USRE46432E1 - System and method for spinal implant placement - Google Patents

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blades to enable the blades to pivot with respect to the connecting element to a position in which they can be withdrawn from the connecting element.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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

ThisNotice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 8,002,798. The reissue applications are U.S. application Ser. No. 13/972,493, U.S. application Ser. No. 13/973,462, and the present application. The present application is a continuation reissue of U.S. application Ser. No. 13/973,462, filed on Aug. 22, 2013, which is a continuation reissue of U.S. application Ser. No. 13/972,493, filed on Aug. 21, 2013, which is an application for reissue of U.S. Pat. No. 8,002,798, which is a continuation-in-part of U.S. application Ser. No. 10/868,075, filed on Jun. 15, 2004, which claims the benefirbenefit of U.S. Provisional Application No. 60/518,580, filed Nov. 8, 2003, the disclosuredisclosures of which are incorporated herein by reference. This application claimU.S. Pat. No. 8,002,798 claims the benefit of U.S. Provisional Application No. 60/682,783, filed on May 19, 2005, the disclosure of which is incorporated herein by reference.

This application relates to U.S. Application Ser. No. 10/669,927, filed on Sep. 24, 2003, the disclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to implantable devices, and more precisely, to posterior spinal fusion systems.

2. The Relevant Technology

Many people experience joint pain in one form or another. In particular, back pain may result from the occurrence of a wide variety of spinal pathologies. Some such pathologies are currently treated by fusing adjacent vertebrae to prevent their relative motion. According to one known method, pedicle screws are implanted in the pedicles and are rigidly secured to a rod passing posterior to the pedicles.

Unfortunately, current procedures often involve the exposure of a relatively large area to permit implantation of the rod. Some current procedures cannot be used to implant a rod that secures more than two vertebrae together. Other known procedures are somewhat complex, and therefore require many parts and surgical steps. Accordingly, there is a need for new fusion rod implantation systems and methods that remedy the shortcomings of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of two adjacent vertebrae of a spine, with guide wires implanted in the pedicles of the right side.

FIG. 2 is a perspective view of three guide wires in isolation, positioned as though implanted in the pedicles of the right sides of three adjacent vertebrae.

FIG. 3 is a perspective view of the guide wires ofFIG. 2, with dilators advanced along the guide wires to dilate surrounding tissue.

FIG. 4 is a perspective view of the guide wires and dilators ofFIG. 3, with hollow dilators placed around the solid dilators.

FIG. 5 is a perspective view of the guide wires and hollow dilators ofFIG. 4, with the solid dilators removed.

FIG. 6 is a perspective view of the guide wires and hollow dilators, with a tapping tool placed over one of the guide wires to tap the corresponding pedicle.

FIG. 7 is an exploded, perspective view of a cannula, abutment member, pedicle screw, cage, set screw, and a portion of a rod according to one embodiment of the invention.

FIG. 8 is a perspective view of the cannula, abutment member, pedicle screw, cage, set screw, and rod portion ofFIG. 7, in assembled form.

FIG. 9 is a perspective view of a screw insertion tool according to one embodiment of the invention.

FIG. 10 is a perspective view of the screw insertion tool ofFIG. 9, in engagement with the assembly ofFIG. 8, excluding the rod portion and the set screw.

FIG. 11 is a perspective view of the screw insertion tool in use to implant the assembly ofFIG. 8, excluding rod portions and set screws, over the first guide wire ofFIG. 2.

FIG. 12 is a perspective view of a fascia clipping tool according to one embodiment of the invention.

FIG. 13 is a perspective view of the fascia clipping tool ofFIG. 12 inserted into one of the cannulas ofFIG. 11 to sever the adjoining fascia.

FIG. 14 is a perspective view of a rod insertion tool according to one embodiment of the invention.

FIG. 15 is a perspective view of the rod insertion tool ofFIG. 14 secured to a rod to facilitate manual insertion of the rod through the cannulas ofFIG. 11.

FIG. 16 is a perspective view of a rod seating tool according to one embodiment of the invention.

FIG. 17 is a perspective view of the rod seating tool ofFIG. 16 inserted into one of the cannulas ofFIG. 11 to help seat the rod in the cages.

FIG. 18 is a perspective view of a rod holding tool according to one embodiment of the invention.

FIG. 19 is a perspective view of the rod holding tool ofFIG. 18 inserted into one of the cannulas ofFIG. 11 to further manipulate the rod.

FIG. 20 is a perspective view of a set screw driver according to one embodiment of the invention.

FIG. 21 is a perspective view of the set screw driver ofFIG. 20 inserted into one of the cannulas ofFIG. 11 to tighten a set screw to retain the rod within the corresponding cage.

FIG. 22 is a perspective view of the pedicle screws, cages, set screws, and cannulas ofFIG. 11, with the abutment members removed to permit removal of the cannulas from the cages.

FIG. 23 is a perspective view of three adjacent vertebrae of the spine, with the rod secured to the pedicle screws to provide posterior spinal fusion.

FIG. 24 is a perspective view of a cannula and cage according to one alternative embodiment of the invention, in which the cannula is secured to the cage by two frangible couplings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to systems and methods for implantation of orthopedic devices. Although the examples provided herein generally relate to insertion of a rod for a posterior spinal fusion system, the present invention may be applied to any procedure in which a device is to be implanted in the body in a minimally invasive manner. Accordingly, the scope of the present invention is not intended to be limited by the examples discussed herein, but only by the appended claims.

As used herein, a “cannula” is an elongated structure having a hollow interior that provides communication between opposite ends of the elongated structure. A “subcutaneous length” is the portion of an object that lies below the surface of a patient's skin. “Transverse” refers to an object or direction that is not parallel with, and not nearly parallel with, another object or direction. A “connecting element” is any man-made structure that is implantable to remain in the body, and is connectable to an anatomic feature and/or another implantable structure. The term “percutaneous” refers to an action carried out at least partially underneath unbroken skin.

