# Patent

## Title
Systems and methods for performing spine surgery

## Abstract

Systems and methods are described for accessing and operating on an intervertebral disc at the lumbosacral junction via a trans-iliac approach. The instruments and methods described employ nerve monitoring to direct passage of the instruments through a safe zone between the L5 nerve root lying posterior to the trans-iliac path and the iliac vein (and iliac artery) lying anterior to the trans-iliac path.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is an non-provisional patent application and claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 61/471,069, entitled “Systems and Methods for Performing Spine Surgery,” filed on Apr. 1, 2011, the entire contents of which is expressly incorporated by reference into this disclosure as if set forth in its entirety herein.


FIELD
The present invention relates to implants and methods for accessing and operating on the lumbosacral spine.
BACKGROUND
The spinal column is a highly complex system of bones and connective tissues that provide support for the body and protect the delicate spinal cord and nerves. The spinal column includes a series of vertebral bodies stacked one atop the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces exerted upon the spinal column. A vertebral canal containing the spinal cord is located behind the vertebral bodies.
There are many types of spinal column disorders including scoliosis (abnormal lateral curvature of the spine), excess kyphosis (abnormal forward curvature of the spine), excess lordosis (abnormal backward curvature of the spine), spondylolisthesis (forward displacement of one vertebra over another), and other disorders caused by abnormalities, disease or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra and the like. Patients that suffer from such conditions usually experience extreme and debilitating pain, as well as diminished nerve function.
A noteworthy trend in the medical community is the move away from performing surgery via traditional “open” techniques in favor of minimally invasive or minimal access techniques. Open surgical techniques are generally undesirable in that they typically require large incisions and high amounts of tissue displacement to gain access to the surgical target site, which produces concomitantly high amounts of pain, lengthened hospitalization (increasing health care costs), and high morbidity in the patient population. Less-invasive surgical techniques (including so-called “minimal access” and “minimally invasive” techniques) are gaining favor due to the fact that they involve accessing the surgical target site via incisions of substantially smaller size with greatly reduced tissue displacement requirements. This, in turn, reduces the pain, morbidity and cost associated with such procedures. On such minimally invasive approach, a lateral trans-psoas approach to the spine, developed by NuVasive®, Inc., San Diego, Calif. (XLIF®) has demonstrated great success in reducing patient morbidity, shortening hospitalization stays and quickening recovery time if it is employed.
Unfortunately, the iliac crest blocks lateral access to the L5/S1 disc space in most individuals, leaving only anterior and posterior approaches available to reach the L5/S1 disc. Thus, in a patient requiring a multi-level operation including L5-S1, for example, a lateral trans-psoas approach may be utilized to treat the spinal condition at one or more levels above the L5/S1 disc, and the patient may be moved into a new position to access the L5/S1 disc through either the anterior or posterior approach. The systems and methods described herein are directed towards eliminating, or at least reducing, these challenges.
The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art.
SUMMARY
Access to the L5/S1 disc space (also referred to as the 5-1 disc) may be achieved laterally through the iliac crest. One or more instruments are used to create an access hole through the iliac over the L5/S1 disc. Through the access hole one or more instruments may be advanced to the L5/S1 disc, taking care to avoid damaging delicate nerves and blood vessels situated in the space between the iliac crest and spinal column. One of the one or more instruments advanced to the disc space may be a working portal through which the disc may be operated on (e.g. discectomy and fusion may be performed).
FIGS. 3-5 illustrate the iliac crest, L5/S1 disc, and the space that separates them—referred to herein as the iliac space. As best appreciated in FIGS. 3-4 traversing the path between the iliac crest and the L5/S1 disc is complicated by an abundance of nerve tissue and vascular tissue. Of particular concern are the L5 nerve root and the iliac vein and iliac artery as damage to any of these tissues could result in serious consequences to the patient. However, as best pictured in FIGS. 6-8, it is possible to access the 5-1 disc through the space between the L5 nerve root and the iliac vein. This space is termed the “safe zone” herein and is bordered posteriorly by the L5 nerve root and anteriorly by the iliac vein. Trans-iliac access to the 5-1 disc may thus be safely achieved by passing an access device through the safe zone to the disc to create a corridor through which work on the disc may be performed without danger to the vessels or nerve root.
