Multi-function Robotized Surgical Dissector for Endoscopic Pulmonary Thromboendarterectomy: Preclinical Study and Evaluation

TL;DR

This work addresses the challenge of accessing deep, slender branches of the pulmonary artery during Pulmonary Thromboendarterectomy by introducing a slender, CPPR-based dissector with dual-segment steering and integrated visualization channels. A compact 3.5 mm outer-diameter device with six DoFs is paired with an optimization-based inverse kinematics model to achieve tip-position accuracy near $2$ mm on a $60$ mm tool, under open-loop control. Experimental validation shows robust forward/inverse kinematics performance (RMSE around $0.09$–$2$ mm, depending on task), higher stiffness for tenon-mortise slits than square slits, and ex vivo porcine-lung demonstrations of thrombus removal and suction in tortuous PA geometries. The results suggest endoscopic PTE is feasible with improved dexterity and visualization, potentially shortening operative time and reducing tissue trauma, with future work focusing on imaging, force sensing, and advanced materials such as NiTi to enhance safety and durability.

Abstract

Patients suffering chronic severe pulmonary thromboembolism need Pulmonary Thromboendarterectomy (PTE) to remove the thromb and intima located inside pulmonary artery (PA). During the surgery, a surgeon holds tweezers and a dissector to delicately strip the blockage, but available tools for this surgery are rigid and straight, lacking distal dexterity to access into thin branches of PA. Therefore, this work presents a novel robotized dissector based on concentric push/pull robot (CPPR) structure, enabling entering deep thin branch of tortuous PA. Compared with conventional rigid dissectors, our design characterizes slenderness and dual-segment-bending dexterity. Owing to the hollow and thin-walled structure of the CPPR-based dissector as it has a slender body of 3.5mm in diameter, the central lumen accommodates two channels for irrigation and tip tool, and space for endoscopic camera's signal wire. To provide accurate surgical manipulation, optimization-based kinematics model was established, realizing a 2mm accuracy in positioning the tip tool (60mm length) under open-loop control strategy. As such, with the endoscopic camera, traditional PTE is possible to be upgraded as endoscopic PTE. Basic physic performance of the robotized dissector including stiffness, motion accuracy and maneuverability was evaluated through experiments. Surgery simulation on ex vivo porcine lung also demonstrates its dexterity and notable advantages in PTE.

Figures (13)

• Figure 1: (a) Basic workflow of PTE surgery. (b) Illustration clots removal procedure. The clots and intima are stripped by an dissector. (c) Robotized steerable dissector enables to enter thin branches of PA easily.
• Figure 2: Basic working principle of one CPPR manipulator. (a) One steerable segment consists of two patterned tubes and are assembled with the patterned section oppositely configured. (b) One rotation DoF enables 3D bending. (c) Distal segment passes through the central hollow lumen of the proximal segment. Tip head integrates an endoscopic camera, irrigation passage and an instrument channel which can also be used for suctioning residual blood. (d) Tenon-mortise slits on the inner tube and outer tubes are well designed. ‘I’-shaped slits are designed on the distal segment, which overlap with the steerable section of the proximal segment. The shape of the 'I'-shaped slits section follows the shape of proximal segment.
• Figure 3: (a) One CPPR steerable segment is assumed as a cantilever beam, and deflection $w$ reflects the capability of withstanding external load $F$. (b) Cross section of one tenon-mortise slit, and the stiffness is mainly defined by the central angle $\alpha$ of the uncut area and tube's size. (c) Cross section of one tenon-mortise slit in maximum bending or in with-load status, where tenon and mortise interlock together to increase the second moment of inertia. (d) Cross section of square slit. It also has an uncut area parameterized by $\alpha$, but the stiffness is relatively lower compared with tenon-mortise slit design.
• Figure 4: Overall Design of the dissector. (a) Handheld part. (b) Quick release and assemble for sterilization convenience. (c) Instrument component and actuation component. Static and mobile parts are highlighted. (d) Basic working principle of actuating a single segment with compact module. (e) Actuator design for a single segment. (f) Wireless control unit for teleoperation. (g) Coordination between joystick frame and bending frame.
• Figure 5: (a) Bending angle $\theta$ with pulling distance $D$ of a single manipulator. (b) The dual-segment CPPR manipulator's shape can be accordingly solved, and the tip pose w.r.t the base frame is computed via the shape. (c) The distal segment is nested nest into the proximal segment, but their bending curvature should be identical to avoid mutual interaction and even breakage. (d) Task space illustration.