Abstract:
A method for treating stenosis in a spine of a patient having a median plane, wherein the spine includes a spinal canal having a posterior surface, a dural sac and an epidural space between the posterior surface and dural sac, the location of the stenosis determining a region of interest in the spine. In an embodiment the method comprises the steps of a) generating at least one view of a portion of the spinal canal in the region of interest; b) compressing the dural sac in the region of interest by injecting a fluid to form a safety zone and establish a working zone in the region of interest, the safety zone lying between the working zone and the dural sac; c) percutaneously accessing the epidural space in the region of interest on a first side of the median plane; d) inserting a tissue removal tool into tissue in the working zone on the first side of the median plane; e) using the tissue removal tool to percutaneously reduce the stenosis on the first side of the median plane; and f utilizing the at least one view to position the tissue removal too during at least a part of step d) and at least part of step e)

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to minimally invasive methods, devices and systems for treating spinal disorders using imaging guidance. This invention also relates to devices used to reduce stenosis and increase the cross-sectional area of the spinal canal available for the spinal cord. This invention also relates to methods, devices, therapies and medications used to treat disorders that involve the epidural space within the spinal canal.  
         [0005]     2. Background of the Invention  
         [0006]     The vertebral column (spine, spinal column, backbone) forms the main part of the axial skeleton, provides a strong yet flexible support for the head and body, and protects the spinal cord disposed in the vertebral canal, which is formed within the vertebral column The vertebral column comprises a stack of vertebrae with an intervertebral disc between adjacent vertebrae. The vertebrae are stabilized by muscles and ligaments that hold the vertebrae in place and limit the movements of the vertebrae.  
         [0007]     As illustrated in  FIG. 1 , each vertebra  10  includes a vertebral body  12  that supports a vertebral arch  14 . A median plane  210  generally divides vertebra  10  into two substantially equal lateral sides. Vertical body  12  has the general shape of a short cylinder and is anterior to the vertebral arch  14 . The vertebral arch  14  together with vertebral body  12  encloses a space termed the vertebral foramen  15 . The succession of vertebral foramen  15  in adjacent vertebrae  10  along the vertebral column define the vertebral canal (spinal canal), which contains the spinal cord.  
         [0008]     Vertebral arch  14  is formed by two pedicles  24  which project posteriorly to meet two laminae  16 . The two laminae  16  meet posteriomedially to form the spinous process  18 . At the junction of pedicles  24  and laminae  16 , six processes arise. Two transverse processes  20  project posterolaterally, two superior articular processes  22  project generally superiorly and are positioned superior to two inferior articular processes  25  that generally project inferiorly.  
         [0009]     The vertebral foramen  15  is generally an oval shaped space that contains and protects the spinal cord  28  Spinal cord  28  comprises a plurality of nerves  34  surrounded by cerebrospinal fluid (CSF) and an outermost sheath/membrane called the dural sac  32 . The CSF filled dural sac  32  containing nerves  34  is relatively compressible. Posterior to the spinal cord  28  within vertebral foramen  15  is the ligamentum flavum  26 . Laminae  16  of adjacent vertebral arches  14  in the vertebral column are joined by the relatively broad, elastic ligamentum flavum  26 .  
         [0010]     In degenerative conditions of the spine, narrowing of the spinal canal (stenosis) can occur. Lumbar spinal stenosis is often defined as a dural sac cross-sectional area less than 100 mm 2  or an anterior-posterior (AP) dimension of the canal of less than 10-12 mm for an average male.  
         [0011]     The source of many cases of lumbar spinal stenosis is thickening of the ligamentum flavum. Spinal stenosis may also be caused by subluxation, facet joint hypertrophy, osteophyte formation, underdevelopment of spinal canal, spondylosis deformans, degenerative intervertebral discs, degenerative spondylolisthesis, degenerative arthritis, ossification of the vertebral accessory ligaments and the like. A less common cause of spinal stenosis, which usually affects patients with morbid obesity or patients on oral corticosteroids, is excess fat in the epidural space. The excessive epidural fat compresses the dural sac, nerve roots and blood vessels contained therein and resulting in back, leg pain and weakness and numbness of the legs. Spinal stenosis may also affect the cervical and, less commonly, the thoracic spine.  
         [0012]     Patients suffering from spinal stenosis are typically first treated with exercise therapy, analgesics, and anti-inflammatory medications. These conservative treatment options frequently fail. If symptoms are severe, surgery is required to decompress the spinal cord and nerve roots.  
         [0013]     In some conventional approaches to correct stenosis in the lumbar region, an incision is made in the back and the muscles and supporting structures are stripped away from the spine, exposing the posterior aspect of the vertebral column. The thickened ligamentum flavum is then exposed by removal of a portion of the vertebral arch, often at the laminae, covering the back of the spinal canal (laminectomy). The thickened ligamentum flavum ligament can then be excised by sharp dissection with a scalpel or punching instruments such as a Kerison punch that is used to remove small chips of tissue. The procedure is performed under general anesthesia. Patients are usually admitted to the hospital for approximately five to seven days depending on the age and overall condition of the patient. Patients usually require between six weeks and three months to recover from the procedure. Further, many patients need extended therapy at a rehabilitation facility to regain enough mobility to live independently.  
         [0014]     Much of the pain and disability after an open laminectomy results from the tearing and cutting of the back muscles, blood vessels, supporting ligaments, and nerves that occurs during the exposure of the spinal column. Also, because the spine stabilizing back muscles and ligaments are stripped and detached from the spine during the laminectomy, these patients frequently develop spinal instability post-operatively.  
         [0015]     Minimally invasive techniques offer the potential for less post-operative pain and faster recovery compared to traditional open surgery. Percutaneous interventional spinal procedures can be performed with local anesthesia, thereby sparing the patient the risks and recovery time required with general anesthesia. In addition, there is less damage to the paraspinal muscles and ligaments with minimally invasive techniques, thereby reducing pain and preserving these important stabilizing structures.  
         [0016]     Various techniques for minimally invasive treatment of the spine are known. Microdiscectomy is performed by making a small incision in the skin and deep tissues to create a portal to the spine. A microscope is then used to aid in the dissection of the adjacent structures prior to discectomy. The recovery for this procedure is much shorter than traditional open discectomies. Percutaneous discectomy devices with fluoroscopic guidance have been used successfully to treat disorders of the disc but not to treat spinal stenosis or the ligamentum flavum directly. Arthroscopy or direct visualization of the spinal structures using a catheter or optical system have also been proposed to treat disorders of the spine including spinal stenosis, however these devices still use miniaturized standard surgical instruments and direct visualization of the spine similar to open surgical procedures. These devices and techniques are limited by the small size of the canal and these operations are difficult to perform and master. In addition, these procedures are painful and often require general anesthesia. Further, the arthroscopy procedures are time consuming and the fiber optic systems are expensive to purchase and maintain.  
         [0017]     Still further, because the nerves of the spinal cord pass through the spinal canal directly adjacent to and anterior to the ligamentum flavum, any surgery, regardless of whether open or percutaneous, includes a risk of damage to the nerves of the spinal cord.  
         [0018]     Hence, it remains desirable to provide simple methods, techniques, and devices for treating spinal stenosis and other spinal disorders without requiring open surgery. It is further desired to provide a system whereby the risk of damage to the dural sac containing the spinal nerves may be reduced.  
       SUMMARY OF THE INVENTION  
       [0019]     The present invention provides methods, devices and systems for treating spinal stenosis or other spinal disorders using image guidance in combination with percutaneous techniques. Embodiments of the present approach are referred to as an ipsilateral approach minimally invasive ligament decompression procedure (ILAMP). In some embodiments, the present invention provides a means for compressing the thecal sac within the epidural space so as to provide a safety zone in which further surgical procedures may be performed without risk of damaging nearby tissues or the thecal sac itself.  