The precise size and location of the safe zone may vary from patient to patient, thus it is important to assess the safe zone prior to creating the access corridor. The safe zone may be assessed through pre-operatively through the study of pre-operative images (e.g. CT scans and/or MRI). The L5 nerve root and the iliac vein (and artery) can be identified in the images and the size of the safe zone determined. By way of example, the size of the safe zone may generally vary between a range of approximately 10 mm and 20 mm, though the range is not inclusive.
Once the safe zone has been assessed during pre-operative planning, the information may be used during surgery to avoid the iliac vessels and the L5 nerve root. This is accomplished by using nerve monitoring techniques to locate the L5 nerve root. By way of example, stimulation signals are emitted from the distal end of an access instrument (e.g. dilator) and muscles innervated by the nerve are monitored for a neuromuscular response. The stimulation current level required to elicit a significant response (stimulation threshold) is determined, and preferably repeatedly updated, which provides an indication of the nerve proximity (and optionally, direction) to the distal end of the access instrument. The higher the stimulation threshold the farther away the nerve is, and vice versa. Thus, to seek out the L5 nerve root the user can direct the access instrument such that the stimulation threshold gets lower and lower (indicating that the access instrument is getting closer to the nerve) until the threshold drops below a certain level (e.g. 3 mA) indicating that the instrument is right next to the nerve, but not contacting the nerve. Directionality may be determined to ensure that the instrument is anterior to the nerve. With the position of the nerve now know, the position of the iliac vein is also known (based on the pre-operative planning data) and the access instrument may be docked to the 5-1 disc in the safe zone. By following the path of the initial access instrument, additional instruments can safely advance through to the L5/S1 disc and the desired procedure may be completed on the disc. Nerve monitoring may be conducted with one or more of the additional instruments.
As described herein, two sets of dilators are used to create the access corridor to the 5-1 disc. The first set of dilators is used for dilating the iliac crest and the dilators are designed to be impacted through the iliac bone. The second set of dilators are used for dilating through the iliac space and are designed to be used with a neurophysiology monitoring system to determine the location of the L5 nerve root as the dilators are advanced. It should be appreciated that two different sets of dilators are not necessarily required, provided that the both functions (i.e. impaction through bone and nerve monitoring) may be completed with the dilators chosen.
According to the example method described, a jamshidi is first advanced into the iliac bone at the appropriate entry point. The needle of the jamshidi is removed and a K-wire or similar guide is advanced into the iliac. The cannula of the jamshidi is removed and the initial dilator of the first dilator set (impaction dilators) is advanced into the iliac crest, over the K-wire, and wagged around. The supplemental dilators of the first dilator set are the advanced in turn into the iliac bone until the access hole created is of the appropriate size. The dilators are then removed and the initial dilator of the second dilator set (electrified dilators) is advanced to the access hole. The initial dilator is connected to the neurophysiology monitoring system to perform nerve detection as described above and the dilator is advanced toward the L5 nerve root. Once the nerve root is located the initial dilator is docked in the desired position on the 5-1 disc with the K-wire. The supplemental dilators of the second set of dilators are then advanced in turn through the safe zone onto the disc space until the desired size is achieved. The outer dilator is fixed in position (e.g. by penetrating into the disc or vertebral body, or, with a table mount) and the inner dilators are removed.
The inner lumen of the outer dilator becomes a working portal through which instruments may be passed to perform the desired procedure on the L5/S1 disc. For example, the instruments may be curettes, reamers, shavers, etc. . . . for performing a discectomy. Implants may also be deposited in the disc space to facilitate fusion. The implant may be a collapsible bag that is advanced through the working corridor in a collapsed configuration and then filled with a filler material in situ. The filler material may be a bone growth promoting material (e.g. bone chips, synthetic or cellular bone matrix, etc. . . . ). The implant may also be an expandable implant that is implanted into the disc space in a first smaller configuration and then expanded via any number of suitable expansion mechanisms. The implant may also be a modular implant that is inserted through the working portal in several smaller pieces and assembled in the disc space to form a larger implant. Bone growth promoting material may be packed in or around any of the implants described. Once work on the 5-1 disc is complete, the working portal is removed and the wound closed.