The term “discrete” refers to parts that are not formed as a single piece, but are separate pieces from each other. The term “coupled” refers to two elements that are secured together, whether they have been formed separately and secured together via a secondary operation, or they have been formed as a single piece (i.e., formed in a coupled state). The term “securable” refers to elements that are capable of being coupled together, or are already coupled together. A “blade” is an elongated, thin structure. “Polyaxial motion” refers to motion along or about multiple orthogonal axes.

Referring toFIG. 1, a perspective view illustrates a portion of aspine10.FIG. 1 illustrates only the bony structures; accordingly, ligaments, cartilage, and other soft tissues are omitted for clarity. Thespine10 has acephalad direction12, acaudal direction14, ananterior direction16, aposterior direction18, and a medial/lateral axis20, all of which are oriented as shown by the arrows bearing the same reference numerals. In this application, “left” and “right” are used with reference to a posterior view, i.e., a view from behind thespine10. “Medial” refers to a position or orientation toward a sagittal plane (i.e., plane of symmetry that separates left and right sides from each other) of thespine10, and “lateral” refers to a position or orientation relatively further from the sagittal plane.

As shown, the portion of thespine10 illustrated inFIG. 1 includes afirst vertebra24, which may be the L5 (Fifth Lumbar) vertebra of a patient, and asecond vertebra26, which may be the L4 (Fourth Lumbar) vertebra of the patient. The systems and methods may be applicable to any vertebra or vertebrae of thespine10 and/or the sacrum (not shown). In this application, the term “vertebra” may be broadly interpreted to include the sacrum.

As shown, thefirst vertebra24 has abody28 with a generally disc-like shape and twopedicles30 that extend posteriorly from thebody28. A posterior arch, orlamina32, extends between the posterior ends of thepedicles30 to couple thepedicles30 together. Thefirst vertebra24 also has a pair oftransverse processes34 that extend laterally from thepedicles30 generally along the medial/lateral axis20, and aspinous process36 that extends from thelamina32 along theposterior direction18.

Thefirst vertebra24 also has a pair ofsuperior facets38, which are positioned toward the top of thefirst vertebra24 and face generally medially. Additionally, thefirst vertebra24 hasinferior facets40, which are positioned toward the bottom of thefirst vertebra24 and face generally laterally. Each of thepedicles30 of thefirst vertebra24 has asaddle point42, which is positioned generally at the center of the juncture of eachsuperior facet38 with the adjacenttransverse process34.

Similarly, thesecond vertebra26 has abody48 from which twopedicles50 extend posteriorly. A posterior arch, orlamina52, extends between the posterior ends of thepedicles50 to couple thepedicles50 together. Thesecond vertebra26 also has a pair oftransverse processes54, each of which extends from the correspondingpedicle50 generally along the medial/lateral axis20, and aspinous process56 that extends from thelamina52 along theposterior direction18.

Thesecond vertebra26 also has a pair ofsuperior facets58, which are positioned toward the top of thesecond vertebra26 and face generally inward. Additionally, thesecond vertebra26 hasinferior facets60, which are positioned toward the bottom of thesecond vertebra26 and face generally outward. Each of thepedicles60 of thesecond vertebra26 has asaddle point62, which is positioned generally at the center of the juncture of eachsuperior facet58 with the adjacenttransverse process54.

Thesuperior facets38 of thefirst vertebra24 articulate (i.e., slide and/or press) with theinferior facets60 of thesecond vertebra26 to limit relative motion between the first andsecond vertebrae24,26. Thus, the combination of eachsuperior facet38 with the adjacentinferior facet60 provides a facet joint64. The first andsecond vertebrae24,26 thus define twofacet joints64 that span the distance between the first andsecond vertebrae24,26. Theinferior facets40 of thefirst vertebra40 and thesuperior facets58 of thesecond vertebra26 are part of other facet joints that control motion between the first andsecond vertebrae24,26 and adjacent vertebrae (not shown) and/or the sacrum (also not shown).

Thevertebrae24,26 and/or the intervertebral disc (not shown) between them, may be damaged or diseased in some manner that makes it desirable to secure thevertebrae24,26 together in a manner that prevents relative motion between them. Accordingly, posterior spinal fusion may be employed to secure thepedicles30,50 together.FIGS. 1 through 23 illustrate one system and method for installing a posterior spinal fusion system.FIG. 24 illustrates a cannula and cage according to one alternative embodiment of the invention.

As further illustrated inFIG. 1, afirst guide wire70 has been inserted into the right-side pedicle30 of thefirst vertebra24, and asecond guide wire72 has been inserted into the right-side pedicle50 of thesecond vertebra26. Theguide wires70,72 pass through the saddle points42,62, respectively, of thepedicles30,50. Each of theguide wires70,72 has aproximal end74 and adistal end76. As shown, the proximal ends74 are exposed, and the distal ends76 are implanted in thepedicles30,50. The distal ends76 may be implanted by methods known in the surgical arts.

Referring toFIG. 2, a perspective view illustrates the first andsecond guide wires70,72 ofFIG. 1, with thevertebrae24,26 removed for clarity. Athird guide wire78 is also shown. Thethird guide wire78 is positioned adjacent to the first andsecond guide wires70,72 as though thethird guide wire78 were implanted in the right-hand pedicle of a vertebra (not shown) directly superior to thesecond vertebra26. Accordingly, the method ofFIGS. 1 through 23 may be used to secure together vertebrae on multiple levels, not just two adjacent vertebrae.

