Myoelectric Prosthetic Componentry Is Coming Of Age

High-Tech Prosthetics for Upper-Limb Amputees

Having evolved gradually over the last three decades, myoelectric systems for upper-limb amputees are hitting their stride. Technological advances in the computer industry, in motor and battery design, and even in cell phones and hand-held video wizardry have been put to use to aid in the search for highly functional prosthetic systems.

By means of surface electrodes embedded in the prosthesis socket, myoelectric systems detect and amplify muscle action potentials from voluntarily contracting muscles in the residual limb. These signals control one or more motors to actuate terminal device movement, wrist rotation and/or elbow flexion and extension.

Programmable microprocessor circuits have reduced the need for laborious adjustments in these advanced prostheses. Advanced sensory controls and lighter, more durable batteries are making upper-limb prosthetics more adaptable for the majority of patients and easier to adjust as their capabilities change.

Specialized prosthetic manufacturers have developed comprehensive systems for replacement of hands, wrists, elbows and even shoulders. The two highlighted below have passed through several generations of design and innovation, assisted by feedback from rehabilitation professionals and patients.

The Boston Digital Arm System from Liberating Technologies incorporates a variety of advanced control features to augment the function of the company’s core product, the Boston Elbow. The system’s advanced microprocessors can control up to four other prosthetic devices in addition to the elbow – hand, wrist rotator, shoulder lock actuator, etc. Recent digital improvements now enable settings and adjustments to be made even while the patient is wearing the prosthesis. The internal microprocessor also allows for monitoring the system as it is being worn. These improvements reduce the need for prosthesis downtime for disassembly and adjustments.

Motion Control’s Utah Arm 3, the latest version of the pioneering system that first appeared a quarter-century ago, incorporates microprocessor technology and a computer interface to allow either the wearer or prosthetist to fine tune adjustments to the system. The Utah Arm 3 incorporates proportional control, which allows the wearer to move the arm and hand slowly or quickly in any position, providing more natural movement with less effort. Another significant Utah Arm 3 advance is that wearers can control its elbow and hand function simultaneously.

Additional notable componentry innovations include:

• The Otto Bock Sensor-Hand SPEED electric terminal device adds a quieter motor and unprecedented opening and closing speed to its SensorHand “Autograsp” technology, which senses when an object held in the hand requires more grip force, then automatically adjusts tension, such as when filling a glass with water.
• Motion Control’s powered terminal devices for the Utah Arm system include several hand components and a water-resistant hook-type component known as the ETD or Electric Terminal Device. The ETD’s hook “fingers” generally permit finer functioning than hand-type fingers. Moreover, its ability to resist liquids allows wearers to engage in “wet” activities of daily living, such as showering, with the device in place.
• Motion Control hands and the ETD all can be equipped with a new option called the Flexion Wrist, which can be set to one of three positions, allowing wearer the to flex or extend the wrist thus placing the hand in a more natural position for performing specific tasks.
• Liberating Technologies’ recently introduced LTI Locking Shoulder Joint for high-level deficiencies is designed to provide a free-swinging joint that can also be locked in multiple positions, as required, with either manual or electronic control. Its lighter weight and relatively smaller profile make this component adaptable for both pediatric and adult use.
• As electric prostheses have become more functional, the need for a reliable, longer-lasting power source has become more critical. Recently improved lithium ion battery packs provide all-day power, if used appropriately, from a surprisingly lightweight package.

Please call LeTourneau & Family Orthotics and Prosthetics today for your free initial consultation. Offices are located in Beaumont, Jasper and Nederland, Texas.