BRIEF DESCRIPTION OF THE DRAWINGS
Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein:
FIG. 1 is an anterior view of the skeletal, nerve, and blood vessel anatomy in and around the iliac space;
FIG. 2 is a lateral view looking through the ilium of the skeletal, nerve, and blood vessel anatomy in and around the iliac space;
FIG. 3 is a lateral perspective is a perspective view of a first (impaction) dilator set that may be used during formation of a trans-iliac access corridor to the L5/S1 disc, according to one example embodiment;
FIG. 4 is the lateral perspective view of FIG. 3 with all but the L5 nerve root and iliac vessels hidden and highlighting a safe zone between the L5 nerve root and iliac vessels through which an access corridor to the L5/S1 disc may be created, according to one example embodiment;
FIG. 5 is a lateral view looking through the ilium with all but the L5 nerve root and iliac vessels hidden and highlighting a safe zone between the L5 nerve root and iliac vessels through which an access corridor to the L5/S1 disc may be created, according to one example embodiment;
FIG. 6 is a top down view of the S1 vertebra depicting relative to the L5/S1 disc the position of the L5 nerve root, the iliac vessels, and the safe zone situated there between;
FIG. 7 is a perspective view of a jamshidi like needle that may be used during formation of a trans-iliac access corridor to the L5/S1 disc, according to one example embodiment;
FIG. 8 is a perspective view of a first (impaction) dilator set that may be used during formation of a trans-iliac access corridor to the L5/S1 disc, according to one example embodiment;
FIG. 9 is a perspective view of a second (nerve monitoring) dilator set that may be used during formation of a trans-iliac access corridor to the L5/S1 disc, according to one example embodiment; and
FIGS. 10-19 are lateral perspective views of the iliac space depicting certain steps carried out during an example method for forming a trans-iliac access corridor to the lateral aspect of the L5/S1 disc space, according to one example embodiment.



