Radio frequency surgical instrument

A radio frequency surgical instrument comprising:

• a tubular body having a distal end and a proximal end, and provided therein with at least a first lumen and a second lumen;
• a metal wire having a tip end and a base end, and including a first portion exposed from and disposed outside a distal portion of the tubular body and a second portion disposed in the first lumen, the metal wire configured such that a radio frequency current is applied thereto;
• and
• a fixture fixed to a tip end portion of the metal wire, being in contact with an inner wall of the first lumen, and having a tip end and a base end, wherein
• the fixture has a first segment at least including a portion decreased in outer diameter toward the tip end and not including a portion increased in outer diameter toward the tip end, and
• when the first segment is equally tripartitioned into a tip portion, a center portion, and a base portion, a cross-sectional shape of a base end of the tip portion of the first segment is different from a cross-sectional shape of a base end of the base portion of the first segment in a cross-section perpendicular to a longitudinal direction of the fixture, and
• the cross-sectional shape of the base end of the base portion of the first segment has a contour including a plurality of corners arranged at equal intervals in a circumferential direction perpendicular to the longitudinal direction, so that the plurality of corners contact with the inner wall of the first lumen of the tubular body.