II. FIELD OF THE INVENTION
This application relates to medical devices and more particularly to a stimulator system for treating muscles and neural pathways of the back.
III. BACKGROUND OF THE INVENTION
The human lumbar spine is comprised of a spinal column consisting of vertebrae and ligaments (e.g. spinal ligaments, disc annulus, and facet capsules) and muscles that maintain spinal stabilization. It is believed that in some patients with back pain, the spinal stabilization system is dysfunctional. With soft tissue injury, mechanoreceptors may produce corrupted signals about vertebral position, motion, or loads, leading to an inappropriate muscle response.
The multifidus is the largest and most medial of the lumbar back muscles. It consists of a repeating series of fascicles which stem from the laminae and spinous processes of the vertebrae, and exhibit a constant pattern of attachments caudally. These fascicles are arranged in five overlapping groups such that each of the five lumbar vertebrae gives rise to one of these groups. At each segmental level, a fascicle arises from the base and caudolateral edge of the spinous process, and several fascicles arise, by way of a common tendon, from the caudal tip of the spinous process. Although confluent with one another at their origin, the fascicles in each group diverge caudally to assume separate attachments to the mamillary processes, the iliac crest, and the sacrum. Some of the deep fibers of the fascicles which attach to the mamillary processes attach to the capsules of the facet joints next to the mamillary processes. All the fasicles arriving from the spinous process of a given vertebra are innervated by the medial branch of the dorsal ramus that issues from below that vertebra. Each multifidus fascicle is innervated by a nerve from the medial branch of the dorsal ramus.
Training of this multifidus muscle will provide numerous benefits including improved muscle tone, endurance and strength. Further, training may improve voluntary and involuntary control of the muscles involved with spinal stabilization, eliminating lower back pain.
U.S. Patent Application Publication No. US2008/0228241 to Sachs, assigned to the assignee of the present invention, and incorporated herein in its entirety by reference, describes an implanted electrical stimulation device that is designed to restore neural drive and rehabilitate the multifidus muscle. Rather than masking pain signals while the patient's spinal stability potentially undergoes further deterioration, the stimulator system described in that application is designed to reduce the propensity for instability of the spinal column, which in turn is expected to reduce persistent or recurrent pain.
While the stimulator system described in the Sachs application seeks to rehabilitate the multifidus and restore neural drive, use of that system necessitates the implantation of one or more electrode leads in the vicinity of the patient's muscles, such as the multifidus muscles. Because surgical implantation of such electrode leads has the potential to weaken the target muscles, it would be desirable to implant the electrode leads used for neuromuscular stimulation in a manner that will not injure the target muscles, or require an extended recuperation period.
In view of the foregoing, it would be desirable to provide electrode leads and methods of implantation that avoid open surgical procedures.
It further would be desirable to provide electrode leads and methods of implantation that minimize injury to the target muscles, and avoid extended recuperation periods.
It also would be desirable to provide electrode leads and methods of implantation that permit the clinician to visualize and confirm the implantation site during the procedure.
IV. SUMMARY OF THE INVENTION
In view of the drawbacks of previously-known methods and apparatus for implanting electrode leads, the present invention provides electrode leads and methods of implantation that avoid open surgical procedures. In particular, the present invention provides electrode leads and methods of implanting such leads that reduces injury to the target muscles, and avoids extended recuperation periods. The methods of the present invention further facilitate electrode lead implantation, by enabling the clinician to visualize and confirm the implantation site of the electrode leads during the implantation procedure.
V. BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the lumbar portion of the human spine.
FIG. 2 is a sectional view showing a percutaneous method of implantation of an electrode lead suitable for use with a neuromuscular electrical stimulation system.
FIG. 3 is a sectional view showing a minimally invasive method of implantation of an electrode lead suitable for use with a neuromuscular electrical stimulation system.
FIGS. 4A to 4E are, respectively, side and perspective views of tools and implantable electrode leads suitable for use in a minimally invasive implantation method in accordance with the principles of the present invention.
