unlocked configuration, in which the blade is removable from the connecting element, wherein each of the first and second blades is movable between the locked and unlocked configurations in response to rotation of the blade with respect to the connecting element. 
     
     
       5. The system of  claim 4 , wherein each of the first and second blades is movable between the locked and unlocked configurations in response to rotation of the blade about an axis substantially perpendicular to a longitudinal axis of the first cannula. 
     
     
       6. The system of  claim 1 , further comprising an abutment member configured to engage the first and second blades to restrict relative motion between the first and second blades. 
     
     
       7. The system of  claim 6 , wherein the abutment member is lockable with respect to the first and second blades by a locking mechanism that restricts withdrawal of the abutment member from the first and second blades. 
     
     
       8. The system of  claim 7 , wherein the locking mechanism comprises a plurality of proximal tabs of the first and second blades, wherein the proximal tabs are bendable to permit withdrawal of the abutment member from the first and second blades. 
     
     
       9. The system of  claim 1 , further comprising an abutment member encircling at least a portion of the first cannula to abut an exterior skin surface of the patient, wherein the abutment member is movable along the first cannula to define a variable subcutaneous length of the first cannula. 
     
     
       10. The system of  claim 9 , wherein the abutment member is shaped such that a combined length of the first cannula and the abutment member does not change in response to motion of the abutment member along the first cannula. 
     
     
       11. The system of  claim 1 , wherein the first and second blades are shaped such that, when positioned to define the first cannula, the first and second blades provide a first slot in a side wall of the first cannula. 
     
     
       12. The system of  claim 11 , wherein the first and second blades are further shaped such that, when positioned to define the first cannula, the first and second blades provide a second slot in the side wall, wherein the second slot is arranged with respect to the first slot to permit passage of a rod through the first cannula along a direction transverse to a longitudinal axis of the first cannula. 
     
     
       13. The system of  claim 12 , wherein the distal end is insertable into the patient proximate the spine such that each of the first and second slots extends unbroken along an entire subcutaneous length of the cannula. 
     
     
       14. The system of  claim 1 , further comprising a second cannula securable to a second connecting element implantable in a second vertebra of the spine, and a third cannula securable to a third connecting element implantable in a third vertebra of the spine, wherein the first, second, and third cannulas cooperate to facilitate attachment of a rod to the first, second, and third connecting elements to restrict relative motion of the first, second, and third vertebrae. 
     
     
       15. The system of  claim 1 , wherein the first and second blades have arcuate profiles, whereby the first cannula is defined by a partially cylindrical shape. 
     
     
       16. The system of  claim 1 , wherein the first and second blades each have a distal end including a tab insertable into a corresponding slot of the first connecting element. 
     
     
       17. The system of  claim 1 , further comprising an abutment member configured to prevent the first and second blades from becoming disconnected from the first connecting element. 
     
     
       18. A system for providing access to a spine of a patient, the system comprising:
 a cannula adapted to receive at least a portion of a spinal fusion rod therealong, the cannula comprising a proximal end and a distal end insertable into the patient proximate the spine, the distal end comprising a docking element discrete from and securable to a connecting element implantable in a first vertebra of the spine;   wherein the docking element is receivable by the connecting element in both a docked configuration and an undocked configuration, the distal end being secured to the connecting element in the docked configuration, and the distal end being received by and removable from the connecting element in the undocked configuration, and wherein the docking element is movable between the docked and undocked configurations in response to rotation about an axis substantially perpendicular to a longitudinal axis of the cannula.   
     
     
       19. The system of  claim 18 , wherein the connecting element comprises a pedicle screw implantable in a pedicle of the first vertebra, and a cage polyaxially movable with respect to the pedicle screw, wherein the docking element is configured to dock with the cage. 
     
     
       20. The system of  claim 19 , wherein the cannula comprises:
 a first blade; and   a second blade discrete from the first blade;   wherein the first and second blades are positionable substantially parallel to each other to provide the first cannula;   wherein each of the first and second blades comprises a locked configuration, in which the blade is secured to the connecting element, and an unlocked configuration, in which the blade is removable from the connecting element.   
     