Referring toFIG. 3, a perspective view illustrates theguide wires70,72,78, in conjunction with afirst dilator80, asecond dilator82, and athird dilator88. Each of thedilators180,82,88 has aproximal end92 and adistal end94. The proximal ends92 may be shaped for gripping by hand, or for attachment to a handle or the like. The distal ends94 are rounded to permit relatively gentle spreading of tissues surrounding theguide wires70,72,78 by thedilators80,82,88.

Each of thedilators80,82,88 has a bore sized to receive theproximal end74 of thecorresponding guide wire70,72, or78, so that thedilators80,82,88 are able to slide along theguide wires70,72,78 toward the distal ends74, thereby spreading the tissues away from theguide wires70,72,78. Each of thedilators80,82,88 may optionally include a plurality of nesting elements that permit discretely gradual dilation. As an alternative to theguide wires70,72,78 and thedilators80,82,88, a variety of other guiding devices and/or dilation devices may be used within the scope of the present invention.

Referring toFIG. 4, a perspective view illustrates theguide wires70,72,78 anddilators80,82,88 ofFIG. 3, with first, second, and thirdhollow dilators100,102,104 placed around thedilators80,82,88, respectively. Each of thehollow dilators100,102,104 has a generally tubular shape with aproximal end106, adistal end108, and abore110 extending from theproximal end106 to thedistal end108. Each of thebores110 is sized to receive the outward-facing surface of the correspondingdilator80,82,88.

Accordingly, thehollow dilators100,102,104 may simply slide along theanterior direction16 between the outward-facing surfaces of thedilators80,82,88 and the adjoining tissues. Thehollow dilators100,102,104 then reach the positions shown inFIG. 4, thereby removing thedilators80,82,88 from significant contact with the tissues to be dilated.

Referring toFIG. 5, a perspective view illustrates theguide wires70,72,78 andhollow dilators100,102,104 ofFIG. 4, with thedilators80,82,88 removed. Thedilators80,82,88 are simply withdrawn along theposterior direction18 from within thehollow dilators100,102,104 to leave thebores110 of thehollow dilators100,102,104 unobstructed.

Referring toFIG. 6, a perspective view illustrates theguide wires70,72,78 andhollow dilators100,102,104, with atapping tool120 placed over thefirst guide wire70 to tap the corresponding pedicle (not shown inFIG. 6). As shown, thetapping tool120 may have ahandle122 shaped to be gripped by hand, and ashank124 extending from thehandle122. Theshank124 has aproximal end126 coupled to thehandle122 and adistal end128 having a plurality ofthreads130.

Thetapping tool120 also has a bore (not shown) extending through theshank124 and through at least a portion of thehandle122. The bore is sized to receive any of theguide wires70,72,78 so that thetapping tool120 can be guided sequentially along each of theguide wires70,72,78 to tap thepedicle30 of thefirst vertebra24, thepedicle50 of thesecond vertebra26, and the pedicle of the third vertebra (not shown inFIG. 6). Tapping is carried out by rotating thehandle122 clockwise while exerting axial pressure on thehandle122 to cause thedistal end128 to penetrate the bone. After a pedicle has been tapped, thedistal end128 is withdrawn from the tapped cavity by rotating thehandle122 counterclockwise.

Referring toFIG. 7, an exploded, perspective view illustrates a connectingelement140, acannula142, anabutment member144, and arod portion146 according to one embodiment of the invention. Therod portion146 is a segment of a longer rod that may be used to secure thefirst vertebra24, thesecond vertebra26, and the third vertebra (not shown inFIG. 7) together. The connectingelement140 is used to secure therod portion146 to one pedicle of the vertebrae to be secured together. Thecannula142 is used to maintain access to the connectingelement140 after it has been implanted in the pedicle in a manner that facilitates percutaneous placement of therod portion146 and attachment of therod portion146 to the connectingelement140. Theabutment member144 helps to hold thecannula142 together and keep it secured to the connectingelement140 in a manner that will be described subsequently.

As embodied inFIG. 7, the connectingelement140 has apedicle screw150, acage152, and aset screw154. Thepedicle screw150 is the portion of the connectingelement140 that is implanted in the corresponding pedicle. Thepedicle screw150 is able to hold thecage152 against the pedicle at any of a variety of orientations of thecage152 with respect to thepedicle screw150. Thus, thecage152 is polyaxially movable with respect to thepedicle screw150 until theset screw154 is tightened into thecage152 to lock the orientation of thecage152 with respect to thepedicle screw150.

Thepedicle screw150 has ahead160 and ashank162. Thehead160 has a convex semispherical underside that engages thecage152 in any of a variety of relative orientations to provide the polyaxial coupling described previously. Thehead160 also has ahexagonal recess164 designed to receive a hexagonal end of a pedicle screw driver (not shown inFIG. 7), which will be shown and described subsequently. Theshank162 has a plurality ofthreads166 that rotate into threaded engagement with the tapped pedicle. Thepedicle screw150 also has a bore (not shown) extending through theshank162 and thehead160 to receive any of theguide wires70,72,78 to facilitate guiding of thepedicle screw150 into engagement with the corresponding pedicle.

Thecage152 has a base168 in which anaperture170 is formed. Theaperture170 is sized such that theshank162 of thepedicle screw150 may be inserted through theaperture170. Thehead160 of thepedicle screw150 then rests on a concave semispherical surface of thebase168, within which thehead160 is polyaxially rotatable. Thecage152 also has a pair ofarms172 that extend from thebase168, generally parallel to each other. Each of thearms172 has aslot174 and anexterior recess176. Theslots174 pass through thearms172 to communicate with theslots174. Each of thearms172 has an inward-facing surface on which a plurality ofthreads178 are formed to receive theset screw154. Thearms172 define recesses therebetween, and the recesses form ends of a trough in which therod portion146 is able to rest.