         [0020]     In another embodiment, the present invention provides a method for treating stenosis in a spine of a patient. In an embodiment, the method comprises the steps of a) generating at least one view of a portion of the spinal canal in the region of interest; b) percutaneously accessing the epidural space in the region of interest; c) compressing the dural sac in the region of interest by injecting a fluid to form a safety zone and establish a working zone, the safety zone lying between the working zone and the dural sac; d) inserting a tissue removal tool into tissue in the working zone; e) using the tool to percutaneously reduce the stenosis by removing at least a portion of the ligamentum flavum by inserting an excision tool into the ligamentum flavum in the region of interest, wherein the portion of the ligamentum flavum removed is on the same side of the ligamentum flavum where the excision tool is inserted into the ligamentum flavum; and f) utilizing the at least one view to position the tool during at least a part of step d) and at least part of step e).  
         [0021]     The foregoing has outlined rather broadly the features and technical advantages of embodiments of the present invention in order that the detailed description that follows may be better understood Additional features and advantages of embodiments of the present invention will be described hereinafter that form the subject of the claims. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes. It should also be realized by those skilled in the art that such equivalent constructions do not depart from and scope of the invention as set forth in the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     For a more complete understanding of the invention, reference is made to the accompanying drawings, wherein:  
         [0023]      FIG. 1  is cross-section of the spine viewed from the space between two vertebrae, showing the upper surface of one vertebra and the spinal canal with the dural sac and a normal (un-stenosed) ligamentum flavum therein:  
         [0024]      FIG. 2  is an illustration of the same section as  FIG. 1 , showing the spinal canal with the dural sac and a thickened ligamentum flavum therein;  
         [0025]      FIG. 3  is an enlarged cross-section of a vertebral foramen, showing a safety zone created by compression of the dural sac;  
         [0026]      FIG. 4  is the cross-section of  FIG. 3 , showing a tissue excision tool positioned in the ligamentum flavum according to a first method (ILAMP);  
         [0027]      FIG. 5  is the cross-section of  FIG. 3 , showing a tissue excision tool positioned in the ligamentum flavum according to an alternative method (MILD);  
         [0028]      FIG. 6  is a partial cross-section of the lumbar portion of the vertebral column taken along lines  6 - 6  in  FIG. 1 ;  
         [0029]      FIG. 7  is the cross-section of  FIG. 6 , showing the orientation of an imaging tool relative to the vertebral column;  
         [0030]      FIG. 8  is the cross-section of  FIG. 6 , showing the orientation of an instrument relative to the vertebral column;  
         [0031]      FIGS. 9-13  are a series of illustrations showing tissue excision by a tissue-excision tool constructed in accordance with a first embodiment of the invention;  
         [0032]      FIGS. 14-18  are a series of illustrations showing tissue excision by a tissue-excision tool constructed in accordance with a second embodiment of the invention;  
         [0033]      FIGS. 19 and 21  are sequential illustrations showing removal of tissue from a tissue-excision tool by a tissue-removal device constructed in accordance with an embodiment of the invention;  
         [0034]      FIGS. 20 and 22  are end views of the tissue-removal device of  FIGS. 19 and 21 , respectively;  
         [0035]      FIG. 23  is cross-section of a tissue-removal device constructed in accordance with an alternative embodiment of the invention;  
         [0036]      FIG. 24  shows an alternative embodiment of a grasping needle with a corkscrew shape;  
         [0037]      FIG. 25  is a perspective view of a tissue-excision tool constructed in accordance with a third embodiment of the invention;  
         [0038]      FIGS. 26 and 27  are enlarged cross-sectional and perspective views, respectively, of the grasping device of  FIG. 25  in its retracted position;  
         [0039]      FIGS. 28 and 29  are enlarged cross-sectional and perspective views, respectively, of the grasping device of  FIG. 25  in its extended position;  
         [0040]      FIG. 30  is a schematic illustration of one embodiment of a double-ended ligament anchor being deployed in a ligamentum flavum;  
         [0041]      FIG. 31  shows the device of  FIG. 30  after full deployment;  
         [0042]      FIG. 32  is a perspective view of an entire tool constructed in accordance with preferred embodiments;  
         [0043]      FIG. 33  is an enlarged cross-sectional view of the distal tip of the tool of  FIG. 32  with the aperture partially opened; and  
         [0044]      FIG. 34  is a cross-sectional view of the handle end of the tool of  FIG. 32 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment  
         [0046]     For purposes of this discussion, the x-, y-, and z-axis are shown in  FIGS. 1, 3 ,  5 ,  6 , and  7  to aid in understanding the descriptions that follow. The x-, y-, and z-axis have been assigned as follows. The x-axis is perpendicular to the longitudinal axis of the vertebral column and perpendicular to the coronal/frontal plane (i.e., x-axis defines anterior vs. posterior relationships). The y-axis runs substantially parallel to the vertebral column and perpendicular to the transverse plane (i.e., y-axis defines superior vs. inferior relationships). The z-axis is perpendicular to the longitudinal axis of the vertebral column and perpendicular to the median/midsagittal plane (i.e., z-axis defines the lateral right and left sides of body parts). The set of coordinate axes (x-, y-, and z-axis) are consistently maintained throughout although different views of vertebrae and the spinal column may be presented.  
         [0047]     It is to be understood that the median/midsagittal plane passes from the top to the bottom of the body and separates the left and the right sides of the body, and the spine, into substantially equal halves (e.g., two substantially equal lateral sides). Further, it is to be understood that the frontal/coronal plane essentially separates the body into the forward (anterior) half and the back (posterior) half and is perpendicular to the median plane. Still further, it is to be understood that the transverse plane is perpendicular to both the median plane and coronal plane and is the plane which divides the body into an upper and a lower half.  
         [0000]     The Spinal Canal and Spinal Stenosis  
         [0048]     Referring again to  FIG. 1 , vertebral foramen  15  contains a portion of the ligamentum flavum  26 , spinal cord  28 , and an epidural space  27  between ligamentum flavum  26  and spinal cord  28 . Spinal cord  28  comprises a plurality of nerves  34  surrounded by cerebrospinal fluid (CSF) contained within dural sac  32  Nerves  34  normally comprise only a small proportion of the dural sac  32  volume. Thus, CSF filled dural sac  32  is somewhat locally compressible, as localized pressure causes the CSF to flow to adjacent portions of the dural sac. Epidural space  27  is typically filled with blood vessels and fat. The posterior border of the normal epidural space  27  generally defined by the ligamentum flavum  26 , which is shown in its normal, non-thickened state in  FIG. 1 .  
         [0049]      FIG. 2  illustrates a case of spinal stenosis resulting from a thickened ligamentum flavum  26 . Since vertebral foramen  15  is defined and surrounded by the relatively rigid bone its volume is essentially constant. Thus, thickening of ligamentum flavum  26  within vertebral foramen  15  call eventually result in compression of spinal cord  28 . In particular, the thickened ligamentum flavum  26  may exert a compressive force on the posterior surface of dural sleeve  32 . In addition, thickening of ligamentum flavum  26  may compress the blood vessels and fat occupying epidural space  27 .  
         [0050]     Compression of spinal cord  28 , particularly in the lumbar region, may result in low back pain as well as pain or abnormal sensations in the legs. Further, compression of the blood vessels in the epidural space  27  that houses the nerves of the cauda equina may result in ischemic pain termed spinal claudication.  