     
       21. The system of  claim 18 , wherein the docking element includes a plurality of tabs, each of the first and second blades comprising at least one of the tabs at a distal end thereof, the tabs enabling rotation of the blades between the locked configuration and the unlocked configuration. 
     
     
       22. The system of  claim 18 , further comprising an abutment member configured to engage the first and second blades to restrict relative motion between the first and second blades to restrict motion of the blades to the unlocked configuration. 
     
     
       23. The system of  claim 22 , wherein the abutment member is lockable with respect to the first and second blades by a locking mechanism that restricts withdrawal of the abutment member from the first and second blades. 
     
     
       24. The system of  claim 23 , wherein the locking mechanism comprises a proximal tab of each of the first and second blades, wherein the proximal tabs are bendable to permit withdrawal of the abutment member from the first and second blades. 
     
     
       25. A system for providing access to a spine of a patient, the system comprising:
 a cannula adapted to receive at least a portion of a spinal fusion rod therealong, the cannula comprising a distal end insertable into the patient proximate the spine and securable to a connecting element implantable in a first vertebra of the spine, the cannula further comprising a proximal end and a longitudinal axis extending between the proximal and distal ends; and   an abutment member encircling at least a portion of the cannula and adapted to abut an outward facing surface of skin of the patient, the entire length of the abutment member along the longitudinal axis of the cannula being disposed between the proximal and distal ends of the cannula, wherein the abutment member is adapted to move along the cannula from the proximal end to the distal end such that the abutment member can be moved to a position abutting the outward facing surface of skin when the distal end of the cannula is secured to the connecting element, whereby a variable subcutaneous length of the cannula is defined, and wherein a combined length of the cannula and the abutment member does not change in response to motion of the abutment member along the cannula.   
     
     
       26. The system of  claim 25 , wherein the cannula comprises:
 a first blade; and   a second blade discrete from the first blade;   wherein the first and second blades are positionable substantially parallel to each other to provide the cannula.   
     
     
       27. The system of  claim 26 , wherein the abutment member is configured to engage the first and second blades to restrict relative motion between the first and second blades. 
     
     
       28. The system of  claim 25 , wherein the abutment member is lockable with respect to the cannula by a locking mechanism that restricts withdrawal of the abutment member from the cannula. 
     
     
       29. The system of  claim 28 , wherein the locking mechanism comprises a plurality of proximal tabs of the cannula, wherein the proximal tabs are bendable to permit withdrawal of the abutment member from the cannula. 
     
     
       30. The system of  claim 25 , wherein the cannula comprises a first slot extending longitudinally along a side wall of the cannula. 
     
     
       31. The system of  claim 25 , wherein the cannula comprises a docking element that couples the cannula to a connecting element implantable in a vertebra of the spine, wherein the docking element comprises a frangible coupling configured to fracture in response to application of a threshold force against the frangible coupling to permit removal of the distal end from the connecting element. 
     
     
       32. A system for providing access to a spine of a patient, the system comprising:
 a cannula comprising:
 a first component; and 
 a second component discrete from the first component; 
   and   an abutment member;   wherein the first and second components are configured to be assembled to a connecting element implantable in a first vertebra of the spine, wherein each of the first and second components has a distal end receivable in the connecting element in a receiving position and a locked position, each of the first and second components being movable between the receiving position and the locked position in response to rotation about an axis substantially perpendicular to a longitudinal axis of the cannula, wherein the abutment member configured to engage the first and second components to restrict relative motion between the first and second components, and wherein the abutment member is lockable with respect to the first and second components by a locking mechanism that restricts withdrawal of the abutment member from the first and second blades.   
     
     
       33. The system of  claim 32 , wherein the first component comprises a first blade, and the second component comprises a second blade, wherein the first and second blades are positionable substantially parallel to each other to provide the cannula. 
     
     
       34. The system of  claim 33 , wherein the distal end comprises a docking element securable to a connecting element implantable in a first vertebra of the spine, wherein each of the first and second blades is secured to the connecting element in the locked position and received within but removable from the connecting element in the receiving position. 
     
