Development of an electrically driven elbow orthosis for patients with severe weakness of elbow flexors

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A prominent weakness of shoulder abduction characterizes some cases of cervical spondylosis as an easily recognizable disability. In such patients, the motor deficits also involve external rotators of the shoulder and, to a lesser degree, elbow flexors, usually without a clear sensory loss. This condition called 'cervical spondylotic amyotrophy', 'the dissociated motor loss', or 'the shoulder girdle disc', probably results from segmental cord or root involvement. More recent designation, 'postoperative C-5 radiculopathy', implies a relatively frequent appearance of this syndrome as a neurologic complication of a decompressive cervical spine surgery. As a result of poor recovery of the elbow flexors after severe axon loss, the patients have difficulty in feeding oneself and doing up buttons despite fine finger movement preserved. To provide elbow flexion in such patients, we developed an electrically driven orthosis. We attached a motor (DME44SA-12V, Japan Servo Corp, Japan) with a decelerator (CDF-11-30-2A-R, Harmonic Drive Corp) to the standard elbow orthosis. The electromyographic discharge that was picked up with a pair of surface electrodes placed on the biceps muscle activated the motor. The printed circuit plate was developed so that the motor output can be controlled by the magnitude of the electromyographic discharge of the biceps muscle. Artifacts resulting from 60 Hz interference caused by the electrostatic or electromagnetic fields of nearby electrical appliances were controlled by specifying high- and low-frequency filters. The electric noise occurring when the switch closes and opens and was minimized by shielding the entire circuit.