As shown, theset screw154 has ahexagonal recess180 that enables theset screw154 to be rotated by a driver that will be shown and described subsequently. Theset screw154 also has an outward-facing surface on which a plurality ofthreads182 are formed to enable theset screw154 to rotate into threaded engagement with thecage152. Once therod portion146 is positioned between thearms172 of thecage152, theset screw154 may be tightened to press therod portion146 against thehead160 of thepedicle screw150, thereby resisting further relative rotation between thecage152 and thepedicle screw150.

Upon assembly, thecannula142, which is shown in exploded form inFIG. 7, will have aproximal end190 and adistal end192. Thecannula142 may be dimensioned such that theproximal end190 protrudes above the skin, while thedistal end192 is securable to thecage152 and is insertable through the skin along with thecage152. Thecannula142 includes afirst blade194 and asecond blade196, which may be substantially identical to each other. Each of theblades194,196 has aproximal end198 corresponding to theproximal end190 of thecannula142, and adistal end200 corresponding to thedistal end192 of thecannula142.

Eachproximal end198 has aproximal tab202, and eachdistal end200 has adistal tab204. Eachproximal tab202 has a lockingridge206 that protrudes generally outward, and extends generally circumferentially. Eachproximal tab202 is also elongated, with a thin cross section that permits bending toward and away from the axis (not shown) of the cannula. Eachdistal tab204 hasbends208 that cause thedistal tab204 to jut outward, while remaining generally parallel with the remainder of thecorresponding blade194 or196.

Each of thedistal tabs204 is insertable through theslot174 of theadjacent arm172 of thecage152 when thecorresponding blade194 or196 is tilted to position theproximal end198 inward relative to thedistal end200. Once thedistal tabs204 have passed through theslots174, rotation of theblades194 or196 back to a position generally parallel to each other, and to the axis of thecage152, causes thedistal tabs204 to lie within the exterior recesses176 of thearms172 such that thebends208 are unable to slide back through theslots174. Thus, theblades194,196 are then in a locked configuration, and cannot be detached from thecage152 until they are again moved to the unlocked configuration, i.e., tilted to position the proximal ends198 inward.

As long as theblades194,196 remain generally parallel to each other, thedistal end192 of thecannula142 remains secured to thecage152. Thus, thedistal tabs204 form a docking element that removably secures thecannula142 to the connectingelement140. Theabutment member144 serves to keep theblades194,196 parallel to each other to keep thecannula142 in assembled form and to simultaneously keep thecannula142 secured to thecage152 by keeping theblades194,196 from rotating into the unlocked configuration. When thecannula142 is secured to thecage152, thecannula142 is in its “docked configuration.” When thecannula142 is removed from thecage152, thecannula142 is in its “undocked configuration.”

As shown, theabutment member144 is generally disc-shaped with acentral opening212 and anopen side214 that provides access to thecentral opening212. Theabutment member144 also has aninterior recess216 in communication with thecentral opening212. Furthermore, theabutment member144 has a pair ofarcuate slots218 that extend around opposing portions of thecentral opening212 and are generally coaxial with thecentral opening212. Thearcuate slots218 are sized to receive the first andsecond blades194,196 and to keep the first andsecond blades194,196 generally parallel to each other, and perpendicular to theabutment member144. Thus, theblades194,196 are unable to pivot to the unlocked configuration and thecannula142 maintains a generally tubular shape.

After the distal ends200 of theblades194,196 are coupled to thecage152, the proximal ends198 may be inserted through thearcuate slots218 of theabutment member144. Each of the lockingridges206 has a wedge-like profile. Accordingly, as the lockingridges206 pass through thearcuate slots218, theproximal tabs202 are urged to bend inward. Once the lockingridges206 move out of thearcuate slots218, theproximal tabs202 snap back to an undeflected orientation, and the lockingridges206 are then positioned outboard of thearcuate slots218 to interfere with withdrawal of theproximal tabs202 from thearcuate slots218. Thus, theproximal tabs202 act as a locking mechanism that restricts withdrawal of theabutment member144 from around thecannula142.

After theblades194,196 have been inserted into thearcuate slots218, theabutment member144 may be positioned at any of a range of positions along thecannula142. Thus, upon implantation of thepedicle screw150 in the corresponding pedicle, theabutment member144 will abut the outward-facing surface of the patient's skin through which thecannula142 passes. Theabutment member144 helps to stabilize thecannula142 with respect to the tissues it passes through.

Referring toFIG. 8, a perspective view illustrates the connectingelement140, thecannula142, theabutment member144, and therod portion146 ofFIG. 7, in assembled form. Theshank162 of thepedicle screw150 has been inserted through theaperture170 such that thehead160 of thepedicle screw150 rests against thebase168 of thecage152. Therod portion146 has been positioned between thearms172 and theset screw154 has been rotated into engagement with thethreads166 of thearms172 to keep therod portion146 in place and restrict further rotation of thecage152 relative to thepedicle screw150.

Thedistal tabs204 have also been inserted through theslots174 of thearms172 of thecage152, and theblades194,196 have been rotated into the locked configuration. The proximal ends198 of theblades194,196 have been inserted through thearcuate slots218 of theabutment member144 to keep theblades194,196 in assembled form to define thecannula142, and to keep thecannula142 secured to thecage152. When one or both of theblades194,196 are oriented in the unlocked configuration, theblades194,196 may still be said to define thecannula142, although thecannula142 then has a tapered shape.

Once assembled, thecannula142 hasslots220 extending along its entire longitudinal length, along opposite sides of thecannula142. Theslots220 extend to thecage152, and are therefore contiguous with the recesses defined by thearms172 of thecage152. Upon implantation of thepedicle screw150, theslots220 will extend along the entire subcutaneous length of thecannula142. Therefore, therod portion146 may be inserted percutaneously through theslots220 along a direction transverse to the axis of thecannula146, and may then be moved through theslots220 along theanterior direction16, directly into the trough of thecage152.

