Lateral spondylolisthesis reduction cage and instruments and methods for non-parallel disc space preparation

An intervertebral fusion device comprising inferior and superior fusion cage devices that provide an ability to correct spondylolisthesis via in-situ adjustment.

BACKGROUND OF THE INVENTION

Lateral interbody fusion procedures are currently indicated for patients with ≤grade 1 spondylolisthesis. However, correction from the lateral approach is currently limited to regaining height and lordosis with only a low degree of spondylolisthesis correction, as the straight or lordotic cage is impacted during insertion to expand the disc space. Significant spondylolisthesis reduction is currently accomplished via a posterior approach with supplemental posterior fixation devices, including facet screws, translaminar screws, pedicle screws and rods, as well as intraspinous process devices or plates.

Although current lateral cages are characterized by symmetric superior and inferior geometries, the normal and degenerated discs do not have such similar superior and inferior endplate geometries. The lack of conformity of the cage endplate to the pertinent vertebral body can promote cage malpositioning during insertion, improper load balancing, increased settling and/or subsidence, as well as device movement following implantation.

Some surgeons using lateral cages attach lateral plating to the cage to achieve enhanced cage securement accompanied by some degree of biomechanical stabilization. However, most currently available lateral cages do not provide for plate attachment.

US 2004-0220668 (Eisermann) discloses a method for correcting spondylolisthesis from the lateral approach is provided in which a pair of insertion members are inserted laterally into upper and lower vertebrae, a connecting member is affixed to the insertion members, and a rotating force is applied to the connecting member to encourage the upper and lower vertebrae into a desired position relative to one another. In FIG. 9-11 of Eisermann, in an alternative embodiment, a slidable prosthetic joint can be used to help with the lateral approach for treating spondylolisthesis. The sliding joint extends generally along the longitudinal axis and includes a first slidable component and a second slidable component. The slidable components cooperate to form the sliding joint which is sized and configured for disposition within an intervertebral space between adjacent vertebral bodies. The sliding joint provides movement between the adjacent vertebral bodies to maintain or restore some of the motion similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, the slidable components are permitted to translate relative to one another in the axial plane.

US Patent Publication No. 2010-0016968 (Moore) discloses an apparatus and method that allow for the realignment and stabilization of adjacent vertebrae. An implant of this invention both repositions adjacent vertebrae and remains in situ to maintain the new position. The implant has two halves which are interlocked such that they can slide horizontally with respect to each other. Movement of the implant halves and their respective positions are controlled by external set screw and internal locking block within the implant. The implant includes radial anchors which fit into alignment slots made in the misaligned vertebra by the disclosed method. The set screws are used to advance the halves of the implant which in turn move the misaligned vertebrae back into correct positions. The correct position of the vertebrae is locked in place through a bolt and a plate.

U.S. Pat. No. 6,342,074 (Simpson) discloses a spinal fusion implant and method for maintaining proper lumbar spine curvature and intervertebral disc spacing where a degenerative disc has been removed. The one-piece implant comprises a hollow body having an access passage for insertion of bone graft material into the intervertebral space after the implant has been affixed to adjacent vertebrae. The implant provides a pair of screw-receiving passages that are oppositely inclined relative to a central plane. In one embodiment, the screw-receiving passages enable the head of an orthopedic screw to be retained entirely within the access passage. A spinal fusion implant embodied in the present invention may be inserted anteriorally or laterally.FIG. 4discloses a device having fixtures for attaching to a lateral side of a vertebral body.

U.S. Pat. No. 6,878,167 (Ferree) discloses an osteotomy of a portion of a vertebral endplate and/or vertebral body allowing for easier insertion of a device that fits tightly into a disc space. It also discloses a mechanical device to hold the osteotomized portion of the vertebra against the vertebral body after the intradiscal device is placed. The device may be removed after the pieces of vertebra heal and fuse together. It further discloses a device secured to a side of the vertebral body inFIG. 4C.

The lateral access approach is frequently utilized to deliver interbody fusion cages to the lumbar spine. In comparison to conventional anterior or posterior approaches to the lumbar spine, the lateral approach is thought to minimize posterior and/or anterior tissue damage as well as reduce surgery time, associated blood loss, and infection risk.

When multi-level access to the spine is provided through a single minimal access port, the insertion trajectory to the superior and inferior levels is not parallel to those levels. In addition, direct lateral access parallel to the L4/5 and L5/S1 levels is prevented by the presence of the iliac crest.

Accordingly, the angled trajectory required for lateral access to these lower levels requires the cages to be implanted at a “malpositioned” angle that prevents balanced loading across the vertebral endplates and spine. SeeFIG. 1. This “malpositioned” access, associated endplate damage and device placement can initiate subsidence and spinal instability.

Current spreader and shaver technology includes varying paddle shapes and cutting geometries with rigid drive shafts. US Patent Publication No. 2008-00445966 discloses a chisel cutting guide for excising a portion of a vertebral body.

Conventional dilation systems used in intervertebral fusion procedures are typically rigid and non-steerable. Accordingly, they require a line of sight insertion towards the target disc.

US Patent Publication No. US 2007-0225815 (Annulex) discloses a curved stylet for steering within a disc space Annulex does not disclose an assembly comprising a curved guide wire and a flexible dilator tube.

SUMMARY OF THE INVENTION

The present invention relates to an intervertebral fusion device comprising inferior and superior fusion cages that provide an ability to correct spondylolisthesis via lateral insertion and in-situ adjustment.

Therefore, in accordance with the present invention, there is provided an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and an upper surface for contacting an upper vertebral body and a lower surface,

b) a lower cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and a lower surface for contacting a lower vertebral body and an upper surface, wherein the lower surface of the upper cage slidingly mates with upper surface of the lower cage.

Also in accordance with the present invention, there is provided a method for correcting spondylolisthesis in a patient, comprising the steps of:

a) selecting a fusion device comprising an upper cage and a lower cage,

b) fixing the upper cage to an upper vertebral body of the patient and the lower cage to a lower vertebral body of the patient, and

c) moving the upper cage relative to the lower cage to correct the spondylolisthesis.

Also in accordance with the present invention, there is provided an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and an upper surface for contacting an upper vertebral body and a lower surface having a first groove therein,

b) a lower cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and a lower surface for contacting a lower vertebral body and an upper surface having a second groove therein, and

c) a locking plate, wherein the lower surface of the upper cage contacts the upper surface of the lower cage so that the first and second grooves form a first throughhole running from the proximal wall to about the distal wall. wherein the locking plate is disposed in the first throughole.

