BIPOLAR ELECTRODE ASSEMBLY INCLUDING A CANNULA WITH PROXIMAL AND DISTAL CONTACTS OF DIFFERING SURFACE AREAS

RELATED APPLICATIONS

[0001] This application claims the benefit of United States Provisional

Patent Application Serial No. 60/883,627, filed January 5, 2007, hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention is related generally to a bipolar electrode assembly that can be used to perform a denervation procedure or other medical procedure in which tissue is to be cut, shaped, coagulated, ablated, or otherwise treated.

BACKGROUND OF THE INVENTION

[0003] Electrosurgical tool systems are used to treat tissue (e.g., cut tissue, shape tissue, coagulate tissue, or ablate tissue) at surgical sites. Generally, an electrosurgical tool system includes an electrode assembly with at least one electrically active contact. An electrode assembly that has a single active contact is referred to as monopolar. An electrode assembly with at least two active contacts is typically referred to as bipolar. A control console, also part of the system, supplies an RF signal to the electrode assembly. Often this signal is between 50 KHz and 10 MHz. The RF signal is applied to the active contact(s). If the system includes the monopolar electrode, a second dispersive electrode, is placed in contact with the patient to serve as a return path for the RF signal. If the system includes a bipolar electrode, the active proximal and distal contacts alternate as active and return poles during the RF cycle.

[0004] One medical specialty in which electrosurgical tools are used with increasing frequency is pain management. Pain is felt as a consequence of first, a stimulus being applied to a first nerve. Then, a signal representative of the pain is transmitted from the first nerve through other nerves in the neural network to the brain. An individual can suffer chronic pain if the biological conditions are such that

the first nerve latches into a condition in which it continually transmits the pain signal through the neural network to the brain.

[0005] In a pain management process, an electrosurgical tool is used to treat either the initial pain transmitting nerve or one of the associated downstream nerves from the neural network. This disconnection reduces and can eliminate the flow of pain messages to the brain. Medically, the process of removing the nerve from the neural network is called denervation. In a denervation process, the RF energy emitted by the electrode assembly is applied to the nerve. The nerve absorbs this energy and, as a consequence, is modified to a level at which it ceases to function or is ablated. This is achieved through either heat or pulsed RF energy.

[0006] Presently, the common practice is to employ a monopolar electrode assembly to apply the RF energy to the nerve. There are many situations however wherein it is desirable to use a bipolar electrode assembly in order to apply RF energy to perform the denervation procedure. This is because the energy flow when using this type of electrode assembly is essentially between the two active contacts. Thus the energy flow at the surgical site is more directed than when a monopolar electrode assembly when a large external ground pad is employed. As a consequence of this more directed energy flow, more energy is applied in a shorter amount of time to the tissue, the nerve, to be ablated. Inversely, less energy is absorbed by nearby tissue that is not to be subjected to ablation. Thus, using a bipolar electrode assembly to perform the ablation process would further result in a denervation process that is less likely to harm surrounding tissue.

[0007| However, to date, there have been obstacles to using bipolar electrode assemblies for denervation procedures. This is because it has proven difficult to provide bipolar electrode assemblies that are capable of focusing energy at a desired location to treat (e.g., cut, shape, coagulate, ablate) tissue without inadvertently affecting surrounding tissue that is located adjacent to the contacts. This problem is particularly noticeable when the proximal and distal contacts of the bipolar electrode assembly are positioned adjacent to different tissue types, which heat at different rates, and have different treatment thresholds. In some cases, it may be desirable to treat tissue nearest the distal contact, while the tissue nearest the proximal contact is not to be affected. In this instance, the bipolar electrode assembly

needs to be configured such that energy is focused at the distal contact and not the proximal contact. Therefore, there is a need in the art to design a bipolar electrode assembly that includes proximal and distal contacts adapted to be adjacent to different tissue types, while only affecting the tissue adjacent to one of the contacts during operation to prevent undesirable or inadvertent treatment of surrounding tissues that are not to be affected.