         [0051]     In order to relieve the symptoms associated with a thickened or enlarged ligamentum flavum  26 , methods, techniques, and devices described herein may be employed to reduce the compressive forces exerted by the thickened ligamentum flavum on spinal cord  28  and the blood vessels in epidural space  27  (e.g., decompress spinal cord  28  and blood vessels in epidural space  27 ). In particular, compressive forces exerted by the thickened/enlarged ligamentum flavum  26  may be reduced by embodiments of a minimally invasive ligament decompression (MILD) procedure described herein. In some embodiments, the MILD procedure may be performed percutaneously to reduce the size of ligamentum flavum  26  by excising portions of ligamentum flavum  26 . In particular, in some embodiments of the MILD procedure, the ligamentum flavum  26  is accessed, cut and removed ipsilaterally (i.e., on the same side of vertebral arch  14 ) by a percutaneous cranial-caudal approach. Such an embodiment of the MILD procedure may be described hereinafter as Ipsilateral Approach MILD Procedure (ILAMP).  
         [0000]     Creation of a Safety Zone  
         [0052]     As shown in  FIGS. 1 and 2 , ligamentum flavum  26  is posteriorly apposed to spinal cord  28 . Thus, placement of tools within ligamentum flavum  26  to excise portions of ligamentum flavum  26  creates a risk of for inadvertent damage to the spinal cord  28 , dural sac  32 , and/or nerves  34 . Thus, in preferred embodiments of the procedures described herein, prior to insertion of tissue removal tools into the ligamentum flavum  26 , a gap is advantageously created between ligamentum flavum  26  and spinal cord  28  to provide a safety zone between ligamentum flavum  26  and spinal cord  28 .  
         [0053]      FIG. 3  illustrates an enlarged cross-sectional view of a vertebral foramen  15  within a vertebral Vertebral foramen  15  includes epidural space  27  and spinal cord  28  containing nerves  34  and CSF within dural sac  32  Further, a thickened/enlarged ligamentum flavum  26  extends into vertebral foramen  15 . To reduce the risk of damage to dural sac  32  and spinal cord  28 , a safety zone  40  is created between ligamentum flavum  26  and dural sac  32 .  
         [0054]     As previously described, spinal cord  28  comprises nerves  34  surrounded by CSF and is contained within dural sac  32 . Since more than 90% of the volume of dural sac  32  in the lumbar, region is filled by CSF, dural sac  32  is highly compressible. Thus, even when stenosis is causing compression of spinal cord  28 , in most cases it is possible to temporarily compress spinal cord  28  further. Thus, according to preferred embodiments, dural sac  32  is further compressed in the region of interest by injecting a fluid into epidural space  27  to create safety zone  40 . The presence of the injected fluid comprising safety zone  40  gently applies an additional compressive force to the outer surface of dural sac  32  so that at least a portion of the CSF within dural sac  32  is forced out of dural sac  32  in the region of interest, resulting in safety zone  40  between dural sac  32  and ligamentum flavum  26 .  
         [0055]     According to some embodiments, dural sac  32  is compressed by injecting a standard radio-opaque non-ionic myelographic contrast medium or other imagable or non-imagable medium into epidural space  27  in the region of interest. This is preferably accomplished with a percutaneous injection. Sufficient injectable fluid is preferably injected to displace the CSF out of the region of interest and compress dural sac  32  to at least a desired degree. The injected medium is preferably substantially contained within the confines of epidural space  27  extending to the margins of the dural sac  32 . The epidural space is substantially watertight and the fatty tissues and vascularization in epidural space  27 , combined with the viscous properties of the preferred fluids, serve to substantially maintain the injected medium in the desired region of interest. This novel method for protecting spinal cord  28  column may be referred to hereinafter as “contrast-guided dural protection.” 
         [0056]     Once a safety zone  40  has been created, a tool  100  may be inserted into the ligamentum flavum  26 , as will be described in more detail below. Tool  100  may comprise any suitable device, tool or instrument for relieving stenosis caused by the thickened/enlarged ligamentum flavum  26  including without limitation, embodiments of tissue excision devices and tissue retraction devices described in more detail below. Further, as best illustrated in  FIG. 4 , tool  100  is inserted and positioned in the ligamentum flavum  26  on the same side (ipsilateral) of median plane  210  as tool  100  percutaneously accesses the body, such that tool  100  does not cross median plane  210 . In another embodiment, as best illustrated in  FIG. 4 , tool  100  is positioned in the ligamentum flavum  26  on the opposite side of median plane  210  as tool  100  percutaneously accesses the body, such that tool  100  crosses median plane  210 .  
         [0057]     While it is preferred that the tip of tool  100  remain within ligamentum flavum  26  as shown, the presence of safety zone  40  reduces the likelihood that dural sac  32  will be damaged, even if the tool breaks through the anterior surface of ligamentum flavum  26 .  
         [0058]     Because the present techniques are preferably performed percutaneously, certain aspects of the present invention may be facilitated by imaging. Imaging windows (e.g., a fluoroscopic window of access—FWA) may be employed to aid in performance of all or, part of the procedures described herein. For instance, an imaging window may be employed to aid in insertion of tool  100  into ligamentum flavum  26  as shown in  FIG. 4A  Preferable imaging windows/views are described in mote detail below.  
         [0059]     In this context, the spine can be imaged using any suitable technology, including without limitation, 2D fluoroscopy, 3D fluoroscopy, CT, MRI, ultrasound or with direct visualization with fiber optic or microsurgical techniques. Stereotactic or computerized image fusion techniques are also suitable. Fluoroscopy is currently particularly well-suited to the techniques disclosed herein. Flouroscopic equipment is safe and easy to use, readily available in most medical facilities, relatively inexpensive. In a typical procedure, using direct biplane fluoroscopic guidance and local anesthesia, epidural space  27  is accessed for injection of contrast media adjacent to the surgical site.  
         [0060]     If the injected medium is radio-opaque, as are for example myelographic contrast media, the margins of expanded epidural space  27  will be readily visible using fluoroscopy or CT imaging. Thus, safety zone  40  created by the present contrast-guided dural compression techniques can reduce the risk of damage to dural sac  32  and spinal cord  28  during MILD procedures to remove or displace portions of ligamentum flavum  26  and/or laminae  16  in order to treat spinal stenosis.  
         [0000]     Injectable Medium  
         [0061]     If desired, the injected medium can be provided as a re-absorbable water-soluble gel, so as to better localize safety zone  40  at the site of surgery and reduce leakage of this protective layer from the vertebral/spinal canal. An injectable gel is a significant improvement on prior epidural injection techniques. The gel is preferably substantially more viscid than conventional contrast media and the relatively viscid and/or viscous gel preferably tends to remain localized at the desired site of treatment as it does not spread as much as standard liquid contrast media that are used in epidurography. This may result in more uniform compression of dural sac  32  and less leakage of contrast out of the vertebral/spinal canal. In addition, preferred embodiments of the gel are re-absorbed more slowly than conventional contrast media, allowing for better visualization during the course of the surgical procedure.  
         [0062]     In some embodiments, a contrast agent can be included in the gel itself, so that the entire gel mass is imagable. In other embodiments, an amount of contrast can be injected first, followed by the desired amount of gel, or an amount of gel can be injected first, followed by the desired amount of contrast. In this case, the contrast agent is captured on the surface of the expanding gel mass, so that the periphery of the mass is imagable.  
         [0063]     Any standard hydrophilic-lipophilic block copolymer (Pluronic) gel such as are known in the art would be suitable and other gels may be used as the injectable medium. The gel preferably has an inert base. In certain embodiments, the gel material is liquid at ambient temperatures and can be injected through a small bore, such as a 27 gauge needle. The gel then preferably becomes viscous when warmed to body temperature after being injected. The viscosity of the gel can be adjusted through the specifics of the preparation. The gel or other fluid is preferably sufficiently viscid or viscous at body temperature to compress and protect dural sac  32  in the manner described above and to remain sufficiently present in the region of interest for at least about 30 minutes. Thus, in some embodiments, the injected gel attains a viscosity that is two, three, six or even ten times that of the fluids that are typically used for epidurograms.  
