Abstract:
To shield the spinal cord from an external compression, a barrier device having a self-expanding frame and covered with a non-porous elastomeric sheet is routed through either the subarachnoid or intradural space to the site of the compression through the lumen of a delivery catheter that is percutaneously inserted using an introducer needle. When the distal end of the delivery catheter is proximate the site of the compression, the barrier device is pushed out the distal end of the catheter and allowed to self-expand so as to be interposed between the compression and the spinal cord to prevent impingement.

Description:
I. FIELD OF INVENTION 
       [0001]    The present invention relates to a medical device deployed through a minimally invasive procedure to protect the spinal cord from external compression. 
       II. BACKGROUND OF INVENTION 
       [0002]    External compression of spinal cord through variety of sources including retrograde movement of a vertebral body or disc, a tumor, or a vascular malformation remains major causes of myelopathy. The external compression of the spinal cord leads to paraparesis, segmental sensory loss, and sometimes urinary and fecal incontinence. 
         [0003]    In humans, the vertebral column is a column usually consisting of 33 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsal aspect of the torso. The vertebral canal follows the different curves of the spinal column. It is large and triangular in those parts of the column which enjoy the greatest freedom of movement, such as the cervical and lumbar regions and is small and rounded in the thoracic region, where motion is more limited. The spinal cord is located inside the vertebral canal and extends from the foramen magnum down to the level of the first and second lumbar vertebrae (at birth, down to second and third lumbar vertebrae). The spinal cord is composed of 31 segments: 8 cervical (C), 12 thoracic (T), 5 lumbar (L), 5 sacral (S), and 1 coccygeal (Co), mainly vestigial. The spinal nerves comprise the sensory nerve roots, which enter the spinal cord at each level, and the motor roots, which emerge from the cord at each level, which is formed by the foramina of 7 cervical, 12 thoracic, 5 lumbar, and 5 sacral vertebrae, which together form the spine. The conus medullaris is the cone-shaped termination of the caudal cord. The pia mater continues caudally as the filum terminale through the dural sac and attaches to the coccyx. The coccyx has only one spinal segment. Several macroscopic grooves are discernible on the surface of the spinal cord. Most prominent is the anterior median fissure, which is occupied by the anterior spinal artery. The posterior median sulcus is less prominent. The anterior and posterior nerve rootlets emerge at the anterolateral and posterolateral sulci. 
         [0004]    Within the vertebral canal, both spinal cord (CNS) and spinal roots (PNS) are enveloped by meninges. Spinal dura mater is separated from periosteum lining the vertebral canal by an epidural space that contains a variable amount of fat (in the cranial cavity, dura mater and periosteum merge so an epidural space does not exist). Three layers of meninges envelop the spinal cord and the roots of spinal nerves. The most superficial menix is dura mater. It is protective by virtue of its high collagen content. Arachnoid (arachnoid membrane) is thin and delicate, being composed of flattened fibrocytes and flimsy strands of collagen. In life, arachnoid contacts dura mater due to cerebrospinal fluid pressure within the subarachnoid space. Arachnoid trabeculae are delicate strands of arachnoid that traverse the subarachnoid space to join pia mater. The subarachnoid space filled with cerebrospinal fluid forms a space where devices can be advanced and deployed between the vertebral, disc, and external compression and spinal cord itself. Pia mater consists of flattened fibrocytes that line the subarachnoid space and collagen bundles in contact with glial cells at the surface of the spinal cord and spinal roots. Bilaterally, pia mater collagen is thickened to form denticulate ligaments. Processes of the ligaments periodically join dura mater and thus, within dura mater, the spinal cord is suspended by bilateral denticulate ligaments and thereby surrounded by protective cerebrospinal fluid within the subarachnoid space. 
