Coaxial needle insertion assistant for epidural puncture

Detection of internal puncture during manual needle insertion is challenging due to the large friction force between a needle shaft and surrounding tissue, which masks small changes in force at the needle tip. A novel robotic coaxial needle insertion assistant was developed to enhance operator perception during epidural puncture. The coaxial needle separates the cutting force at the needle tip from shear friction on the needle shaft. When the assistant is inactive, the human operator controls the motion of the coaxial needle. When the assistant is active under position control, a motor controls the motion of the outer needle, while the operator controls only the motion of the inner needle. When the assistant is active under force control, the operator controls the motion of the entire needle, but receives force feedback that is a scaled version of the force applied by the needle tip to the tissue. The effectiveness of the assistant in enabling puncture detection was tested in an experiment in which users were asked to puncture artificial tissues with the assistant inactive and active. Results show that the ratio of successful to unsuccessful puncture detection was higher with the assistant than without. In addition, users were more confident that they could perceive the moment of puncture. However, when the users successfully perceived puncture, overshoot with the assistant was larger than without.