         [0064]     In certain embodiments, the injected medium undergoes a reversible change in viscosity when warmed to body temperature so that it can be injected as a low-viscosity fluid, thicken upon injection into the patient, and be returned to its low-viscosity state by cooling. In these embodiments, the injected medium is injected as desired and thickens upon warming, but can be removed by contacting it with a heat removal device, such as an aspirator that has been provided with a cooled tip. As a result of localized cooling, the gel reverts to its initial non viscous liquid state and can be easily suctioned up the cooled needle or catheter.  
         [0065]     An example of a suitable contrast medium having the desired properties is Omnipaque® 240 available from Nycomed, New York, which is a commercially available non-ionic iodinated myelographic contrast medium. Other suitable injectable media will be known to those skilled in the art. Because of the proximity to spinal cord  28  and spinal nerves  34 , it is preferred not to use ionic media in the injectable medium The preferred compositions are reabsorbed relatively rapidly after the procedure. Thus any residual gel compression on dural sac  32  after the MILD procedure dissipates relatively quickly. For example, in preferred embodiments, the gel would have sufficient viscosity to compress dural sac  32  for thirty minutes, and sufficient degradability to be substantially reabsorbed within approximately two hours.  
         [0066]     The injected contrast medium further may further include one or more bioactive agents. For example, medications such as those used in epidural steroid injection (e.g. Depo medrol, Celestone Soluspan) may be added to the epidural gel to speed healing and reduce inflammation, scarring and adhesions. The gel preferably releases the steroid medication slowly and prolongs the anti-inflammatory effect, which can be extremely advantageous. Local anesthetic agents may also be added to the gel. This prolongs the duration of action of local anesthetic agents in the epidural space to prolong pain relief during epidural anesthesia. In this embodiment the gel may be formulated to slow the reabsorption of the gel.  
         [0067]     The present gels may also be used for epidural steroid injection and perineural blocks for management of acute and chronic spinal pain. Thrombin or other haemostatic agents can be added if desired, so as to reduce the risk of bleeding.  
         [0068]     In some embodiments, the gel may also be used as a substitute for a blood patch if a CSF leak occurs. The gel may also be used as an alternative method to treat lumbar puncture complications such as post-lumbar puncture CSF leak or other causes of intracranial hypotension. Similarly, the gel may be used to patch postoperative CSF leaks or dural tears. If the dural sac were inadvertently torn or cut, then gel could immediately serve to seal the site and prevent leakage of the cerebral spinal fluid.  
         [0000]     Ipsilateral Approach for MILD Procedure (ILAMP)  
         [0069]     Once safety zone  40  has been created, the margins of epidural space  27  are clearly demarcated by the injected medium and may be visualized radiographically if an imageable medium has been used. As mentioned above, percutaneous procedures can then more safely be performed on ligamentum flavum  26  and/or surrounding tissues with reduced potential for injuring dural sac  32  and spinal cord  28 .  
         [0070]     A variety of suitable techniques may be employed to reduce the size of the thickened/enlarged ligamentum flavum  26 , thereby decompressing spinal cord  28  as well as blood vessels contained within the epidural space  27 . Examples of suitable decompression techniques include without limitation, removal of tissue from ligamentum flavum  26 , laminectomy, laminotomy, and retraction and anchoring of ligamentum flavum  26 . In some embodiments, all or a portion of ligamentum flavum  26  is excised using a tissue excision tool (e.g., tool  100 ). Embodiments of tissue excision tools are described in more detail below.  
         [0071]     Accessing ligamentum flavum  26  with a tool  100  to remove portions of ligamentum flavum  26  can present significant challenges For instance, in some conventional approaches to correct stenosis caused by an enlarged ligamentum flavum, an incision is made in the back of the patient and then the muscles and supporting structures of the vertebral column (spine) are stripped away, exposing the posterior aspect of the vertebral column. Subsequently, the thickened ligamentum flavum is exposed by removal of a portion of vertebral arch  14 , often at lamina  16 , which encloses the anterior portion of the spinal canal (laminectomy). The thickened ligamentum flavum ligament can then be excised by sharp dissection with a scalpel or punching instruments. However, this approach is usually performed under general anesthesia and typically requires an extended hospital stay, lengthy recovery time and significant rehabilitation. Referring briefly to  FIG. 2 , as another example, some MILD procedures access ligamentum flavum  26  percutaneously by boring a hole through the vertebral arch  14  of vertebra  10 , often through a lamina  16 . A cannula and/or tool  100  may be passed through the bore and/or anchored to the bore to access ligamentum flavum  26  for excisions However, while such a MILD approach is minimally invasive and reduces recovery time, such an approach requires the additional step of boring a hole in the posterior of the vertebra  10  of interest. Thus, in some cases it will be preferable to employ a MILD that percutaneously accesses ligamentum flavum  26  without the need to cut or bore through the vertebrae.  
         [0072]      FIG. 6  is a partial cross-sectional lateral view of a segment of a vertebral column  80 . The segment of vertebral column  80  illustrated in  FIG. 5  includes three vertebrae  10   a,    10   b,  and  10   c.  Each vertebra  10   a,    10   b,    10   c  includes a vertebral body  12   a,    12   b,    12   c,  that supports a vertebral arch  14   a,   14   b,    14   c,  respectively. Vertical body  12   a,    12   b,    12   c  is anterior to vertebral arch  14   a,    14   b,    14   c,  respectively. Each vertebral arch  14   a,    14   b,    14   c  together with vertebral body  12   a,    12   b,    12   c,  respectively, encloses a vertebral foramen  15   a,    15   b,    15   c.  The succession of vertebral foramen  15   a,    15   b,    15   c  in adjacent vertebrae  10   a,    10   b,    10   c  define vertebral canal  81  (spinal canal) that runs along the length of vertebral column  80 . Vertebral canal  81  contains the spinal cord (not shown in  FIG. 5 ).  
         [0073]     As previously described, each vertebral arch  14   a,    14   b,    14   c  includes two pedicles  24   a,    24   b,    24   c,  which project posteriorly to meet two lamina  16   a,    16   b,    16   c,  respectively It is to be understood that in this view, one pedicle has been removed from each vertebra  10   a,    10   b,    10   c  and only the cross-section of one lamina  16   a,    16   b,    16   c  is visible The two lamina  16   a,    16   b,    16   c  meet posteriomedially to form the spinous process  18   a,    18   b,    18   c,  respectively.  
         [0074]     Lamina  16   a,    16   b,    16   c  of adjacent vertebra  10   a,    10   b,    10   c  are connected by ligamentum flavum  26  (shown in cross-section). The relatively elastic ligamentum flavum  26  extends almost vertically from superior lamina to inferior lamina of adjacent vertebrae In particular, ligamentum flavum  26  originates on the inferior surface of the laminae of the superior vertebrae and connects to the superior surface of the laminae of the inferior vertebrae. For instance, ligamentum flavum  26  originates on the inferior surface of lamina  16   a  of superior vertebra  10   a  and connects to the superior surface of lamina  16   b  of the inferior vertebra  10   b.  Thus, ligamentum flavum  26  spans an interlaminar space  82  (i.e., space between laminae of adjacent vertebrae). Interlaminar space  82  is generally the space between laminae of adjacent vertebrae in spinal column  80 .  