     
       35. The system of  claim 32 , wherein the locking mechanism comprises a plurality of proximal tabs of the first and second components, wherein the proximal tabs are bendable to permit withdrawal of the abutment member from the first and second components. 
     
     
       36. The system of  claim 32 , wherein the first and second components have arcuate surfaces, whereby the cannula is defined by a partially cylindrical shape. 
     
     
       37. A system for providing access to a spine of a patient, the system comprising:
 a cannula adapted to receive at least a portion of a spinal fusion rod therealong, the cannula having a longitudinal axis and comprising a distal end insertable into the patient proximate the spine, and a proximal end, the distal end comprising a docking element securable to a connecting element implantable in a first vertebra of the spine; and   an abutment member encircling at least a portion of the cannula, the abutment member having an abutment surface substantially normal to the longitudinal axis, the abutment surface adapted to abut an exterior skin surface of the patient, wherein the abutment member is adapted to move along the cannula from the proximal end to the distal end such that the abutment member can be moved to a position wherein the abutment surface abuts the exterior skin surface when the docking element is secured to the connecting element implanted in the first vertebra of the spine, whereby a variable subcutaneous length of the cannula is defined.   
     
     
       38. The system of  claim 37 , wherein the connecting element comprises a pedicle screw implantable in a pedicle of the first vertebra, and a cage polyaxially movable with respect to the pedicle screw. 
     
     
       39. The system of  claim 37 , wherein the abutment member is lockable with respect to the cannula by a locking mechanism that restricts withdrawal of the abutment member from the cannula. 
     
     
       40. The system of  claim 39 , wherein the locking mechanism comprises a plurality of proximal tabs of the cannula, wherein the proximal tabs are bendable to permit withdrawal of the abutment member from the cannula. 
     
     
       41. The system of  claim 37 , wherein the abutment member is shaped such that a combined length of the cannula and the abutment member does not change in response to motion of the abutment member along the cannula. 
     
     
       42. The system of  claim 37 , wherein the cannula further comprises a first slot portion formed in a side wall of the cannula. 
     
     
       43. The system of  claim 42 , wherein the cannula further comprises a second slot portion formed in the side wall, wherein the second slot is arranged with respect to the first slot to permit passage of a rod through the cannula along a direction transverse to the longitudinal axis of the cannula. 
     
     
       44. The system of  claim 43 , wherein the distal end is insertable into the patient proximate the spine such that each of the first and second slots extends unbroken along the entire subcutaneous length. 
     
     
       45. The system of  claim 37 , wherein the docking element comprises a frangible coupling configured to fracture in response to application of a threshold force against the frangible coupling to permit removal of the distal end from the connecting element. 
     
     
       46. The system of  claim 37 , wherein the cannula comprises:
 a first blade; and   a second blade discrete from the first blade;   wherein the first and second blades are positionable substantially parallel to each other to provide the cannula, and wherein the abutment member is configured to engage the first and second blades to restrict relative motion between the first and second blades.   
     
     
       47. A system for providing access to a spine of a patient, the system comprising:
 a cannula adapted to receive at least a portion of a spinal fusion rod therealong, the cannula comprising a distal end insertable into the patient proximate the spine and securable to a connecting element implantable in a first vertebra of the spine, the cannula further comprising a proximal end and a first slot extending longitudinally between the distal and proximal ends; and   an abutment member encircling at least a portion of the cannula, the abutment member having an abutment surface extending substantially laterally from an outer surface of the cannula, the abutment surface adapted to abut an exterior skin surface of the patient, wherein the abutment member is adapted to move along the cannula from the proximal end to the distal end such that the abutment member can be moved to a position wherein the abutment surface abuts the exterior skin surface when the distal end of the cannula is secured to the connecting element implanted in the first vertebra of the spine, whereby a variable subcutaneous length of the cannula is defined.   
     
     
       48. The system of  claim 47 , wherein the abutment member is lockable with respect to the cannula by a locking mechanism that restricts withdrawal of the abutment member from the cannula. 
     
