A Finer Grasp on the Electronic Hand A Second Generation Neural Hand Prosthesis makes Life Easier for Patients From: Design News, Lifesavers: The Components behind Today's Medical Breakthroughs - May 5, 2003 - page 17 By: Amy Castor Six years ago, the Cleveland Functional Electrical Stimulation (FES) Center brought hope to quadriplegics with its FDA-approved Freehand neural hand prosthesis. By using electrical impulses to move paralyzed muscles on command, the device restores some movement to the hand. In forging onward with its work, the Center is now testing a second generation electronic hand, with an implantable sensor, additional output channels, and a more naturally means of operation. Similar to the original Freehand, the new implant targets people with nerve damage at the 5th or 6th cervical root. Although these individuals can move their shoulders and upper arms, their hands remain paralyzed. With the ability to grasp objects, they gain the independence to do simple tasks like brush their teeth or pour themselves a cup of coffee. Called "the second generation neural hand prosthesis," the new device retains the basic components as the original. With Freehand, the user controls hand movement through voluntary shrugs of his opposite shoulder. Moving the shoulder forward and back, opens and closes the hand. An external joystick position sensor near the shoulder reads the movements and sends the data to a battery-powered controller on the wheelchair. The controller processes the information into RF signals in order to send power and control an implanted stelemeter/telemeter (IST) in the chest. (A coil taped to the chest transmits the signals through the skin.) Caption 1a: In the original Freehand, the user controlled hand movements through voluntary movements of the opposite shoulder. A position sensor taped near the shoulder transduced the motion and sent the data to a battery-powered control unit. Caption 1b: In the second generation neural hand prosthesis, the shoulder position sensor is replaced by an implantable joint angle transducer in the wrist. Eight subcutaneous wires carry the signals to electrodes sutured onto the muscles of the forearm and hand to produce coordinated hand movements. Less to Dress Putting on the original Freehand was a chore. It consisted of taping the coil antennae and the joystick position in place and running wires from both objects under the shirt to a large black controller that hooked onto the wheelchair. The process, which took about 10 mihutes, usually required some assistance. "The whole idea for these neuroprostheses is to have essentially nothing outside the body," says Dr. Hunter Peckham, director of the Cleveland FES Center. "And that makes it considerably easy for patients because they don‘t have things to put on and take off." Fewer external parts makes life easier for the patient. In the second generation neural hand prosthesis, gone is the cumbersome shoulder-position sensor. And in its place is an implantable joint angle transducer (IJAT) that screws into the small bones of the wrist. The tiny device consists of a titanium encapsulated array of three Hall effect sensors and support circuitry implanted in the radius and an encapsulated rare earth magnet implanted across the joint into the lunate. With the IJAT in place, users control hand movement more naturally with their wrist instead of their shoulder. Dropping the wrist opens the hand, and lifting it closes the hand. For patients who have CS injuries and cannot move their wrists, the device also can be implanted in the shoulder. Another advantage is that because the IJAT receives its power through the IST, the user has one less wire coming down from his chest to plug into the external controller. Caption 2: Neuroprostheses like Freehand give quadriplegics, people paralyzed from the neck down, the ability to use their hands for basic everyday things, like answering a telephone. As an alternative to using the voluntary muscles in the shoulder or wrist to control hand movements, researchers at Cleveland FES are testing devices that read the electric activity of muscles in the arm or neck. "One of the advantages to myoelectric activity is we can use it as a control technique for people who have no wrist control, because their injuries are higher up in their neck," says Peckham. "It would be more difficult to implement but would be applicable to a larger number of people." More Mobility As surgeons got the hang of implanting Freehand in patients, they realized that the eight output channels it offered for muscle stimulation were used up pretty quickly. Although originally, the eighth channel was intended for sensory feedback - a buzzing sound indicated how hard the hand was contracting - it was more often gobbled up for additional motor function in the wrist or fingers. A new IST in the second generation neural prosthesis offers 12 channels. The four additional channels are used to give patients finer grasp, sensory feedback, and as an added bonus, the ability to reach overhead. People with C5 and C6 level injuries often can work their biceps but not their triceps, so they can‘t extend their elbows. The ability to reach overhead opens up a new world for some. "When you think about it, there's a lot of things above your head," says Peckham. "When you're in a grocery store, for instance, you're not just working at eye level or below." A new controller is more good news for patients using the second generation neural hand prosthesis. No longer are they anchored to their wheelchairs by Freehand‘s hefty black box controller, which had to be lugged with them when they moved elsewhere. The new controller resembles a pager, clips on to a belt buckle, and uses AAA batteries. "The old controller was built as a research device to be programmable for multiple devices," Peckham says. The new pager specifically tailored for use with the neural hand prosthesis. Onward and Upward Researchers at the Cleveland FES Center have expanded the technology behind the electronic hands to restore some movement in the legs of quadriplegics so they can stand or transfer themselves out of the wheelchair, to control bladder and bowel function, and to allow some patients to breath without a respirator. Although these neural prostheses give those who are paralyzed a new found freedom, in the scheme of things to come, the devices are still rudimentary. Now in the works at the Cleveland FES Center is an implantable system with a rechargeable battery, a central processor, and a network cable backbone. From a cable extending down the arm or leg, surgeons can attach various simulation and sensor components to meet the individual needs of the patient. Perhaps, in as soon as 10 years, we'll see neuroprostheses that are smarter, more modular, and fully implantable, with no batteries to change and no wires dangling outside the body. Caption 3: The implantable joint angle transducer consists of a series of three Hall effect sensors implanted in the radius and a rare earth magnet screwed into the lunate.