         [0075]     Still referring to  FIG. 6 , each lamina  16   a,    16   b,    16   c  comprises a relatively broad flat plate of bone that extends posteromedially and slightly inferiorly from pedicles  24   a,    24   b,    24   c,  respectively. Along the length of vertebral column  80 , the lamina  16   a,    16   b,    16   c  overlap like roofing shingles, with each lamina substantially parallel to and at least partially overlapping the adjacent inferior lamina Further, the adjacent substantially parallel laminae are separated by the intervening ligamentum flavum  26  and interlaminar space  82 . For instance, lamina  16   a  is substantially parallel to and partially overlaps adjacent inferior lamina  16   b  and is separated from lamina  16   b  by ligamentum flavum  26  and interlaminar space  82 .  
         [0076]      FIG. 7  illustrates vertebral column  80  as it may be oriented with the anterior side positioned down and posterior back surface  85  positioned upward, as may be encountered during a spinal procedure or surgery. In addition, in the embodiment illustrated in  FIG. 6 , ligamentum flavum  26  is thickened/enlarged, resulting in spinal stenosis In particular, the anterior portions of enlarged ligamentum flavum  26  are extending into spinal canal  81 , potentially exerting compressive forces on the spinal cord (not shown) that resides within spinal canal  81 .  
         [0077]     As previously discussed, to relieve compressive forces on the spinal cord and hence relieve the associated symptoms of spinal stenosis, portions of ligamentum flavum  26  may be excised. However, to percutaneously excise portions of ligamentum flavum  26  via minimally invasive techniques, the innate structure of vertebral column  80  and each vertebra may present significant imaging challenges. For instance, lateral imaging windows/views of ligamentum flavum  26  substantially in the direction of the z-axis may be obscured by the various processes of the vertebrae (e.g., transverse processes, superior articular processes, inferior articular processes), the laminae of each vertebra, etc. Further, some anterior-posterior (A-P) imaging windows/views of ligamentum flavum  26  substantially in the direction of the x-axis may also be obscured by the laminae. In particular, in the A-P radiographic imaging planes substantially in the direction of the x-axis, the posterior edges of parallel laminae overlap and obscure ligamentum flavum  26  and interlaminar space  82 , particularly the anterior portions of ligamentum flavum  26  and interlaminar space  82  closest to spinal canal  81 . However, with an imaging window/view in a plane substantially parallel to the X-Y plane, at an angle θ generally in the direction of arrow  83 , and slightly lateral to the spinous process, interlaminar space  82  and ligamentum flavum  26  may be viewed without significant obstruction from neighboring laminae. In other words, imaging windows/views generally aligned with arrow  83  ( FIG. 6 ) allow a more direct view of interlaminar space  82  and ligamentum flavum  26  from the posterior back surface with minimal obstruction by the vertebrae, laminae in particular.  
         [0078]     Typically, the long axis of the substantially parallel laminae (e.g., laminae  16   a,    16 , b,    16   c ) and interlaminar spaces (e.g, interlaminar spaces  82 ) are generally oriented between 60 and 75 degrees relative to posterior back surface  85 . Thus, preferably the imaging means (e.g., x-ray beam, fluoroscopy tube, etc.) is positioned generally in the direction represented by arrow  83 , where θ is substantially between 60 and 75 degrees relative to the anterior back surface  85 . In other words, the imaging means is positioned substantially parallel to the surface of the laminae. The resulting imaging window/view, termed “caudal-cranial posterior view” hereinafter, permits a clearer, more direct, less obstructed view of interlaminar space  82  and ligamentum flavum  26  from the general posterior back surface  85 . The caudal-cranial posterior view permits a relatively clear view of interlaminar space  82  and ligamentum flavum  26  in directions generally along the y-axis and z-axis. However, the caudal-cranial posterior view by itself may not provide a clear imaging window/view of interlaminar space  82  and ligamentum flavum  26  in directions generally along the x-axis In other words, the caudal-cranial posterior view by itself may not provide a clear imaging window/view that can be used to accurately determine the posterior-anterior depth, measured generally along the x-axis, of a device across the ligamentum flavum  26 .  
         [0079]     Thus, in preferred embodiments, an additional imaging window/view, termed “caudal-cranial posterior-lateral view” hereinafter, is employed to provide a clearer, unobstructed view of interlaminar space  82  and ligamentum flavum  26  in directions generally along the y-axis and z-axis. The caudal-cranial posterior-lateral view is generated by orienting an imaging means generally at an angle θ relative to outer surface of the patient and also angling such imaging means laterally in an oblique orientation, revealing a partial lateral view of interlaminar space  82  occupied by ligamentum flavum  26  on the anterior side of the lamina and posterior to the underlying dural sac (not shown) and spinal cord (not shown).  
         [0080]     By employing at least one of the caudal-cranial posterior view and the caudal-cranial posterior-lateral views, relatively clear imaging windows/views of the interlaminar space  82  and ligamentum flavum  26  in directions along the x-, y-, and z-axis may be achieved.  
         [0081]      FIG. 8  illustrates vertebral column  80  and an instrument  101 . Once unobstructed imaging windows/views of interlaminar space  82  and ligamentum flavum  26  are established in the manner described above, instrument  101  is employed to percutaneously access interlaminar space  82  and ligamentum flavum  26 . Instrument  101  may be any suitable device necessary to perform the MILD procedures described herein including without limitation, a cannula, a tissue excision tool, or combinations thereof. Tissue excision tools are described in more detail below.  
         [0082]     More specifically, using images of the interlaminar space  82  and ligamentum flavum  26  obtained from the desired direction(s), (e.g., caudal-cranial posterior view and the caudal-cranial posterior-lateral view), instrument  101  can be employed to penetrate the skin and soft tissue in the posterior back surface  85  of the patient. In preferred embodiments, the skin entry point for instrument  101  is between 5 and 10 cm inferior (caudal to) the posterior surface of the interlaminar space  82  of interest. For instance, if the portion of ligamentum flavum  26  between lamina  16   a  and lamina  16   b  is the area of interest, then instrument  101  may be inserted into the patient&#39;s back about 5 to 10 cm inferior to posterior surface  84  of interlaminar space  82 .  
         [0083]     Referring now to  FIG. 7 , instrument  101  is preferably initially inserted into the posterior tissue and musculature of the patient generally parallel to the longitudinal axis of spinal column  80 . In other words, the angle β between the posterior back surface  85  and tool  100  is between 0 and 10 degrees when tool  100  is initially inserted. Further, instrument  101  is preferably inserted into the posterior tissue and musculature of the patient on the same side (ipsilateral) of the median plane as the area of interest (e.g., the targeted portion of ligamentum flavum  26 ), as best seen in  FIG. 4 . Once tool  100  is inserted into the posterior tissue and musculature of the patient, instrument  101  then may be oriented 5 to 90 degrees relative to the posterior back surface  85  in order to create a trajectory across ligamentum flavum  26  in the area of interest. It is to be understood that once instrument  101  is inserted into the patients posterior back surface  85 , the ends of instrument  101  are free to pivot about the insertion location in posterior back surface  85  in the general direction of the y-axis and the z-axis, and may be advanced posteriorly or anteriorly generally in the direction of the x-axis.  
         [0084]     Once inserted into the posterior tissue and musculature of the patient, instrument  101  can be positioned to provide a pathway across interlaminar space  82  in the area of interest, generally towards the anterior surface of the lamina superior to the area of interest. For example, if interlaminar space  82  between lamina  16   a  and lamina  16   b  is the area of interest, instrument  101  is positioned to provide a trajectory that will allow a cutting instrument to be inserted across interlaminar space  82  between lamina  16   a  and lamina  16   b  towards the anterior surface of lamina  16   a  (superior lamina).  
