A medical sheath tube that is used in minimally invasive diagnosis and treatment surgery is configured to establish passages, deliver or withdraw instruments, deliver drugs, or guide body fluid out, etc. An adjustable bend sheath tube with an adjustable bend at the distal end may reach a target diseased position quickly and reliably to reduce the operation time. In the minimally invasive interventional field, one end relatively far away from an operator is usually defined as a distal end, and the other end relatively close to the operator is defined as a proximal end.
U.S Patent document U.S. Pat. No. 6,945,956B2 disclosed an adjustable bend sheath tube, including a tube body, a traction mechanism and a handle having a control system; the traction mechanism includes a radiopaque ring annularly arranged in a side wall of a distal elastic segment of the tube body, and a traction wire arranged in the side wall of the tube body; a distal end of the traction wire is directly fixed on a ring wall of the radiopaque ring by welding, and a proximal end of the traction wire is connected to the control system. The traction wire is pulled by the control system, the force and displacement are transferred to the traction wire to drive the traction wire to relatively move in the axial direction of the tube body, and then the force and displacement are transferred to the radiopaque ring through welding points to drive the distal elastic segment of the tube body to be bent, thereby achieving adjustable bending of the distal end of the tube body.
According to the requirements imposed on the diameter size and angle range of the adjustable bend sheath tube, when reaching a maximum adjustable bending angle, the tensile force applied onto the traction wire is generally larger, which may reach a maximum of 5 Kgf. If a larger instrument is delivered with the distal end of the sheath being bent, the instrument will apply a certain back tensile force to a bent channel, so that the tensile force applied on the traction wire is larger, thereby putting forward higher requirements on the tensile strength of a traction system. In general, it is better for the inner diameter of a medical sheath tube to be larger, and for the outer diameter thereof to be smaller. The smaller outer diameter may reduce the damage to the human blood vessels, and the larger inner diameter allows larger instruments to be delivered, thus requiring that the tube wall of the tube body must be as thin as possible; i.e., requiring that the volume of a portion of the traction system disposed in the tube wall must be as small as possible, in order to be covered in the tube wall and to reduce the thickness of the tube wall. The doctor will carry out the adjustable bending operation repeatedly before and during surgery, and is required to continuously and accurately adjust the angle of the distal end of the tube body, in order to enable the bending angle to adapt to the complex anatomical structure of the lumen in different human bodies. The traction system is required to have outstanding tensile fatigue performance for adjustable bending. Therefore, the tensile strength, the tensile fatigue strength and the wall thickness of the tube body, are all crucial to an adjustable bend sheath tube.
The traction wire is usually thin, and the corresponding welding area is small, thus not only resulting in great difficulty during the welding process, but also leading to stress concentration of the welding point, change of the section size, change of the surface morphology, residual stress, and so on. Moreover, according to the theory of metal welding, it is known that the physical strength after welding is only half or less of that during non-welding, so that the material strength is decreased significantly, thus resulting in insufficient tensile strength and low reliability of the traction wire. Not only is the welding process difficult to control, but also the procedure qualification rate in the process is low. In addition, the welding point has an increased fracture risk, the portion with welding points under a larger traction force or after being bent repeatedly can be fractured very easily, so that the product then lacks an adjustable bending function, thereby resulting in failure of the surgery and even injury to the human body. Furthermore, the welding is a rigid connection, which is difficult to meet the requirement of repeated adjustable bending, and the fatigue strength is poor. If a thicker traction wire were utilized, the wall thickness of the tube body would be increased, thereby greatly reducing the possibility of successfully entering target blood vessels and also reducing flexibility of the tube body.
In view of this, U.S. Patent document U.S. Pat. No. 7,553,305B2 adopts a fixed anchor to implement a part of the functions of the radiopaque ring. The fixed anchor is connected to the distal end of the traction wire and located within the side wall of the tube body, and at least one end has a rim around the axial direction of the traction wire. When the traction wire is pulled, the traction force is transferred to the fixed anchor, and the fixed anchor acts as a force bearing body to drive the tail end of the tube body so as to achieve the adjustable bending function.
The fixed anchor has a rim unfolding around the radial direction of the traction wire. Due to the large diameter of the rim, the side wall should have sufficient thickness to completely cover the fixed anchor. However, the medical sheath tube requires that the wall thickness of the tube body should be as small as possible. The rim will certainly increase the wall thickness of the sheath tube. In the case of a fixed size of a delivery lumen, if the outer diameter of the tube body is larger, the injury to the human body during delivery of the instrument of the same specification into the human body is greater. Moreover, the fixed anchor is a longitudinal structure along the axial direction of the tube body, and the distal end of the tube body opposite to the fixed anchor is also provided with a radiopaque ring, so that the length of a distal rigid segment of the tube body is increased and the flexibility of an elastic adjustable bend segment is reduced; when the distal end of the tube body is bent to a certain angle, compared with the tube body with a short rigid segment, the distal end of the tube body with this structure has a larger radius of deflection, which influences the flexibility of the sheath tube during pushing; if the radius of deflection is large in the lumen of the human body lumen with small space, there is not enough space available for bending the sheath tube.