ahead and get started. I want to welcome everybody to the AAP virtual didactics today. We're excited for today's speakers. As always, we want to recognize and appreciate those who have been affected most by this COVID-19 pandemic, recognize that not everyone has been affected equally. So for those of you that have been particularly hard hit, we appreciate you and support you in this difficult time. I want to also make an additional announcement. I've been contacted several times and asked how long these lectures will be hosted in the recorded format on the website that you're looking at right there physiatry.org slash webinars. Yesterday I was contacted by somebody from one of the programs in New York and told that their program specifically has been hard hit in terms of didactics and with a request that these be hosted for an extended period. We discussed it as a committee and these will be hosted online at least through the end of 2020 with the opportunity to go beyond that. You can tell your colleagues who are unable to make it or who may want to review these in the future, they will be available at least through the end of this calendar year. The goals for this again are to augment didactic curricula that are ongoing at your home institutions, to offload overstretched faculty due to some of the logistical difficulties associated with the pandemic, to provide learning opportunities for off-schedule residents again with some of the scheduling changes that have occurred, and then to develop more digital learning opportunities and support physiatrists in general during COVID-19. As always we're going to keep everybody video and audio muted to preserve both bandwidth and attention. If you have any questions, my name is Sterling Herring, so if you click on your participant list you should see me up near the top somewhere. Again, Sterling Herring. You can double click my name and send me any questions that come up over the course of the lecture and then at appropriate question and answer times I can ask those of our presenter. If you have any general questions, suggestions, concerns, that is Candice's email address there on the screen. Candice from AAP and there's a Twitter handle. So without further ado, today's presenter we're excited to have Dr. Rebecca Speckman on. Thank you very much Dr. Speckman. Are you there? Thank you for joining us. It's my pleasure to join. Let me just figure out how to share my screen here. Sure. Click that green share screen arrow and it should ask you if you want to take over from me. There we go. Looks great. All right. Well, Dr. Herring, thank you so much for the invitation to do this and for all the work you've put into organizing. And Candice, I wanted to thank you as well for all of your work. I really appreciate that. So today I'm gonna talk about prosthetic knees and hopefully I'm gonna demystify it for some of you. If it's your first time learning about prosthetic knees, might be more that you're confused and it'll be demystified if you come back to this approach and reviewing things later. Also, before I start, I wanted to thank the University of Utah residents who've given me some really great input on a contextualization for prosthetic knees. So why did I pick this topic? Well, prosthetic componentry and amputation rehab, it's one of our core knowledge areas. And if we understand or get a working knowledge of how prosthetic knees work, that really helps us understand function in persons with transfemoral amputation. But it's really tough to learn. And a lot of the resources that we typically use and are often great, when you read them, it's a little hard to make sense of prosthetic knees. So I think that the more times you hear about prosthetic knees and the more approaches that you hear, that all is gonna help you get to a better understanding. So my prediction, if this is your first lecture on prosthetic knees, is that in three to four years, somebody else will give you your fourth lecture and you'll say, Dr. So-and-so, that was the most amazing lecture I've ever heard. But hopefully this lecture can be that for some of you. All right, so when I think about our knowledge and how we're trying to understand prosthetic knees, I think of it as an iceberg. So what we're seeing above the water, that is what we're hoping to understand as physicians. And my theory is that for a lot of what we know, there's a big amount of expert knowledge underneath that we're just blissfully unaware of and we just are able to operate as doctors with our little bit of working knowledge that we have. But for prosthetics and biomechanics and some other things that we encounter in rehab, we can see underneath the water better and it's very scary. Most of us are not engineers or prosthetists. And so we can see these things that we don't understand, but just tell yourself, it's okay that I don't understand all of the things that are happening here as long as I get some basic working knowledge. Our objectives today, I want you to know the big picture context of rehabilitation for persons with transfemoral amputation. And a real key point is that not everyone is gonna be able to use a prosthesis. Then I want everyone to learn a three category framework for thinking about prosthetic knees. And those three categories are axis, swing control and stance control. And then to know some types of componentry within each category, to understand how microprocessor knees fit into that framework. And then hopefully some of you will think about doing an amputation rehab fellowship someday. But we'll start with big picture, just basic introduction