Patent ID: 8475452

Claim:
An electrosurgical instrument for thermal tissue treatment comprising: a. an elongate shaft having a proximal end, a distal end and a longitudinal axis, wherein said proximal end is configured for connection to a power source and said a distal end is configured for connection to an electrode assembly; b. an electrode assembly mounted to the distal end of said elongate shaft, said electrode assembly comprising: i. an insulator formed from a nonconductive dielectric material and comprising discrete proximal and distal portions, wherein said proximal and distal portions comprise opposed walls that extend laterally away from and transverse to said elongate shaft; ii. a planar active electrode formed from an electrically conductive material, connected via cabling disposed within said elongate shaft to a power source, and comprising top and bottom surfaces and an edge surface extending therebetween, wherein said active electrode extends between said proximal and distal insulator portions; and iii. a floating electrode positioned in close proximity to said active electrode, wherein said floating electrode is formed from an electrically conductive material, is not directly electrically connected to either the elongate shaft or a power source, and shields said top surface and at least a portion of said edge surface of said active electrode; wherein said floating electrode extends between said proximal and distal insulator portions to form an inverted open fluid-fillable cavity in which said active electrode is suspended; and c. a tubular member for supplying an irrigant directly to said inverted open fluid-fillable cavity; wherein the distalmost end of said active electrode is laterally recessed relative to the distalmost end of the floating electrode; further wherein powering of said active electrode in the presence of said irrigant results in flow of current from said active electrode to said floating electrode, heating of said irrigant and generation of steam within said inverted open fluid-fillable cavity, wherein said heated irrigant and steam flow out of said inverted open fluid-fillable cavity and thermally treat target tissue upon contact.