Referring toFIG. 9, a perspective view illustrates ascrew insertion tool230 according to one embodiment of the invention. In the embodiment ofFIG. 9, thescrew insertion tool230 has adriver232 designed to rotate thepedicle screw150 into threaded engagement with the corresponding tapped pedicle, and acountertorque member234 that maintains the orientation of thecage152 during rotation of thepedicle screw150.

Thedriver232 has ahandle236 designed to be rotated by hand, and ashank238 extending from thehandle236. Theshank238 has aproximal end240 and distal end242 shaped to drive thepedicle screw150. The distal end242 has ahexagonal projection244 that fits into thehexagonal recess164 of thehead160 of thepedicle screw150. Thedriver232 also has abore246 sized to receive any of theguide wires70,72,78; thebore246 extends through at least a portion of theshank238 and, optionally, through all or part of thehandle236 to permit thescrew insertion tool230 to be easily guided along each of theguide wires70,72,78.

Thecountertorque member234 has abore248 that extends along its entire length, through which theshank238 of thedriver232 passes. Thebore248 is large enough to permit easy relative rotation between thedriver232 and thecountertorque member234. Thecountertorque member234 also has a generally tubular shape with aproximal end250 and adistal end252. Theproximal end250 has a plurality oflongitudinal ridges254 designed to be gripped by a user's fingers to restrict rotation of the countertorquemember234. Thedistal end252 has a plurality ofthreads256 designed to threadably engage thethreads178 of thearms172 of thecage152.

Thus, thedistal end252 of the countertorquemember234 can be rotated into engagement with thecage152 to secure thecountertorque member234 to thecage152, thereby allowing a user to hold thelongitudinal ridges254 to keep thecage152 stationary during rotation of thedriver232. Thecountertorque member234 also haslongitudinal slots258 that provide access to thebore248 of the countertorquemember234 for cleaning or other purposes.

Referring toFIG. 10, a perspective view illustrates thescrew insertion tool230 ofFIG. 9, in engagement with the assembly ofFIG. 8, excluding therod portion146 and theset screw154. Thethreads256 of thedistal end252 have been rotated into engagement with thethreads178 of thearms172, and thehexagonal projection244 has been inserted into thehexagonal recess164 of thehead160 of thepedicle screw150. Thescrew insertion tool230 is thus ready to implant thepedicle screw150 into the corresponding tapped pedicle.

In the alternative to the embodiment illustrated inFIGS. 9 and 10, a screw insertion tool may have a countertorque member that functions independently of threaded engagement with thecage152. For example, an alternative counter-torque member (not shown) may have et projections that slide into the recesses between thearms172, or engage other features of thecage152, to prevent relative rotation between thecage152 and the countertorque member.

Referring toFIG. 11, a perspective view illustrates thescrew insertion tool230 in use to implant the assembly ofFIG. 8, excludingrod portions146 and setscrews154, over thefirst guide wire70 ofFIG. 2. Thehandle236 may be used to actuate the connectingelement140, thecannula142, and theabutment member144 along thefirst guide wire70. Upon contact of thepedicle screw150 with the tapped pedicle30 (not shown inFIG. 11), thehandle236 is rotated while thecountertorque member234 is restrained from rotation via application of pressure on thelongitudinal ridges254. Thus, thepedicle screw150 is rotated into engagement with the pedicle while keeping thecage152, thecannula142, and theabutment member144 at a relatively constant orientation. As shown, thecannula142 is oriented such that theslots220 generally face in thecephalad direction12 and thecaudal direction14.

As also shown, a second connectingelement260 has been implanted in thepedicle50 of the second vertebra26 (not shown inFIG. 11). Asecond cannula262 and asecond abutment member264 have been secured to the second connectingelement260 in a manner similar to that of thecannula142 and theabutment member144. A third connectingelement270 has been implanted in the pedicle of the third vertebra (not shown inFIG. 11). Athird cannula272 and athird abutment member274 have been secured to the third connectingelement270 in a manner similar to that of thecannula142 and theabutment member144. The second connectingelement260,cannula262, andabutment member264 and the third connectingelement270,cannula272, andabutment member274 may be substantially identical to the connectingelement140, thecannula142, and theabutment member144, as shown inFIGS. 7 and 8.

Referring toFIG. 12, a perspective view illustrates afascia clipping tool280 according to one embodiment of the invention. As shown, thefascia clipping tool280 has afirst member282 and asecond member284 pivotably secured to thefirst member284 through the use of apin286. Thefirst member282 has afinger loop288 designed to receive a user's finger, and ablade290 extending at a predefined angle from the remainder of thefirst member282. Similarly, thesecond member284 has afinger loop292 and ablade294. Theblades290,294 have inwardly-oriented sharp edges that provide a scissoring effect when theblades290,294 are brought into a parallel configuration.

Referring toFIG. 13, a perspective view illustrates thefascia clipping tool280 ofFIG. 12 inserted into thecannula142 ofFIG. 11 to sever the adjoining fascia (not shown). The skin between thecannulas142,262,272 need not be severed; rather, only the subcutaneous fascia is cut to provide unimpeded percutaneous access to thecages152 of the connectingelements150,260,270. Theopen side214 and theinterior recess216 of each of theabutment members144,264,274 provides the appropriate range of relative motion in the cephalad andcaudal directions12,14 for the first andsecond members282,284 to permit relatively easy cutting of the fascia with little or no damage to the surrounding tissue (not shown).