Also in accordance with the present invention, there is provided an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and an upper surface for contacting an upper vertebral body and a lower surface,

b) a lower cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and a lower surface for contacting a lower vertebral body and an upper surface, wherein the anterior wall is connected to the proximal wall by a first dual linkage and to the distal wall by a second dual linkage, wherein the posterior wall is connected to the proximal wall by a third dual linkage and to the distal wall by a fourth dual linkage. wherein the linkages allow the upper plate to pivot relative to the lower plate in the plane of the proximal wall.

Also in accordance with the present invention, there is provided an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper wall having an upper surface adapted for contacting an upper vertebral body and an inner surface,

b) a lower wall having a lower surface adapted for contacting a lower vertebral body and an inner surface,

c) proximal and distal walls extending between the upper and lower walls,

d) anterior and posterior walls extending between the upper and lower walls,

e) a rack-and-pinion mechanism located between the inner surfaces of the upper and lower walls wherein the pinion extends substantially from the distal wall to the proximal wall, wherein the rack extends substantially from the anterior wall to the posterior wall,

so that rotation of the pinion effects relative movement of the upper and lower walls in the anterior-posterior direction.

The present inventors have developed flexible shavers and curved access ports that reduce the above-mentioned access and trajectory problems associated with conventional lateral approaches to the lower spine. The devices and methods of the present invention allow the surgeon to present disc preparation instruments to a disc space in the lower spine in a manner that is parallel to the disc space. Consequently, these devices and methods allow for preparing with less endplate damage and higher preparation symmetry.

Therefore, in accordance with the present invention there is provided a flexible shaver for preparing a vertebral endplate, comprising:

a) a shaft having a proximal end portion and a distal end portion,

b) a handle attached to the proximal end portion of the shaft, and

c) a shaving head attached to the distal end portion of the shaft, the head comprising:

ii) a first face forming a first cutting edge, and wherein the shaft and head comprise a universal joint.

Also in accordance with the present invention there is provided a method of intervertebral disc space preparation, comprising the steps of:

a) selecting a shaver having a flexible shaft;

b) inserting the shaver into an intervertebral disc space bounded by opposed vertebral endplates, and

c) contacting the shaver to a vertebral endplate.

Also in accordance with the present invention there is provided a method of preparing an intervertebral disc space between opposing vertebral endplates, comprising the steps of:

a) inserting a curved (preferably flexible) port into a lateral aspect of the disc space, the curved port having a bore.

Also in accordance with the present invention there is provided a assembly comprising:

a) a curved port having a bore having a transverse cross-section; and

b) a vertebral endplate shaver having a transverse cross-section, wherein the shaver is disposed within the bore of the curved port,

wherein the transverse cross-section of the bore substantially corresponds to the transverse cross-section of the shaver so as to determine the orientation of the shaver within the bore.

Also in accordance with the present invention there is provided a port for use in preparing an intervertebral disc space, comprising:

a) an outer cannula having a bore, and

b) an inner cannula having a bore having a non-circular transverse cross-section,

wherein the inner cannula is disposed within the bore of the outer cannula.

Also in accordance with the present invention there is provided a port for use in preparing an intervertebral disc space, the port comprising a longitudinal bore therethrough, the bore having a proximal end portion having a transverse cross-section and a distal end portion having a transverse cross-section, wherein the transverse cross-section of the proximal end portion of the bore is greater than that transverse cross-section of the distal end portion of the bore.

Also in accordance with the present invention there is provided a port for use in preparing an intervertebral disc space, comprising:

a) an outer cannula having a bore having a proximal end portion and a distal end portion,

b) an upper insert disposed at least in the distal end portion of the bore, and

c) a lower insert disposed at least in the distal end portion of the bore.

Also in accordance with the present invention there is provided a assembly for providing access to an intervertebral disc, comprising;

a) a catheter having a steerable tip,

b) a first flexible dilator tube having a first bore defining a first longitudinal axis,

c) a second flexible dilator tube having a second bore defining a second longitudinal axis, wherein the first flexible dilator tube is received with the bore of the second flexible dilator tube, and wherein the steerable tip is received within the bore of the first flexible dilator tube.

Also in accordance with the present invention there is provided a method of accessing a target intervertebral disc, comprising the steps of:

a) advancing a steerable catheter having a tip through an incision and towards the target disc,

b) imparting a first curve in the tip of the steerable catheter,

c) docking the curved tip upon the target disc,

d) advancing a first flexible dilator tube over the curved tip to impart a first curve in the first flexible dilator tube.

The present invention also relates to an assembly comprising a steerable, curvable guide wire and a set of flexible dilator tubes having sequentially increasing bore diameters. When a flexible dilator tube is passed over the curved guide wire, the flexible dilator tube curves in an arc substantially similar to that of the curved guide wire. Thus, the set of curved dilator tubes can open up a curved access path to the L4/5 and L5/S1 levels that previously could not be directly accessed due to the presence of the iliac crest.

Also in accordance with the present invention there is provided a flexible shaver for preparing a vertebral endplate, comprising:

a) a shaft having a proximal end portion and a distal end portion,

b) a handle attached to the proximal end portion of the shaft, and

c) a shaving head attached to the distal end portion of the shaft, the head comprising:

ii) a first face forming a first cutting edge, and wherein the shaft comprises a flexible portion.

Also in accordance with the present invention there is provided a method of performing a procedure on a spine, comprising the step of:

a) advancing an instrument along a curved path, the path being substantially in a coronal plane, towards a lateral aspect of an intervertebral disc.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a side view of a functional spinal unit having grade 1 spondylolisthesis characterized by a 20-25% slip.

In use, the devices of the present invention accomplish improved and controlled spondylolisthesis correction with fusion from the lateral approach. The lateral cage devices of the present invention also provide for intra-operative trialing and selection to enhance conformance of the cage geometry to the vertebral body endplates bounding the targeted disc space. The fusion device of the present invention provides for direct attachment of its superior and inferior cages to the lateral aspects of the opposing vertebral bodies.

Several devices and methods for correcting spondylolisthesis with fusion from the lateral approach are disclosed. All incorporate a superior and inferior fusion cages that are fixedly attached to the corresponding vertebral bodies. The fixed attachment can be accomplished by using pre-attached plates, or by incorporating internal screws (e.g., the STALIF approach) and/or lateral keels. Following implantation, the superior and inferior cages are aligned in-situ via various activation means that are further discussed below, and then locked in place.

The interior, contacting surfaces of the cages that effect intra-device attachment contain alignment and securement features that allow for controlled intra-operative manipulation of the spine in the sagittal plane following individual fixed attachment of the cages to the superior and inferior vertebral bodies. These features can include but are not limited to teeth, barbs, and dovetails.

Both the superior and inferior cages can include features on their outer surfaces that can enhance securement to the vertebral body endplate. These features include fins, barbs, teeth, osteoconductive surface morphology (porosity) and coatings (such as HA and TCP). The superior and inferior cages can also include graft-retention windows and pockets to facilitate the long-term fusion of the two vertebral bodies of the functional spinal unit.

