Myoelectric Orthosis restores function to chronic brachial plexus injuries
In 2004, researchers at MIT sought to determine whether myoelectric control technology used in upper extremity prosthetics could be applied to orthotics as a means of supporting and restoring function to a paretic limb. Starting with Spinal Cord Injuries and progressing through chronic stroke, traumatic brain injury, Multiple Sclerosis and ALS, the technology has undergone several generations of improvement that have been commercialized by a spin out company, Myomo Inc. and a custom fabricated myoelectric orthosis, the MyoPro. Leading institutions such as the Mayo Clinic are increasingly using myoelectric orthotics as an assistive device for Brachial Plexus Injuries.
The MyoPro brace is a lightweight elbow orthosis consisting of a motor, myoelectric sensors, a wrist/hand orthosis appropriate for the users' individual abilities, and a rechargeable battery. Patented EMG (electromyography) control software continuously monitors and senses, but does not stimulate, the affected muscles. The user self initiates and achieves natural movement patterns by their own muscular signals that indicate intention to move. The system senses even a very weak EMG muscle signal and then processes data to a motor on the device that enables desired motion. Based on the individual's abilities, system parameters such as response time, sensitivity, and level of assistance are tuned and updated over time. The power assist applies an amount of force proportional to what users exert naturally and can lift upwards of 5 – 7 pounds (about the weight of a small bowling ball). The brace moves when and only to the extent that effort is exerted and has a battery life of several hours. Like myoelectric prosthetics, a myoelectric orthosis is a FDA Class I device. The MyoPro is registered with the FDA as a Limb orthosis (890.3475).
When the user's arm needs support for function, the rigid brace's frame provides medial/lateral support, anterior/posterior support, rotational stability, and hyperextension prevention. Examples of how it is used include:
- Support the weight of a laundry basket. The MyoPro also restricts the motion, in the elbow, to protect the arm and hold the basket. By supporting the arm at the desired angle, the brace then restricts downward motion (and thereby loss of control over the basket).
- Assist in sit-to-stand for a patient's arm that would otherwise buckle or hyperextend. In this case, the MyoPro restricts the motion of hyperextension, and also provides medial-lateral support.
- Support a weak arm to hold a cooking pot in the kitchen. Without this support, the weak arm would not be able to support the pot at the required angle to avoid spilling. Many tasks require different angles when support to a weak arm is needed. In this case, the patient uses the motor to flex to the required angle, then stops. Next, during the carrying task, the brace restricts motion/collapsing of the weakened arm.
- Carry a grocery bag. Simultaneous use of both arms is needed by many patients, especially if they are dependent on a walking aid for balance. Patients with arm weakness often are not able to carry objects because of the medial-lateral forces or hyperextension pressure. The rigid support from the MyoPro will protect the arm from these forces. If the patient lacks movement, the motor will provide assistance.
The concept of myoelectric orthotics & prosthetics is simple. The electrical activity naturally generated by contracting muscle in a paretic or residual limb is amplified, processed, and used to control the flow of electricity from a battery to a motor, which operates a myoelectric orthosis or prosthesis. Myoelectric control was first implemented by Reinhold Reiter in 1945 at Munich University. O&P practitioners have provisioned myoelectric orthotics on a limited basis for decades with the first publication dating back to 1967. Published research conducted since the late 1960s demonstrates myoelectric orthotics restore function to users with a variety of diagnosis and return of a wide range of ADL/IADLs ranging from feeding and grooming to occupational activitiesiii,iv,v,vi. What the MyoPro lends to this body of evidence is a streamlined, lightweight device that can be fabricated and tuned to individual needs.
The MyoPro is ordered by physicians and furnished by certified Orthotics & Prosthetics professionals. During the evaluation consultation, the Orthotist or Prosthetist will provide education regarding aspects of use, ensure the patient is a medically appropriate candidate, discuss insurance benefits, coverage and potential cost.
Each MyoPro brace is custom fitted to the patient using a plaster mold for optimum performance and comfort. Fabrication typically takes 2-4 weeks, the patient will then return for a fitting. During this fitting, the device will be calibrated to the user's individual muscle signal profile and minor adjustments to the brace can be made to optimize comfort. The user will be provided with initial training and a set of take home tasks to practice with the brace donned. Research studies have shown that orthotic and prosthetic users do better when they receive additional training on how to best use their accommodation device. Follow up training may take place at a MyoPro certified therapy or rehabilitation center or at the O&P practice.
Appropriate Candidates include:
- Long term arm weakness or paralysis
- Full Passive Range of Motion, Some Active Range of Motion
- May have mild to moderate flexor tone
- May have some shoulder subluxation
Disqualifying conditions include:
- Elbow contracture or acute injury in the arm
- Shoulder dislocation or subluxation of 3 fingers
- Severe pain in shoulder or arm
- Unable to cognitively participate in therapy activity
- Flexor tone greater than a 3 on the Modified Ashworth Scale
Most commercial payers, Worker's Comp, and the VA are reimbursing for myoelectric orthotics based on medical necessity. There is specific detail required in physician notes addressing patient goals, past interventions including passive orthotics, physical evaluation specific to an orthotic intervention, and justification for it as the least costly and most functional intervention.
- Springer (2004) Powered Upper Limb Prosthetics
- Pudulski (1969) The Boston Arm. Forum IEEE Spectrum 6
- Waring W Antonelli D (1967) Myoelectric Control for a Quadriplegic. Orthopedic and Prosthetic Appliance Journal, vol 21, no 4, pp 255-258
- Prentke E (1969) A Surface Electrode Design for Myoelectric Control. Orthopedic and Prosthetic Appliance Journal, vol 23, no 2, pp 63-67
- Sauter,WF, Bush G (1989) Myoelectrically controlled exoskeletal mobilizer for amytrophic lateral sclerosis (ALS) patients. Prosthetics and Orthotics International, 13:145-148
- Slack M, Berbrayer D. (1992) A myoelectrically controlled Wrist-Hand orthosis for Brachial Plexus Injury. Journal of Prosthetics and Orthotics, vol 4, no 3, pp 171-175