DESCRIPTION OF A PREFERRED EMBODIMENT
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The methods and devices described herein include a variety of inventive features and components that warrant patent protection, both individually and in combination.
As described hereafter, access to the L5/S1 disc space is achieved laterally through the ilium. One or more instruments are used to create an access hole through the ilium over top of the L5/S1 disc. Through the access hole one or more instruments may be advanced to the L5/S1 disc, taking care to avoid damaging delicate nerves and blood vessels situated in the space between the iliac crest and spinal column. One of the one or more instruments advanced to the disc space may form a working portal through which the disc may be operated on, for example, a discectomy and fusion may be performed.
Prior to describing the trans-iliac method for access the L5/S1 disc, the relevant anatomy, including the iliac crest 10, L5/S1 disc 12, and the space that separates them—referred to herein as the iliac space 14, are described with reference to FIGS. 1-6. As best appreciated in FIGS. 1-3, the iliac space 14 between the iliac crest 10 and the L5/S1 disc 12 is filled with an abundance of nerve and vascular tissue. Of particular concern when traversing the iliac space 14 are the L5 nerve root 16, the iliac vein 18, and iliac artery 20, as damage to any of these delicate tissues could result in serious consequences to the patient. FIGS. 4-5 highlight the position of these structures (L5 nerve root 16, iliac vein 18, and iliac artery 20) with the remaining peripheral tissues hidden for the sake of clarity. There is a small space between the L5 nerve root 16, which exits the spinal canal just posterior to the L5 vertebral body 22 and S1 vertebral body 24, and the iliac vein 18, which passes along an anterior portion of the lateral side of the L5 and S1 vertebral bodies 22, 24. This small space represents a window through which the L5/S1 disc may be access. This window is termed the “safe zone” 26 herein and is bordered posteriorly by the L5 nerve root 16 and anteriorly by the iliac vein 18. Thus, trans-iliac access to the L5/S1 disc 12 may be safely achieved by passing an access device through the safe zone 14 to the disc 12 to create a corridor through which work on the disc may be performed without danger to the vessels or nerve root.
The size and precise layout of the safe zone 26 varies from patient to patient. For example, though not limited to it, the size of the safe zone (i.e. distance between the L5 nerve root 16 and iliac vein 18) may generally range from approximately 10 mm to 20 mm. Accordingly, it is preferable that the safe zone be identified and assessed during pre-operative planning. This is accomplished through the review of CT and/or MRI images on which the L5 nerve root 16 and the iliac vein 18 can be identified and the distance between them measured. This information will then be used later during the procedure to ensure the access instrument(s) stay within the safe zone during passage through the iliac space 14.
According to the example method described herein, L5/S1 access is achieved using a jamshidi type needle, K-wire, and two sets of dilators. With reference to FIG. 7 the Jamshidi like needle includes an inner stylet 32 and a cannula 34. The inner stylet 32 is initially situated within the cannula 34 and the two components are locked together via a handle 36. The working tip 38 of the inner stylet 32 extends beyond the cannula 34 and is configured to penetrate into bone to form a pilot hole. The inner stylet 32 may be unlocked and removed from the cannula 34 which remains in place in the pilot hole. A K-wire or similar guide structure may then be passed through the cannula 34 and into the pilot hole.
FIG. 8 depicts the first dilator set 40 which is used for dilating through the ilium 10 to form an access hole 28 through the ilium. The first dilator set 40 includes an initial dilator 42 and at least one supplemental dilator 44. The dilators 42 and 44 of the first set are advanced, sequentially one over the other, into the iliac crest 10 until an access hole 28 of the appropriate size is created. The first of the at least one supplemental dilators 44 is advanced over the initial dilator 42 and any remaining supplemental dilators 44 are advanced in sequence over the outer dilator. The initial dilator 42 may be guided over a K-wire 46 or similar guide (e.g. Steinman pin, etc. . . . ). The dilators of the first dilator set 40 are preferably made of a rigid material such as metal (e.g. stainless steel, aluminum, etc. . . . ) or impact resistant plastic (e.g. polycarbonate, etc. . . . ) that can be impacted through the bone of the iliac crest 10.
The second dilator set 48, illustrated in FIG. 9, is used for dilating through the iliac space 14 to the L5/S1 disc 12. The second dilator set 48 includes an initial dilator 50 and at least one supplemental dilator 52. The dilators 50 and 52 of the second set are advanced, sequentially one over the other, through the access hole 28 in the iliac crest 10 to the L5/S1 disc 12. To accomplish this safely, at least the initial dilator 50, and preferably the supplemental dilators 52 of the second dilator set 48 can be linked to a neurophysiology monitoring system. The dilators 50, 52 include an insulated body 54 with a stimulation electrode 56 at the distal end 58 and an attachment point 60 (for connecting to the neurophysiology system, for example, via a clip or other suitable connector) at the proximal end 62. The dilators 50, 52 may be made of a conductive material coated with an insulating material or they may be made of a non-conductive material with a conductive lead extending between the attachment point 60 and the stimulation electrode 56. The dilators of the second dilator set 48 are advanced, sequentially one over the other, through the iliac crest 10 to the L5/S1 disc 12 while stimulation signals are delivered to the surrounding tissue through the stimulation electrode 56 to detect the presence (and optionally the direction) of nerves, and particularly the L5 nerve root 16 near the distal end. While two different dilator sets are described, it should be appreciated that two different sets of dilators are not necessarily required, provided that the both functions (i.e. impaction through bone and nerve monitoring) may be completed with the dilators chosen.
With reference to FIG. 10 and according to the example method described, with the patient preferably in a lateral decubitus position, the jamshidi needle 30 is first advanced to the appropriate entry point on the ilium 10 and docked in position. The entry point should be on the lateral surface of the ilium 10 and generally centered over the l5/S1 disc 12, which can be confirmed with a lateral fluoroscopy image. With the position confirmed the jamshidi 30 is advanced through the ilium 10 to form an initial pilot hole 27. The inner stylet 32 is removed and a k-wire 46 or similar guide is advanced through the jamshidi cannula 34 and the cannula 34 is removed leaving the k-wire to serve as a guide for the first dilator set 40. In an alternative step, the initial pilot hole 27 can be formed directly with a guide member of sufficient rigidity (e.g. Steinman pin) or the initial dilator 42.
