Steerable Mechanical Joint for High Load Transmission in Minimally Invasive Instruments

As minimally invasive operations are performed through small portals, the limited manipulation capability of straight surgical instruments is an issue. Access to the pathology site can be challenging, especially in confined anatomic areas with few available portals, such as the knee joint. The goal in this paper is to present and evaluate a new sideways-steerable instrument joint that fits within a small diameter and enables transmission of relative high forces (e.g., for cutting of tough tissue). Meniscectomy was selected as a target procedure for which quantitative design criteria were formulated. The steering mechanism consists of a crossed configuration of a compliant rolling-contact element that forms the instrument joint, which is rotated by flexural steering beams that are configured in a parallelogram mechanism. The actuation of cutting is performed by steel wire that runs through the center of rotation of the instrument joint. A prototype of the concept was fabricated and evaluated technically. The prototype demonstrated a range of motion between −22° and 25° with a steering stiffness of 17.6 Nmm/rad (min 16.9 – max 18.2 Nmm/rad). Mechanical tests confirmed that the prototype can transmit an axial load of 200 N on the tip with a maximum parasitic deflection of 4.4°. A new sideways steerable mechanical instrument joint was designed to improve sideways range of motion while enabling the cutting of strong tissues in a minimally invasive procedure. Proof of principle was achieved for the main criteria, which encourages the future development of a complete instrument.