         [0085]     By switching between the caudal-cranial posterior view and the caudal-cranial posterior-lateral view, or by viewing both the caudal-cranial posterior view and the caudal-cranial posterior-lateral view at the same time, instrument  101 , or an excision tool passing through instrument  101  (e.g., tool  100 ), can be advanced and inserted into ligamentum flavum  26  in the area of interest with more certainty than has heretofore been present. Once instrument  101 , or an excision tool passing therethrough, is inserted into ligamentum flavum  26 , portions of ligamentum flavum  26  may be excised so as to relieve pressure on the spinal nerves In some embodiments, resection can be performed generally from posterior to anterior across interlaminar space  82  and then laterally along the anterior portion of ligamentum flavum  26  if desired. The actual depth of the instrument tip in the general direction of the x-axis may be adjusted with guidance from the caudal-cranial posterior-lateral view and appropriate retraction/advancement of instrument  101  and appropriate adjustment of instrument  101  between 5 and 90 degrees relative to the posterior back surface  85 .  
         [0086]     In the manner described, portions of the ligamentum flavum can be excised by a percutaneous MILD procedure. In particular, with the approach described and as best illustrated in  FIGS. 4 and 6 , ligamentum flavum  26  can be accessed, and portions thereof removed via the interlaminar space on the same lateral side (ipsilateral) of median plane  210  as the entry point for the cannula (e.g., instrument  101 ) and cutting instrument (e.g., tool  100 ). This approach may sometimes hereinafter be referred to as an Ipsilateral Approach MILD Procedure (ILAMP).  
         [0000]     Percutaneous Tissue Excision  
         [0087]     Referring to  FIG. 4 , an excision tool  100  is shown schematically within ligamentum flavum  26 . In particular, tool  100  has accessed ligamentum flavum  26  according to the ILAMP method previously described. Thus, tool  100  is positioned to excise portions of ligamentum flavum  26  on the same lateral side of median plane  210  as tool  100  is inserted. In other words, in the view shown in  FIG. 4 , tool  100  is inserted into the body on the right side of median plane  210  and enters ligamentum flavum  26  on the right side of median plane  210  to excise portions of ligamentum flavum  26  on the tight side of median plane  210 . In  FIG. 4 , tool  100  does not cross median plane  210 .  FIG. 5  illustrates an embodiment of an alternative MILD method in which tool  100  is positioned to excise portions of ligamentum flavum  26  on the opposite lateral side of median plane  210  as tool  100  is inserted. More specifically, tool  100  is inserted into the body on the rights side of median plane  210  and enters ligamentum flavum  26  on the right side of median plane  210 , to excise portions of ligamentum flavum  26  on the left side of median plane  210 . In  FIG. 5 , tool  100  crosses median plane  210 .  
         [0088]     Embodiments of the present tissue excision devices and techniques can take several forms. In the discussion below, the distal ends of the tools are described in detail. The construction of the proximal ends of the tools, and the means by which the various components disclosed herein are assembled and actuated, will be known and understood by those skilled in the art.  
         [0089]     By way of example, in the embodiment illustrated in  FIG. 9 , device  100  may be a coaxial excision system  50  with a sharpened or blunt tip that is placed obliquely into the thickened ligamentum flavum  26  posterior to safety zone  40  under fluoroscopic guidance. Excision system  50  is preferably manufactured from stainless steel, titanium or other suitable durable biocompatible material. As shown in  FIGS. 9-13 , an outer needle or cannula  51  has an opening or aperture  52  on one side that is closed during insertion by an inner occluding member  54 . Aperture  52  is readily visible under imaging guidance. Once needle  51  is positioned in the ligamentum flavum or other tissue removal site, inner occluding member  54  is removed or retracted so that it no longer closes aperture  52  ( FIG. 10 ). Aperture  52  is preferably oriented away from the epidural space so as to further protect the underlying structures from injury during the surgical procedure. If it was not already present in the tool, a tissue-engaging means  56  is inserted through outer needle  51  to aperture  52  so that it contacts adjacent tissue, e.g. the ligamentum flavum, via aperture  52 .  
         [0090]     Tissue-engaging means  56  may be a needle, hook, blade, tooth or the like, and preferably has at least one flexible barb or hook  58  attached to its shaft. The barb  58  or barbs may extend around approximately 120 degrees of the circumference of the shaft. Barbs  58  are preferably directed towards the proximal end of the tool. When needle  56  is retracted slightly, barbs  58  allow it to engage a segment of tissue. Depending on the configuration of barbs  58 , the tissue sample engaged by needle  56  may be generally cylindrical or approximately hemispherical. Once needle  56  has engaged the desired tissue, inner occluding means  54 , which is preferably provided with a sharpened distal edge, is advanced so that it cuts the engaged tissue section or sample loose from the surrounding tissue. Hence occluding means  54  also functions as a cutting means in this embodiment. In alternative embodiments, such as  FIGS. 14-18  discussed below, a cylindrical outer cutting element  60  may extended over outer needle  51  and used in place of occluding member  54  to excise the tissue sample.  
         [0091]     Referring still to  FIGS. 9-13 , once the tissue sample has been cut, tissue-engaging needle  56  can be pulled back through outer needle  51  so that the segment of tissue can be retrieved and removed from the barbs ( FIG. 12 ). The process or engaging and resecting tissue may be repeated ( FIG. 13 ) until the canal is adequately decompressed.  
         [0092]     Referring briefly to  FIGS. 14-18 , in other embodiments, a tissue-engaging hook  64  can be used in place of needle  56  and an outer cutting member  60  can be used in place of inner occluding member  54 . Hook  64  may comprise a length of wire that has been bent through at least about 270°, more preferably though 315°, and still more preferably through about 405°. Alternatively or in addition, hook  64  may comprise Nitinol™, or any other resilient metal that can withstand repeated elastic deflections In the embodiment illustrated, hook  64  includes at least one barb  58  at its distal end. In some embodiments, hook  64  is pre-configured in a curvilinear shape and is retained within tool  100  by outer cutting member  60 . When cutting member  60  is retracted, the curved shape of hook  64  urges its outer end to extend outward through aperture  52 . If desired, hook  64  can be advanced toward the distal end of tool  100 , causing it to extend farther into the surrounding tissue In some embodiments, hook  64  is provided with a camming surface  66 . Camming surface  66  bears on the edge of opening  52  as hook  64  is advance or retracted and thereby facilitates retraction and retention of hook  64  as it is retracted into the tool. In these embodiments, hook  64  may not extend through aperture  52  until it has been advanced sufficiently for camming surface  66  to clear the edge of the opening. Hook  64  may alternatively be used in conjunction with an inner occluding member  54  in the manner described above. As above, hook  64  can be used to retrieve the engaged tissue from the distal end of the tool.  
         [0093]     In still other embodiments, the tissue-engaging means may comprise a hook or tooth or the like that engages tissue via aperture  52  by being rotated about the tool axis. In such embodiments (not shown) and by way of example only, the tissue-engaging means could comprise a partial cylinder that is received in outer cannula  51  and has a serrated side edge. Such a device can be rotated via a connection with the tool handle or other proximal device. As the serrated edge traverses aperture  52  tissue protruding into the tool via the aperture is engaged by the edge, whereupon it can be resected and retrieved in the maimer disclosed herein.  
         [0094]     In preferred embodiments, the working tip of tool  100  remains within the ligamentum flavum and does not penetrate the safety zone  40 . Nonetheless, safety zone  40  is provided so that even an inadvertent penetration of the tool into the epidural space will not result in damage to the dural sac. Regardless of the means by which the tissue is engaged and cut, it is preferably retrieved from the distal end of the tool so that additional tissue segments can be excised without requiring that the working tip of the tool be repositioned. A tissue-removal device such as that described below is preferably used to remove the tissue from the retrieval device between each excision.  