to prosthetic componentry, an introduction to knee and gait biomechanics. And then that is gonna set us up to really talk about prosthetic knees. And I have a lot of pictures of prosthetic knees in here, but I'm not endorsing any particular knees. I'm just trying to give you a lot of different examples. Amputation rehab. I feel like it's the redheaded stepchild sometimes, but actually it has been part of rehabilitation medicine from the beginning. So Dr. Rusk, who was one of the founders of physical medicine and rehabilitation in this great paper in JAMA in the 40s, he said, we need doctors who understand these medical conditions that lead to impaired function because we need a team of experts. But if that team doesn't have a doctor, then you kind of miss the link to patient care. And specifically for amputation rehab, Dr. Rusk said, a physician needs to know that not all limbs are suitable for all amputees and that not every person with an amputation is gonna be able to wear a prosthesis profitably. So in our milestones, in our core knowledge areas, amputation rehab is one of nine areas, I believe, or eight or nine. And today we're talking about a few of the milestones that are explicitly about prosthetic componentry, but we're also touching on things that we think about even aside from the prosthesis. So what does it mean if my patient who has a diabetic foot infection, what does it mean if the surgeons were to do a transmetatarsal, a partial foot amputation versus an above knee amputation or versus a below knee amputation for this patient? So implied in the milestones is that part of our job is to think about functional potential for a patient. And that includes prosthesis candidacy, also includes if they aren't wearing a prosthesis. And I want you all to know we are the only ACGME medical specialty that is supposed to learn this content. So you may meet some surgeons or other folks that know it, but we're the only ones that are really supposed to learn it and who have it on our boards. So we should own this topic. And today we're gonna focus on transfemoral amputation, that's above knee amputation. And I give you a few pictures of persons with transfemoral amputation. Here you go. We call amputated limbs, residual limbs, not stumps, but patients will usually talk about their stump. All right, so part of our setting for transfemoral amputation is to understand that it can be due to trauma, but often lower limb amputation is due to so-called dysvascular disease, which is really two things. It's the downstream effects of diabetes and or peripheral arterial disease. So you might have a person with primarily peripheral arterial disease, often it's overlap between the two. So about two thirds of the amputations are in the setting of diabetes. So putting this together, most of our new above knee amputees, or many of them at least, depending on where you practice, will be elderly with diabetes or dysvascular disease. And another key point is that sometimes amputation rehab, or thinking about a person with amputation gets boiled down to just thinking about them not having a leg, but it's much more complicated than that. So these patients are complex rehabilitation patients. So if the etiology of the amputation was diabetes or peripheral arterial disease, they may have peripheral neuropathy that's so bad that they can't feel their feet or the foot that they have left. They have really impaired balance. Their hands might not work very well because of neuropathy affecting their hands. They often have comorbidities like stroke, things that cause cognitive impairments, cardiopulmonary disease that causes functional impairments. Their contralateral limb might have really severe hip and knee DJD. They might have edema that affects prosthesis use. So it's a really complicated situation. And a person with a traumatic amputation, that can also be very complicated. Maybe they've got more than one amputation. Maybe their contralateral lower limb was limb salvage. And what limb salvage means is usually surgeons were talking to me about amputation, but I convinced them not to amputate. And what you have left is a limb that maybe doesn't have full use of the muscles that it had before, or maybe the joints have post-traumatic DJD or the ankle is fused. May have traumatic brain injury, PTSD, and other neurologic injuries often too. Okay, and then every person who has an amputation almost is not gonna have that limb back. So the exception is that there are transplanted limbs, and that's something that I hope will be able to happen more in the future, but that's certainly not the norm. So even a person who's a really fantastic prosthesis user, who's skiing every weekend, is not gonna use their prosthesis 100% of the time. So it could be that they, well, usually it's not worn at night. And if a person gets up at night to go to the bathroom, are they putting their prosthesis on? Many people don't wanna do that. Maybe come home, wanna take the prosthesis off just to relax. If a person comes to us with a wound on their residual limb, part of our plan is for them, usually if we can accomplish it, to not use their prosthesis while that wound is healing. And then prosthesis fit issues come up. So the socket's too tight, the socket's too loose, and they may be able or not be able to wear it at a given time. And then, especially for transfemoral amputees who are elderly, less than half of them are going to be able to use a prosthesis. And so that number comes from single site studies. So depending on where you practice, you might find it to be more than that, but it's