SUMMARY OF THE INVENTION

[0008] This present invention is directed to a new and useful cannula for receiving a supply electrode of a matable supply electrode unit to provide a bipolar electrode assembly. The cannula comprises a coupling assembly having a hub for engaging the supply electrode unit. An elongated body is mounted to the hub. The elongated body has a proximal end mounted to the hub and extends to a distal end. The elongated body defines a through-bore for receiving the supply electrode of the supply electrode unit. First and second spaced apart and electrically conductive contacts are disposed adjacent to the distal end. Insulating material is disposed between the first and second contacts. The first contact has a first exposed surface area and the second contact has a second exposed surface area at least two times greater than the first exposed surface area for concentrating energy toward the first contact when the supply electrode unit is mated to the cannula and energized.

[0009] The present invention also provides a bipolar electrode assembly comprising a cannula and a supply electrode unit. The cannula includes a first coupling assembly having a hub. An elongated body having a proximal end is mounted to the hub and projects from the hub to a distal end. First and second spaced apart and oppositely charged contacts are disposed adjacent to the distal end of the elongated body. The supply electrode unit includes a supply electrode having spaced apart proximal and distal ends. The supply electrode is dimensioned to be slidably inserted into the elongated body so as to be positioned to electrically contact the first contact. A second coupling assembly is attached to the proximal end of the supply electrode. The first and second coupling assemblies are configured to mate. The first contact has a first exposed surface area and the second contact has a second exposed surface area at least two times greater than the first exposed surface area for

concentrating energy toward the first contact when the supply electrode unit is mated to the cannula and energized.

[00010] The present invention provides a bipolar electrode assembly capable of focusing RF energy on a targeted tissue area without impacting tissues that are not to be affected. In particular, the cannula of the bipolar electrode assembly includes proximal and distal contacts adapted to be adjacent to different tissue types, while only affecting the tissue adjacent to one of the contacts during operation to prevent undesirable or inadvertent treatment of surrounding tissues that are not to be affected.

BRIEF DESCRIPTION OF THE DRAWINGS

[00011] These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiment and accompanying drawings in which:

[00012] Figure 1 is a perspective view of a bipolar electrosurgical system embodying the present invention;

[00013] Figure 2 is an exploded perspective view of a bipolar electrode assembly comprising a cannula and a supply electrode unit;

[00014] Figure 3 is an exploded perspective view of the cannula ;

[00015] Figure 4 is a top view of the cannula with a terminal removed to show internal detail;

[00016] Figure 5 is a cross section of the cannula taken along line 5-5 of

Figure 4 with a terminal fixed to a hub of the cannula;

[00017] Figure 5A is a blown-up view from Fig. 5 illustrating a body of the cannula fixed to a hub of the cannula;

[00018] Figure 6 is a trailing end view of the cannula;

[00019] Figure 7 is a partial top view of the bipolar electrode assembly in the operational state;

[00020] Figure 8 is an enlarged, partial, cross sectional view of the bipolar electrode assembly in the operational state taken from circle 8 of Figure 7; and

[00021] Figure 9 is an end view of the bipolar electrode assembly in the operational state.

DETAILED DESCRIPTION

[00022] Referring in more detail to the drawings, FIG. 1 illustrates a bipolar electrosurgical system 20 of the present invention having a control console 22 for generating electrical energy of a controlled radiofrequency. A bipolar electrode assembly 24 of the system 20 plugs into the control console 22 at one end and delivers radio frequency (RF) energy to a targeted tissue area of a patient at an opposite end. The targeted tissue may be any tissue that is to be treated (e.g., cut, shaped, coagulated, or ablated) including nerve cells. Preferably, the system 20 has a remotely located controller 26 that communicates with and preferably plugs into the control console 22 enabling an operating physician to control multiple functions. Further aspects of the control console 22 are disclosed in United States Patent Application Serial Number 1 1/122,702, filed May 5, 2005 and entitled "SYSTEM AND METHOD FOR CONTROLLING ELECTRICAL STIMULATION AND RADIOFREQUENCY OUTPUT FOR USE IN AN ELECTROSURGICAL PROCEDURE", hereby incorporated by reference in its entirety.