         [0000]     Tissue Removal  
         [0095]     Each piece of tissue may be removed from barbs  58  by pushing tissue-engaging means  56  through an opening that is large enough to allow passage of the flexible barbs and supporting needle but smaller than the diameter of the excised tissue mass. This pushes the tissue up onto the shaft, where it can be removed with a slicing blade or the like or by sliding the tissue over the proximal end of the needle. Alternatively, needle  56  can be removed and re-inserted into the tool for external, manual tissue removal.  
         [0096]     It is expected that in some embodiments, approximately 8-10 cores or segments of tissue will be excised and pushed up the shaft towards the hub during the course of the procedure. Alternatively, a small blade can be used to split the tissue segment and thereby ease removal of the segment from the device. If desired, a blade for this purpose can be placed on the shaft of needle  56  proximal to the barbs.  
         [0097]     In an exemplary embodiment, shown in  FIGS. 19-22 , the tissue removal device may include a scraper  120  that includes a keyhole slot having a wide end  122  and a narrow end  124 . To remove a tissue sample from needle  56  or hook  64 , the tissue-engaging device with a mass of excised tissue  110  thereon can be retracted (pulled toward the proximal end of the tool) through wide end  122  of the slot and then re-inserted (pushed toward the distal end of the tool) through narrow end  124  of the slot. Narrow end  124  is large enough to allow passage of the barbed needle, but small enough to remove the tissue mass as the needle passes through. The removed tissue can exit the tool through an opening  113  in the tool body. By shuttling the tissue-engaging device through scraper  120  in this manner, each excised segment of tissue  110  can be removed from the device, readying the device for another excision.  
         [0098]     In an alternative embodiment shown in  FIG. 23 , the tissue removal device may be constructed such that tissue is removed from the tissue-engaging device by retracting the tissue-engaging device through narrow end  124  of the slot. As above, narrow end  124  is large enough to allow passage of the shaft of the tissue-engaging device, but small enough to remove the tissue mass as the needle passes through. If the tissue-engaging device is constructed of a tough material, the barbs or the like will cut through the tissue and/or deform and release the tissue. As above, the removed tissue can exit the tool through an opening  113  in the tool body. By shuttling the tissue-engaging device through scraper  120  in this maimer, each excised segment of tissue  110  can be removed from the device, readying the device for another excision.  
         [0099]     In another alternative embodiment (not shown) an alternative mechanism for removing the tissue segment from needle  56  includes an adjustable aperture in a disc. After the tissue-bearing needle is pulled back through the aperture, the aperture is partially closed. Needle  56  and flexible hooks  58  then can pass through the partially closed aperture but the larger cylinder of tissue cannot. Thus the tissue segment is pushed back onto the shaft. The tissue segment can either be pulled off the proximal end of the shaft or cut off of it. A small blade may be placed just proximal to the barbs to help cut the tissue segment off the shaft. The variable aperture can formed by any suitable construction, including a pair of metal plates with matching edges that each define one half of a central opening. The two pieces may be held apart by springs. The aperture may be closed by pushing the two edges together. In other embodiments, this process can be mechanically automated by using a disc or plate with an opening that is adjustable by a variety of known techniques, including a slit screw assembly or flexible gaskets,  
         [0100]     Other cutting and/or grasping devices can be used in place of the system described above. For example, embodiments of the grasping mechanism include but are not limited to: needles with flexible barbs, needles with rigid barbs, corkscrew-shaped needles, and/or retaining wires. The corkscrew-shaped needle shown in  FIG. 24  works by screwing into the ligamentum flavum in the manner that a corkscrew is inserted in a cork. After the screw engages a segment of tissue, outer cutting element  60  slides over the needle, cutting a segment of tissue in a manner similar to that of the previous embodiment. In some embodiments, the cutting element can be rotated as it cuts.  
         [0101]     In other embodiments, shown in  FIGS. 25-29 , cannulated scalpel  51  houses a grasping device  70  that includes at least one pair of arcuate, closable arms  72 . Closable arms  72  may be constructed in any suitable manner. One technique for creating closable arms is to provide a slotted sleeve  74 , as shown. Slotted member  74  preferably comprises an elongate body  75  with at least one slot  76  that extends through its thickness but does not extend to either end of the body. Slot  76  is preferably parallel to the longitudinal axis of the sleeve. On either side of slot  76 , a strip  77  is defined, with strips  77  being joined at each end of sleeve  74 . It is preferred that the width of each strip  77  be relatively small. In some embodiments, it may be desirable to construct slotted member  74  from a portion of a hollow tube or from a rectangular piece that has been curved around a longitudinal axis. Be inner edge of each strip that lies along slot  76  forms an opposing edge  78 . The width of the piece is the total of the width of strips  77  and slot  76 .  
         [0102]     Advancing one end of sleeve  74  toward the other end of sleeve  74  causes each strip  77  to buckle or bend. If strips  77  are prevented from buckling inward or if they are predisposed to bend in the desired direction, they will bend outward, thereby forming arcuate arms  72 , which extend through aperture  52  of cannulated scalpel  51 , as shown in  FIG. 29 . As they move away from the axis of body  75 , arms  72  move apart in a direction normal to the axis of body  75 . Likewise, moving the ends of sleeve  74  apart causes arms  72  to straighten and to move together and inward toward the axis of the device, as shown in  FIG. 27 . As the arms straighten, opposing edges  78  close and a segment of tissue can be capture between them. Tissue within the grasping device may then be resected or anchored via the other mechanisms described herein.  
         [0103]     Closable arms  72  may include on their opposing edges  78  ridges, teeth, or other means to facilitate grasping of the tissue. In other embodiments, edges  78  may be sharpened, so as to excise a segment of tissue as they close. In these embodiments, closable arms  72  may also be used in conjunction with a hook, barbed needle, pincers or the like, which can in turn he used to retrieve the excised segment from the device.  
         [0104]     Once aims  72  have closed on the tissue, if arms  72  have not cut the tissue themselves, the tissue can be excised using a blade such as cutting element  60  above. The excised tissue can be removed from the inside of needle  51  using a tissue-engaging hook  64  or other suitable means. The process of extending and closing arms  72 , excising the tissue, and removing it from the device can be repeated until a desired amount of tissue has been removed.  
         [0105]     If desired, this cycle can be repeated without repositioning the device in the tissue. Alternatively, the tool can be rotated or repositioned as desired between excisions It is possible to rotate or reposition the tool during an excision, but it is expected that this will not generally be preferred. Furthermore, it is expected that the steps of tissue excision and removal can be accomplished without breaching the surface of the ligament, i.e. without any part of the device entering the safety zone created by the injected fluid. Nonetheless, should the tool leave the working zone, the safety zone will reduce the risk of injury to the dural sac.  
         [0000]     Ligament Retraction  
         [0106]     In some embodiments, the spinal canal may also be enlarged by retracting the ligamentum flavum, either with or without concurrent resection. Retraction is preferably but not necessarily performed after dural compression has been used to provide a safety zone. In addition, the dural compression techniques described above have the effect of pressing the ligamentum flavum back out of the spinal canal and thereby making it easier to apply a restraining means thereto.  
