Intraspinal device deployed through percutaneous approach into subarachnoid or intradural space of vertebral canal to protect spinal cord from external compression

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.

I. FIELD OF INVENTION

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

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.

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.

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.

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

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.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, the present invention comprises a self-expanding, generally flat, dumbbell-shaped, implantable barrier device10which 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 frame12formed from a material exhibiting shape memory properties and consisting of a closed loop of wire where the frame is enclosed within a covering14of a selected non-porous membrane material. Without limitation, the frame12may be formed from one or more strands of Nitinol wire with plural strands being wound as a cable. The non-porous membrane covering14for 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.

FIG. 1shows the implantable barrier device10in its fully expanded state and the dumbbell shape includes a central rectilinear segment16on opposed ends of which are formed somewhat circular lobes18,20.

As will be explained in greater detail herein below, the rounded lobes18,20coact with spongy tissue of the subarachnoid or intradural space consisting of delicate connective tissue filaments termed trabeculae to hold the barrier device10in place within a patient's spinal canal. If the frame12is 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.

Referring to the cross-sectional view ofFIG. 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 device10will 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 frame12serve to maintain a separation or barrier between the external compression point and the adjacent spinal cord nerves.

In the embodiment ofFIG. 3, the non-porous membrane14′ only partially surrounds the frame12over the rectilinear portion of the dumbbell and the rounded end lobes18′,20′ are left uncovered. A centrally disposed, longitudinally extending strand of Nitinol wire22connects the upper and lower ends of the dumbbell-shaped implantable barrier device10together within the center of the device for axial support. Here, the porous membrane14′ is wrapped around the two, spaced-apart linear frame segments16aand16band may be attached to the frame at the four corner points, as at24, using a suitable adhesive. Again with regard toFIG. 4, the two parallel segments26,28of 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.

Referring now toFIG. 5, there is shown an introducer needle29which, for the present application, could be a 16 gauge needle having a sharpened and beveled distal end30and a flared or funnel-shaped proximal end32for ease in handling and maneuvering.

FIG. 6is a longitudinal view of a flexible plastic tube34, referred to herein as a delivery catheter that is comprised of a distal flexible component36and a somewhat stiffer proximal component38. The distal flexible component36may, 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 portion36may have a short bent portion40at its distal end to facilitate navigation through the subarachnoid or intradural space of the vertebral canal by manipulation of the delivery tube's external proximal end42. The flexible portion36of 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 portion38of 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 catheter34that will be resident within the skin40, soft tissue42, intervertebral space44, the supraspinous ligament46, the interspinous ligament48and the ligamentum flavum50shown in the saggital view ofFIG. 7which has been included herein to illustrate the trajectory of the needle29placement through the intervertebral foramen. The needle also penetrates through dura mater to enter the subarachnoid or intradural space. The bevel30of the needle faces cephalad to insure that passage of the delivery catheter34will be in the cephalad direction.

FIG. 8shows the insertion of the implantable barrier device10in 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 wire60that 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.

Referring next toFIG. 9, it shows the introducer needle29inserted into the subarachnoid space52and with the delivery catheter or tube34being fed through the introducer needle and across the site of compression at54. 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 space52. The delivery tube34can be navigated and advanced through the vertebral canal by manipulation at the external proximal end42thereof.

Ideally, the delivery tube is placed between the spinal cord and vertebral column56within the subarachnoid or intradural space52and the distal end extends past the anterior compartment of the vertebral canal between the vertebral bodies VB, disks D and external compressive lesion54and spinal cord.

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.

It has been found expedient to include a radio-opaque marker at the distal end40of the delivery tube34to 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 lesion54is enhanced. A second radio-opaque marker58(FIG. 6) may be placed approximately 5 cms proximal to the distal end40of the delivery catheter. This second marker will allow detection of a pushing tool crossing a point after which the self-expanding, dumbbell-shaped barrier device10will be ejected out of the delivery catheter with further advancement of the pusher.

To deploy the implantable barrier device, once the distal opaque marker of the pusher and the proximal marker58on the delivery catheter overlap, the delivery catheter is slowly withdrawn in the proximal direction while holding the pusher wire60stationary. As the delivery catheter uncovers the implant device10as seen inFIG. 10, it self-expands to its dumbbell shape within the subarachnoid or intradural space in a stepwise manner. First, the distalmost rounded end18will self-expand, followed by unfurling of the rectilinear central section16and finally the proximal founded end portion20. The flaring of both rounded ends and the concave shape facing the vertebral body, disk and external compression as seen inFIGS. 11 and 12insure successful fixation in the location of the deployment. The delivery catheter is now removed.

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 inFIG. 13. Then, a wire snare70can be used to fragment the lesion. InFIG. 13, the snare comprises an elongated pull wire72preferably made of Nitinol whose proximal end extends exteriorly to the proximal end of the delivery catheter34and having a loop74at its distal end can be advanced through the delivery catheter34and 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 catheter34is advanced in the distal direction while the pull wire72is 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.

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.