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Main Question: Would hip attached cybernetic legs result in atrophy of nearby tissue?

Follow-Up Question: How could this be avoided, minimalized or resolved?

Context:

The patient has both of their legs removed up to the hip socket. The other bones of the pelvic region are left intact. For simplicity, let's assume the patient is male.

Hip Structure

The cybernetic legs in question are completely mechanical*. They are not connected to any of the nearby muscles, ligaments, tendons, and the like. The attachment point is the area of the hip socket. The 'connector' used to fix bone to cybernetic leg is something akin to "bolting it on"*.

The cybernetic legs have a fully range of function that is on par with or mildly exceeds that of a normal human's (flesh) legs.

  • By mechanical, I mean that there are no fleshy parts or flesh simulating parts (such as artifical muscles using push-pull muscle-like materials). These legs are basically what we have nowadays for robots (think Boston Dynamics) or as in the T-800/Model 101 (Arnold S.) in Terminator 1. As mentioned, they are not grafted onto any of the muscles, tendons, and so on and are instead completely seperate from the surrounding tissues.

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  • By "bolted on", I mean something like the legs being attached in some way. Honestly, I haven't thought that through, but I'd assume the area of the hip joint has something attached which the legs then attach to or the legs somehow attach directly to the pelvis by some means.

Speculation:

My impression is that muscle atrophy would definitely occur. I'd assume unnecessary tissues would be trimmed away (ligaments, tendons, etc.), but that the muscles would remain for asthetic purposes (along with a host of other probably important biological reasons). However, I'm honestly not entirely sure that this would occur. There definitely seems to be cases where amputees still have a moderate amount of muscle surrounding their amputation point, yet this is probably because the muscles are shifting prosethics (if this is possible) and we could assume that the cybernetics would almost minimize all muscle use down to zero.

Another thing I wonder about is the extent of the muscle wastage. Without any actual use, would the muscles completely atrophy or does the body have some means to deal with this? Long term coma patients and the like often have trouble moving for some time after regaining conciousness due to atrophy caused by the very minimal use of their body's muscles during their time spent in a coma and so it could be assumed that cybernetic legs of the type described could cause similar issues. Maybe postural muscle use accounts for something here?

Otherwise, I figure the easiest way to overcome this issue would be medication. Testostrone comes to mind. Or, perhaps some kind of muscle stimulation like those electric pads people use to 'get abs'. Then again, maybe for the patient just letting the unneeded muscle atrophy is not a concern beyond appearance. Because they can move normally, there's no need to worry about it. I'd really like to hear everyone's thoughts on all of the above. Thanks.

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  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented Feb 10 at 19:25
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    $\begingroup$ This question is profoundly unclear. What specific muscles do you have in mind? I'd say that muscles such as the gluteus maximus (= buttocks) which insert both on the thigh and the pelvic bones will have to be handled with care, because in addition to moving the legs they also serve to keep the upper body erect, so they will clearly have effort to do. Muscles which are entirely in the legs are of course gone with the legs. (And muscles can only pull. They can't push.) $\endgroup$
    – AlexP
    Commented Feb 10 at 19:42
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    $\begingroup$ more often those with prosthetic fear falling and therefore they become less active which leads to atropy... that's just my opinion. $\endgroup$
    – user6760
    Commented Feb 11 at 2:28
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    $\begingroup$ You're asking the question the wrong way. As it is, it should be closed as opinion-based. Theoretically, one would hope to use everything the body can offer to improve the prosthetic experience. Technologically, it may not be possible to do so. That choice is yours, not ours, because we can help you rationalize either choice. And that's what you should be doing: make your choice then asking us to help you rationalize it. $\endgroup$
    – JBH
    Commented Feb 11 at 5:44
  • $\begingroup$ @JBH Sorry if my question was unclear. My question refers to a situation where, for whatever reason, the technology of the cybernetic legs do not attach in with the muscles. My focus was on whether or not atrophy would occur. I'd assume in a future world that the muscles and other tissues would anchor into the tech, but for this example that is not so. The why of that isn't that important, however, because my inquiry is more of a whether or not one with a hint of how can we fix the atrophy situation if it occurs. $\endgroup$
    – user108243
    Commented Feb 11 at 7:56

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If you want something medically accurate, you aren't going to do something like "slice diagonally along the plane of the hip socket." The idea that a prosthetic's extents can be defined by the bones is a fiction.

For instance, the muscle that you use to lift your knee while standing upright connects to the femur, runs through the inner core of the abdomen, and anchors to the pelvis. This passes through any line of connection. You wouldn't get any bionic capabilities without replacing the gluteus maximus because that's the center of our running and jumping power.

A proper medical analysis would have to identify each muscle and decide if it needed to be replaced. Then it would have to figure out how to coordinate the replaced ones with the original ones.

No, you wouldn't get atrophy. Atrophy suggests that you leave muscles in place when you no longer need them. A more likely case would be a lot of cramping during training while the patient tuned the balance of the remaining muscles and the robotic actuators. It could also result in tearing of muscles if they're working against stronger synthetic counterparts.

The cramping and tearing problems would be limited by starting the power levels of the prosthetic low and raising them as the person got used to them. It is inevitable that they would identify at-risk muscles, and alter the procedure and power levels to avoid them, possibly adding the torn muscles to the list of those replaced.

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  • $\begingroup$ This is a solid answer to my question and I am also strongly leaning in the direction myself. Probably a software solution that involves yet doesn't overstrain muscles as well as modifies movement at times to avoid putting too much load on them at any given time is the way. Still, one thing I am interested in is (and I mention this above in another comment) atrophy of muscles that would normally only perform some action on a fleshy leg. Likely there aren't that many that are like this, but where there is do you think atrophy would occur? How could that be resolved? $\endgroup$
    – user108243
    Commented Feb 11 at 8:16
  • $\begingroup$ Atrophy only occurs when you don't use a muscle. If you don't use it anymore, then the only real impact would be aesthetic. That can be handled with implants. You could also apply standard physical therapy practices, but that would be hard if the muscle no longer moves anything. If you absolutely need an answer to this, you could go with "anabolic steroids". $\endgroup$ Commented Feb 11 at 21:46

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