[00023] In a pain management procedure, the system 20 is used to modify nerve cells to the point at which they no longer function. This procedure is called a denervation procedure. In a denervation procedure, the modification of nerve cells is considered to result in the formation of a lesion. In other procedures wherein the system of this invention is used to modify or remove cells, the process results in tissue ablation. The control console 22 applies preferably temperature-controlled, RF energy into targeted nerve tissue adjacent to the bipolar electrode assembly 24. The system 20 may also be used in "pulsed mode." Instead of creating heat lesions, RF energy is pulsed with a duty cycle low enough that tissue temperature rise is kept below a level which can kill cells. Pain relief is achieved by influencing the nerve cells through the pulsed E field. It is theorized that the intense E field created by the pulsed RF influences gene expression in the nerve cells. This changed gene expression provides a pain reduction. More specifically, the system 20 may be used for selective denervation and tissue destruction procedures that may be performed on the lumbar, thoracic, and cervical regions of the spinal cord, peripheral nerves, and nerve roots for the relief of pain. Examples include, but are not limited to, Facette

Denervation, Percutaneous Chordotomy/Dorsal Root Entry Zone (DREZ) Lesion, Trigeminus Neuralgia, and Rhizotomy.

[00024] Referring to FIG. 2, the bipolar electrode assembly 24 has a cannula 28 and a supply electrode unit 36. The cannula 28 and the supply electrode unit 36 are preferably separate components that releasably mate to one another during the denervation procedure, and the cannula 28 is bipolar when electrically active. The supply electrode unit 36 is connected by a cable 114 and a plug 1 12 to the control console 22 (see FIG. 1). Internal to the cable 1 14 are a plurality of insulated conductors (not shown). A supply electrode 1 18 of the supply electrode unit 36 extends from a housing 134 attached to the proximal end of the cable 1 14. The cable 1 14 extends flexibly between the plug 1 12 and a coupling assembly 1 16. The supply electrode 118 is supported by and projects outward from the coupling assembly 116. The supply electrode 1 18 serves as the component that completes the conductive path from the control console 22 through plug 1 12 and cable 1 14, to the cannula 28. The supply electrode 118 also functions to house a temperature sensitive transducer (not shown).

[00025] The supply electrode unit 36, temperature sensitive transducer, other components to be utilized with the cannula 28, and methods of using the bipolar electrode assembly 24 are disclosed in United States Patent Application Serial Number 1 1/381,064, filed May 1, 2006 and entitled, "MEDICAL BIPOLAR ELECTRODE ASSEMBLY WITH A CANNULA HAVING A BIPOLAR ACTIVE TIP AND A SEPARATE SUPPLY ELECTRODE AND MEDICAL MONOPOLAR ELECTRODE ASSEMBLY WITH A CANNULA HAVING A MONOPOLAR ACTIVE TIP AND A SEPARATE TEMPERATURE-TRANSDUCER POST", hereby incorporated by reference.

[00026] Referring to FIG. 3, the cannula 28 has a generally tubular body projecting axially forward along an axis 50 from a coupling assembly 44. The coupling assembly 44 is configured for mating with the coupling assembly 1 16 of the supply electrode unit 36 when mating the supply electrode unit 36 to the cannula 28. The coupling assembly 44 has an electrically insulated hub 46 that is generally ribbed for gripping by the user e.g. a physician. The body of the cannula 28 is mounted to the hub 46 and has an electrically conductive and elongated inner member or tube 48,

an elongated inner insulating member or sleeve 52, an electrically conductive and elongated outer member or tube 54 and preferably an elongated outer insulating member or sleeve 56. The tubes 48, 54 are preferably formed of a conductive material such as 304 stainless steel. The insulating sleeves 52, 56 are preferably formed of a electrically insulative material such as polyester heat shrink (PET). In some embodiments, the outer sleeve 56 is absent.