The inner contacting surfaces of the cage can be flat to allow for the incremental lineal adjustment of the relative cage positions. Alternatively, these surfaces can be domed so as to enable the accurate adjustment of the vertebral bodies to a centered position in the flexion/extension plane (i.e., to the center of rotation).

The external geometry of the superior and inferior cages can be flat or lordotic, and can be domed or angled in various plans to enhance their conformance to the vertebral body endplates and to address spinal deformity and/or scoliosis.

Following fixed attachment to the vertebral body, the superior and inferior cages may be aligned by several means, including the following:

FIGS. 2a-2band3disclose the implantation of a first embodiment of a fusion device of the present invention, in which the cages501,502of the device are implanted into the disc space, brought together, and then locked in place with a locking plate503.FIGS. 4a-4dshow various views of the intervertebral fusion device of the present invention.FIGS. 4e-4fshow various views of the cages of an intervertebral fusion device of the present invention locked with a locking plate.

FIG. 2aandFIG. 2brespectively show the relative positions of the fixed cage before and after alignment. In theFIG. 2bposition, the cages have properly aligned the vertebral bodies, and thereby corrected the spondylolisthesis. The superior and inferior cages can also have features that provide or enhance the connection of the cages to the compressor. These features include recesses, pilot holes and threads located on the proximal walls of the two cages (and optionally extending therethrough) that receive mating features located on the cage inserter. These features may also assist in the alignment of the cages. Lastly, the upper portion of the proximal wall of the upper cage and the lower portion of the proximal wall of the lower cage each extend past the anterior and posterior walls of the respective cages, and each has a transverse throughhole. Fixation screws may extend through these holes and into the lateral walls of the corresponding vertebral bodies to provide the immediate fixation of the cages to these vertebral bodies. Such screw locking features are well known in the art.

As shown inFIGS. 4a, 4band 4d, the superior and inferior cages together preferably form a dovetail joint (or other joint having an expanding recess) that allows linear anterior-posterior relative movement of the fixed cages to effect the desired alignment of the vertebral bodies. The contacting surfaces of the superior and inferior cages may also have matching ratchet teeth, as inFIG. 4d, that provide incremental adjustment of the relative cage positions, and the short term inter-cage securement following the compression.

As shown inFIGS. 4eandf, once the superior and inferior cages are aligned together, this desired position may be fixed by attaching a single locking plate to the proximal ends of each cage. This locking plate may be attached to the cages by passing screws through the holes in the plate and into the corresponding holes in the lower portion of the proximal wall of the upper plate and the upper portion of the proximal wall of the lower plate.

Now referring toFIGS. 4a-4f, there is provided (claim1) an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage1having an anterior wall3, a posterior wall5, and a proximal wall7and a distal wall9connecting the anterior and posterior walls, and an upper surface11for contacting an upper vertebral body and a lower surface13,

b) a lower cage15having an anterior wall17, a posterior wall19, and a proximal wall21and a distal wall23connecting the anterior and posterior walls, and a lower surface25for contacting a lower vertebral body and an upper surface27, wherein the lower surface of the upper cage slidingly mates with upper surface of the lower cage.

In some embodiments, the lower surface of the upper plate and the upper surface of the lower cage include tongue-and-groove feature. Preferably, the tongue-and-groove feature runs from about the anterior wall to about the posterior wall. Preferably, the tongue-and-groove feature comprises an expanding recess29and more preferably comprises a dovetail31.

In some embodiments, the lower surface of the upper cage and the upper surface of the lower cage include a ridge and recess feature33that runs in a proximal-distal direction.

In some embodiments, the proximal wall of the upper cage has a height Hu-p, the anterior wall of the upper cage has a height Hu-a, and wherein the height of the proximal wall of the upper cage is greater than the height of the anterior wall of the upper cage.

In some embodiments, the proximal wall of the upper cage has an upper portion35having a upper through-hole37located above the anterior wall and adapted for receiving a bone screw.

In some embodiments, the proximal wall of the lower cage has a height Hl-p, the anterior wall of the lower cage has a height Hl-a, and wherein the height of the proximal wall of the lower cage is greater than the height of the anterior wall of the lower cage.

In some embodiments, the proximal wall of the lower cage has a lower portion39having a lower through-hole41located beneath the anterior wall and adapted for receiving a bone screw.

In some locking plate embodiments, the proximal wall of the upper cage has a lower portion43having an lower through-hole45located beneath the anterior wall of the upper cage and adapted for receiving a screw. Likewise, the proximal wall of the lower cage has an upper portion47having an upper through-hole49located above the anterior wall of the lower cage and adapted for receiving a bone fastener such as a screw. The device further comprises:

c) a locking plate51having a first and second throughholes53, and

d) first and second bone fasteners (such as screws)55, wherein the locking plate is fixed to the proximal wall of the upper and lower cages by passing the first bone fastener through the first throughhole of the locking plate and into the lower throughhole of the upper cage, and by passing the second bone fastener through the second throughhole of the locking plate and into the upper throughhole of the lower cage.

In some embodiments that promote fusion, the upper cage further comprises a lower surface13and a throughole59running from the upper surface to the lower surface. In some embodiments that promote fusion, the lower cage further comprises an upper surface and a throughole running from the upper surface to the lower surface. Likewise, the anterior wall further comprises a throughole61running therethrough. These throughholes are of a size adapted to promote fusion

In some embodiments, the distal end wall of each of the upper and lower cages has a taper63for ease of insertion.

In the first embodiment, and now referring toFIGS. 5a-7b, the alignment means is compression-activated. This preferred embodiment uses a compression instrument to bring the anterior and posterior walls of the inferior and superior cages into alignment, and thereby correct spondylolisthesis.

FIGS. 5a-bdisclose a compression-directed inserter65of the present invention having distal pins67, and the insertion of a cage of the present invention with this inserter.FIGS. 5c-ddisclose a compression-directed inserter69of the present invention having distal blades71, and the insertion of a cage of the present invention with this inserter.FIGS. 6a-7bdisclose how a compression-directed inserter of the present invention having nested blades72,73aligns the cages of the present invention when activated.

Now referring toFIG. 5a-d, the compressor instrument may have distal extensions such as blades71(FIG. 5c) or pins67(FIG. 5a) that act to align the anterior and posterior walls of the cages via compression. The blades ofFIG. 5csimply push the anterior and posterior walls of the cages towards each other, thereby removing any overlap and bringing the anterior and posterior walls of these cages into vertical alignment.FIGS. 6a-7bdisclose the nesting details of the distal portions of the pinned compressor instrument that allow the instrument's distal pins (not shown) to become aligned.

