A Case Study on Designing a Passive Feeding-Assistive Orthosis for Arthrogryposis

Passive arm-assistive devices play an important role in the rehabilitation of patients with neuromuscular disorders or injuries by overcoming their motor deficit. Routine human activities such as feeding are not possible without the aid provided by one of these devices or by a caregiver. In this study, a body-powered assistive device was designed for feeding purposes using a compact spherical scissors mechanism and zero-free-length (ZFL) springs (rubber bands) to leverage the patient's residual biceps and healthy triceps function. This partially balanced and lightweight orthosis was also projected to accommodate the spring attachment points closer to the elbow joint center. The performance of the prototype was evaluated on a young adult with bilateral amyoplasia of the biceps due to arthrogryposis who could not initially reach the superior anterior aspect of the close-to-torso region of the reachable three-dimensional (3D) workspace (RWS). That was accomplished by measuring the anatomical RWS of the patient before and while wearing the device. The results show that the patient, with the assistance provided by the device, was able to attain positions in the frontal close-to-torso region of the body that included reaching her mouth, thus enabling independent feeding.