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#apaperaday: Design requirements of upper extremity supports for daily use in Duchenne muscular dystrophy with severe muscle weakness

In today’s #apaperaday, Prof. Aartsma-Rus reads and comments on the paper titled: Design requirements of upper extremity supports for daily use in Duchenne muscular dystrophy with severe muscle weakness

Today’s pick is from the Journal of Rehabilitation and Assistive Technologies Engineering by Filius et al on the design requirements for upper extremity supports in Duchenne patients with severe weakness. DOI: 10.1177/20556683241228478

Duchenne patients experience loss of muscle tissue and function, starting with the lower extremities, but later also affecting the upper extremities and respiratory muscles.

A wheelchair can help with mobility after losing ambulation, but loss of upper limb function has a major impact on independence & participation. Authors here focus on upper limb support for patients in Brook scale 4, who can move their hand to the mouth but not with a small glass.

There are already arm supports for these individuals but they are not user-friendly and therefore underused. Authors explain that devices can be passive (e.g. with a spring) or active (motorized). As in Brook scale 4 patients are very weak, active devices are needed.

However, patients should still use some force, as when the support system fully takes over, they will not use their muscle and this leads to a loss of muscle tissue and function. Authors here studied patients to assess how to optimally design an arm support.

The work was based on publications and the @duchennecentrum database. Authors studied upper extremity strength and range of motion. Duchenne patients in Brook scale 4 have 2-10% torque in elbow flexors and 3-22% in elbow extensors compared to healthy peers.

For shoulder abductors, this is 4-18% of healthy peers. Also, the range of motion is 130 degrees for the shoulder and the elbow instead of 160 and 150 for healthy peers, respectively. Furthermore, many patients have joint stiffness (increased impedance).

This stiffness is 20 times more than in healthy individuals and increases with time due to reduced muscle strength, but also shorter tendons and muscles and connective tissue in the muscle.

As the upper limb supports need to be fitted, the body dimensions of patients also need to be taken into account. Most Duchenne patients are shorter than average and many are overweight. Further, some patients have scoliosis and all have reduced bone density.

The reduced bone density means the body should not be loaded too much as this may cause e.g. vertebral fractures. Authors also looked into what the upper limb support should and could be doing and what would be nice to haves. For the full table, click here.

The velocity of the motorized support should not be too slow, but also not too fast, as that is dangerous. A human interface must be intuitive and able to control the support. Personalization is important, as is a safety stop. Furthermore, the support must fit through doors.

With a motorized system, there will be a weight and cable issue. Ideally, the system does not make too much noise and definitely the system should not allow overstretching and potentially causing trauma.

Authors discuss options where systems can be operated through the electric signals in the motor neurons, to be picked up with EMG but this is something that requires more work. Authors stress that more work is needed per se, as little data are available for this group of patients.

They caution for overdesigning, making the system unnecessarily complex and expensive. The say that the most pragmatic approach would be to make a system first that has the most important criteria and then improve later upon it, also with feedback from users.

I am not an expert on these devices, but I did find it educational to see the huge amounts of aspects to study and take into account when developing this for Duchenne patients. Appreciate the authors sharing this.