[00027] The inner tube 48 preferably defines a substantially straight and axial extending through-bore 57 (see FIG. 6), and projects axially forward from the hub 46 to a distal end 58. The inner tube 48 is electrically insulated from the outer tube 54 by the inner sleeve 52, which is also tube shaped. The inner sleeve 52 is oriented concentrically about and radially outward from the inner tube 48 and projects axially from the hub 46 to a generally annular distal end 60 located adjacent to and trailing the distal end 58 of the inner tube 48. Because the inner sleeve 52 does not extend axially forward as much as the inner tube 48, a ring shaped portion of the inner tube 48 at the most distal end of the inner tube 48 is exposed to the environment. This section of inner tube 48 is the first active contact or electrode terminal 62 (see FIG. 8) of cannula 28.

[00028] The outer tube 54 is spaced radially outward from the inner tube 48 by the inner sleeve 52 and preferably projects axially forward to a distal end 64. The distal end 64 of the outer tube 54 is spaced proximally from the first active contact 62. The outer sleeve 56 is preferably a tubular jacket orientated concentrically about and radially outward from the outer tube 54 and projecting axially from the hub 46 to a generally annular distal end 66 trailing the distal end 64 of the outer tube 54. Because the outer sleeve 56 does not extend axially forward as much as the outer tube 54, there is ring shaped exposed section of the outer tube 54 at its distal end 64. This section of the outer tube 54 is the second active contact or electrode terminal 68. When a potential is applied across contacts 62 and 68, a RF energy field develops between the contacts 62, 68 thereby sending a current through the tissue and completing the circuit (see FIG. 8).

[00029] The insulating inner 52 and outer 56 sleeves are preferably heat shrinkable tubing made of a polyester or Teflon material having a wall thickness of about 0.0008 inches to 0.0012 inches. With regard to the inner 48 and outer 54 tubes,

the first active contact 62 of the inner tube 48 is preferably the supply or power electrode terminal and the second active contact 68 is preferably the return or ground electrode terminal. However, one skilled in the art would know that the electrical charge of the contacts 62, 68 can be reversed. Moreover, the control console 22 may function to fluctuate polarities.

[00030] Referring to FIG. 8, because the first active contact 62 and the second active contact 68 are separated axially by an insulating ring 69 of the inner sleeve 52, a current path or energy field 71 is generated between the contacts 62, 68 by the control console 22 when the bipolar electrode assembly 24 is in the operating state thus creating a lesion in the target tissue. The size of the lesion can be varied by changing or varying an axial length or surface area of any one of the active contacts 62 and 68 or insulating ring 69 which alters the current path 71. Consequently, a surgeon can select an appropriate cannula 28 that meets his or her particular needs.

[00031] Because physicians are typically familiar with the lesion sizes formed by active tips of monopolar systems unlike the present invention, the axial spacing of the active contacts 62 and 68 or insulating ring 69 can be referenced as equivalents to known active tip lengths of monopolar systems, such that physicians can use the bipolar electrosurgical system 20 and get the same results as they may have using a known monopolar device. Testing has been completed for this purpose with the results reproduced as follows:

Surface Area (mm2) of Length (mm) of Equivalent Bipolar Cannula

Contact 62, Ins. Ring Contact 62, Ins. Ring Monopolar Active Diameter 69, Contact 68 69, Contact 68 Tip Length (mm)

10.84, 6.22, >27.57 4.93, 2.46, >9.86 5 2OG

17.59, 9.71, >44.74 8, 3.84, >16 10 2OG

26.39, 14.59, >67.1 12, 5.77, >24 15 2OG

[00032] It should be appreciated that the above 2OG (20 Gauge) diameter is the outer diameter of the outer sleeve 56. This diameter is exemplary, not limiting. Other cannulae of this invention may have outer diameters ranging from 12G to a smaller diameter 26G. For bipolar electrode assemblies 24 used for

denervation procedures, the diameter of the cannula 28, is preferably 16G or smaller (e.g., 18G) and more preferably 18G or smaller (e.g., 20G).