FIG. 5 is a perspective view depicting deployment of an electrode lead in the medial branch of the dorsal root of a human spine.
FIG. 6 is a sectional view showing an electrode lead fixed adjacent to the medial branch of the dorsal root and having its proximal end located subcutaneously.
FIGS. 7A to 7E are, respectively, partial side views of various embodiments of lead fixation arrangements and a perspective view of the lead distal end when located in situ.
FIGS. 8A and 8B are, respectively, a partial side view of a further alternative embodiment of electrode lead and a perspective view of the electrode lead located in situ.
FIG. 9 is a partial sectional view of a further alternative of an electrode lead configured to facilitate removal upon the completion of NMES therapy.
FIGS. 10A to 10C are respectively, perspective views depicting an electrode lead disposed in a crossing orientation, an adjacent orientation, and a trans-spinous orientation relative to a target nerve.
VI. DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to methods and apparatus for implanting electrode leads suitable for use with an implantable neuromuscular electrical stimulation (“NMES”) device, such as described in the above-incorporated U.S. Patent Application Publication No. US2008/0228241 to Sachs. The device described in that application supplies electrical pulses to nerves innervating the spinal muscles, such as the multifidus muscle, and induces contraction of those muscles to effect a therapy designed to restore neural control and rehabilitation of the muscle. The implantable stimulator is disposed subcutaneously, and is coupled to one or more electrode leads having electrodes in contact with the target muscle, or nerves innervating the target muscles, or other anatomical structures associated with the muscle, such as ligaments and tendons. The NMES stimulation supplied by the stimulator applies a pulse regime that is very different than those employed by previously-known Spinal Cord Stimulation therapy devices, where the goal of the stimulation is simply to reduce or block the transmission of pain signals to the patient's brain, rather than rehabilitate the muscle.
While NMES electrode leads may be implanted surgically, the iatrogenic injury arising from such implantation may impede the rehabilitation process. Accordingly, the present invention is directed toward implanting the stimulation leads into muscle, fascia, ligament, or bone via surgical access and direct visualization using either minimally invasive or percutaneous techniques.
Referring to FIG. 1, the L3, L4 and L5 portions of the lumbar spine are described. The dorsal root D, dorsal ramus medial branch MB, intermediate branch I, and a representation of multifidus fascicular innervations A, B, and C are identified. Also shown in FIG. 1 are the superior articular process SAP, the spinous process SP, pedicle P, inferior anterior process IAP, and the transverse process TP.
With respect to FIG. 2, percutaneous deployment of electrode lead into the spine to effect multifidus stimulation is described, and is accomplished using a large gauge hypodermic needle 10. Using fluoroscopic, acoustic, anatomic or CT guidance, needle 10 is delivered transcutaneously and transmuscularly, to the vertebra. More specifically, lead 12 then is attached to the pedicle of the vertebra or within the fascia near the medial branch of the dorsal ramus nerve. Alternatively lead 12 may be deployed into the multifidus muscle M, in the vicinity of the medial branch MB nerve, and proximal to the fascicle branches A, B and C. When deployed in this location, the NMES stimulation is expected to provide recruitment of the nerve and the multifidus fascicles.
Referring now to FIG. 3, a minimally invasive approach for implanting an electrode lead for NMES stimulation is described. In this method, a separation is formed along natural tissue planes, for example, at the plane between multifidus muscle M and longissimus muscle LT, thereby providing access to the medial branch MB. Preferably, the tissue separation is accomplished using cannula 13 having a blunt dissection tool and an endoscope, as described below. Other muscle planes, such as between the multifidus fascicles, also could be separated using the similar methods and instrumentation.
With respect to FIG. 4A, cannula 13 comprises of one or more tubes 14 and 14′, transparent distal blunt dissection cone 16, through which tissue can be visualized, and side port 18 for delivery of fluids and application of vacuum. Tube 14 houses an endoscope for visualization and is fitted with tip 15 configured for blunt dissection. Tube 14′ remains in position when tube 14 is removed for deployment of lead 16, depicted in FIG. 4B. The cannula for blunt dissection may have a predetermined shape suitable separating the natural tissue plane between the multifidus and longissimus muscles or be malleable such that the clinician can customize the curvature of the cannula as needed for specific patient anatomy.