certainly, you don't wanna take it as a given that they're going to be able to benefit from a prosthesis. So as physiatrists, our job is to say, how will this patient achieve mobility and ADLs when they aren't using a prosthesis, or if they can't use a prosthesis at all, in addition to thinking about a prosthesis? Okay. If you have a transfemoral amputation, walking is not the same as walking was before. So a trans-tibial amputation increases the metabolic cost of ambulation a little bit. This is in persons with amputation due to trauma, but if you lose the knee joint, so if you're going up to KD is knee disarticulation, TF is transfemoral, then the metabolic cost of ambulation is increased a fair amount, and it's even more so in the setting of diabetes or dysvascular being the etiology of the amputation. And it's a similar story for rates of metabolic energy expenditure, which is sort of cardiac work. So cardiac work, if we have a person walk at a set walking speed, it's higher for transfemoral versus trans-tibial versus no amputation, higher for dysvascular diabetes versus traumatic. For cardiac work though, a person can walk slower to make the cardiac work similar to what it was when they didn't have an amputation. However, that isn't the case for a person with a dysvascular transfemoral amputation. So how I explain this to patients who are elderly with a new above knee amputation is to say, first of all, walking on your heart is gonna be like running was before, and most people were not running before they have a diabetes or dysvascular amputation. And then to say, there's a threshold of how hard your heart is working, and it might be that your body just can't get above that threshold no matter how much rehabilitation you do. Standing up is also harder for a person with transfemoral amputation. And of course we have to stand before we can walk, it's part of walking. So on the top, so you can look at these graphs if you've seen stuff like this and it makes sense. If it's confusing to you, just try to imagine the scenario I'm describing. On the top, this graph is showing a person with two intact lower limbs. Each of these lines is showing how much force goes through the limb as the person is standing. So as a person with two intact lower limbs stands up, their weight is about equally split between their two legs. In a person with a below knee amputation, they're still getting a fair amount of the weight through the leg that has the amputation, so through the trans-tibial prosthesis. But for a person with a transfemoral amputation and above knee amputation, this is with their prosthesis on. When they stand up, the majority of their weight, almost all of it is in the contralateral limb. So we say to patients, to try to help them understand this, the prosthesis is not gonna stand you up if you get a prosthesis. It's your other leg that will stand you up. And what we then find is that for many persons with amputation, or for some of them at least, they have all those comorbidities that we talked about. They may be deconditioned and they may not be able to stand up with a single limb at modified independent level. So the big picture for us as physiatrists is that when we have a patient with a new above knee amputation, or just when we're thinking about what would that possibility mean for this patient, we have to think about single limb mobility and activities of daily living. And really, prosthetists will understand this situation and some therapists, but not all therapists will understand it. Most patients and other physicians and providers aren't gonna understand it. They're gonna think that you're getting this patient a leg and things will be back to normal once they get their prosthesis. So what does thinking about single limb mobility mean? For some of our patients in working with the therapist and our rehab knowledge and history, we might think this patient, I'm not sure they're gonna get beyond wheelchair level mobility. So is their home accessible? Or maybe we'll think this patient, I think they could get to using forearm crutches and upright single limb ambulation. But if that's the plan, then can they get up and down the stairs in front of their home or inside of their home? And then to keep in mind, as we said before, that for a person who's elderly or with diabetes or dysvascular is the etiology, it might be that a prosthesis doesn't end up helping them. And you might even decide that it doesn't make sense to try. So I might think this, it could be unsafe if I put this patient in a prosthesis, it could be a fall risk, or I could be asking them to put out a really big co-pay when they're probably not gonna end up using this prosthesis. All right, so in thinking about knee and gait biomechanics, there's a few concepts that help you understand why we have the different features of prosthetic knees that we will talk about. Our knees and our other joints have an inherent range of motion. So our knees bend into knee flexion. So when we're squatting or crouching, our knees are flexing and our knees do not bend in the other direction. So we get to extension and the knee is not bending backwards unless something is really wrong with the knee. And what stops our knee from bending backwards, it's the ligaments that are pulled taut when your knee is extended. So when we are standing or when we're walking, if our knees bent, it wants to collapse. It wants to collapse in deflection and we call that buckling. And why does it want to collapse? Because our weight is creating torque or a moment around the knee. And because the range of motion