The present invention relates generally to nerve electrodes, and more particularly to a claw-like electrode assembly or array which is implemented for ease of implantation on and electrical stimulation of a nerve of the patient.
U.S. Pat. No. 4,573,481 ("the '481 patent") discloses an implantable helical electrode assembly in which the configuration is composed of one or more flexible ribbon electrodes each partially embedded in a portion of the peripheral surface of a helically formed dielectric support matrix adapted to be threaded around a selected nerve or nerve bundle during surgical implantation of the electrode assembly. The resiliency of the assembly allows it to expand in the event of swelling of the nerve. The electrode assembly is utilized to electrically trigger or measure an action potential or to block conduction in nerve tissue.
Such a helical electrode has been found somewhat difficult to mount on the patient's nerve during implantation, because it is necessary to unravel the helical configuration and then reform it about the nerve. An improvement over the '481 patent electrode design is disclosed in U.S. Pat. No. 4,920,979 to the same inventor, in which a flexible electrode-supporting matrix has two oppositely directed helical portions which are centrally joined and have free outer ends. The helical portions extend circumferentially at least one turn and up to as much as about two turns. A thin, flexible conductive ribbon is secured to the inner surface to provide multiple electrodes on one or both portions, with a connecting electrical cable to couple the electrode array to an electronics package implanted elsewhere in the body.
The central passage through the two oppositely directed helical portions accommodates a pair of pins which extend at an acute angle from the respective closed legs of a tweezer-like installation tool. When the pins are inserted through the central passage and the legs of the tweezers are opened, the helical portions are distorted and spread open so that the assembly can be slipped over the nerve with the two open-sided portions restrained in a direction generally perpendicular to the length of the nerve. When released by withdrawing the pins of the installation tool, the two end portions return to a helical shape to encircle the nerve with their electrode portions conductively contacting the nerve surface. This type of electrode assembly simplifies installation of the electrode and reduces trauma to the nerve during implantation.
In U.S. patent application Ser. No. 07/695,543 filed May 3, 1991 ("the '543 application"), assigned to the same assignee as is the instant application, another improved helical nerve electrode or electrode array is disclosed. In this invention, the helix is locked together by a backbone which may be one-piece or divided into multiple segments. The electrode array is cut lengthwise through the entire helix at the side diametrically opposite to the backbone. The array is then spreadable at the cut ends of each loop, either one at a time or all together, and either manually or using an appropriate tool, to place it properly over the nerve. The array may then be allowed to collapse, as a consequence of its resiliency, into its unrestrained normal helical configuration about the nerve.
This provides the desirable features of a conventional helical electrode array, but with an improved configuration which allows it be opened in a manner similar to a clamshell when desired to install it on or remove it from the nerve. The array is relatively simple to install and unlikely to cause serious trauma to the nerve during or after implantation. In the latter respect, any subsequent swelling of the nerve is not restricted by the electrode. Some resistance to expansion may be experienced with a closed helical electrode array of the type described in the '481 patent, because of the tendency of the central portion of such a helix to resist expansion as the helix is subjected to outwardly directed radial forces.
In an alternative configuration of the electrode array of the '543 application, the cut in each loop or band of the helix is staggered relative to the cuts in the other bands to assure that the electrode array does not slip or otherwise become displaced from the nerve in the usual event of swelling of the nerve following the surgical implantation. Such swelling is likely to occur before stabilization, in the first few days following implantation of the electrode array. Fibrotic growth occurs and tends to retain everything in place after the first week to ten days following the surgery.
The nerve electrode array of the '543 application is made by forming an electrically insulative helix having a plurality of bands linked together by a lengthwise member, securing a electrically conductive strip to the underside of one of the bands and across the linking member, and severing each of the bands at a point away from the linking member so that each band remains linked to the member and may be spread open for mounting about the nerve.
It is a principal object of the present invention to provide an improved electrode or electrode array for nerve stimulation which is configured to permit relative ease of implantation and yet secure retention on a nerve compared to the prior art nerve electrodes.
Another object of the invention is to provide an improved nerve electrode which is simple to manufacture and simple to install without need for any special installation tool.