Referring toFIG. 14, a perspective view illustrates arod insertion tool300 according to one embodiment of the invention. As shown, therod insertion tool300 has ahandle302 shaped to be grasped by hand, and ashank304 extending from thehandle302. Thehandle302 has aknob306 that can be rotated by hand to control retention of a rod (not shown inFIG. 14) by therod insertion tool300. Theshank304 has aproximal end308 secured to thehandle302 and adistal end310 that receives and is securable to the end of the rod.

More precisely, thedistal end310 may have arod coupling312 securable to the rod through the use of a mechanism such as a collet or gripper. Such a mechanism may be actuated by rotating theknob306. According to alternative embodiments of the invention, an interference fit or another similar mechanism may be used to retain the rod in such a manner that the rod can be removed when a threshold removal force is applied. Theshank304 has a plurality ofslots314 distributed along the length of theshank304 to provide access to a bore (not shown) of theshank304 for cleaning or other purposes.

Referring toFIG. 15, a perspective view illustrates therod insertion tool300 ofFIG. 14 secured to arod316 to facilitate manual insertion of therod316 through thecannulas142,262,272 ofFIG. 11. As shown, therod316 has aleading end317 and a trailingend318 secured to therod coupling312 of therod insertion tool300. Prior to insertion underneath the skin, therod316 may be contoured based on the morphology of the patient's spine so that therod316 will maintain the proper lordotic angle between thefirst vertebra24, thesecond vertebra26, and the third vertebra. Alternatively, therod316 may be pre-lordosed to provide a lordotic angle suitable for most patients. Therod316 may optionally be selected from a kit (not shown) containing multiple, differently angled rods.

Theleading end317 is first inserted through the skin (not shown) of the patient by inserting theleading end317 through theproximal end190 of thecannula142, and through thecentral opening212 of theabutment member144. Once underneath the skin, thehandle302 is manipulated to insert theleading end317 through the opening formed in the fascia, through theslots220 of thesecond cannula262, and through at least oneslot220 of thethird cannula272 and/or through at least one recess of thecage152 of the third connectingelement270. Then, therod316 may be detached from therod insertion tool300.

Referring toFIG. 16, a perspective view illustrates arod seating tool320 according to one embodiment of the invention. As shown, therod seating tool320 has ahandle322 shaped to be gripped by hand, and ashank324 extending from thehandle322. Theshank324 has aproximal end326 adjacent to thehandle322 and adistal end328 shaped to push therod316 into place. More precisely, thedistal end328 may have ablade330 with a generally thin cross section. Theblade330 may terminate in anarcuate recess332 with a radius matching that of therod316.

Referring toFIG. 17, a perspective view illustrates therod seating tool320 ofFIG. 16 inserted into thesecond cannula262 ofFIG. 11 to help seat therod316 in thecages152 of the connectingelements140,260,270. As shown, thedistal end328 of therod seating tool320 may simply be inserted through thesecond cannula262 until thearcuate recess332 of theblade330 abuts therod316. Then, pressure is applied via thehandle322 to urge therod316 to slide along theslots220, in theanterior direction16 until therod316 is seated generally within the troughs of thecages152 of the connectingelements140,260,270. Thedistal end328 may similarly be inserted into thecannula142, thethird cannula272, or any combination of thecannulas142,262,272 until therod316 has been positioned to pass through all of thecages152.

Referring toFIG. 18, a perspective view illustrates arod holding tool18 according to one embodiment of the invention. Therod holding tool18 is designed to grip therod316 to permit translation of therod316 along its axis or rotation of therod316 about its axis. As embodied inFIG. 18, therod holding tool18 hasfirst handle342, asecond handle344, acentral body346, ashank348, apin350, afirst leaf spring352, asecond leaf spring354, and a pair ofscrews356.

Thefirst handle342 has aproximal end360 and adistal end362. Theproximal end360 has atransverse extension364 that facilitates gripping of thefirst handle342, for example, with the fingers of one hand. Theproximal end360 also has ahole366 with threads designed to receive threads (not shown) of thecorresponding screw356. Thedistal end362 has ablade368 that is pivotably coupled to thecentral body346 by thepin350.

Thesecond handle344 has aproximal end370 and adistal end372. Theproximal end370 has a hole (not shown) similar to thehole366 of theproximal end360 of thefirst handle342. Thedistal end372 may be formed as a single piece with thecentral body346. Thecentral body346 has aslot374 that receives theblade368 of thedistal end362 of thefirst handle342. Thepin350 passes through theslot374 to extend through theblade368, thereby providing the pivotable coupling between thecentral body346 and thefirst handle342. Thecentral body346 also has aprojection376 that extends generally distally.

Theshank348 has aproximal end380 at which theshank348 is secured to theprojection376 of thecentral body346, and adistal end382 designed to grip therod316 in response to pressure applied to squeeze the first andsecond handles342,344 together. More precisely, thedistal end382 has anarcuate recess384 with a radius matched to that of therod316, and anarcuate extension386 with a radius equal or similar to that of thearcuate recess384.

Theshank348 also has astationary arm387 and a slidingarm388, each of which has a generally half-circular cross sectional shape. Thestationary arm387 is rigidly attached to theprojection376, and the slidingarm388 is slidably coupled to thestationary arm387. Thearcuate extension386 is on thestationary arm387, and thearcuate recess384 is on the slidingarm388. The slidingarm388 is coupled to theblade368 of thefirst handle342 within thecentral body346 such that pivotal motion of thefirst handle342 urges the slidingarm388 to slide distally along thestationary arm387.