         [0005]    Spinal cord compression develops when the spinal cord is compressed by bone fragments from a vertebral fracture, a tumor, abscess, ruptured intervertebral disc or other lesion. It is regarded as a medical emergency independent of its cause, and requires swift diagnosis and treatment to prevent long-term disability due to irreversible spinal cord injury. Surgery is indicated in localized compression with or without postoperative radiation is delivered within 2-3 weeks of surgical decompression. Surgery usually comprises of a laminectomy to relieve pressure on the spinal cord or the nerve roots. The lamina is the bony roof of the spinal canal. Laminectomy is the term used to refer to the process of removing the lamina (usually both sides). Removing the lamina increases the size of the spinal canal, giving more room for the spinal cord or nerve roots. However, the process is extensive and is associated with complications such as bleeding within the operative sites, or worsening of neurological deficits. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention meets the above-described need by providing a method to deploy a self expanding device around the spinal cord using a small microcatheter through a percutaneous needle puncture at lumbar interspace from posterior approach. The process is similar to a lumbar puncture and introduction of a lumbar drain. However, a flexible introducer sheath is advanced through a percutaneous needle under fluoroscopic guidance towards the cephalic direction. A microcatheter is then advanced through the sheath and under fluoroscopic guidance through the anterior space between spinal cord and vertebral bodies and discs. The selected microcatheter could be advanced over a 0.014-inch microguidewire and navigated to the site of compression. A device comprised on a substantially flat, but slightly rounded dumbbell-shaped structure that is comprised of meshwork of Nitinol, and porous membrane. The device is introduced in a compressed manner through the microcatheter. The device is pushed through the microcatheter by a microwire until it reaches the distal end of the microcatheter. The microcatheter is withdrawn once the device reaches the distal end of the microcatheter, The device is unsheathed by the withdrawal of the microcatheter and self expansile properties of the device. The device is deployed between the spinal cord and vertebral bodies and disc. The device is aligned so the long axis is parallel to the axis of the spinal cord and provides a protective barrier in front of the spinal cord. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is an antereo-posterior view of the self-expanding, dumbbell-shaped, barrier device in its expanded form; 
           [0009]      FIG. 2  is cross-section view of the self-expanding, dumbbell-shaped, barrier device taken along the line  2 - 2  in  FIG. 1 ; 
           [0010]      FIG. 3  is an antereo-posterior view of an alternative embodiment of the self-expanding, dumbbell-shaped, barrier device in its expanded form; 
           [0011]      FIG. 4  is a cross-section view taken along the line  4 - 4  in  FIG. 3 ; 
           [0012]      FIG. 5  is a longitudinal view of a 16 gauge needle used for standard lumbar drain placement; 
           [0013]      FIG. 6  is a longitudinal view of a flexible plastic delivery catheter that is comprised of a distal flexible component and a proximal stiff component; 
           [0014]      FIG. 7  illustrates the percutaneous introduction of the needle of  FIG. 5  into the subarachnoid space through the skin, soft tissue, ligametum favum via the 2 nd , 3 rd  or 4 th  intervertebral space in a saggital view; 
           [0015]      FIG. 8  illustrates the introduction of the delivery catheter of  FIG. 6  and the barrier device of  FIG. 1  or  3  through the introducer needle in a longitudinal view, also identifying the radio-opaque markers at a distal end of the delivery catheter; 
           [0016]      FIG. 9  is a saggital view demonstrating the advancement of the delivery catheter through the subarachnoid space in the anterior compartment between the external compressive lesion and the spinal cord; 
           [0017]      FIG. 10  is a longitudinal view illustrating the advancement of the barrier device of  FIG. 1  in its compressed form through the central lumen of the delivery catheter; 
           [0018]      FIG. 11  is an enlarged lateral view demonstrating the expansion of the barrier device of  FIG. 1  within the subarachnoid space upon the withdrawal of the delivery catheter while holding the pusher stationary; 
           [0019]      FIG. 12  is an enlarged anterior view illustrating the dumbbell-shaped barrier device after complete expansion within the subarachnoid space following withdrawal of the delivery catheter; and 
           [0020]      FIG. 13  illustrates the use of a fragmentation tool having its loop deployed across a protubering portion of a lesion. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring to  FIG. 1 , the present invention comprises a self-expanding, generally flat, dumbbell-shaped, implantable barrier device  10  which can be introduced in a compressed form through a flexible delivery tube into the subarachnoid or intradural spaces within the vertebral canal under fluoroscopic guidance. The implantable barrier device includes a frame  12  formed from a material exhibiting shape memory properties and consisting of a closed loop of wire where the frame is enclosed within a covering  14  of a selected non-porous membrane material. Without limitation, the frame  12  may be formed from one or more strands of Nitinol wire with plural strands being wound as a cable. The non-porous membrane covering  14  for the frame may be polyurethane, latex or another synthetic material that is somewhat flexible so as to be capable of being readily rolled or folded and which is otherwise body-compatible. 