Therefore, in accordance with the present invention, there is provided (claim16) a method for correcting spondylolisthesis in a patient, comprising the steps of:

a) selecting a fusion device comprising an upper cage and a lower cage,

b) fixing the upper cage to an upper vertebral body of the patient and the lower cage to a lower vertebral body of the patient,

c) moving the upper cage relative to the lower cage to correct the spondylolisthesis. Preferably, the method further comprises the step of: d) locking the upper cage to the lower cage. In some embodiments, the locking step is accomplished by a locking plate. In some embodiments, the moving step is accomplished with a compression-directed inserter.

In some embodiments, the moving step is accomplished with a rotary spreader.

In a second embodiment, and now referring toFIG. 8a-8d, the alignment means is rotary spreader-activated.FIGS. 8a-8ddisclose how the cages of one embodiment of the present invention are aligned by a rotary spreader, and are locked by a particular locking plate. A modified spreader or shaver can be inserted into a space formed in the proximal end wall of the unaligned device. Rotating the spreader causes relative anterior-posterior movement of the upper cage vis-a-vis the lower cage to enable alignment of the cages and thereby intraoperative adjustment of a spondylosed functional spinal unit (FSU).

Now referring toFIG. 8b, optional locking plates can be employed to fix the device after the spondylolisthesis has been corrected. These plates are preferably inserted into bilateral, aligned, longitudinal recesses that extend across the interface of the aligned cages to provide inter-cage locking. In some embodiments, these plates are locked into place via a snap-lock mechanism, as shown inFIG. 8d.

In some embodiments, and now referring toFIG. 8a, the upper surface of the lower cage and the lower surface of the upper cage may be configured in matching domes in order to mimic the natural relative arced movement of adjacent vertebral bodies.

Now referring toFIGS. 8a-8d, there is provided (claim21) an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage75having an anterior wall77, a posterior wall79, and a proximal wall81and a distal wall83connecting the anterior and posterior walls, and an upper surface85for contacting an upper vertebral body and a lower surface87having a first groove89therein,

b) a lower cage91having an anterior wall93, a posterior wall95, and a proximal wall97and a distal wall99connecting the anterior and posterior walls, and a lower surface101for contacting a lower vertebral body and an upper surface103having a second groove104therein, and

c) a pair of locking plates105, wherein the lower surface of the upper cage contacts the upper surface of the lower cage so that the first and second grooves form a first throughhole107running from the proximal wall to about the distal wall, wherein the locking plate is disposed in the first throughole.

In some embodiments, the first groove is present upon the lower surface of the anterior wall of the upper cage, and the second groove is present upon the upper surface of the anterior wall of the lower cage. In other embodiments, the first groove is present upon the lower surface of the posterior wall of the upper cage, and the second groove is present upon the upper surface of the posterior wall of the lower cage.

In some embodiments, the device of the second embodiment further comprises a third groove109present upon the lower surface of the upper cage between the anterior and posterior walls, and a fourth groove111present upon the upper surface of the lower cage between the anterior and posterior walls, and wherein the lower surface of the upper cage contacts the upper surface of the lower plate so that the third and fourth grooves form a second throughhole113running from the proximal wall to about the distal wall, the second throughhole adapted for insertion of a spreader therein.

In a third embodiment, and now referring toFIGS. 9a-9g, the attachment means is linkage activated.FIGS. 9a-9gdisclose various views of a dual linkage embodiment of the present invention Single- or double-linkage can be used to correct spondylolisthesis by moving this cage from a pre-activated (FIG. 9a) to a post-activated state. (FIG. 9b) In some linkage embodiments, the anterior and posterior walls of the cages also function as linkage bars, providing for pivoting connection with both an upper wall component and a lower wall component to allow for relative anterior-posterior movement of the upper wall vis-a-vis the lower wall and thereby spondylolisthesis correction.

In some embodiments, and now referring toFIGS. 9c-9d, the upper portion of the upper wall and the lower portion of the lower wall extend outwardly, and transverse holes in these portions provide a means to fix the upper and lower walls to the respective lateral walls of the vertebral bodies.

In some embodiments, and now referring toFIG. 9d, the upper wall and the lower wall have transverse throughholes that extend into a chamber formed in the interior of the device. These throughholes and this chamber facilitate the fusion of the opposing vertebral bodies through the device. Also referring toFIG. 9d, the anterior and posterior walls may likewise have transverse throughholes that extend into a chamber formed in the interior of the device, and thereby facilitate the fusion of the opposing vertebral bodies through the device.

Now referring toFIG. 9e-9g, optional locking plates can be employed to fix the device following spondylolisthesis correction. These plates are preferably inserted into bilateral, aligned, longitudinal recesses that extend from the upper wall to the lower wall to provide inter-cage locking. In some embodiments, these plates are locked into place via a snap-lock mechanism, as shown inFIG. 9e.

Now referring toFIGS. 9a-9g, there is provided (claim31) an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage115having an anterior wall117, a posterior wall119, and a proximal wall121and a distal wall123connecting the anterior and posterior walls, and an upper surface125for contacting an upper vertebral body and a lower surface127,

b) a lower cage131having an anterior wall133, a posterior wall135, and a proximal wall137and a distal wall139connecting the anterior and posterior walls, and a lower surface141for contacting a lower vertebral body and an upper surface143, wherein the anterior wall is connected to the proximal wall by a first dual linkage145and to the distal wall by a second dual linkage (not shown), wherein the posterior wall is connected to the proximal wall by a third dual linkage149and to the distal wall by a fourth dual linkage (not shown), wherein the linkages allow the upper plate to pivot relative to the lower plate in the plane of the proximal wall.

In some aspects of this third embodiment, the proximal wall of the upper cage has a height, the anterior wall of the upper cage has a height, and wherein the height of the proximal wall of the upper cage is greater than the height of the anterior wall of the upper cage. In some embodiments thereof, the proximal wall of the upper cage has an upper portion153having a upper through-hole155located above the anterior wall and adapted for receiving a bone screw.

In other aspects of this third embodiment, the proximal wall of the lower cage has a height, the anterior wall of the lower cage has a height, and wherein the height of the proximal wall of the lower cage is greater than the height of the anterior wall of the lower cage. In some embodiments thereof, the proximal wall of the lower cage has a lower portion157having a lower through-hole159located beneath the anterior wall and adapted for receiving a bone screw.

In some embodiments, the upper cage has a throughole161running from the upper surface to the lower surface. This throughhole is adapted for promoting fusion

In a fourth embodiment, the alignment means includes a rack-and-pinion. A pinion located between the upper and lower walls and extending laterally can be rotated to move racks extending in the anterior-posterior direction and thereby reduce spondylolisthesis.FIGS. 10a-ddisclose full and partial views of a rack-and-pinion embodiment of the present invention, some of which are inserted into a disc space.FIGS. 11a-11edisclose various views of the rack-and-pinion embodiment of the present invention.