     
       49. The system of  claim 48 , wherein the locking mechanism comprises a plurality of proximal tabs of the cannula, wherein the proximal tabs are bendable to permit withdrawal of the abutment member from the cannula. 
     
     
       50. The system of  claim 47 , wherein the abutment member is shaped such that a combined length of the cannula and the abutment member does not change in response to motion of the abutment member along the cannula. 
     
     
       51. The system of  claim 47 , wherein the cannula further comprises a second slot portion formed in the side wall, wherein the second slot is arranged with respect to the first slot to permit passage of a rod through the cannula along a direction transverse to a longitudinal axis of the cannula. 
     
     
       52. The system of  claim 51 , wherein the distal end is insertable into the patient proximate the spine such that each of the first and second slots extends unbroken along the entire subcutaneous length. 
     
     
       53. The system of  claim 47 , wherein the cannula comprises a docking element that couples the cannula to a connecting element implantable in a vertebra of the spine, wherein the docking element comprises a frangible coupling configured to fracture in response to application of a threshold force against the frangible coupling to permit removal of the distal end from the connecting element. 
     
     
       54. The system of  claim 47 , wherein the cannula comprises:
 a first blade; and   a second blade discrete from the first blade;   wherein the first and second blades are positionable substantially parallel to each other to provide the cannula, and wherein the abutment member is configured to engage the first and second blades to restrict relative motion between the first and second blades.   
     
     
       55. A method for providing access to a spine of a patient, the method comprising:
 implanting a first connecting element through a first incision in the skin of the patient and into a first vertebra of the spine with a first passageway device formed as a single piece with the first connecting element so that the first passageway device extends proximally from the implanted first connecting element through the first incision, the first passageway device providing a first longitudinal passageway therealong;   moving an implant into engagement with the first connecting element through at least a portion of the first longitudinal passageway;   fracturing a frangible portion between the first passageway device and the first connecting element; and   removing the first passageway device from the body of the patient while the first connecting element remains implanted in the first vertebra.   
     
     
       56. The method of claim 55, wherein the first connecting element comprises a pedicle screw having a cage connected thereto for receiving the implant, the step of implanting the first connecting element in the first vertebra comprising implanting the pedicle screw in a pedicle of the first vertebra. 
     
     
       57. The method of claim 55, wherein the implant is a spinal fusion rod. 
     
     
       58. The method of claim 55, wherein the frangible portion comprises a necked-down region designed to fracture in response to application of a certain pre-established linear force or angular moment. 
     
     
       59. The method of claim 55, wherein the first passageway device defines a transverse opening therethrough, and wherein the step of moving the implant into engagement with the first connecting element comprises subcutaneously passing the implant through the transverse opening along a direction transverse to the first longitudinal passageway. 
     
     
       60. The method of claim 55, further comprising:
 inserting a cutting tool along the first longitudinal passageway; and   using the cutting tool to cut subcutaneous tissue proximate to the first longitudinal passageway.   
     
     
       61. The method of claim 55, further comprising engaging the first passageway device with an abutment member. 
     
     
       62. The method of claim 61, further comprising moving the abutment member along the first passageway device. 
     
     
       63. The method of claim 62, further comprising moving the abutment member to a position abutting an outward facing surface of the skin of the patient. 
     
     
       64. The method of claim 61, further comprising restricting withdrawal of the abutment member from the first passageway device. 
     
     
       65. The method of claim 55, wherein the first passageway device is defined by a first blade and a second blade positioned adjacent to one another and providing the first longitudinal passageway therebetween. 
     
     
       66. The method of claim 65, wherein the frangible portion between the first passageway device and the first connecting element comprises a first frangible portion connecting the first blade to the first connecting element and a second frangible portion connecting the second blade to the first connecting element, and wherein the step of fracturing frangible portion between the first passageway device and the first connecting element comprises fracturing the first and second frangible portions. 
     
     
       67. The method of claim 66, wherein fracturing the first and second frangible portions comprises tilting each of the first and second blades with respect to the first connecting element. 
     
