I have one of the most advanced prosthetic arms in the world – and I hate it | Hacker News Reader

I have one of the most advanced prosthetic arms in the world – and I hate it

inputmag.com

Having lived with a relative who used a prosthetic, I saw how it was a struggle every day to get the leg fitting just right, and how fatiguing it was to use for more than an hour. The popular perception seems to be way off here, most people think that modern prosthetics “solve the problem” when in fact, as this article explains, they are inconvenient and painful at best and worse than useless in many cases. I’ve got great respect for prosthetists and the “art” side of their work - the dozens of adjustments they make for each patient - but people should be aware of just how much time, effort, pain and inconvenience prosthetics cause their wearers, the technology is impressive but has a very long way to go.

> It was only three pounds or so, but three pounds feels like a ton to a limb that typically carries no weight, and the heft of the prosthetic hand pulled hard on the socket and made me sweat. In order to open and close, myoelectric hands require that you flex your muscles where sensors inside of the socket can detect your movement.

I wonder how much of the problem is because those muscles are underdeveloped.

Just walk around with a 3 pound weight strapped to your arm and tell me how it feels afterwards.

That's a bit heavier than a large water bottle. 1 liter water is 1 kg = 2.2 lbs. Definitely wouldn't make me sweat.

1 liter of water can be very, very heavy for your arm. Here's an experiment for you: take a bottle of water, lift it up so your arm would make 90° angle and hold it for 3 minutes without lowering your arm. When you carry a bottle, you keep passing it from one hand to another: inability to do so will make it very challenging in probably less than 20min.

That assumes all the weight is at the end of the arm, which it isn't in this case.

I do have a weight on my shoulder: my arm. Holding your arm up for a long time is hard anyway. A human arm weights 8 pounds.

> When you carry a bottle, you keep passing it from one hand to another

That's a good point.

> inability to do so will make it very challenging in probably less than 20min

That seems a bit extreme.

Anyway grip is the part that fails, not the shoulder strength.

>very challenging??

Yes, challenging. It's not the weight of the bottle per se that'd make it difficult but the fact that muscle groups responsible for gripping the bottle can't be relaxed,even for a short period, compared to when changing hands from time to time. I had situations where as simple action as using a screwdriver can make your body sweat like a pig if you overdo it for too long.

> groups responsible for gripping the bottle

The prosthetic user isn't required to grip the arm though. It's strapped on.

Correct. However, a well functioning shoulder is a pretty complex mechanism. If any part of it is removed,the others struggle or fail altogether. A removal of the entire arm, offloads all the work onto the edge of a shoulder that would normally receive help from the arm and its connected muscles. I did break humerus in my left arm,which resulted in functional degradation of my arm: I can't lift heavier things in a certain way, some movements are restricted, the arm gets stiff if I sleep on it,etc.) All in all it's not too bad but that's the result of some muscle damage,so try to imagine how bad it is when the whole arm is missing.

Put your money where your mouth is. Get a 3 pound weight, strap it to your arm. See how comfy you are with it. Or don't, but don't assume you know better without an experiment.

"don't assume you know better" than what? Why is it assumed that I'm wrong by default? Anybody who has an opinion about this can test it themselves.

Because you make a claim that is based on nothing against a claim based on evidence.

I didn't see evidence in either direction. Maybe I missed it?

Question: What exactly makes it so hard to interface with the actual motor nerves directly? The tech to stimulate nerves seems to be regularly used in e.g. cochlear implants. We also can sense neuron activity e g. through EEG. So why are even the most advanced prosthetics still relying on kludges like the "flex to cycle through settings" routine described in the article?

We can read motor nerves invasively (ie after puncturing the skin) quite well, but noninvasive is much worse and often not useful for prosthetic control (although there are exceptions). The problem for invasive monitoring is you then have infection risks in the short-medium term. In the long term, biocompatibility is an issue and leads to tissue reaction to reject the device, impairing signal detection.

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