Now referring toFIG. 10a-11e, there is provided (claim41) an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper wall171having an upper surface173adapted for contacting an upper vertebral body and an inner surface175,

b) a lower wall177having a lower surface179adapted for contacting a lower vertebral body and an inner surface181,

c) proximal183and distal185walls extending between the upper and lower walls,

d) anterior187and posterior189walls extending between the upper and lower walls,

e) a rack-and-pinion mechanism located between the inner surfaces of the upper and lower walls wherein the pinion191extends substantially from the distal wall to the proximal wall, wherein the rack193extends substantially from the anterior wall to the posterior wall, so that rotation of the pinion effects relative movement of the upper and lower walls in the anterior-posterior direction.

In some aspects of the fourth embodiment, the length of the device is at least three times the height of the device.

In some embodiments, the upper and lower walls each have at least one hole195therethrough to facilitate fusion through the device. In others, the anterior and posterior walls each have at least one hole197therethrough to facilitate fusion through the device.

In some embodiments, the rack extends from the inner surface of the upper wall. In others, the rack extends from the inner surface of the lower wall.

In some embodiments, the pinion comprises a proximal end199having a feature201for receiving a rotary tool.

In some embodiments, at least one of the anterior and posterior walls is integral with at least one of the upper and lower walls.

In some embodiments, at least one of the anterior and posterior walls is removable.

The embodiments of the present invention may optionally a securement plate that attaches to both the device of the present invention and the vertebral bodies. This securement plate secures the position of the device and provides supplemental stabilization.

In general, the devices of the present invention are suited for substantially lateral insertion into the disc space. In some embodiments, the cages are inserted through a more anterolateral insertion angle.

Now referring toFIGS. 4aand 4c, the length L of the device is characterized as the distance from the distal wall to the proximal wall. The width W of the device is characterized as the distance from the anterior wall to the posterior wall. The height H of the device is characterized as the distance from the lower surface to the upper surface, excludes the upper and lower portions that extend past the anterior wall, and generally corresponds to the height of the disc space. In general, the length of the lateral devices of the present invention are typically at least twice and often three times the width of the device. In general, the length of the lateral devices of the present invention are typically at least twice and often three times the height of the device. Typically, the width of the device is greater than the height of the device.

In some embodiments, as inFIG. 11b, the anterior wall of the cage may have a convex curve203to mimic the convex shape of the anterior portion of the disc space

The lateral spondylolisthesis reduction fusion devices of the present invention may be produced from a single material or from multiple materials. These materials include metallics (such as Ti, Ti alloys such as nitinol, stainless steel, and cobalt-chrome), polymeric materials (including PEEK, PEAK, polypropylene, polyethylene terephthalate (PET), UHMWPE), biologic materials (including allograft, hydroxyapatite, TCP and CaPO4), and ceramic materials including silicon nitrides, and zirconia-containing ceramics. The plate, fasteners, or locking mechanisms can be produced from metallics or polymers for enhance durability.

Additionally, modified versions of this concept can be designed to correct spondylolisthesis with superior and inferior cages that are inserted from the anterior, anterior-lateral or posterior approaches.

The cages of the present invention are preferably inserted either from a right lateral or left lateral approach.

Following standard access and disc preparation procedures, the superior and inferior cages are inserted and affixed to the opposed vertebral bodies with screws or bone fasteners. Spondylolisthesis correction is then performed with the disclosed compressor or with a rotary tool. Optionally, locking members are then applied to the superior and inferior cages to fix the orientation of the segments.

Also in accordance with the present invention, there is provided a method of implanting an intervertebral device between opposed vertebral bodies, comprising the steps of:

i) selecting an intervertebral device comprising:

a. an upper half component having an anterior wall, a posterior wall, and two side walls connecting the anterior wall and posterior wall;

b. a lower half component having an anterior wall, a posterior wall, and two side walls connecting the anterior wall and posterior wall;

ii) inserting the device between opposed vertebral bodies, whereby the anterior walls are not aligned,

iii) moving (preferably by pivoting) one of the components with respect to the other component so that the anterior walls are substantially aligned, and

iv) fixing the device to the opposed vertebral bodies.

In some embodiments of the present invention, the fusion device is angled to provide either lordosis or kyphosis. In embodiments in which lordosis is desired, the height of the anterior wall exceeds the height of the posterior wall. An example of such a lordotic implant is shown inFIG. 4c. In embodiments in which kyphosis is desired, the height of the anterior wall is less than the height of the posterior wall.

It is believed by the present inventors that the devices disclosed herein appear to be the first intervertebral devices having a flange that connects to a side of a vertebral body. Therefore, in accordance with the present invention, there is provided a method of inserting a fusion device between opposed vertebral bodies, comprising the steps of:

a) selecting an intervertebral device having an anterior wall, a posterior wall and a pair of side walls connecting the anterior and posterior walls, wherein at least one of the side walls has a flange axially extending beyond the anterior wall and the posterior wall, wherein the flange has a throughhole,

b) inserting the device between the opposed vertebral bodies, and

c) inserting a fixation device through the throughhole to fix the device to a side of one of the opposed vertebral bodies.

Although the cages of the present invention are disclosed as having flanges that extend beyond the disc space for attachment to the sides of the opposed vertebral bodies, it is also contemplated that the cages of the present invention may be attached to the opposed vertebral bodies via zero profile throughholes. These zero profile throughholes are provided both a) at the upper edge of the proximal side wall of the upper half component and b) at the lower edge of the proximal side wall of the lower half component.

Therefore, in accordance with the present invention, there is provided an intervertebral fusion device for correcting spondylolisthesis in a patient, comprising:

a) an upper cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and a throughole present at the upper edge of the proximal wall for receiving a bone fixation device,

b) a lower cage having an anterior wall, a posterior wall, and a proximal wall and a distal wall connecting the anterior and posterior walls, and a lower surface for contacting a lower vertebral body and an upper surface, and a throughole present at the lower edge of the proximal wall for receiving a bone fixation device, wherein the lower surface of the upper cage slidingly mates with upper surface of the lower cage.

Although the above description discloses how to make and use implantable devices to correct spondylolisthesis, it is within the scope of the invention to use these devices as instruments to correct retrolisthesis as well. Therefore, in accordance with the present invention, there is provided a method for correcting spondylolisthesis in a patient, comprising the steps of:

a) selecting an instrument comprising an upper cage and a lower cage, wherein each cage is attached to a handle

b) attaching the upper cage to an upper vertebral body of the patient and the lower cage to a lower vertebral body of the patient (preferably with caspar pins),

c) moving the upper cage relative to the lower cage to correct the spondylolisthesis (preferably with a distractor that engages the caspar pins), and

d) removing the instrument from the patient.