With the K-wire 46 (or other guide member) in place, the initial dilator 42 of the first dilator set 40 (impaction dilators) is advanced into the pilot hole, over the K-wire, as depicted in FIG. 11. The K-wire 42 is removed and the initial dilator 42 is impacted through the ilium 10, to form the access hole 28. After impaction, wagging of the dilator 42 (e.g. moving the dilator around in a conical motion) may be done to further increase the size of the access hole 28 prior to inserting the supplemental dilator(s) 44. Turning to FIG. 12, each of the supplemental dilators 44 are advanced in turn over the previous dilator and impacted through the ilium, increasing the size of the access hole 28 with each new dilator 44. As with the initial dilator 42, wagging of the dilator(s) 44 can be done to help increase the hole 28 size and facilitate easier insertion of the subsequent dilator 44. According to the example method described, three supplemental dilators 44 (for a total of four dilators in the first dilator set 40) are used, as pictured in FIG. 12. However, the number of dilators 44 and size of the access hole 28 may vary between patients and may depend on the size of the safe zone (determined during pre-operative planning). With the access hole 28 through the ilium 10 expanded to its final size, the first dilator set 40 is removed making way for insertion of the second dilator set 48 through the iliac space 14 to the L5/S1 disc (FIG. 13).
Turning to FIG. 14, the initial dilator 50 of the second dilator set 48 is advanced into the iliac space 14 through the access hole 28. In order to safely target the safe zone 26 the initial dilator 50 is connected to a neurophysiology monitoring system (not shown) to perform nerve detection as the dilator 50 is through the iliac space 14. As will now be described, the neurophysiology system is used to detect presence of nerves in the path of the initial dilator 50 and to direct the distal end of the initial dilator 50 towards the L5 nerve root. The neurophysiology system detects the presence of nerves by delivering electrical stimulation signals 64 of known currents through the stimulation electrode 56 on the distal end of the dilator 50 and monitoring for neuromuscular responses from muscles innervated by the nerves. The stimulation current amplitude required to elicit a response (i.e. stimulation threshold) is determined which provides an indication of nerve proximity (and optionally, direction) to the distal end of the dilator 50. The higher the stimulation threshold the farther away the nerve is, and vice versa. The threshold determination is performed repeatedly during advancement of the initial dilator 50 to continually update the proximity (and optionally directionality) indication.
To ensure the second dilator set 48 is passed through the safe zone, the surgeon first directs the initial dilator 50 towards the L5 nerve root 16, which marks the posterior border of the safe zone. To seek out the L5 nerve root 16 the surgeon advances the initial dilator 50 such that the stimulation threshold gets lower and lower (indicating that the dilator is getting closer to the nerve root) until the threshold drops below a certain level, for example, 3 mA. When the stimulation threshold drops to this predetermined level, the surgeon knows that the distal end of the dilator 50 is indicating that the instrument is next to, but not contacting the nerve root 16. The goal at this stage is to position the dilator 50 right next to the nerve root 16 without injuring the root and keeping the dilator 50 anterior to the nerve root. Directionality may be determined (for example, by rotating the dilator to determine the direction that gives the lowest stimulation threshold) to ensure that the instrument is anterior to the nerve. With the location of the L5 nerve root 16 now known, the position of the iliac vein 18 is also known based on the information gained from the preoperative pre-operative planning. That is, the distance between the nerve root 16 and the iliac vein 18 is determined during pre-operative planning such that with the dilator 50 positioned right next to the nerve root 16, the surgeon knows how much room there is to work anterior to the nerve root 16 before encroaching on the iliac vein 18 (and iliac artery 20). Using this information, the initial dilator 50 is adjusted anteriorly into the safe zone to provide room relative to the L5 nerve root 16 for advancement of the supplemental dilator(s) 52, and is then docked on the L5/S1 disc 12 with a k-wire 46 to hold the position of the second dilator set 48 (FIG. 15) and prevent unwanted movement during dilation.
As illustrated in FIG. 16, the supplemental dilators 52 of the second dilator set 48 are then advanced in turn through the safe zone onto the disc space. Preferably, advancement of each of the supplemental dilators 52 is carried out with neurophysiology monitoring to maintain the safe relationship with the L5 nerve root 16. In addition, fluoroscopy may also be used to verify the position of the dilators in the safe zone 26. The outermost dilator is fixed in position (e.g. by penetrating into the disc or vertebral body, or, with a table mount) and the inner dilators are removed, leaving the outermost dilator 52 to define a protected working corridor 66 through which the L5/S1 disc can be accessed and operated on, as illustrated in FIG. 17. The size of the outermost dilator, and thus the size of the operative corridor, may be determined based on the size of the safe zone.
With reference to FIG. 18, the working corridor 66 provides a protected passage through which instruments 68 may be passed to perform the desired procedure on the L5/S1 disc. For example, the instruments may be curettes, reamers, shavers, etc. . . . for performing a discectomy. The instruments 68 may also be implant inserters for introducing implants which may also be deposited in the disc space to facilitate fusion or disc replacement. The implant may be a collapsible bag that is advanced through the working corridor in a collapsed configuration and then filled with a filler material in situ. The filler material may be a bone growth promoting material (e.g. bone chips, synthetic or cellular bone matrix, etc. . . . ). The implant may also be an expandable implant that is implanted into the disc space in a first smaller configuration and then expanded via any number of suitable expansion mechanisms. According to one example, the expandable implant is a collapsible textile bag with structural supports formed at the corners. The structural supports may be solid blocks (e.g. PEEK blocks) molded or otherwise adhered to bag in the corners. The implant may also be a single insert (e.g. PEEK block) dimensioned to be passed through the working corridor 66 and to extend across the L5/S1 disc space. The implant may also be a modular implant that is inserted through the working corridor 66 in several smaller pieces and assembled in the disc space 12 to form a larger implant. Bone growth promoting material may be packed in or around any of the implants described. Once work on the repaired L5/S1 disc 70 is complete, the final dilator 52 forming the working corridor 66 is removed and the wound closed. Though not necessary, the access hole 28 may be filled with bone graft 72 to promote bone growth and ultimately, the closure of the access hole (FIG. 19).
As evident from the above discussion and drawings, the apparatus and methods described accomplish the goals of gaining access to the 5/1 disc space in a fashion less invasive than traditional “open” surgeries, while still achieving significant disc preparation. And while the apparatus and methods have been described in terms of a best mode for achieving these objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.