Referring to FIG. 4B, electrode lead 16 comprises of distal end 17 having two or more electrodes 18 for stimulation, and proximal end 19 for connection to an implantable stimulator or subcutaneous receiver. Distal end 17 may include two or more electrodes made of stainless steel, platinum-iridium or other suitably biocompatible material for delivery of electrical stimulation pulses. The electrodes may be cylindrical, planar or other suitable geometry, have at least 5 sq mm of surface area and may vary in length, width and diameter depending on lead body. Electrode lead 16 further may include an internal lumen that extends from proximal end 19 to distal tip 17, through which stylet 20 may be inserted. Stylet 20 may have a flat-blade tip suitable for engaging the proximal section of fixation screw 21, such that stylet 20 may be used to advance or withdraw the fixation screw by rotating the stylet. As depicted in FIG. 4C, a portion of the surface of electrode 18 may be masked with non-conductive insulating material 22, and thus used to orient the lead and direct stimulation current toward a selected nerve, e.g., the medial branch of the dorsal ramus nerve.
In addition, as illustrated in FIG. 4D, the body of the electrode lead need not be round. Instead electrode lead 23 has a ribbon-like cross section to facilitate passage between muscle planes, improve flex fatigue in one axis, provide better stability in vivo, and provide better guidance of stimulation current to targeted nerve(s). Proximal end 24 has an equal number of terminations as there are electrodes 25 on distal end 26, with one independent conductor for each electrode. Each termination may be connected to an output of the NMES stimulator, and each conductor coupling the terminations on the proximal end to electrodes 25 may comprise a cable or thin film structure. Electrode lead 23 also may include fixation screw 27 that is driven using removable stylet 28.
Referring now to FIG. 4E, alternative lead implantation cannula 30 is described. Cannula 30 is configured having a first lumen that accepts endoscope 32 and a second lumen that accepts minimally invasive surgical instrument 34, with which lead 16 or 23 may be deployed under endoscopic visualization. Cannula 30 is passed through a small incision made anterior to the natural tissue plane between the multifidus muscle M and the longissimus muscle LT. Under endoscopic visualization, a tract then is created using blunt dissection, during which tissue planes, blood vessels, ligaments, and fascia may be directly visualized using endoscope 32. Upon reaching the vertebra and visualizing superior articular process SAP, and more particularly pedicle P and medial branch MB of dorsal root D, as depicted in FIG. 5, the electrode lead is deployed. The lead may be deployed under endoscopic visualization and fixed in bone, ligament, or fascia using a fixation feature, such as corkscrew 21 above, or a suitable hook, barb or tine, as described below.
FIG. 6 shows one possible lead configuration after implantation, in which the proximal end of an electrode lead 35 is located subcutaneously. Proximal end 36 of electrode lead 35 may include a receiver for wirelessly receiving energy using a transcutaneous energy transmission system (TETS), which are known in the art, or may be coupled to an implantable NMES stimulator, as described in the above-incorporated patent publication to Sachs. Distal tip 37 of electrode lead 35 may be fixed in the pedicle adjacent medial branch MB, such that lead 35 lies between multifidus muscle M and longissimus muscle LT. Stimulation energy from an external pulse generator may be transmitted to the subcutaneous receiver; alternatively electrode lead 35 could be tunneled subcutaneously to an implantable pulse generator.
Whether a minimally invasive or percutaneous approach is employed, an electrode lead suitable for NMES therapy preferably includes a fixation feature that permits the distal end of the lead to be attached to the mamillary process, the anterior process, the pedicle, or locations in between. FIGS. 7A through 7E depict, respectively, various embodiments of fixation features. FIG. 7A shows electrode lead 40 having cork-screw fixation feature 41, similar to that described with respect to the embodiment of FIG. 4B, suitable for installation in a crossing orientation. In this manner of attachment, as shown in FIG. 7E, the lead crosses over the nerve. Lead 40 also may include bands 42 of polyester or other material that promotes tissue ingrowth to fasten the lead in position.
