RESNA Annual Conference - 2019

The Design and Development of a Wrist Hand Orthosis

A. Gatto1, S. Sundarrao1, S.L. Carey1
1University of South Florida, Department of Mechanical Engineering


According to the most recent data available through 2016, the United States has approximately 282,000 persons living with a spinal cord injury (SCI), and that number is estimated to increase by nearly 17,000 new cases each year [1]. Between 45%-60% of all reported SCI cases are classified as incomplete quadriplegia, ranking it as the most common category of SCI [1, 2]. The majority of cervical spinal cord injuries occur in the C5-C7 segments, which cause patients to lose upper and lower limb functionality, along with loss of the ability to control certain bodily functions [3]. Among quadriplegic SCI patients, studies have shown that restoring arm and hand function is their highest priority, therefore, providing them the ability to grasp objects will allow for independent completion of activities of daily living (ADLs) that would otherwise require assistance [3-6]. Patients with an incomplete C5-C7 SCI lose prehension abilities, but wrist function is almost universally retained [3, 7-9], thus most prehension rehabilitation techniques apply the tenodesis grasp and release effect. This orthopedic phenomenon takes advantage of retained wrist function and is achieved through wrist extension for grasping and wrist flexion for releasing [7, 8, 10]. However, these motions are exactly opposite to the way able-bodied individuals grasp and release objects. Given that approximately 90% of all SCI cases are non-congenital, the target population was able-bodied prior to their SCI, therefore, if grasping could be achieved through more intuitive motions, rehabilitation could be easier for patients [1,2]. Current wrist-hand orthoses (WHOs) may help with ADL completion, providing some degree of independence, but they cannot be donned/doffed (put on/take off) independently [11], meaning, individuals with a SCI never feel a complete sense of independence.

Figure 1: Prototype: Linkage Assembly (Left), Full WHO Assembly (Middle), Flex Sensor (Right)
This technology is a student-designed powered wrist-hand orthosis to help individuals with a C6- C7 (SCI) independently complete ADLs. This prototyped WHO utilizes a modified tenodesis grasp to operate in a more intuitive manner, allowing for whole-hand gripping and completion of more ADLs. There are only two mechanical linkages: a thumb linkage and an index finger linkage, each configured with a slight angle to mimic the natural bend in fingers during grasping/releasing motions (left image of Figure 1). The current prototype requires securing linkages to respective fingers creating a pincer-like design; index, middle, ring and little fingers are bound as one side and the thumb acts as the other side (middle image of Figure 1). An Arduino microcontroller allowed the orthosis to be programmed to operate via wrist motion input that is detected by a flex sensor on either the dorsal or ventral side of the wrist (right image of Figure 1). Wrist flexion sends a signal to the motor, driving the linkages (and by extension the fingers) into a grasping motion. Conversely, wrist extension creates a releasing motion. The programming allows for smooth grasping and releasing motions, as well as, wrist motion being directly proportional to orthosis grasping/releasing motion.
The main purpose of this study was to test this prototyped WHO on healthy subjects to demonstrate its feasibility in helping individuals with a SCI grasp items and independently complete activities of daily living.


This study showed orthosis feasibility and before testing on the target population, the device was tested on 10 healthy subjects without hand injuries. This approach demonstrated the orthosis as a workable design. Participants were instructed to completely relax their hand, not use their own grip ability, and allow the device to control their fingers during grasping.
Testing began with each participant donning the orthosis and completing a series of ADLs in front of a motion capture (MOCAP) system. Participants used the prototyped WHO to complete ADLs involving feeding, grooming, and donning/doffing the orthosis. These activities are a compilation of ADLs that specifically assess unilateral hand performance of individuals with a SCI [2, 3, 12]. The activities chosen have the greatest likelihood of being completed with this orthosis. Excluded activities, such as acute digital manipulation, are not in the design scope of this orthosis. Success was based on whether the individual could fully complete the task. The activities of daily living included:

  • Feeding
    • Pick up empty and full cup/glass/mug. Drink from full cup/glass/mug
    • Pick-up (horizontal/vertical orientation) & use utensils
    • Pour liquids
  • Grooming
    • Picking up tooth brush (horizontal/vertical orientation) and brush teeth
    • Brushing/Combing Hair (horizontal/vertical orientation)
  • Other
    • Independently Don/Doff orthosis


All participants were able to easily grasp all items placed in a vertical orientation. That is, each had the ability to grasp tapered drinking cups, mugs, and common cylindrical beverage containers on the first attempt. Items that are typically found in a horizontal orientation (utensils, tooth brush, hairbrush, comb) were more difficult for the users to grasp, however, given that participants were healthy subjects, the task was able to be completed after multiple attempts. When these same items were placed in a vertical orientation, participants were able to easily grasp all items. For example, a standing electric toothbrush and toothpaste tube/container that was designed to stand in an upright position. Similar solutions were applied to the other items, such as the hairbrush, comb, and utensils. Again, since testing was completed by healthy subjects, there was little to no difficulty in picking up and using any of the items.
Finally, in order to test the feasibility of whether the orthosis could be donned/doffed independently by an individual with a SCI, participants were told they could only use their other hand in the same way an individual with a SCI would use their other hand to aid in donning/doffing. That is, participants could only use their thumb to hook through Velcro loops or use thumb and index finger to grasp and fasten/unfasten the Velcro strips. None of the participants could independently don/doff the orthosis.


This study was designed to demonstrate orthosis feasibility in helping individuals with a SCI grasp items and independently complete activities of daily living. Observations made during testing, coupled with initial results and feedback from the participants led to the distribution of a survey to the target SCI population. This survey’s aim is to gather information on type (complete or incomplete) and level of SCI, whether wrist function is maintained, and if so, how much wrist flexion/extension exists, prior experience with other orthoses including likes/dislikes, and the what ADLs are most important to the individual. This survey will help the prototyped WHO be re-designed to better fit the needs of the target population. Given that healthy subjects could not independently don/doff the device, the SCI population will also be unsuccessful. Therefore, a main part of the re-design process will include a way for the prototyped WHO to be independently donned/doffed. Results from MOCAP will be analyzed through OpenSim, a modeling software, to optimize key features/parameters of the WHO during the on-going prototyping phase and help define adjustments required for customization. Once the re-design process is complete, the new orthosis will be tested on individuals with a SCI.


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