         [0107]     Thus, in preferred embodiments, after a safety zone is created by epidural injection of contrast medium or gel, a retraction device  90  as shown in  FIG. 30  is used to retract and compress the thickened soft tissues around the posterior aspect of the spinal canal, thereby increasing the available space for the dural sac and nerves In the embodiment shown, retraction device  90  is a double-headed anchor that includes at least one distal retractable tissue-engaging member  91  and at least one proximal tissue-engaging member  92 , each of which are supported on a body  94  Retraction device  90  is preferably constructed from an implantable, non-biodegradable material, such as titanium or stainless steel, but may alternatively be polymeric or any other suitable material. In certain preferred embodiments, body  94  is somewhat flexible. In some instances, flexibility in body  94  may facilitate the desired engagement of barbs  91 ,  92 . Barbs  91 ,  92  may comprise hooks, arms, teeth, clamps, or any other device capable of selectively engaging adjacent tissue. Barbs  91 ,  92  may have any configuration that allows them to engage the ligamentum flavum and/or surrounding tissue. Similarly, barbs  91 ,  92  may be covered, sheathed, pivotable, retractable, or otherwise able to be extended from a first position in which they do not engage adjacent tissue to a second position in which they can engage adjacent tissue.  
         [0108]      FIG. 30  shows schematically the distal and proximal retractable arms  91 ,  92  of a preferred ligament anchor  90 . The proximal end of the anchor preferably includes a threaded connector  96  or other releasable mechanism that attaches to a support rod  100 . Ligament anchor  90  may be attached to a support shaft  112  and sheathed in a guide housing  114 . The distal and proximal barbs  91 ,  92  are prevented by guide housing  114  from engaging surrounding tissue. Housing  102  is preferably a metal or durable plastic guide housing.  
         [0109]     The distal end of the device is preferably positioned in the ligamentum flavum under fluoroscopic guidance. If desired, an accessway through the lamina may be provided using an anchored cannula or the like. The device is held in position by support shaft  112 . Distal barbs  91  are unsheathed and optionally expanded by pulling back guide housing  102 , as shown in  FIG. 30 . Distal barbs  91  are secured in the ligamentum flavum by pulling back on the support shaft  112 . With barbs  91  engaging the tissue, the ligamentum flavum is retracted posteriorly by pulling back on support shaft  112 . While maintaining traction on the now-retracted ligament, proximal barbs  92  are uncovered and expanded by retracting guide housing  114 , as shown in  FIG. 31 . Barbs  92  are preferably positioned in the soft tissues  116  in the para-spinal region so that the device is firmly anchored behind the posterior elements of the spinal canal Once the proximal end of the anchor is engaged, support shaft  112  may be detached from body  94  as shown in  FIG. 31 . In this manner, the posterior margin  95  of the ligamentum flavum can be held in a retracted position, thereby expanding the canal. The procedure can then be repeated on adjacent portions of the ligamentum flavum until it is sufficiently retracted.  
         [0110]     In an alternative embodiment, the proximal end of ligament anchor  90  may be adapted to engage the lamina. This may be accomplished by having the arm posterior to the lamina or by using the laminotomy and suturing the device to the lamina there. A knotted or knotless system or a suture plate can be used.  
         [0111]     A second embodiment of the present method uses a plurality of retraction devices  90 . In this embodiment, the retraction device is inserted through one lamina in an oblique fashion, paralleling the opposite lamina. After the distal anchor is deployed, the retraction device is pulled back and across the ligamentum flavum, thereby decompressing the opposite lateral recess of the spinal canal. This is repeated on the opposite side. This same device can also be deployed with a direct approach to the lateral recess with a curved guide housing.  
         [0112]     While retraction device  90  is describe above as a double-headed anchor, it will be understood that other devices can be used. For example sutures, barbed sutures, staples or the like can be used to fasten the ligament in a retracted position that reduces stenosis.  
         [0113]     Using the percutaneous methods and devices described herein, significant reductions of stenosis can be achieved. For example, a dural sac cross-sectional area less than 100 mm 2  or an anteroposterior (A-P) dimension of the canal of less than 10-12 mm in an average male is typically considered relative spinal stenosis. A dural sac cross-sectional area less than 85 mm 2  in an average male is considered severe spinal stenosis. The present devices and techniques are anticipated to cause an increase in canal area of 25 mm 2  per anchor or 50 mm 2  total. With resection and/or retraction of the ligamentum flavum, the cross-sectional area of the dural sac can be increased by 10 mm 2 , and in some instances by as much as 20 mm 2  or even 30 mm 2  Likewise, the present invention can result in an increase of the anteroposterior dimension of the canal by 1 to 2 mm and in some instances by as much as 4 or 6 mm. The actual amount by which the cross-sectional area of the dural sac and/or the anteroposterior dimension of the canal are increased will depend on the size and age of the patient and the degree of stenosis and can be adjusted by the degree of retraction of the ligament.  
         [0000]     Dural Shield  
         [0114]     In some embodiments (not shown), a mechanical device such as a balloon or mechanical shield can also be used to create a protective guard or barrier between the borders of the epidural space and the adjacent structures. In one embodiment a durable expandable device is attached to the outside of the percutaneous laminectomy device, preferably on the side opposite the cutting aperture. The cutting device is inserted into the ligamentum flavum with the expandable device deflated. With the aperture directed away from the spinal canal, the expandable device is gently expanded via mechanical means or inflated with air or another sterile fluid, such as saline solution, via a lumen that may be within of, adjacent to the body of the device. This pushes the adjacent vital structures clear from the cutting aperture of the device and simultaneously presses the cutting aperture into the ligament. As above, the grasping and cutting needles can then be deployed and operated as desired. The balloon does not interfere with tissue excision because it is located on the side opposite the cutting aperture. The cutting needle may be hemispherical (semi-tubular) in shape with either a straight cutting or a sawing/reciprocating blade or may be sized to be placed within the outer housing that separates the balloon from the cutting aperture.  
         [0115]     In another embodiment, a self-expanding metal mesh is positioned percutaneously in the epidural spaces. First the epidural space is accessed in the usual fashion. Then a guide catheter is placed in the epidural space at the site of the intended surgical procedure. The mesh is preferably compressed within a guide catheter. When the outer cover of the guide catheter is retracted, the mesh expands in the epidural space, protecting and displacing the adjacent dural sheath The mesh may be configured to have an expanded shape that generally corresponds to the shape of the desired safety zone within the spinal canal. At the conclusion of the surgical procedure, the mesh is pulled back into the guide sheath and the assembly removed. The mesh is deformable and compresses as it is pulled back into the guide catheter, in a manner similar to a self-expanding mesh stent. While there are commercially available self-expanding stents approved and in use in other applications, using a self-expandable mesh configured to expand within the epidural space so as to protect and displace the dural sac is novel.  
         [0116]     The ILAMP methods, techniques, and devices described herein allow spinal decompression to be performed percutaneously, avoiding the pain, lengthy recovery time, and risk associated with open surgery. In addition, the ILAMP methods, techniques, and devices described herein permit clearer, less obstructed imaging views of the interlaminar spaces and ligamentum flavum between the laminae in the areas of interest. Such improved imaging views offer the potential for enhanced accuracy and safety in the placement of tools within the ligamentum flavum proximal the epidural space and spinal cord. Further, the ILAMP methods, techniques, and devices described herein permit the excision of portions of the ligaments flavum on the same lateral side of the median plane as that into which instruments and tools for the procedure are inserted.  
         [0117]     Through the provision of a safety zone and improved imaging, the present devices and techniques offer reduced risk of spinal cord damage. In addition to improving nerve function, it is expected that decompression of the spinal canal in the manner described herein will result in improved blood flow to the neural elements by reducing the extrinsic pressure on the spinal vasculature. For these reasons, it is believed that spinal decompression performed according to the present invention will be preferable to decompression operations performed using currently known techniques.  
         [0118]     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. For example, the means by which the safety zone is formed may be varied, the shape and configuration of the tissue excision devices may be varied, and the steps used in carrying out the technique may be modified. Accordingly, the invention is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims Likewise, the sequential recitation of steps in a claim, unless explicitly so stated, is not intended to require that the steps be performed in any particular order or that a particular step be completed before commencement of another step.