Although the above description discloses how to make and use devices in the context of correcting spondylolisthesis, it is within the scope of the invention to use similar devices to correct retrolisthesis as well.

FIG. 12discloses a lateral cage of the present invention with oblique screwholes301.

FIG. 13discloses an inserter303of the present invention.FIG. 13is a top view of a second type of spondylolisthesis reduction tool that comprises a proximal handle portion305and two vertebral body engaging beams307. On the distal end of the beams are bone engaging features309for the respective superior and inferior vertebral bodies. At the proximal end of the beams the inferior beam is fixed within the handle and the superior is attached with a pivot so that its distal end can move posterior and anterior with respect to the lower. Conversely, the lower beam could also be affixed in a pivoting fashion so that both beams move as in a scissor fashion. This intended motion corresponds to a posterior transverse plane motion of the superior vertebral body in order to reduce the spondylolisthesis. By slightly rotating the handle or tilting the tool prior to engagement, a saggital plane component is introduced to the reduction motion (it may be beneficial to increase the height of one body over the other as you move that body posteriorly).

The cross section of the beams are sufficiently wide in the anterior-posterior direction making them resistant to bending in the transverse plane. The mechanism within the handle is to pivot the beams. This can be done with a ratchet and pawl linkage which moves the top beam one click with each squeeze, or a sliding collar that advances distally along the beams to bring them in line with each other, or a wedge/roller that advances along the edge of the superior beam or a post and angled slot mechanism that aligns the two beams, or with a geared scissor mechanism such that the full motion of the handle corresponds to a small angular change of the beams. The controlled motion of the beams relative to each other is advantageous as the operating surgeon generally has a pre-determined amount of reduction in mind for the surgery. This amount can be determined via radiograph or inter-operatively. For example if a total of 6 mm of reduction is desired, the handle can be ratcheted 1 mm at a time until the value of 6 mm is reached. Therefore, there is provided a spondylolisthesis reduction tool comprising:

a) a proximal handle portion, and

b) first and second vertebral body-engaging beams having a longitudinal axis, a proximal end portion and a distal end portion, the distal end portion of each beam forming bone engaging features, wherein the proximal end portion of the first beams is fixedly attached to the handle portion, and wherein the proximal end portion of the second beam is pivotally attached to the handle portion so that the second beam can move transversely with respect to the longitudinal axis of the first beam. Preferably, the handle portion comprises a trigger311adapted to pivotally move the second beam.

The present invention relates to flexible spreaders and shaver devices and methods for parallel preparation of an intervertebral disc space in the context of a non-parallel access trajectory. The flexible shavers utilize curved guide tubes to enable their placement, insertion, flexing, bending and/or pivoting in the disc space.

In some embodiments, the flexible shaft can have a flexibility-imparting geometry that includes use of at least one of a) a spring (available from SS White of Piscataway, N.J.), b) a slotted tube (available from Necomed of Hicksville, Ohio), and c) a standard universal joint. Now referring toFIGS. 15A through 15D, in some embodiments, the flexible shaver11of this embodiment also includes a proximal handle15, an intermediate shaft19comprising a universal joint20, and a distal shaver head23.

Therefore, now referring toFIGS. 15A through 15D, there is provided a flexible shaver11for preparing a vertebral endplate, comprising:

a) a shaft19having a proximal end portion21and a distal end portion22,

b) a handle15attached to the proximal end portion of the shaft, and

c) a shaving head23attached to the distal end portion of the shaft, the head comprising:

ii) a first face25forming a first cutting edge, and wherein the shaft comprises a universal joint20.

FIG. 15Dshows flexible shavers11of this embodiment disposed within respective disc spaces, wherein the shaving heads are disposed parallel to the disc space. Therefore, use of the shaver results in shaved endplates that are substantially parallel to the natural endplates, and so will easily accommodate a lateral fusion cage without causing asymmetry.

The flexible spreader/shaver comprises a distal rigid or non-rigid shaver head having a blade. This shaver head is attached to a partially flexible drive shaft that is in turn connected to a proximal handle. The handle is rotated to turn the drive shaft and the shaving head. The flexible shaft allows variable angulations of the handle relative to the shaver blade, thereby allowing the surgeon to use an angled approach to prepare the disc space in a manner that nonetheless keeps the shaving head substantially parallel to the disc space. Typically, the shaver angulation angle α relative to the drive shaft can be up to 90 degrees, but is preferably between 10 and 45 degrees. In some embodiments, the shaving head of the flexible shaver has a bullet tip26for ease of entry into the disc space.

Now referring toFIGS. 16A through 16C, in some embodiments, the flexible shaver1of the present invention includes a proximal handle3, an intermediate flexible shaft5, and a distal shaver head7. The flexible shaft can be a solid shaft made from a flexible material, or can be a spring (available from SS White of Piscataway, N.J.), or a slotted tube (available from Necomed of Hicksville, Ohio). Such flexible materials include metals such as nitinol, and polymers such as polyether ether ketone (PEEK), acrylonitrile butadiene styrene (ABS), polypropylene, and polyethylene. Stainless steels, titanium alloys, cobalt chromium alloys or combinations, mixtures and/or blends thereof. The flexible shaft may be the flexible material itself or the shaft may be constructed of strands which are wound or shafts which are slotted to impart flexibility.FIGS. 16A through 16Bshow a flexible shaver having a shaft made of a flexible material in its straight and curved configurations, respectively.FIG. 16Cshows two flexible shavers1of this embodiment disposed at least partially within respective disc spaces, wherein each shaving head is disposed parallel to the disc space.

Therefore, now referring toFIGS. 16A through 16C, there is provided a method of intervertebral disc space preparation, comprising the steps of:

a) selecting a shaver having a flexible shaft;

b) inserting the shaver into an intervertebral disc space bounded by opposed vertebral endplates, and

c) contacting the shaver to a vertebral endplate to cut the endplate. As shown inFIG. 16C, the use of the flexible shaver allows the shaving head to be essentially parallel to the opposed vertebral endplates. Thus, when the shaver is rotated about its longitudinal axis, the shaving head cuts in a manner parallel to the endplates, thereby preserving symmetry about the disc space.

The flexible shaft can be made flexible in many different ways. For example, in some embodiments, the flexible shaft is made of a flexible material. In other embodiments, the geometry of the shaft imparts flexibility thereto. In some embodiments thereof, the flexible shaft has a universal joint. In other such embodiments, the flexible shaft is slotted to impart flexibility. In other such embodiments, the flexible shaft comprises a spring.FIGS. 16C through 16Ddisclose a flexible port2in its straight and curved configuration.FIGS. 17A through 17Bdisclose a flexible port4having reinforcements6, the port being in its straight and curved configuration.FIGS. 17C through 17Ddisclose a port having slots8in its straight and curved configuration.

