Endoscope treatment tool

1. An endoscope treatment tool comprising:

a flexible sheath;

a manipulation wire inserted through the flexible sheath so as to freely advance and retract; and

a basket portion which is connected at a proximal end of the basket portion to a distal side of the manipulation wire, the basket portion including a locking portion provided at a distal end of the basket portion, the basket portion including a plurality of elastic wires integrated by the locking portion, the basket portion opens and closes in a radial direction orthogonal to a central axis of the manipulation wire, wherein

the basket portion defines a longitudinal extent with a center, and a maximum outside diameter portion of the basket portion is at a position closer to the locking portion and the center of the longitudinal extent of the basket portion,

the plurality of elastic wires is formed in a shape of a helix in which each of the plurality of elastic wires is helically wound in a same direction over an entire length of the plurality of elastic wires, and a winding pitch of the plurality of elastic wires becomes gradually smaller in a direction from a proximal side of the manipulation wire to the distal side of the manipulation wire, and a gap between the plurality of elastic wires is smaller at a portion between the locking portion and the maximum outside diameter portion than at a portion between the proximal end of the basket portion and the maximum outside diameter portion, with the winding pitch at its smallest at the distal end of the basket portion, and

a tangential line of each of the plurality of elastic wires in the maximum outside diameter portion is inclined at an angle of 45° or less with respect to a plane orthogonal to the central axis without an external force applied to the basket portion, and thereby, when a proximal side of the basket portion is reduced, the maximum outside diameter portion is pushed outward in the radial direction by a first amount which is substantially the same as a second amount by which the proximal side of the basket portion is reduced inward in the radial direction, and an outside diameter of the maximum outside diameter portion is maintained at substantially a same size as the outside diameter before the proximal side of the basket portion is reduced.

2. The endoscope treatment tool according to claim 1 ,

wherein the basket portion includes a support member coupled to the locking portion which is at least partially inserted into the flexible sheath.

3. The endoscope treatment tool according to claim 2 ,

wherein the support member is arranged at a position shifted from a centerline of the plurality of elastic wires integrated by the locking portion.

4. The endoscope treatment tool according to claim 2 , further comprising a coupling portion further extending to a distal side of the basket portion from the locking portion,

wherein the support member is fixed to the coupling portion.

5. The endoscope treatment tool according to claim 1 ,

wherein the elastic wires are made of a nickel titanium alloy.

6. The endoscope treatment tool according to claim 1 ,

wherein the plurality of elastic wires is wound counterclockwise, as seen from a proximal end of the manipulation wire toward a distal end of the manipulation wire.

7. The endoscope treatment tool according to claim 1 ,

wherein each of the plurality of the elastic wires is wound counterclockwise, when viewed from the distal side of the manipulation wire toward the locking portion.

8. The endoscope treatment tool according to claim 1 ,

wherein each of the plurality of the elastic wires has two inflection points from the proximal end to the distal end of the basket portion.