restraints dictate that that's the direction the knee is going to collapse. Think back to our high school physiology or physics, torque or moment is a rotational force. So it's a force applied to a lever about a pivot. And from here on out, we're gonna talk about axis instead of the word pivot. So the axis of rotation is in the middle of a seesaw. And when the weight is placed on an edge of the seesaw, it's creating torque around that axis. And another concept related is that if we move a given weight out further or a given force out further, then that increases the torque because the torque is force times lever arm length. So I like to bring things back to situations that we've experienced or kind of intuitive even before we got to med school. And one of those is, if you were ever trying to strengthen up your quadriceps, you might've learned an exercise, the wall sit exercise. And so you can remember without having to think through biomechanics that if somebody does a wall sit their quads are going to burn they're going to put their hands down on their quads and Have to stand up because their quads are burning so what's happening here from a biomechanics perspective is that This gentleman's weight is trying to pull him down into knee flexion So those knees are trying to collapse further And he's engaging his quadriceps his knee extensors To create an opposing torque to create a knee extension torque to counteract The knee flexion moment created by his weight If you're standing and crouch meaning your knees are sort of bent The same thing is happening your weight's trying to pull you down and collapse that knee and Picture on the right is that your quadriceps your knee extensors are contracting To create a knee extension moment to keep your knee from buckling So To think about for these stick figures, what is the person's weight doing to the knee? What kind of moment is it creating? If we get their weight so that it's a little bit in front of the knee axis. This is on the left Then their weight is creating a knee extension moment just a little bit of the knee extension moment But we said the knee can't buckle into extension it's not going to go backwards because the ligaments stop it Now in the middle picture the knee is a little bit bent. So now the weight is behind the knee axis This knee is going to buckle into flexion if the person doesn't engage their quads On the right the knee is more flexed. So that weight force vector. It's further from the knee So that lever arms further so it's creating more of a knee flexion moment that knee really wants to buckle Unless the person engages their knee extensors So now we're just going to switch to thinking about instead of weight the ground reaction force vector which is the force the ground exerts on the person And the really easy way to think about ground reaction force vector is that if you're standing It's just the opposite of the weight and then if you're walking it's a little more complicated Um, but honestly you can usually just kind of in your mind fudge it and think about the standing situation and get by So same slide we just saw but now we're using the different terminology So the ground reaction force vector is just the opposite of what the weight was before and it's just pointing upwards But if it's easier for you to think what's the weight doing to this person what's gravity trying to do that's fine. Um, I probably do that myself, too All right, so here's ground reaction force vectors, uh illustrated for a person who's walking And in which of these pictures is there? A knee flexion moment just think to yourself for a little bit Okay, so in both pictures the ground reaction force vector is behind the knee so it's behind the axis And it's wanting to make the knee collapse into flexion On the right side the ground reaction force vector is further behind the knee farther behind the knee So there's more of the knee flexion moment on the right As we are thinking about how prosthetic knees work we As we are thinking about how prosthetic knees work we uh, we we talk about How is this part of the knee? What's it doing during the gait cycle? Um, so if you've never been exposed to the gait cycle, we're just going to think about really simple terms right now So stance phase is when your limb is in contact with the ground And you're putting weight through the limb in most of stance phase Swing phase is when you lift that limb off the ground and you're swinging it through forward To prepare for the next time that you put your foot down to enter into stance phase So stance phase limbs on the ground bearing weight swing phase Swinging through and we're bending the knee in order to clear the toe So Prosthesis prescription framework is that We well the knees in the middle and what's above the knee? on the right in our transfemoral prosthesis The socket is the structure that is the communication between the residual limb and the rest of the componentry Suspension is whatever is holding this limb on the person And In this case, it's probably suction suspension Interface is what's between the socket and the limb And then whether it's upper or lower limb prosthesis, we have joints and for an above knee amputation That's the knee and then we have a terminal device Um, and so that's what we say for Upper limb componentry typically instead of hands, but for lower limb, we typically say foot or ankle Okay, we are finally ready to dive into prosthetic knees So first i'll introduce the key attributes or key features that we could use to describe any prosthetic knee That's axis swing control and stance control Then