In some embodiments, a flexible port is used to dock onto a bone adjacent the disc space and thereby guide disc space preparation instruments into the disc space in a minimally invasive manner. The flexibility allows the port to curve at its distal end portion to produce a curve having an angle of, for example, 20 degrees. This curve allows a shaver to enter the port at a downward trajectory (which occurs when using a single spinal access site for multiple levels) and then orient parallel to the endplates (in order to best prepare the endplates). In some embodiments, the angle of the shaver is between 10 and 45 degrees.

Now referring toFIGS. 18A through 18B, in some embodiments, the port may include one or more fixed or actuatable securement features35, including a spike or teeth, extending from its distal end portion33. These securement features fix to the bone and thereby insure secure docking of the port adjacent the target disc space.FIGS. 18A and 18Bpresent a perspective view of a port of the present invention, wherein the securement feature35is respectively retracted and advanced.

Now referring toFIG. 19A through 19C, in some embodiments, the port31may comprise an outer cannula34and inserts37and39. These inserts may, when installed, form an inner cannula that helps fix the orientation of the shaver when the shaver passes therethrough. Therefore, in some embodiments thereof, there is provided a port for use in preparing an intervertebral disc space, which comprises:

a) an outer cannula34having a bore, and

b) an inner cannula having a bore having a non-circular transverse cross-section, wherein the inner cannula is disposed within the bore of the outer cannula.

Preferably, the port further has features that allow it to securely dock onto the vertebral bone adjacent the disc space. Preferably, this comprises a securement feature disposed upon a distal end portion of at least one of the outer cannula and inner cannula.

In some embodiments, the port having the inner and outer cannulae has a distal end portion that is curved. In some embodiments thereof, the curve in the distal end portion is between 10 and 45 degrees. In some embodiments, the cannulae are made of flexible materials, while in others each cannula has a geometry that imparts flexibility. Because the shaver typically has a much smaller cross-section than the typical lateral cage implant, it is expected that the areal-cross section of the bore of the inner cannula will be much smaller than the areal cross-section of the bore of the outer cannula. For example, in some embodiments, the bores of the cannulae each have an areal cross section, wherein the areal cross section of the bore of the inner cannula is less than 50% of the areal cross section of the bore of the outer cannula. More preferably, the areal cross section of the bore of the inner cannula is less than 25% of the areal cross section of the bore of the outer cannula. Preferably, the inner cannula is modular in order to customize for various angles of approach and inner geometry to guide various instruments. Thus, in some such embodiments, the inner cannula comprises upper37and lower39inserts having opposing faces38,40. Preferably, the opposing faces each comprise a longitudinal groove45,46therein. These opposing grooves may help form the bore through which the shaver passes. Therefore, these grooves dictate the orientation of the shaver passing therethrough. Preferably, the lower insert is disposed only in a curved distal end portion of the port. This allows for easier access to the disc space in the portion of the port in which shaver head orientation is not critical.

In one particular embodiment thereof, the port comprises an outer cannula having a bore, and an inner cannula (disposed within the bore of the outer cannula) having internal guiding features. In these embodiments, these internal guiding features (such as grooves45,46and ridges) only allow the shaver is to be inserted into the disc space in such an orientation that the cutting surface of the shaver is parallel to the disc space.

The port can have variable distal angulations β within its distal end portion to ensure “snug” docking and control shaver angulations. The internal geometry of inserted or assembled port directs shaver into the disc space and maintains the axis of rotation.

Still referring toFIGS. 19A through 19C, in some embodiments, there is provided a port for use in preparing an intervertebral disc space, which comprises a longitudinal bore51therethrough, the bore having a proximal end portion53having a transverse cross-section and a distal end portion55having a transverse cross-section, wherein the transverse cross-section of the proximal end portion of the bore is greater than that transverse cross-section of the distal end portion of the bore. The requirement that the transverse cross-section of the proximal end portion of the bore is greater than that transverse cross-section of the distal end portion of the bore provides the surgeon with greater room in the proximal section of the bore to maneuver the instruments, while insuring that the instrument is still properly oriented by the time it passes through the distal end of the port.

Preferably, the port having the larger proximal bore has a distal end portion that is curved in order to insure proper orientation of the instruments passing therethrough. Preferably, the curve in the distal end portion is between 10 and 45 degrees.

In some embodiments, the transverse cross-section of the proximal end portion of the bore is defined by an upper insert, and the transverse cross-section of the distal end portion of the bore is defined by a lower insert and an upper insert. These embodiments possess larger proximal bores whose advantages are discussed above. The inserts may be tailored to specifically and particularly accommodate and orient the different instruments that enter the port.

Thus, now referring toFIGS. 19A through 19C and 20A through 20C, in some embodiments, there is provided a port for use in preparing an intervertebral disc space, comprising:

a) an outer cannula34having a bore36having a proximal end portion65and a distal end portion67,

b) an upper insert37disposed at least in the distal end portion of the bore, and

c) a lower insert35disposed at least in the distal end portion of the bore.

Preferably, the lower insert is disposed only in the distal end portion of the bore. Its absence in the proximal portion provides room for the surgeon to maneuver the shaver in the proximal portion of the port. Preferably, the upper insert is disposed in both the proximal and distal end portions of the bore. This is advantageous because it improves the ease and insertion along the entire length and provides the superior internal geometry to control insertion angle and axis of rotation. Preferably, the proximal end portion of the bore is straight, and the distal end portion of the bore is curved. The straight proximal end portion of the bore allows for accurate placement of the distal end portion of the port near the target disc space. Preferably, the distal end portion of the upper insert has a face38, and the lower insert has a face40, and the faces oppose each other, thereby forming a bore therebetween that dictates the orientation of the shaver passing therethrough.

Thus, and now referring toFIGS. 20A through 20C, there is provided an assembly comprising:

a) a curved port91having a bore having a transverse cross-section; and

b) a vertebral endplate shaver95having a transverse cross-section, wherein the shaver is disposed within the bore of the curved port, wherein the transverse cross-section of the bore substantially corresponds to the transverse cross-section of the shaver so as to determine the orientation of the shaver within the bore.

In some embodiments, the curved port has a distal end portion33having a securement feature35for securing the curved port to vertebral bone adjacent the target disc space. Preferably, the shaver is bendable so that it can pass through the curved portion of the port. In some embodiments thereof, the bendable shaver has a shaft96made of a flexible material, while in others the bendable shaver has a shaft having a universal joint.