## Claims

1. A method for accessing the L5/S1 disc of the lumbosacral junction, comprising the steps of:
creating an access hole through the ilium;
advancing an initial dilator through the access hole and towards the L5/S1 disc while and electrical stimulation signal is delivered from a stimulation electrode on the distal end of the initial dilator;
assessing the neuromuscular response to the stimulation signal to indicate the proximity of the L5/S1 nerve root to the distal end of the initial dilator;
directing the distal end of the dilator closer to the L5/S1 nerve root until the neuromuscular response indicates that the distal end of the initial dilator is next to but not contacting the L5 nerve root;
advancing the distal end of the initial dilator through a safe zone between the L5 nerve root and the iliac vein to the L5/S1 disc; and
advancing at least one supplemental dilator over the initial dilator through the access hole and safe zone to the L5/S1 disc; and
removing all but the outermost dilator.

2. The method of claim 1, comprising the additional step of adjusting the position of the initial dilator anteriorly to the center of the safe zone.

3. The method of claim 2, comprising the additional step of docking the initial dilator to the spine by advancing a K-wire through the initial dilator and penetrating the annulus of the L5/S1 disc.

4. The method of claim 3, wherein three supplemental dilators are advanced over the initial dilator the access hole and safe zone to the L5/S1 disc.

5. The method of claim 1, wherein while advancing the at least one supplemental dilator an electrical stimulation signal is delivered from a stimulation electrode on the distal end of the at least one supplemental dilator to detect nerve proximity during advancement of the at least one supplemental dilator to the L5/S1 disc.

6. The method of claim 1, comprising the additional step of performing a procedure on the L5/S1 disc through a passageway in the outermost dilator.

7. The method of claim 6, wherein the procedure performed on the L5/S1 disc is a discectomy.

8. The method of claim 7, where the procedure performed on the L5/S1 disc further includes a fusion.

9. The method of claim 8, wherein the fusion procedure includes implanting a fusion implant in the L5/S1 disc space through the passageway in the outermost dilator.

10. The method of claim 9, wherein the fusion implant include an expandable textile bag that is inserted in a deflated stated and expanded within the L5/S1 disc space by introducing bone growth promoting materials into the bag.

11. The method of claim 10, wherein the textile bag includes integrated structural supports.

12. The method of claim 11, wherein the integrated structural supports are comprised of polymer blocks attached to the corners of the textile bag.

13. The method of claim 8, wherein the fusion implant is a single insert dimensioned to extend across the L5/S1 disc space.

14. The method of claim 13, wherein the single insert includes a fusion aperture extending from a top surface to a bottom surface that is packed with bone growth promoting materials prior to introduction of the implant.

15. The method of claim 1, wherein the step of creating the access hole through the ilium comprises:
advancing an instrument into the ilium and forming a pilot hole;
advancing an initial dilator into the pilot hole and impacting the dilator through the ilium to create an access hole; and
advancing at least one supplemental dilator over the initial dilator and impacting the dilator through the ilium to enlarge the access hole.

16. The method of claim 15, wherein the instrument advanced into the ilium to form the pilot hole is a jamshidi needle.

17. The method of claim 16, comprising the additional steps of:
removing an inner stylet from a cannula of the jamshidi needle;
introducing a K-wire through the cannula;
removing the cannula; and
introducing the initial dilator into the pilot hole over the K-wire.

18. The method of claim 15, wherein the instrument advanced to the ilium to form the pilot hole is a Steinman pin.

19. The method of claim 15, wherein three supplemental dilators are advanced over the initial dilator and impacted through the ilium to enlarge the access hole.

20. The method of claim 1, wherein the outermost dilator is anchored in position prior to removing the remaining dilators.