An experimental robotic device that provides a "power assist" to weakened muscles shows promising results in improving arm motion in partially paralyzed stroke survivors, according to preliminary research in the April issue of the American Journal of Physical Medicine & Rehabilitation. The principal investigator was Dr. Joel Stein of Harvard Medical School and Chief Medical Officer of Spaulding Rehabilitation Hospital.

The device, which is pending FDA approval, was tested on stroke patients at MIT's Clinical Research Center and at Spaulding Rehabilitation Hospital in Boston. The results show that "the ability of the device to provide a 'power assist' to…muscle groups may help close the feedback loop of brain intention and actual limb movement that is believed to be a key component of cerebral plasticity in motor recovery."

"Exoskeletal or 'wearable' robots can, in principle, provide therapeutic exercise and/or function as powered orthoses to help compensate for chronic weakness," the researchers write.

The wearable, portable neurorobotic device combines a lightweight, motorized elbow brace with a computerized system that detects electrical impulses (electromyographic, or "EMG," signals) from the muscles. The device allows a patient to control affected muscles by attempting to move the arm. The system detects and then processes the EMG signals and translates them into the desired motion, amplifying the movements of the weakened muscles.

"Since motion only occurs in the presence of a patient's EMG signal, the patient, not the machine, is controlling motion of an affected limb, and the robotics is only facilitating motion triggered by the patient's own muscle activity," said Kailas Narendran, research scientist of MIT Active Joint Brace (AJB) and co-founder of Myomo, Inc.

Fellow research scientist and Myomo co-founder John McBean added, "The device functions similar to a car's power steering the patient self-initiates and controls movement and the device provides proportional assistance based on the patient's capability."

Dr. Stein and colleagues performed an initial feasibility study of the AJB in seven stroke survivors with severe weakness and reduced use of one arm. One patient was unable to complete the study because the EMG signals were too weak for the system to read.

Each patient underwent a total of 18 hours of exercise training using the device over a period of six to nine weeks. Each session consisted of approximately 60 minutes of functionally oriented upper extremity task training. All patients were able to successfully control the robotic AJB to help them flex and extend the elbow.

The study showed that patients made significant gains in arm function while not wearing the device. Average score on a standard test of arm movement increased by 23 percent. Scores for muscle spasticity (stiffness) were also improved. There were no complications. Most patients said they enjoyed learning to use the AJB and felt they gained meaningful improvement in elbow control and use of the arm.

"Without the device, many of the individuals we studied were simply unable to complete the movement, and thus had no practical way to improve their performance through practice," said Dr. Stein. "By allowing the user to complete an intended movement though its 'power assist' function, the device helps the user improve his performance through practice. Thus the device acts as a facilitator of the innate capability of the human brain to improve its function through practice."

After a stroke, many patients are left with severe weakness or paralysis on one side of the body. Although current rehabilitation programs can improve functioning to some extent, most individuals with severe arm weakness do not recover satisfactory function. Exercise can stimulate the injured brain's capacity to repair itself, but individuals with severe weakness of the affected muscles may have difficulty in performing the needed exercises.

"This pilot study demonstrates the feasibility of using an EMG-controlled powered exoskeletal orthosis for exercise training in stroke survivors," the researchers write. The results also suggest that the AJB may one day be used to help to improve upper-limb motor function in disabled patients with stroke, brain injury, and other nervous system disorders.

The researchers envision two possible therapeutic uses for the AJB. As in the pilot study, it could be used as an aid to exercise training, either to improve muscle control or to build strength. It might also be used as a powered brace to provide assistance with everyday tasks in patients with chronic weakness or paralysis, such as that caused by spinal cord injuries. More study will be needed to address these issues, along with further development to make the AJB more portable, user-friendly, and comfortable.

About the American Journal of Physical Medicine & Rehabilitation

American Journal of Physical Medicine & Rehabilitation (AJPMR) focuses on the practice, research and educational aspects of physical medicine and rehabilitation. Monthly issues keep physiatrists up-to-date on the optimal functional restoration of patients with disabilities, physical treatment of neuromuscular impairments, the development of new rehabilitative technologies, and the use of electrodiagnostic studies. This well-established journal is the official scholarly publication of the Association of Academic Physiatrists (AAP).

About Lippincott Williams & Wilkins

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