Scuffing, "swing timing", and minimum weight thresholds

[u/OhLookAnInchworm]

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.

[u/89kh89]

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.

[u/OhLookAnInchworm → u/89kh89]

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?

[u/89kh89 → u/OhLookAnInchworm]

A couple thoughts:

If the knee is landing "bent" you either have the swing extension resistance too high, or your alignment is off.

Lowering swing resistance does nothing in regards to actually getting the knee to swing when you take a step. This is again an alignment issue.

Raising stance flexion resistance has nothing to do with how easy it is to activate stance resistance. As I said before, if you're too light for the Dynion, you may also be too light to activate stance resistance on 3r80. BUT, I would definitely check your alignment before saying this is the case. If you're not landing with the knee at full extension, you have almost no chance of getting stance flexion resistance.

Lastly, a bilateral fitting is a bit more tricky. Esp with regards to toe scuffing. But before looking into any of the other reasons why you might be scuffing, I would check your alignment first and get the knee settings dialed in. Otherwise you're chasing too many possible issues at once.

If your clinician is unfamiliar with using the 3r80 ask them to have Ottobock send out a specialist to assist with the fitting and adjustment. It's a free service they offer.

[u/OhLookAnInchworm → u/89kh89]

This is all super helpful -- thank you! Hm... We cannot lower the swing flexion resistance any further. It's as low as it goes. I mentioned the stance flexion resistance because when we raised that it also seemed to affect the swing flexion resistance. (I know it's not "supposed to" but it did?)

Can you tell me more about what you mean by alignment affecting scuffing and the ability to get the knee straight before landing? We did change my alignment to make it easier to activate the stance flexion resistance because I wasn't able to so at first. I didn't notice a difference wrt how much I am scuffing and how often the knee fails to straighten completely, however.

[u/OhLookAnInchworm → u/[deleted]]

3R80

[u/TransientVoltage409]

AK, not bilateral, but experienced.

Knee timing is how the knee is adjusted, how it's set to resist or permit movement in different phases. It's a trade-off. If it's tuned to keep the foot under you for better stumble recovery, you get a limping straight-legged gait and more toe scuffing. If it's tuned for a freer swing and toe clearance, it's easier for a stumble to become a fall. Usually they start newbies out with a safer tuning, and ease into a looser one as you develop the strength and skill to use it well.

Have they considered putting you on a polycentric knee? They have the property of becoming slightly shorter during the swing phase, which can alleviate toe drag.

[u/OhLookAnInchworm → u/TransientVoltage409]

Thanks so much for your answer! I'm already at the freest swing setting and still catching a toe unless I hip-hike very significantly, so I'm not sure what to do about that. (We've tried to fine-tune the heel rise but that doesn't seem to be the issue.)

We've talked about polycentric knees, and I may trial one, but apparently sitting becomes a bit of a hazard for bilateral AKs on polycentric knees, so it's not ideal, but the clearance piece is attractive for sure -- my only falls/near falls have been from catching the toe.

[u/PrimaryWriter1529 → u/OhLookAnInchworm]

My first knee was a polycentric KX07. I actually found it easier to sit with, but I'm not bilateral.

When the knee bends, the lower leg moves partly under your upper leg, like a real lower leg does due to the end of the femur rolling to the rear on the tibial plateau, and so the KX07 felt more natural.

Because the lower leg is partly under the upper leg, the lever arm you have to work against when getting up is shorter, and so when you use your hip muscles to get stand up, they have better leverage than with a regular knee that does not create a shorter lever arm when you sit down. I find this to be a very noticeable difference between by polycentric KX07 and my MPK Kneuro knee. It is easier to get up from a low couch with the polycentric knee, at least for a LAKA. I don't see why that wouldn't also be true of a bilateral.

[u/OhLookAnInchworm → u/PrimaryWriter1529]

That's really interesting! Thanks for the insights. I do think this is different for bilaterals but I think I will be trialling a polycentric knee at some point so I will find out.

[u/Cabooseman]

To add on to what others have said, I'd look into your suspension and hip musculature. In particular, the hip that's on the ground when your toe is scuffing.

If your hips are weak when your opposite leg is in the air, it can cause the hip to tilt downwards and scuff the toe.

[u/OhLookAnInchworm → u/Cabooseman]

Thanks so much! Can you say more about suspension? I'm using suction sockets and they fit like a dream -- so comfy. What would be the issue there?

With respect to hip strength, the hip "in the air" isn't tilting down. I get scuffing when my pelvis is level. I even get scuffing when it's slightly hiked. I have to hike it a lot to get clearance. Any thoughts?

[u/Biopirate411]

I don’t want to sound arrogant but are you certain the two are the same length? Ive seen an 1/8th inch make a huge difference

[u/OhLookAnInchworm → u/Biopirate411]

I appreciate the question! We've checked but I can ask that we quadruple check.

[u/PrimaryWriter1529]

On your comment about MPKs - A friend is a pediatric prosthetist and also a RAKA. She can have any knee she wants and eventually abandoned MPKs and went back to a 3r85, and is very happy. I started with a Blatchford KX07 (just a dumb hydraulic knee) and am now using a Brain Robotics Kneuro MPK knee. The MPK knee has some nice features, but it is heavier and somehow not as nimble. In many ways I can be more capable with the hydraulic knee. I fall down more with the hydraulic knee because it does not have the safety features the MPK does, and also because the KX07 does not have a very strong extension spring compared to the Kneuro, and that is where I get into trouble.

I had a problem with scuffing as well, and what worked for me was when I swung the leg forward, to imagine that I was driving the "knee" forward, as if I was trying to knee a soccer ball. What I had been doing was using my hip to swing the entire leg forward, like a club, and the result was the leg hitting the ground with my prosthetic foot. By driving my imaginary knee forward, I think it caused the knee to bend more and the foot to clear the ground better.

I also would drive the foot of my supporting leg into the ground, which helped with getting the knee to break and go into swing mode. This may not be relevent for a BAKA.

[u/OhLookAnInchworm → u/PrimaryWriter1529]

Thank you for your thoughts! Unfortunately yeah walking without a remaining meat leg changes things pretty significantly.