In one prophetic method of practicing the present invention, the curved port enters the patient through an incision made in the skin. It then proceeds towards the target disc by manual advancement. Once in the general area of the target disc, the distal portion33of the port is then bent by advancing it over a steerable catheter that has itself been bent (as explained below). This leaves the distal end portion of the port adjacent the target disc. The securement tooth is advanced into a neighboring vertebral body to stabilize port placement. After the disc space is cleared, the flexible shaver is then advanced through the curved port and into the disc space. The inner features of the curved port guide the shaver's angulation with respect to the disc space. Once the shaver has been suitably placed, the handle and drive shaft of the shaver are rotated to scrape disc tissue and endplates in a plane that is parallel to the disc space.

Therefore, in some embodiments, there is provided a method of preparing an intervertebral disc space between opposing vertebral endplates, comprising the steps of:

a) inserting a curved port into a lateral aspect of the disc space, the curved port having a bore.

Preferably, the insertion is in a substantially coronal plane, as is generally the case for lateral implants. Preferably, the curved port has a substantially straight proximal end portion and a curved distal end portion. Preferably, the curved distal end portion of the curved port is docked to a vertebral body and is oriented substantially parallel to the opposing vertebral endplates in order to dictate endplate preparation that is parallel to the endplates. Preferably, the curved port has a distal end portion having a securement feature, through which docking of the port to a vertebral body occurs. This provides secure attachment of the port to a neighboring vertebral body.

In other embodiments, the method further comprises the steps of:

b) inserting a substantially straight, bendable shaver into the curved port;

c) advancing the shaver through the port and into an intervertebral disc space bounded by a vertebral endplate so that the shaver bends in the port, and

d) contacting the shaver to the vertebral endplate. Preferably, the bore of the port has a shape corresponding to a cross-section of the shaver so as to determine the orientation of the shaver within the bore. Preferably, the bendable shaver has a shaft made of a flexible material, or has a shaft having a universal joint. Preferably, the target disc space is the L5/S1 or L4/L5 disc space. It is currently very problematic to access these two disc spaces with conventional lateral cage insertion techniques. Preferably, the curved port approaches the disc space during insertion from an upper end of the spine, as is the case with conventional lateral cage insertion techniques.

Now referring toFIGS. 22A through 22C, a catheter101with a steerable tip103is used to laterally access the caudal disc space. It is typically advanced through an incision in the skin of the patient and directed in a straight line towards the target disc. The steering mechanism in the catheter is then actuated to impart a curve in the tip of the catheter. This curve allows the surgeon to steer the tip directly towards the disc. The tip is then advanced until it contacts the target disc.

In some embodiments, a distal end portion105of the catheter includes a neuromonitoring sensor or electrode141. This sensor connects to an external neuro-monitor as the catheter is advanced into the abdomen under fluoroscopic imaging. The function of this sensor is to detect the presence of nerves as the catheter tip is directed towards the target disc.

Once the tip is safely placed against a lateral portion of a disc, a guide wire139is advanced through the steerable tip and into the disc. In some embodiments, the electrode141can be a neuromonitoring band for sensing adjacent neural tissue. The function of this guide wire is to anchor the initial catheter in the disc and set the trajectory for the subsequent advance of dilation tubes.

In some embodiments, the steerable catheter and guidewire system is the VASCOCATH™, available from Polydiagnost of Pfaffenhofen, Germany.

Now referring toFIGS. 23A through 23C, the flexible dilation tubes111,113,115provide a minimally invasive access path for the subsequent advance of instruments or implants. Sequential flexible dilation tubes are advanced over the steerable catheter101and against the disc, thereby sequentially removing more and more tissue from the access path.

The flexible nature of these dilation tubes allows them to curve and thereby provide a parallel trajectory for instruments and implants laterally approaching the L4/L5 or L5/S1 disc spaces.

Therefore, and now referring toFIGS. 23A through 23C, in accordance with the present invention, there is provided an assembly for providing access to an intervertebral disc, comprising;

b) a first flexible dilator tube111having a first bore112defining a first longitudinal axis,

c) a second flexible dilator tube113having a second bore114defining a second longitudinal axis, wherein the first flexible dilator tube is received with the bore of the second flexible dilator tube, and wherein the steerable tip is received within the bore of the first flexible dilator tube.

Preferably, the steerable tip is curved, thereby imparting a curve upon the longitudinal axis of each of the first and second flexible dilator tubes. Preferably, each of the first and second dilator tubes has a proximal end portion and a distal end portion, and wherein the curve upon the longitudinal axis of each of the first and second flexible dilator tubes is located in the distal end portion of each tube.

In some embodiments, the catheter further comprises a guide wire.

In some embodiments, and now referring toFIGS. 23A through 23B, at least one of the flexible dilation tubes comprises a reinforcement member131, preferably a fiber which is preferably metallic.

In some embodiments, each of the first and second flexible dilator tubes has a frustoconical distal end.

In accordance with the present invention, there is provided an assembly for providing access to an intervertebral disc, comprising;

d) a catheter having a steerable tip,

e) a first flexible dilator tube having a first bore defining a first longitudinal axis,

f) a second flexible dilator tube having a second bore defining a second longitudinal axis, wherein the first flexible dilator tube is received with the bore of the second flexible dilator tube, and wherein the steerable tip is received within the bore of the first flexible dilator tube.

In accordance with the present invention, there is provided a method of accessing a target intervertebral disc, comprising the steps of:

a) advancing a steerable catheter having a tip through an incision and towards the target disc,

b) imparting a first curve in the tip of the steerable catheter,

c) docking the curved tip upon the target disc,

d) advancing a first flexible dilator tube over the curved tip to impart a first curve in the first flexible dilator tube.

FIGS. 23C through 23Edisclose telescoping dilation tubes. InFIG. 23C, each tube has helical reinforcement members131that are electrically connected to a neuromonitoring band136. Thus, the ports may be used for neuromonitoring during approach. InFIG. 23D, each tube has vertical reinforcement members131that are electrically connected to a neuromonitoring band136. InFIG. 23E, each tube has helical and vertical members131that are electrically connected to a neuromonitoring band136. It also has slots132that provide additional flexibility.

Now referring toFIG. 24, the flexible dilation tubes comprise elastically deformable materials includes metallics and polymers. The flexible dilation tubes may further comprise axial reinforcing members (such as wires, fibers or struts) in order to provide improved column strength. The wall121of the flexible dilation tube120can have a secondary bore123to accept an endoscope for visualization of the disc and adjacent structures. Once dilation to the desired diameter is accomplished, the smaller dilation tubes may be removed. Inserts may be placed within the final dilation (or “port”) in order to provide internal guiding surfaces for guiding instruments such as flexible shavers.