Arthrogryposis Multiplex Congenita (AMC) is a seriously debilitating condition that renders the patient unable to move their arms or legs due to severe lack of muscle development and joint contractures. The most severe form is congenital amyoplasia. These patients typically require assisted living their entire lives to perform even the most basic of daily functions requiring even the most minimal amount of dexterity in their arms or legs. Approximately 1 in 3000 births are affected by this condition, classifying it as a rare disease. As a result, the needs of this group are commonly overlooked because the development of such a specialized device is too difficult and it is more convenient to serve a larger demographic with a more general device. In short, these patients are in need of a solution that will offer autonomy over basic day-to-day activities.

Affordability, Modularity, and Independence.

Patients with arthrogryposis experience a constant struggle to perform daily tasks. In Reid’s case, he possesses very little active mobility in all his limbs that makes eating, playing with toys, and writing very challenging. Tackling these challenges with an innovative device is further complicated by the high growth rate of children. Any custom-fit product will be rapidly grown out of and if the sizing cannot be easily adjusted, it can be very expensive to update. In addition, our device cannot perform the movements for him. Instead, it needs to assist Reid in his desired action as this will promote his cognitive and physical development. Our device aims at addressing each of these needs to provide Reid with a device that has the best impact on his quality of life from any perspective.

The above photos of Reid depict how he has courageously adapted his way of performing daily tasks to gain independence. It is our goal with the development of the upper body exoskeleton to help facilitate these tasks of eating, playing and writing so that he may lead a happier and more fulfilling life.

Rigorous Device Testing

We completed our first validation steps through Solidworks stress simulation, where we were able to validate the loading stresses in our device to make acceptable design choices to avoid buckling or shearing components. Our next step was to analyze the motion of our four bar mechanism using the Solidworks motion analysis tool to ensure Reid would maintain a full range of motion in the device. To ensure the device would be reliable in scenarios where the user is picking up different objects, we tested the integrity of the device with different items that had varying centers of gravity and overall weight. Most recently, we verified the motor and software capability to ensure that the device operates within a useful range of speeds for playing and eating, but also can withstand holding a 500g load on the end of the arm while lifting it vertically. To ensure the safety of the device, we stress tested the mechanical stops by cantilever-loading the arm and allowing the motor to raise and drop weights between its max rotation angle of 110 degrees.

Usability Testing

The goal for this project was to assist Reid in feeding himself, playing with toys, and writing. We designed usability tests around these three main tasks in order to evaluate the device’s performance. As a baseline, Reid was unable to perform any of the three tasks from a seated position without wearing the device. Typically Reid would try to perform these activities lying down, however, he would still require a significant amount of help. Providing him with the ability to complete these tasks while seated would greatly enhance his independence.

Eating

In order to test the effectiveness of the device to assist him in feeding himself, we tasked Reid with bringing a fork with food up to his mouth from a seated position. This activity focused on the simple flexion and extension of the elbow while making him concentrate on flexing to keep the fork by his mouth.

Playing

To evaluate the device’s ability to help Reid in playing with toys, he was tasked to stack blocks from a seated position. This test explored Reid’s motor control planning abilities by adding more complexity to his tasks.

Writing

While testing Reid’s writing capabilities, we focused on the initial steps used for writing in therapy. We began trying simple horizontal/vertical lines and advanced to parallel lines and then shapes. This activity built on his motor planning abilities and challenged his capacity to sequence events. Drawing the simple lines creates an isolated activity to learn, and then parallel lines would build on that skill. Starting in small steps slowly evolves to drawing shapes like a square, then a circle until the ability to write letters is developed.

Modularity

To test the modularity aspect of our device, we adapted our design to Ella, a 13-year-old girl named Ella with merosin deficient muscular dystrophy. We were able to effectively adjust 3D printed beam lengths and body mounting while maintaining the rest of the device constant for Ella, affirming the modularity. 

Device testing proved that our design can:

1. Successfully sustain Reid’s arms vertically for playing and moving while sitting.
2. Support end loads of roughly 600g if lifting directly against gravity.
3. Support different shapes of objects with varying centers of gravity using select portions of elastic bands between the arm and elbow, as well as the elbow and forearm.
4. Ensure the safety of its user while doing everyday tasks through mechanical and electrical stops.
5. Be worn for more than 4 hours due to its low weight (1.6 kg) and skin-sensitive, ergonomic design.  
6. Be serviced easily since each part can be replaced at a small cost if broken.
7. Read the users’ inputs and quantifiably determine intentionality.

From our usability tests, Reid was successful in completing all his tasks, however, we over-estimated his muscular control. We realized a system to help Reid learn to use his muscles will need to be developed. Reid could then gain better control of his device and we can gain a better understanding of his intentionality through the myoelectric sensors. This would be desirable as better control would offer a more natural development for his motor-neuron cortex and expand the usability of this device for more physical development.