FIG. 7B shows electrode lead 43, including cork-screw fixation element 44 that exits through the side wall of the electrode lead. Lead 43 is particularly well-suited for installation in an adjacent orientation, in which the lead lies adjacent to the target nerve or muscle. FIG. 7C depicts electrode lead 45 that includes barbs 46 that may be embedded into the tissue or bone adjacent to the target nerve or tissue to retain the distal end of the electrode lead in position. Finally, FIG. 7C depicts electrode lead 47 having barb 48 that may be extended from within a lumen of the electrode lead, e.g., using a stylet, to drive the barb into the tissue or bone adjacent to the target nerve or tissue to retain the lead in position.
Referring to FIG. 8A, a further alternative embodiment of an electrode lead suitable for use in NMES therapy is described. Electrode lead 49 includes a distal region that forms bracket 50 having electrodes 51, such that bracket 50 may be disposed around a target nerve or muscle to prevent movement of the distal end of the lead, as illustrated in FIG. 8B.
Other suitable means to achieve tissue fixation include both resorbable and non-resorbable tines, and tissue hooks. Many of the same fixation features are suitable for engaging tissues like muscle, fascia or ligaments. The foregoing fixation features are intended to orient stimulation electrodes in adjacent or crossing relationships relative to the medial branch nerve. Still other means of stabilization include polymer and tissue matrix materials intended for the promotion of tissue ingrowth. Such features may take the form of polymer and metal surface treatments to create pores of appropriate diameter, polymers fabricated with pores of appropriate aperture size, and harvested or cultured cellular and extra cellular matrices that may be applied to the lead where fixation is desired.
Still other portions of the electrode leads may include materials and/or material treatments that resist tissue ingrowth, e.g., along regions of the electrode lead intended to lie between or within tissue planes that move. Materials and treatments that have pores suitable for reducing the amount and ability of tissue to become attached to the lead will make removal of the leads simpler once therapy has completed. For example, in FIG. 9, electrode lead 52 comprises flexible metal jacket 53 and outer polymeric cover 54. Flexible metal jacket 53 protects the electrode lead against trauma such as needle sticks post-implant, while polymeric cover 54 prevents tissue ingrowth, significantly improving lead removability upon completion of therapy.
Referring to FIGS. 10A to 10C, various arrangements for disposing the electrodes of an electrode lead in relation to medial branch MB are illustrated. In FIG. 10A, lead 55 is placed so that electrodes 56 are disposed in a crossing orientation with respect to medial branch MB. In FIG. 10B, lead 55 is placed so that electrodes 56 are disposed in an adjacent orientation with respect to medial branch MB, such that lead 55 is disposed substantially parallel to a length of the nerve. In a further alternative arrangement, depicted in FIG. 10C, lead 55 is implanted as a trans-spinous process implant. In this case, a pathway is bored through spinous process SP to the area of lamina LA, exiting near medial branch MB.
FIGS. 10A to 10C depict unilateral deployment of stimulation leads to the right or left of the dorsal ramus medial branch. It should of course be understood that it is within the scope of this invention to provide bilateral stimulation training of the multifidus muscle. It further should be understood that multiple levels, for example the medial branch of the dorsal ramus L3, L4 and L5, may be implanted with leads to train the multifidus muscle to its fullest extent. While the medial branch is described as the targeted nerve for stimulation, it is within the scope of this patent that stimulation of one or more other anatomical structures such as ligaments, tendons, or nerves of other than spine stabilization muscles (e.g., transverse abdominus, psoas, interspinales, longissimus, ileocostalis, intertransversus, quadratus) may comprise adequate therapy.
While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.
Patent Application
20110224682