on top of that we'll layer on microprocessor versus not microprocessor And then that is going to set us up to talk about the confusing terminology Now I have a lot of pictures of prosthetic knees just by themselves So I want you to keep these pictures in your minds that are the prosthetic knees in the middle of an entire Prosthesis that is um being used by a person to stand and to walk So as we're going to talk about prosthetic knees So As we Think about what a prosthetic knee does and and how it's designed Prosthetic knees have a similar range of motion to human knees So most prosthetic knees can buckle into flexion, but they're not going to buckle into extension Then during stance phase the primary job of a prosthetic knee is to prevent the knee from buckling And you'll often hear that described as stability or stance phase stability in swing phase the prosthetic knee Is trying to allow toe clearance and bringing the knee through with a bent knee and then ending with the knee Pretty straight to prepare for the next stance phase These three key features axis swing control and stance control if you can Keep these three categories in mind and then the types That's really that will help you unlock understanding prosthetic knees and making sense of things that you read So Knee axis is how does this knee bend? How does the prosthesis bend at the knee? Swing control is what's the mechanism that's controlling forward movement of the foot during swing phase? And stance control is what's the mechanism that's preventing this knee from buckling during stance phase or the mechanism for stability Okay Same slide Now types underneath each of these categories For axis, there's two types single axis and poly centered axis For swing control there's three types constant friction and then two fluid control types together pneumatic and hydraulic And then under stance control we have manual lock weight activated stance and hydraulic stance control I also put polycentric axis in this category And I also think about how the alignment Of the knee affects stance control and we're going to touch on that when we talk about polycentric axis So here's a whole bunch of modern examples of knees and this is to show you that for any of these knees I could pull this knee and say Um, what's if i'm talking with a prosthetist? I might say so. What is the oster balance knee? Um, okay, they might say it's a polycentric axis and it has a manual lock on top Um or for the endolite kx06 How would I describe this knee to someone that doesn't know what it is? If I say it has a polycentric axis hydraulic swing control and hydraulic stance control Then that person If they speak the language is really going to understand what that knee does and how it works And who they would use that knee for So Axis is It is where the rotation is happening and the two types are single axis and polycentric on the left You see some examples of single axis then on the right polycentric The single axis knee is it's like a door hinge So with the single axis knee you could with your finger point to part of the knee and say that is where the rotation Is happening when when the person bends their knee it's bending right there Um, there's not a whole lot more to say about single axis Um, there's a lot of different single axis knees and you could find it in combination With a lot of other types on a lot of or all the types rather of swing control and stance control that we're going to talk about So A polycentric axis or polycentric knee Um is designed to mimic the human knee so for human knees our ligaments allow not just not a door hinge like Motion, but a really complex hinge in the ap plane And in human knees and then prosthetic knees with polycentric axes There's an instantaneous center of rotation that varies so you couldn't point to Where the rotation is happening at a given point in time Unless you're just a biomechanics genius of some sort The polycentric knee in prostheses, I think it's a little easier to understand With old school prostheses, which we don't really see in practice So these pictures in the in the middle and the left are from a prosthesis textbook So in an old school prosthesis, um, you would have situations where the prosthetist would just literally create these links between the socket on top and Something that's like the tibia on the bottom Those links then when they cross over each other are mimicking what our ligaments are doing when we bend our knees And you can see with these pictures that the knee is effectively shortening when it's flexed So in the middle picture that's mimicking If we flex the knee during swing phase You can see how that would help clear the toe from the ground And our next slide we've got This is on the left a diagram for a particular polycentric knee of how the axis of rotation is varying Depending on the flexion angle of the knee So at the very top of this arc on the left zero degrees. That's when the knee is extended and then the So here You can see the arrow. Here's where the axis of rotation is when this knee is extended So think early stance phase and that axis is high and A little posterior compared to if we had a single axis knee where the axis would be somewhere down here Every polycentric knee will have its own arc, but it's always going to be that the axis is high and posterior in extension compared to where a single axis knee would be So on the right another picture showing how the axis of rotation varies through Stance phase and then swing phase and then as they enter stance phase again on the right Now that axis again is high and posterior Um