An Active Orthosis with Tenodesis Effect for Grasp Force Augmentation in Activities of Daily Life

Abstract

Human hand is an indispensable part for interacting with the surroundings and object manipula-tion. Unfortunately for us, millions of people worldwide suffer from hand function impairments and the number is increasing every year. One of the most common causes of impairment is spinal cord injury which is also the major reason of tetraplegia or some form of paralysis in all four limbs. People with immobilized hand find it extremely challenging to perform activities of daily living (ADLs) due to qual-ified upper limb functions. These people need outside interventions in the form of caregivers or assis-tive devices to execute ADLs. One such assistive device is a Tenodesis or a wrist driven orthosis. This is a passive orthosis designed for individuals with C6-C7, the most common levels of spinal cord injury. With this level of injury patients do retain some form of wrist extension but lack finger motion. If wrist extension is voluntary a Tenodesis grasp is possible. Wrist motion is connected with finger motion by a mechanism called Tenodesis effect. The pinch force produced by Tenodesis grasp is minimal. A te-nodesis orthosis or a wrist driven orthosis assist in closing the hand with active wrist extension and opening with gravity assisted wrist flexion using a four bar linkage mechanism enabling patients a pinch grasp. Prior studies have shown a passive Tenodesis orthosis is able to enhance the pinch force but not sufficient to cover a wider range of ADLs. Most of the hand assist devices are externally powered or active orthosis and can produce much higher grasp force than a passive tenodesis orthosis. The availa-ble active orthoses usually suffer from higher design complexity and cost a lot of money. Our goal of this research is to build a low cost 3D printed active orthosis working on the mechanism of Tenodesis effect enabling patients to do a wider range of ADLs.