         [0022]      FIG. 1  shows the implantable barrier device  10  in its fully expanded state and the dumbbell shape includes a central rectilinear segment  16  on opposed ends of which are formed somewhat circular lobes  18 ,  20 . 
         [0023]    As will be explained in greater detail herein below, the rounded lobes  18 ,  20  coact with spongy tissue of the subarachnoid or intradural space consisting of delicate connective tissue filaments termed trabeculae to hold the barrier device  10  in place within a patient&#39;s spinal canal. If the frame  12  is formed of a Nitinol wire, it will be radio-opaque for visualization under fluoroscopy. However, if a plastic strand of a shape memory material is employed as the frame, radio-opaque markers should be added to it to facilitate placement. 
         [0024]    Referring to the cross-sectional view of  FIG. 2 , it can be seen that the frame is slightly convex and not perfectly flat. Thus, when placed within the spinal canal at a desired target location proximate an external compression of the spinal cord, the concave surface of the barrier device  10  will help separate the defect causing the external compression from engagement with the spinal cord. That is to say, the inner and outer layers of the non-porous membrane fabric enclosing the frame  12  serve to maintain a separation or barrier between the external compression point and the adjacent spinal cord nerves. 
         [0025]    In the embodiment of  FIG. 3 , the non-porous membrane  14 ′ only partially surrounds the frame  12  over the rectilinear portion of the dumbbell and the rounded end lobes  18 ′,  20 ′ are left uncovered. A centrally disposed, longitudinally extending strand of Nitinol wire  22  connects the upper and lower ends of the dumbbell-shaped implantable barrier device  10  together within the center of the device for axial support. Here, the porous membrane  14 ′ is wrapped around the two, spaced-apart linear frame segments  16   a  and  16   b  and may be attached to the frame at the four corner points, as at  24 , using a suitable adhesive. Again with regard to  FIG. 4 , the two parallel segments  26 ,  28  of the dumbbell-shaped structure are curved with a concave aspect which, when placed in the spinal canal will be facing the vertebral bodies to better insure successful fixation at the target location. The unique dumbbell configuration is specifically designed to insure successful fixation following deployment from a delivery catheter next to be described. 
         [0026]    Referring now to  FIG. 5 , there is shown an introducer needle  29  which, for the present application, could be a 16 gauge needle having a sharpened and beveled distal end  30  and a flared or funnel-shaped proximal end  32  for ease in handling and maneuvering. 
         [0027]      FIG. 6  is a longitudinal view of a flexible plastic tube  34 , referred to herein as a delivery catheter that is comprised of a distal flexible component  36  and a somewhat stiffer proximal component  38 . The distal flexible component  36  may, for example, be in a range of from 16 to 26 cms with the length to be chosen depending upon distance measurements acquired from either CT or MRI scans. The flexible end portion  36  may have a short bent portion  40  at its distal end to facilitate navigation through the subarachnoid or intradural space of the vertebral canal by manipulation of the delivery tube&#39;s external proximal end  42 . The flexible portion  36  of the delivery tube allows it to adjust to the curves within the subarachnoid or intradural space along the length of the vertebral canal to be traversed. The proximal stiff end portion  38  of the delivery catheter is relatively short and may range between 5 and 10 cms. This stiff end provides support and prevents collapse in the segment of the delivery catheter  34  that will be resident within the skin  40 , soft tissue  42 , intervertebral space  44 , the supraspinous ligament  46 , the interspinous ligament  48  and the ligamentum flavum  50  shown in the saggital view of  FIG. 7  which has been included herein to illustrate the trajectory of the needle  29  placement through the intervertebral foramen. The needle also penetrates through dura mater to enter the subarachnoid or intradural space. The bevel  30  of the needle faces cephalad to insure that passage of the delivery catheter  34  will be in the cephalad direction. 
         [0028]      FIG. 8  shows the insertion of the implantable barrier device  10  in its compressed state into the proximal end of the delivery catheter. From there, it is pushed through the lumen of the delivery catheter using a pusher wire  60  that is sufficiently flexible to allow its advancement through the curves of the delivery catheter. Again, the distal end of the pusher is made to be radio-opaque to allow visualization of the pusher movements within the delivery catheter. 