a little bit posterior because their knee is extended there so what does That help with moving the axis of rotation posterior Uh, and a lot of textbooks kind of leave out the high part and just talk about posterior and I think that's good for learning So if you can imagine on this in the person standing straight up Let's say the weight Sorry If the weight is in front of that axis That's giving the person a knee extension moment So what if it were a single axis knee Here and their weight were in the same place They might have a knee flexion moment with a single axis knee but in truth, we um, it's all relative for us when we think about axes and um where the ground reaction force vector is so what we can say is that With the polycentric knee if the knee is extended A person is going to have relatively less knee flexion moment or relatively more knee extension moment Than if it were a single axis knee And that is stabilizing so less flexion moment means less tendency for the knee to buckle So the two key characteristics again of a polycentric axis knee are that it's shorter in flexion That helps us with toe clearance and swing and also makes the limb seem shorter when the person is sitting um, so it just it's it's more symmetrical and has a more natural Cosmesis and then that variable axis of rotation that's relatively Posterior in extension is stabilizing in stance phase and maybe for some people that would be too stabilizing but here's some examples of prosthetic knees and Here you can see that Some might be paired with another mechanism under our stance control heading there We might have an additional mechanism to create stability in stance phase or maybe you don't it just depends on the knee And then they it could be used with various types of swing control as well Now swing control is what how is the prosthesis Controlling the forward rotation or forward movement of the foot during swing phase and um often usually I guess we're trying to have the person who's using a prosthesis be able to Bend their knee to clear that toe because that's more of a natural way of walking And then we're hoping for them to reach nearly full knee extension at the end of swing phase So that then when they go to put weight on that knee it doesn't buckle There's three types of swing control constant friction and then the two under fluid control that's hydraulic and pneumatic In a constant friction swing control knee There is a little clamp that's around the knee bolt. And so this picture is of a single axis knee uh, and so around that single axis, there's this friction mechanism that the prosthetist could adjust But the person who's using the prosthesis is not adjusting themself And and it's not varying as they're walking and so that's why it's called constant friction So a constant friction swing control mechanism It's giving the same amount of friction during swing phase and no matter how fast a person's walking So When do we use that swing control mechanism we use it for somebody who's a single speed Or roughly single speed ambulator. So somebody who's walking Slowly and then their step size also won't be that big So here's a couple of examples down at the bottom of knees with constant friction swing control and these examples represent a much larger collection of knees to show that This often goes with single axis and with weight activated stance control But not exclusively Our other type of swing control with two subcategories is fluid controlled So for fluid control in knees think about fluid in a closed system like a capped syringe And think about that Being behind the knee so I always just I imagine if I just reach down and kind of put this syringe behind my knee and for swing control Um, i'm trying to control knee extension so that my toe doesn't drag on the ground in swing phase So i'm pulling on that syringe behind my knee or pulling on that hydraulic or pneumatic cylinder So Features of Both hydraulic and pneumatic so fluid controlled swing is that we get variable resistance Over the course of a single swing phase, but also that varies depending on the speed of walking. So the swing phase Or the fluid controlled swing control naturally accommodates changing how quickly we walk. So when would we use this for patients who are going to walk faster sometimes and slower sometimes? Here are some examples of knees that have fluid-controlled swing control. You can see it paired with both single or polycentric axis and with some different mechanisms of stance control on the right. It is also possible to have a knee that doesn't have a dedicated swing control mechanism. The downside of not having dedicated swing control is that now your foot, when you lift your leg off the ground, it's just a free swinging pendulum and maybe if you walk too fast it swings forward and kind of hits hard at the end of swing phase and then swings back down. So it's not where you want it to be at the end of swing phase. But it's actually okay if somebody's walking slowly or a single cadence ambulator to have no swing control, but it's still worth noting. So when I talk with a prosthetist or physical therapist about the Kenevo knee, we might say, okay, this knee is single axis, hydraulic stance control, and it doesn't have dedicated swing control. It's still notable to us as a characteristic. Stance control, again, is what is preventing the knee from buckling when the knee's on the, or when the foot's on the ground and the person is putting their weight through their leg. Types of stance control, there's three things that are different from what we've talked about before. That's