[00033] Notably, multiple variations of the axial lengths or surface areas of contacts 62 and 68 and ring 69 results in generating similarly sized lesions. However, testing shows that having a much longer (length) or larger (surface area) second active contact 68 relative to the first active contact 62 results in the lesion being concentrated about the first active contact 62. "Longer" it is understood here means that the second active contact 68 has an exposed length L ₂ two (2) times or more, often three (3) times or more, and sometimes four (4) times or more than an exposed length Li of the first active contact 62. See FIG 8. "Larger" it is understood means that the second active contact 68 has an exposed surface area two (2) times or more, often three (3) times or more, and sometimes four (4) times or more than, an exposed surface area of the first active contact 62.

[00034] In one embodiment, the exposed length or exposed surface area of the second active contact 68 is two and a half (2.5) times or more than the exposed length or surface area of the first active contact 62. In another embodiment, the second active contact 68 extends all the way to the hub 46. Thus, the insulating outer sleeve 56 is removed completely in this embodiment. It should be appreciated that the relative lengths and surface areas of the contacts 62, 68 provided may refer not only to the exposed lengths or surface areas of the contacts 62, 68, but also to the portions of the exposed lengths or surface areas actually in contact with, or adjacent to, tissue during use.

[00035] It has been found that the large difference in exposed lengths or surface areas helps concentrate the focus of energy at the first active contact 62. In other embodiments, the relative lengths or surface areas could be reversed, e.g., the first active contact 62 is two (2) or more, three (3) or more, or four (4) for more times longer or larger than the second active contact 68. In any case, the longer or larger contact dissipates the energy more efficiently. If active contacts 62 and 68 are equal in size and the insulating ring 69 is of equal length or smaller in length than a single one of the contacts, during a denervation procedure, the lesion forms around both contacts 62, 68 and the insulating ring 69.

[00036] To facilitate smooth skin piercing, the distal end 58 of the inner tube 48 is beveled or chamfered to a point 70 similar to that of a hypodermic needle. Furthermore, the distal ends 60 and 66 of the insulating inner 54 and outer 56 sleeves are tapered, (tapers not identified.). Moreover, the distal end 64 of the outer tube 54 that forms the second active tip 68 preferably has an annular taper 101 around its outer distal face (see FIG. 8). This tapering substantially reduces or prevents snagging of tissue upon the cannula 28 when the cannula 28 is being inserted thus reducing tissue trauma. Alternatively, the cannula 28 could be inserted into tissue via an introducer needle (not shown), in which case the tapering would not be necessary.

[000371 It should be recognized that alternative methods may be employed to minimize the trauma associated with the insertion of the distal end 64 of the outer tube 54. Instead of a complete taper, the outer tube 54 may be formed with a bevel around its outer perimeter. Alternatively, an adhesive, a plastic or a heat shrink wrapper may be positioned immediately forward of the distal end 64 of the outer tube 54 to form an angled surface that minimizes the trauma associated with the insertion of the outer tube 54.

