Development of Externally Powered Upper Extremity Orthotic Systems.

In recent years an increasing number of patients are surviving with extensive paralysis which includes the loss of hand and arm movements in both upper extremities. This disability occurs in patients with cord lesions from the fourth to the sixth cervical vertebrae who have survived with tetraplegia, as well as in patients with severe paralysis from poliomyelitis, with central nervous system degeneration, with disorders of the spinal motor system and with myopathies. This short report describes the recent developments of a simple yet very useful externally powered orthotic system for the upper limb which resulted from a three-year research project carried out in the Department of Orthotics at the Texas Institute for Rehabilitation and Research and the Baylor University College of Medicine. The most important objective in developing this method was to restore hand and arm movements to chair-bound tetraplegic patients and others similarly handicapped with flaccid paralysis of various types. A simplified pneumatic system controlled by the patient was developed. Not only has this approach cosmetic appeal, but it also allows the patient the dignity of a separate existence because of the direct participation of the patient in the control of the power as well as being a consciously active part of the orthotic system. Each patient has to be assessed carefully and analysed kinesiologically to determine the patterns of function that remain, the strength and usefulness of the principal muscles serving the desired integrated actions, and where the severe losses are located. The patient must be able to tolerate the sitting position at 80 to 90 degrees. Joint tightness or muscle spasm exclude a patient from this orthotic system. Practical experience has repeatedly shown the futility of imposing upon a patient a complicated mechanism that makes him a passive robot and which does not serve a proportionately useful purpose. Such a mechanism will not be used continuously or effectively if the patient, on his own, can find any other way, even when this involves reduced function. The three principal hand and arm actions considered to 1e most useful and which may be restored by this orthotic system are: 1) finger prehension, as used in grasping objects of moderate size and weight and ofdifferent shapes, such as a pencil, pen, paper or eating utensils, a glass, a cup and similar objects; 2) horizontal actions ofhand and forearm, as used in writing, page turning, and similar actions not requiring very forceful actions at the shoulder joint and which can be given by slight alteration of the position of the head and trunk ; and 3) smoothly combined synchronised action of the upper extremity which includes elbow flexion, shoulder flexion, vertical and horizontal abduction, and medial and lateral rotation. These movements allow patients to eat, wash their faces and do their hair. Power actuator-The power actuator used is a McKibben muscle substitute. This consists of a straight piece of braided dacron sleeving, a gas-tight inner rubber tube with end seals for attaching to pressure tubing. When inflated it expands and shortens. Compressed carbon dioxide is used to inflate the “muscle.” This power source has proved to be most practical because it is generally available and the small cylinder used by the patient can easily be refilled. Also it is non-toxic and inexpensive. Confrol system-The usefulness of actions obtained with a powered orthotic system largely depends on the simplicity and efficiency of the control system, and it is desirable that the patient be in control of this system and not the system in control of the patient. A new principle was discovered in developing a simple valve as a control device, consisting of a flexible silastic tube with a spring-loaded pinching arm capable of depressing the tube