Thefirst leaf spring352 has a fixedend390 secured to thefirst handle342 by thecorresponding screw356, and a coupledend392 coupled to thesecond leaf spring354. Similarly, thesecond leaf spring354 has a fixedend394 secured to thesecond handle344 by theother screw356, and a coupledend396 coupled to the coupledend392 of thefirst leaf spring352. The coupled ends392,396 may be interlocked in an interdigitated manner that permits relative rotation of the coupled ends392,396. Thus, theleaf springs352,354 cooperate to provide resilient force urging the first andsecond handles342,344 to move apart, thereby urging thedistal end382 of theshank348 to release therod316 in the absence of force urging thehandles342,344 together.

In order to use therod holding tool340, a portion of therod316 may first be positioned to abut the arcuate surface of thearcuate extension386. When the first andsecond handles342,344 are squeezed together, for example, by hand, the slidingarm388 slides distally along thestationary arm387. As the slidingarm388 slides along thestationary arm387, thearcuate recess384 moves toward thearcuate extension386 until the arcuate surface of thearcuate recess384 is contiguous with the arcuate surface of thearcuate extension386. Thearcuate recess384 then cooperates with thearcuate extension386 to capture therod316 so that therod holding tool340 can be used to axially rotate or translate therod316, as desired.

Referring toFIG. 19, a perspective view illustrates therod holding tool340 ofFIG. 18 inserted into thesecond cannula262 ofFIG. 11 to further manipulate therod316. As shown, thedistal end382 of theshank348 has been inserted through thesecond cannula262 to position thearcuate extension386 adjacent to therod316. The first andsecond handles342,344 have also been squeezed together to slide thearcuate recess384 against therod316 to capture therod316. Thus, therod316 can be translated or rotated in any direction. More particularly, if therod316 is not yet rotated to the proper orientation to pass properly through thecages152, therod316 may be rotated axially through the use of therod holding tool340. Therod316 may also be translated axially if needed. Fluoroscopy or other known methods may be used to check the position and orientation of therod316 with respect to thecages152.

Referring toFIG. 20, a perspective view illustrates aset screw driver400 according to one embodiment of the invention. As shown inFIG. 20, theset screw driver400 has ahandle402 and ashank404 extending from thehandle402. Thehandle402 has a pair of oppositely disposedtransverse extensions406 that protrude to facilitate manual gripping and rotation of thehandle402. Theshank404 has aproximal end408 adjacent to thehandle402 and adistal end410 designed to transmit torque to theset screw154. Thedistal end410 may have ahexagonal projection412 insertable into thehexagonal recess180 of theset screw154.

Referring toFIG. 21, a perspective view illustrates the setscrew driver400 ofFIG. 20 inserted into thecannula142 ofFIG. 11 to tighten thecorresponding set screw154 to retain therod316 within the correspondingcage152. Theset screws154 may be applied after therod316 has been properly positioned with respect to thecages152.

Thehexagonal projection412 may first be inserted into thehexagonal recess180 of theset screw154. Then, thehandle402 may be gripped and used to insert theset screw154 into position adjacent to thethreads178 of thearms172 of thecage152 of the connectingelement140. Thehandle402 may then be rotated clockwise to cause thethreads182 of theset screw154 to rotate into engagement with thethreads178. Thehandle402 may be rotated clockwise until theset screw154 presses firmly against therod316 to keep therod316 in place within the correspondingcage152, and to restrict further rotation of thecage152 with respect to the correspondingpedicle screw150. All three of theset screws154 may be positioned and tightened in this manner to complete assembly of the posterior spinal fusion system.

In addition to theset screw driver400 ofFIGS. 20 and 21, a countertorque member (not shown) may be provided. Such a countertorque member may engage thecage152 to keep thecage152 from rotating while theset screw154 is tightened.

Referring toFIG. 22, a perspective view illustrates the fully assembled posterior spinal fusion system including the connectingelements140,260,270 and therod316, with thecannulas142,262,272 still secured to thecages152 of the connectingelements140,260,270, but with theabutment members144,264,274 removed from thecannulas142,262,272. Theabutment members144,264,274 may be removed from thecannulas142,262,272 by squeezing theproximal tabs202 of eachcannula142,262,272 together, for example, with the thumb and forefinger of a hand. The lockingridges206 are thereby moved into alignment with thearcuate slots218 of theabutment members144,264,274 so that theabutment members144,264,274 can be withdrawn along theposterior direction18 from the correspondingcannulas142,262,272, respectively.

As mentioned previously, once theabutment members144,264,274 have been removed, theblades194,196 of eachcannula142,262,272 may be pivoted into the unlocked configuration. Thedistal tabs204 may then be withdrawn from theslots174 of thearms172 of thecages152, and out of the patient's body. Then, the incisions made to accommodate thecannulas142,262,272 may be closed and treated through the use of methods known in the art.

Referring toFIG. 23, a perspective view illustrates the completed posterior spinal fusion system. In addition to the first andsecond vertebrae24,26,FIG. 23 illustrates athird vertebra428 superior to thesecond vertebra26. Thethird vertebra428 has features similar to those set forth in the description of the first andsecond vertebrae24,26. Most pertinently, thethird vertebra428 haspedicles430 with saddle points432.

As shown, thepedicle screw150 of the first connectingelement140 is implanted in thepedicle30 of the right side of thefirst vertebra24, thepedicle screw150 of the second connectingelement260 is implanted in thepedicle50 of the right side of thesecond vertebra26, and thepedicle screw150 of the third connectingelement270 is implanted in thepedicle430 of the right side of thethird vertebra428. Therod316 passes through the troughs of thecages152 in a manner that preserves the proper lordosis of thespine10. Theset screws154 have been rotated into engagement with thecages152 and tightened to keep therod316 in place within the troughs of thecages152 and to substantially eliminate rotation of thecages152 relative to theirrespective vertebrae24,26,428.