[00038] Referring to FIGS. 3-6, the hub 46 of the coupling assembly 44 of the cannula 28 is preferably made of injection molded plastic that may be molded directly to at least one of the proximal ends of the sleeves 52, 56 and tubes 48, 54 or is attached by adhesive. Preferably, the hub has a counter-bore 72 (see FIG. 6) located rearward of and concentrically to the through-bore 57 and defined by a rearward projecting collar 74 of the hub 46. The counter-bore 72 has a funnel portion 76 that tapers radially inward and forward toward a trailing opening 78 of the through-bore 57. The counter-bore 72 with the funnel portion 76 assists in guiding the supply electrode 118 of the supply electrode unit 36 into the through-bore 57 when mating the supply electrode unit 36 to the cannula 28 in the manner shown and described in United States Patent Application Serial Number 1 1/381 ,064, filed May 1, 2006 and entitled, "MEDICAL BIPOLAR ELECTRODE ASSEMBLY WITH A CANNULA HAVING A BIPOLAR ACTIVE TIP AND A SEPARATE SUPPLY ELECTRODE AND MEDICAL MONOPOLAR ELECTRODE ASSEMBLY WITH A CANNULA HAVING A MONOPOLAR ACTIVE TIP AND A SEPARATE TEMPERATURE- TRANSDUCER POST", hereby incorporated by reference.

[00039] An alcove 82 in the hub 46 of the cannula coupling assembly

44 opens radially outward and axially rearward. Exposed generally through a bottom or window 84 of the alcove 82 defined by the hub 46 is the outer tube 54. As best shown in FIG. 3, a resiliently flexible terminal 86 of the coupling assembly 44 seats to the hub 46 and is generally biased against the tube 54 forming an electrical connection.

[00040] During manufacturing of the cannula 28, the inner tube 48 is cut to length and the bevel at end 58 is cut to form point 70, then the outer tube 54 is cut to length. The inner 52 and outer 56 insulating sleeves are then preferably cut to an approximate length and slid over the respective inner 48 and outer 54 tubes and preferably adhered with glue. Since the sleeves 52, 56 are preferably of a heat shrink type, the tubes 48, 54 with glued sleeves 52, 56 are individually sent through a heating coil to shrink and thus seat the sleeves 52, 56 to the respective tubes 48, 54. The tubes 48, 54 are then individually placed into a fixture and the appropriate amounts of insulation from the sleeves 52, 56 are stripped off the tubes 48, 54 to expose the required axial lengths or surface areas of contacts 62, 68.

[000411 The leading taper of the heat shrunk tubes 52, 56 is then preferably formed by applying a mild abrasive material such as light sandpaper to the sleeves already seated on the tubes. The abrasive may be a paper-backed sand paper that after applied, results in a smooth radial transition between the sleeves 52, 56 and the tubes 48, 54. The ramped annular bead or taper 101 is preferably formed from UV cured adhesive added between the inner sleeve 52 and the outer tube 54 to further smooth-out the leading radial transition of the cannula 28.

[00042] In some versions of the invention, the outer tube 54 has a thinner wall than that of the inner tube 48. This allows the use of a larger sized inner tube 48, while maintaining a slim overall dimension of the body. Preferably, the inner sleeve 52 after heat shrinking is about 22G and the outer sleeve 56 after heat shrinking is about 20G. The proximal end of the body of the cannula 28 is then inserted into an axially extending hole in the hub 46 of the cannula 28 and is connected to the hub 46 preferably by an adhesive such as a UV adhesive, more preferably from the urethane (meth) acrylate class, or an instant adhesive such as ethyl cyanoacrylac. The distal ends of the insulating sleeves 52, 56 are then sanded to

achieve the taper, thus reducing tissue trauma during insertion of the body when in use.

[00043] Referring to FIG. 5A, the bowed terminal 86 is inserted into the alcove 82 defined through a side of the hub 46. The terminal 86 is positioned such that its forward distal end is electrically contacting the outer tube 54 (the outer tube 54 is exposed in the window 84 to make this contact). The terminal 86 is secured in the window 84 by a dimple and/or adhesive added between a leg of the terminal and the hub 46.

[00044] While this description is directed to a few particular embodiments, it is understood that those skilled in the art may conceive of modifications and/or variations to the specific embodiments shown and described herein. Any such modifications or variations which fall within the purview of this description are intended to be included herein as well. It is understood that the description herein is intended to be illustrative only and is not intended to be limited. The numbers provided in the claims is for illustration purposes only and in no way is intended to limit the scope of the claims.