         [0029]    Referring next to  FIG. 9 , it shows the introducer needle  29  inserted into the subarachnoid space  52  and with the delivery catheter or tube  34  being fed through the introducer needle and across the site of compression at  54 . As those skilled in the art appreciate, the use of the introducer needle facilitates passage of the flexible delivery catheter through the skin, soft tissue, intervertebral space, supraspinous ligament, intraspinous ligament and ligamentum flavum and into the subarachnoid or intradural space  52 . The delivery tube  34  can be navigated and advanced through the vertebral canal by manipulation at the external proximal end  42  thereof. 
         [0030]    Ideally, the delivery tube is placed between the spinal cord and vertebral column  56  within the subarachnoid or intradural space  52  and the distal end extends past the anterior compartment of the vertebral canal between the vertebral bodies VB, disks D and external compressive lesion  54  and spinal cord. 
         [0031]    If additional support is necessary for advancing and navigating the delivery tube within the subarachnoid or intradural space, this support can be provided by the temporary introduction of a flexible guidewire (not shown) through the delivery tube as is known in the art. 
         [0032]    It has been found expedient to include a radio-opaque marker at the distal end  40  of the delivery tube  34  to allow for continuous visualization of movement and placement of the tube under fluoroscopic guidance. It is also contemplated that a contrast media may be injected for better fluoroscopic visualization of the subarachnoid space whereby the relationship between the distal end of the delivery catheter and compressive lesion  54  is enhanced. A second radio-opaque marker  58  ( FIG. 6 ) may be placed approximately  5  cms proximal to the distal end  40  of the delivery catheter. This second marker will allow detection of a pushing tool crossing a point after which the self-expanding, dumbbell-shaped barrier device  10  will be ejected out of the delivery catheter with further advancement of the pusher. 
         [0033]    To deploy the implantable barrier device, once the distal opaque marker of the pusher and the proximal marker  58  on the delivery catheter overlap, the delivery catheter is slowly withdrawn in the proximal direction while holding the pusher wire  60  stationary. As the delivery catheter uncovers the implant device  10  as seen in  FIG. 10 , it self-expands to its dumbbell shape within the subarachnoid or intradural space in a stepwise manner. First, the distalmost rounded end  18  will self-expand, followed by unfurling of the rectilinear central section  16  and finally the proximal founded end portion  20 . The flaring of both rounded ends and the concave shape facing the vertebral body, disk and external compression as seen in  FIGS. 11 and 12  insure successful fixation in the location of the deployment. The delivery catheter is now removed. 
         [0034]    In the event a compressive lesion does not allow cephalad progress of the delivery catheter across the lesion, a further step may be employed to rectify this situation. Specifically, the delivery catheter can be placed with its distal end slightly proximal to the lesion as shown in  FIG. 13 . Then, a wire snare  70  can be used to fragment the lesion. In  FIG. 13 , the snare comprises an elongated pull wire  72  preferably made of Nitinol whose proximal end extends exteriorly to the proximal end of the delivery catheter  34  and having a loop  74  at its distal end can be advanced through the delivery catheter  34  and upon exit of the loop from the confines of the delivery catheter, it opens up, allowing the loop to be placed about the lesion to be fragmented. Next, the delivery catheter  34  is advanced in the distal direction while the pull wire  72  is held stationary. This has the effect of closing the loop about the lesion and ultimately excising a fragment. The closing loop acts as a garrote, cutting through the protuberant portion and releasing the fragment in the subarachnoid or intradural space. The fragmentation device is then retracted from the delivery catheter and suction may be applied to the external proximal end thereof using an empty syringe for creating a vacuum as its plunger is retracted. The process of aspiration at the distal end of the delivery catheter functions to remove the severed fragment of the compression lesion from the subarachnoid space. This process can be repeated several times until enough lesion portions have been removed to allow passage of the delivery catheter across the lesion. Thus, a minimally invasive procedure is provided that allows debulking of a compressive lesion within the subarachnoid space surrounding the spinal cord under fluoroscopic guidance several levels high up to the thoracic and cervical levels from a percutaneous insertion at an intervertebral space in the lumbar region. 
         [0035]    It can be seen that the present invention provides a minimally invasive method for implanting a barrier device in the subarachnoid or intradural space of the spinal column in surrounding relation to the spinal cord whereby the effects of external compressions on the spinal cord can be addressed to thereby alleviate pain. The delivery catheter can be inserted in the lumbar region and advanced cephalically to the thoracic and cervical levels via the subarachnoid space or via the intradural layer. 
         [0036]    This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.