A New Method to Determine Muscle and Movement Action During Daily Activities in Patients with Neuralgic Amyotrophy

Neuralgic amyotrophy (NA) is a distinct peripheral nervous system disorder which often results in a diffuse paresis with atrophy of the shoulder muscles, and dysfunctional compensatory movement strategies. NA is often accompanied by severe pain initially and subsequent activity limitations, especially those including reaching above 90 degrees and repetitive movement. It seems that NA patients have inefficient motor control of the shoulder girdle with excessive use of proximal scapular musculature. To gain more insight in muscle activation and kinematics of the affected upper extremity we used accelerometry in combination with electromyography (EMG) in order to provide useful feedback for patients and physical or occupational therapists. In a pilot study, 10 NA patients and 10 controls performed a set of daily activities during a 30-minute period alternating light activities (drinking coffee or reading a newspaper) with more demanding activities (placing books on a shelf or reaching high for a jacket). The order of the activities was standardized, but they were free to perform the activities in their own manner. Muscle activity of the serratus anterior, lateral deltoid and trapezius descendens muscles was recorded constantly using surface EMG. The amount of upper arm movement was recorded using a 3D accelerometer placed on the upper arm. The percentage of time EMG activity was above a set threshold and the sum of accelerations in three directions was calculated by adding the signal magnitude area (SMA) of the accelerations. Timing of substantial activity in the EMG and accelerometer signals corresponded very well with the timing of high demanding upper arm activities (e.g. placing books on a shelf and reaching high for a jacket). This method seems promising to provide non-invasive feedback to therapists and patients. Further research and development of a practical measurement tool for therapeutic use are recommended.