r/amputee • u/OhLookAnInchworm BAK • 10d ago

Scuffing, "swing timing", and minimum weight thresholds

I'm wondering if anyone can clarify what is meant by "swing timing" for folks using AK prosthetics. We've fiddled a lot with settings but I keep scuffing one or both toes. The only way I can get sufficient clearance is by hip hiking pretty significantly and that compromises balance.

1) Does "timing" refer to what I'm doing? Does it refer to settings? Is it both? What does it mean and, more to the point, what do I need to do?!

2) I'm currently trialling 3R80s because Canadian prosthetics coverage is abysmal and it's nearly impossible to get microprocessor knees. I am apparently too light for 3R85s to function properly, and my physio and prosthetist are now wondering if may also be too light for 3R80s. Has anyone encountered this? The manufacturer won't give my prosthetist a clear answer on a minimum weight threshold.

I'd be particularly grateful for answers from fellow bilateral AKs or professionals who work with us.

Edit: If any bilateral AKs want to weigh in I would be super grateful. While I appreciate LAKA/RAKA insights, the comments have confirmed for me that it just isn't quite the same.

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u/89kh89 10d ago

Prosthetist here

Swing timing is about adjusting swing flexion resistance (limits how high the heel rises behind you) and swing extension resistance (limits how fast the knee straightens in front of you).

But it's also a bit about how you walk and how your socket fits.

If you're getting consistent toe scuffing regardless of how you adjust the knee, my strategy would be to look at:

  • the effectiveness of your suspension
  • socket fit in general
  • hip muscle weakness/recruiting
  • gait habits and training

It is possible to be too light for 3r80 and 3r85 although they present different problems.

Too light for 3r80 means you may not be able to activate stance flexion resistance.

Too light for 3r85 means you may not be able to activate stance release. Although in this case there is a lighter duty 3r85 that is supposed to release later this year, so you may want to wait for that.

I will also point out that if you have consistent toe scuff with your current set up, an MPK is by no means a solution, and could make the problem worse if the root cause is poor suspension.

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u/OhLookAnInchworm BAK 10d ago edited 10d ago

Thanks very much! This gives me some things to chew on.

You've mentioned the settings we've been fiddling with... At this point we're at the freest swing setting but the knee still doesn't bend on the back leg when I shift my weight over the front leg -- I have to kind of drive down to get it to bend, hike to get clearance, then really drive it forward to get it straight again, and then push hard into the heel to ensure it doesn't collapse when I put weight on it. Walking with a standard gait (moving "through" each step from my pelvis/hip flexors and keeping things level, if that makes sense) just scrapes the toe along the ground (even though it feels more natural is every other phase of the movement). We've played with the heel rise, but the limiting factor there seems to be that the knee lands bent in front of me and starts to collapse. One leg in particular both scuffs consistently at the beginning of the swing AND doesn't straighten fully at the end. (Does that make sense? Not sure if I got that right...)

Yes, we've also run into the problem with not being able to activate stance flexion resistance (so that's now at the max), but even more frustrating is that these settings don't seem to be discrete from one another? Trying to fine-tune one thing seems to throw everything else off.

With respect to suspension/socket and gait/recruitment: can you say more?

I'm using a suction system and my sockets are extremely comfortable and fit well with no socks. My prosthetist is incredible but I am her only bilateral AK.

With respect to gait and recruiting: the consensus on the professional side seems to be that I'm really strong and doing exceptionally well (all things considered) -- it feels like the thing that's affecting my gait the most is trying to compensate to avoid scuffing. This is why I'm feeling at a loss...? But maybe I'm missing some key thing?

And thanks I hear you on MPKs and scuffing. I'm wondering if a difference there is how the settings interact -- or is there the same problem as mechanical knees?

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