locking mechanism, weight-activated stance control, and hydraulic stance control. And then we already talked about a polycentric axis as giving us stability in stance phase. So I like to think of it as under the stance control umbrella, but as long as you remember that polycentric knee is stabilizing, that's good enough for you to work through thinking about knees. A locking knee is a knee that literally locks so that it can't move when the knee is extended. The classic locking knee is spring-loaded so that when the patient gets their knee extended and they're not putting weight through the knee, then it locks, or the spring pushes the lock into place. And then that lock is staying engaged until the person unloads the knee and pulls on the cord to disengage it. So if you see a picture of something or see a knee in real life that has a cord, that's a manual locking knee. And we can't see inside these knees into how the lock is actually working, so you can just kind of roughly in your head just think of something like this lock on the left from a knee orthosis joint. So this little metal piece comes down on top of this piece so that the knee is not bending. So there's two things on top of each other that are limited in movement. And here's a picture from an old prosthesis, which you wouldn't see anymore, but how you could have a mechanism where this lever goes down into this little slot and then it can't move once it's down in there. So you don't have to understand exactly how it's working, you just know there's something like this in the knee that's stopping the motion. And here's a locking knee in context of a prosthetic limb. And so you can think about our elderly patient with an above knee amputation, they're reaching down trying to maneuver this cord here as they're sitting down to get their knee to bend. So when would we use a knee that's locked? We already talked about swing phase and we said we like people to be able to move their knee forward, just bend it and move it forward in swing phase. You can't do that with a lock. So you're sacrificing a natural swing phase. So we're only going to use a locking knee if we're really, really worried about stability in a person. So this might be a patient that you think, I'm not sure they're going to use a prosthesis safely. So let's put them in something that literally the knee will not buckle. And I'm willing to accept that this might cause them some gait deviations because it's going to help them build up some muscles and help us know if using a prosthesis is going to work out for this person. The gait deviations that you get from a locking knee are the same as if you're wearing a knee brace or had your knee fixed in extension for some other reason. We get circumduction, vaulting, and hip hike to try to clear the toe or not catch the toe. And here's some examples of locking knees. So there's a fair amount of knees out there that are really simple that are just a single axis and a lock, but there's also some more complex knees that have a lock on top of another stance control mechanism, including one of the microprocessor knees. And so that could be the setting of, I'm hoping we can get this patient to progress to being able to have a swing phase, but we'll start with training with a locked knee and then we're going to let it be a weight activated stance knee or a hydraulic knee. Or locking is also useful for people in many real life situations. So I'm standing up to do the dishes. Some knees have a lock that the person who's wearing the prosthesis can engage at a given time. Okay, I already saw that slide, sorry. Okay, weight activated stance control is a friction clamp or friction break around the axis of rotation. So it's usually used with single axis. There is a knee that does it with polycentric, but we're not going to talk about that knee. So you can think about here's your axis, the thing I can point to where the knee bends, and there's this clamp around the knee that when the person puts their weight through the clamp, it clamps down and then the knee doesn't bend. So this picture on the left, this is my favorite weight activated stance picture because it's easy to see where the axis is and how the clamp is working. So just keep this picture in your head, because it makes more sense than when you look at real life weight activated stance knees. On the right, these are the kind of pictures that you'll often see, sort of the yin and yang look. And here you can still see how the clamp works when weight goes through this clamp, it locks down or breaks very hard. It's not a true lock, and that stops the knee from moving. So it stops the knee from buckling. On the right, so here's an example of weight activated stance in context of a whole prosthesis. And so when you look at it, it looks a little more confusing than on the left, but just keep this picture on the left in your head. To activate the break, the person using the prosthesis puts weight through the knee while the knee is extended. So if the knee is bent and they put weight through it, the break is not going to engage. It's only going to engage when the knee is pretty close to being fully extended. And then, ideally, the break is not going to move once they put their weight through the knee. Although it is possible for the prosthesis to loosen up the break so that it doesn't break as hard. Then to deactivate the break, the person takes their weight off of the leg completely off of the knee or gets the weight onto the toe. In context with the other features, weight activated stance control knees, it's almost always with single axis and