The connectingelements140,260,270 thus cooperate with therod316 to restrict relative motion of thevertebrae24,26,428 to form a posterior vertebral fusion system. If desired, a similar system may be implanted in the left-side pedicles30,50,430 of thevertebrae24,26,428 through the method set forth previously to provide a bilateral system. Additionally, the present invention is not limited to a three-level fusion system, but may be used to fuse any number of vertebrae together. To fuse more than three vertebrae together, the steps set forth above may simply be repeated for each additional vertebra, and the rod may be inserted through the skin via a first cannula, and then percutaneously inserted through three or more additional cannulas.

A variety of alternative embodiments of the invention may be used in place of the method and components illustrated inFIGS. 1-23. For example, a variety of different connecting elements known in the art may be used in place of the connectingelements140,260,270 shown and described previously. Polyaxially rotatable cages are an optional feature of such connecting elements. Cannulas different from thecannulas142,262,272 set forth above may be used, and need not be formed of multiple separate pieces, but may instead be single piece structures. Such cannulas may have slots that terminate toward their proximal ends.

A variety of different docking elements may be used in place of thedistal tabs204 and theslots174. Such docking elements may include threaded engagement, collets, pin-and-locking-groove systems, interference fit couplings, snap-fit couplings, and the like. Additionally, a variety of locking mechanisms may be used in place of theproximal tabs202. Such locking mechanisms may include locking members securable to the proximal ends190 of thecannulas142,262,272 to interfere with withdrawal of theabutment members144,264,274 therefrom, or locking members movably coupled to the proximal ends190. Additionally, a wide variety of interfaces may be provided between eachcannula142,262,272 and thecorresponding abutment member144,164,274 to restrict withdrawal of theabutment members144,264,274 from thecannulas142,262,272.

Furthermore, each of the instruments set forth previously, including thescrew insertion tool230, thefascia clipping tool280, therod insertion tool300, therod seating tool320, therod holding tool340, and theset screw driver400, may be replaced with an alternatively configured tool that performs a similar function. The steps recited above need not necessarily be performed in the order provided, but may instead be rearranged, and some steps may be omitted and/or other steps may be added, to provide alternative methods within the scope of the invention.

According to one alternative embodiment of the invention, a connecting element may have a cage pre-attached to a cannula that provides access to the cage. Such an alternative embodiment will be shown and described in greater detail in connection withFIG. 24.

Referring toFIG. 24, a perspective view illustrates acannula442 and acage452 according to one alternative embodiment of the invention in which thecannula442 and thecage452 are initially secured together. Thecage452 may be part of a connecting element like the connectingelements140,260,270 set forth previously. Accordingly, thecage452 may be polyaxially coupled to a pedicle screw like thepedicle screw150 ofFIG. 7, and may be designed to receive arod portion146 like that ofFIG. 7. Thecage452 may also receive aset screw154 like that ofFIG. 7 to keep therod portion146 in place and restrain pivotal relative motion between thecage452 and thepedicle screw150.

As shown inFIG. 24, thecage452 has a base168 with anaperture170 designed to receive thepedicle screw150. Thecage452 has a pair ofarms472 extending from thebase168. Thearms472 need not haveslots174 orexterior recesses176 like thearms172 of thecage152 ofFIG. 7. However, each of thearms472 does have threads478 that face inward to receive theset screw154.

Thecannula442 has a generally tubular shape with aproximal end490 and adistal end492. Thecannula442 includes afirst blade494 and asecond blade496 positioned opposite thefirst blade494. Each of theblades494,496 has aproximal end498 that is substantially free, and adistal end500 pre-attached to thecorresponding arm472 of thecage452. In the embodiment ofFIG. 24, the distal ends500 are formed as a single piece with thearms472, and are separated from thearms472 byfrangible portions504 of the distal ends500. Thecannula442 has a pair ofslots520 positioned opposite to each other to permit percutaneous insertion of therod316 therein, as described in connection with the previous embodiment.

Eachfrangible portion504 may take the form of a necked-down region designed to fracture in response to application of a certain pre-established threshold linear force or angular moment. More precisely, eachfrangible portion504 may fracture in response to force tending to tilt theblades494,496 to push the proximal ends498 inward, toward the axis of thecannula442. Thus, thefrangible portions504 define a frangible coupling between thecannula442 and thecage452.

In use, thecannula442 and thecage452 may be used in a manner similar to that set forth inFIGS. 1-23. However, thecannula442 and thecage452 need not be secured together, since they are formed as a single piece. Additionally, no abutment member may be necessary, although an abutment member (not shown) somewhat similar to theabutment member144 may optionally be used to maintain the proper relative displacement of theblades494,496 during use. After implantation of therod316, removal of theblades494,496 from thecage452 may be accomplished by tilting theblades494,496 inward as described previously to fracture thefrangible portions504, thereby permitting separation of theblades494,496 from thecage452.

According to other alternative embodiments (not shown), blades may be pre-attached to a cage in a manner that does not require the blades to be formed as a single piece with the cage. For example, the blades may be welded, mechanically fastened, or otherwise pre-attached to the cage. Such embodiments may optionally have frangible portions. Alternatively, the blades may be removable in other ways, such as via removal of a mechanical fastener.

The foregoing description discloses a number of different elements that may be combined in various ways to provide a number of alternative implantable systems. Although the foregoing examples relate to implantation of a posterior spinal fusion system, the present invention may be applied to a wide variety of implants, within and outside the orthopedic area.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the systems and methods described above can be mixed and matched to form a variety of other alternatives. As such the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (81)

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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 1, wherein the first and second blades have arcuate profiles, whereby the first cannula is defined by a partially cylindrical shape.

16. The system ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 25, wherein the cannula comprises a first slot extending longitudinally along a side wall of the cannula.

31. The system ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 37, wherein the cannula further comprises a first slot portion formed in a side wall of the cannula.

43. The system ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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.

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