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The Microsurgical Assistant
Humans possess an extraordinary tactile dexterity, yet we are designed to manipulate tools and perform tasks on the scale of our own bodies. Microsurgical operations require exquisite dexterity, yet even the steadiest-handed doctor still has an imperceptible hand tremor, on the order of tens of microns. Moreover, humans cannot accurately gauge tactile forces less than a few grams. These limits on human tactile performance directly determine the feasible limits of microsurgical procedures. Recently, researchers from the JHU School of Engineering and the JHU Medical School collaborated to develop a novel robot to enhance a surgeon’s tactile performance. This new robot, called the “Steady Hand Robot,” extends a surgeon’s ability to perform small-scale manipulation tasks—especially tasks requiring human judgment, sensory integration and eye-hand coordination.
In the steady hand system, the surgical tool is held simultaneously by the surgeon’s hand and a robotic arm. The robotic arm has a controller that senses the forces exerted by the human hand on the tool, and by the tool on the environment. It can then scale down the force of the surgeon’s hand to provide precise, delicate movements that are virtually tremor-free. It also amplifies minute tool-tip forces to the surgeon’s hand, thus “amplifying” the surgeon’s sense of touch. Professor Whitcomb and his students have developed novel control algorithms for this robot. A prototype of the steady-hand system was developed with Professor Russell Taylor of the Department of Computer Science and Eugene deJuan, MD of the JHU Wilmer Eye Institute. They are presently experimentally evaluating the system’s performance in collaboration with Daniel Rothbaum, MD, and John K. NiParko, MD, from JHU’s Department of Otolaryngology.
One form of hearing loss, otosclerosis, is caused by the immobilization of the stapes bone in the middle ear. A surgical procedure to correct it, stapedotomy, involves removing a portion of the stapes bone, drilling a tiny hole in the piece that’s left, and connecting a little piston-like prosthesis to another bone in the middle ear with a wire crimp. With the prosthesis in place, sound vibrations can propagate through to the inner ear, restoring hearing.
To perform this procedure with a steady-hand robot, the surgeon holds a stylus, attached to the robotic arm, with a surgical tool at the tip. The robot operates under a “proportional velocity” control during the crimping procedure, in which virtually no tremor propagates to the instrument tip. Users feel that their hands are “steadied”. In “force-control” mode, used in the drilling procedure, small contact forces between the instrument and the user feel amplified, allowing the surgeon to exert tiny forces that would otherwise be below the threshold of human tactile sensation. Using a full-scale instrumented model of the human ear, the Hopkins researchers are comparing assisted and unassisted outcomes of the drilling and crimping procedures.
The development of the Steady Hand Robot holds enormous promise. From delicate surgical procedures like stapedotomy to the injection of stem cells into the cochlea, which cannot be done manually, to directly breaking up blood clots in veins or arteries, it may well fundamentally change what is considered possible in medicine. Surgical robots may change medicine in a manner similar to the way that the development of the integrated circuit revolutionized information processing in the 20th century. This work done by Hopkins researchers is an example of successful interdisciplinary and interdepartmental work that taps into the extraordinary skills of all the researchers involved.