     
       68. The method of claim 67, wherein tilting each of the first and second blades with respect to the first connecting element comprises tilting the first and second blades inwardly towards a central longitudinal axis of the first passageway device. 
     
     
       69. The method of claim 65, further comprising maintaining the first and second blades in a substantially parallel relationship with an abutment member. 
     
     
       70. The method of claim 55, further comprising maintaining opposing sides of the first incision apart around the first longitudinal passageway with the first passageway device. 
     
     
       71. The method of claim 55, further comprising implanting a second connecting element through a second incision in the skin of the patient and into a second vertebra of the spine with a second passageway device coupled to the second connecting element so that the second passageway device extends proximally therefrom through the second incision, the second passageway device providing a second longitudinal passageway therealong. 
     
     
       72. The method of claim 71, further comprising maintaining opposing sides of the first incision apart around the first longitudinal passageway with the first passageway device, and maintaining opposing sides of the second incision apart around the second longitudinal passageway with the second passageway device. 
     
     
       73. The method of claim 71, further comprising implanting a third connecting element through a third incision in the skin of the patient and into a third vertebra of the spine with a third passageway device coupled to the third connecting element so that the third passageway device extends proximally therefrom through the third incision, the third passageway device providing a third longitudinal passageway therealong. 
     
     
       74. A method for providing access to a spine of a patient, the method comprising:
 implanting a first connecting element through a first incision in the skin of the patient and into a first vertebra of the spine with a first blade and a second blade formed as a single piece with the first connecting element so that each of the first and second blades extends proximally from the implanted first connecting element through the first incision, the first and second blades being positioned adjacent to one another to provide a first longitudinal passageway therealong between the first and second blades;   moving an implant into engagement with the first connecting element through at least a portion of the first longitudinal passageway;   uncoupling the first and second blades from the first connecting element by fracturing a first frangible portion between the first blade and the first connecting element and by fracturing a second frangible portion between the second blade and the first connecting element; and   removing the first and second blades from the body of the patient while the first connecting element remains implanted in the first vertebra.   
     
     
       75. The method of claim 74, wherein the first connecting element comprises a pedicle screw having a cage connected thereto for receiving the implant, the step of implanting the first connecting element in the first vertebra comprising implanting the pedicle screw in a pedicle of the first vertebra. 
     
     
       76. The method of claim 74, wherein the implant is a spinal fusion rod. 
     
     
       77. The method of claim 74, wherein fracturing the first and second frangible portions comprises tilting each of the first and second blades with respect to the first connecting element. 
     
     
       78. The method of claim 77, wherein tilting each of the first and second blades with respect to the first connecting element comprises tilting the first and second blades inwardly towards a central longitudinal axis defined along the first longitudinal passageway. 
     
     
       79. The method of claim 74, further comprising maintaining opposing sides of the first incision apart around the first longitudinal passageway with the first and second blades. 
     
     
       80. The method of claim 71, wherein the implant is a spinal fusion rod, and wherein an unbroken portion of skin extends between the first incision and the second incision, the method further comprising:
 inserting a leading end of the spinal fusion rod into the body of the patient through the first incision and through the passageway device; and   moving the leading end of the spinal fusion rod underneath the unbroken portion of skin to the second passageway device or to the second connecting element.   
     
     
       81. The method of claim 74, wherein the implant is a spinal fusion rod, the method further comprising:
 inserting a second connecting element through a second incision in the skin of the patient and into a second vertebra of the spine with a third blade and a fourth blade formed as a single piece with the second connecting element so that each of the third and fourth blades extends proximally therefrom through the second incision, the third and fourth blades being positioned adjacent to one another to provide a second longitudinal passageway therealong between the third and fourth blades, wherein an unbroken portion of skin extends between the first incision and the second incision;   inserting a leading end of the spinal fusion rod into the body of the patient through the first incision and between the first and second blades; and   moving the leading end of the spinal fusion rod underneath the unbroken portion of skin to the second passageway device or to the second connecting element.