usually with constant friction swing control. So you could think of that as a type of knee, single axis, constant friction swing, and weight activated stance. That's pretty common. And weight activated stance has a lot of synonyms, weight activated break, load activated break, and safety knee. And some textbooks call it a stance control knee, but I really don't like that because in practice we talk about those other stance control mechanisms using the term stance control. So when does this make sense? It's for somebody who's not walking too fast because it is a really safe stance control mechanism. Hydraulic stance control, the first thing I want you to note is that we don't have pneumatic stance control. So pneumatic doesn't give us enough resistance to support a person's weight. Hydraulic, which is oil instead of air, does. And then what this stance control mechanism gives us that the others didn't, is that as this person is bending their knee, so as we're thinking about the cylinder behind the knee that I'm now squashing as I bend my knee, I'm still getting resistance as I'm progressively flexing the knee. And that is called yielding. It's a special characteristic of hydraulic stance control knees. And for each knee, the range of motion over which you get that yielding resistance is a little bit different. So you might have a knee that you read the literature on the knee from the company and they say, oh, this has great yielding control. But if you read it or learn about it, it's only for 15 degrees. And that's not really going to help a person go downstairs, for example. So when do we want this yielding resistance that we get with hydraulic stance control? We want it for going down slopes or stairs. And it's often paired with hydraulic pneumatic swing control. So a person who's generally walking faster and then encountering slopes. But in theory, it could also aid somebody who stumbles. And that was one of the original hopes for this stance control mechanism, is that instead of somebody's knee just completely buckling, it's giving them resistance over a larger range of motion. So it's giving them time to catch themselves or giving them more of a controlled fall. But that didn't really pan out with hydraulic stance control knees initially. So here's the first hydraulic stance control knee. Also had hydraulic swing control that hit the market. And so I had this slide to show you. It's a lot more complex than an actual cap syringe. It took rocket engineers decades to develop the hydraulic swing and stance control knee. So that's our three types. Microprocessor knees, it's actually a lot easier than you think. It just layers on top of those things we already learned. Most microprocessor knees are single axis, hydraulic swing control, hydraulic stance control knees. But on top of the things that we already saw, there's a computer that's modulating how much resistance the hydraulics are giving us in swing phase and stance phase. So on the right, this is an X3 microprocessor knee. And you can see the hydraulic unit on the backside of that knee peeking out. How does the hydraulic microprocessor knee work? You have a complex hydraulic cylinder at the core of it, like we saw before. Then on top of that, there's a bunch of sensors that are gathering information about what's the load on the knee, what's the angle and the motion and so forth. And then you have a computer that's taking all that information, putting it together. And the computer is thinking, is this person in stance phase? Are they in swing phase? Did they just stumble and suddenly put weight on their knee when they were in swing phase? And we call that the environment. So the microprocessor is guessing at the so-called environment. And then the microprocessor, the computer, is in turn causing modulation of the hydraulic flexion and extension dampening by, say, opening and closing valves so that you get more fluid movement or less. And then so this would, for example, if the knee has detected that the person stumbled, then it really ramps up the knee flexion dampening so that their knee doesn't buckle. Characteristics of microprocessor, hydraulic swing and stance knees, good stumble recovery, better on slopes, better adaptation to cadence differences, so swing phase, better adaptation to walking faster, and a lower energy requirement to walking. And each microprocessor knee is a little different. So a characteristic of one knee might not hold for other knees. So here's some examples. Most microprocessor knees, as I said, are single axis hydraulic swing and stance. I've included an example that doesn't have any dedicated swing control. Also included an example at the bottom that has pneumatic swing control. And there is one microprocessor knee that's a polycentric axis. So you'd think about that for somebody, say, with a knee disarticulation so that you get the knee shortening effect. Okay, last couple of slides. To make sense of the confusing terminology, here's what textbooks say. And I was so confused when I tried to learn knees the first time as a resident, probably the first couple of times. So my approach is to help you kind of unlock what these things mean. And when you see these different knee types, what they're actually doing is often just focusing on one of those, one of the three things that we talked about and focusing on that. Something else that's confusing is that a book might be describing a historical setup that you wouldn't see in practice. And sometimes the fluid controlled features for swing or characteristics for swing and stance are kind of all jumbled together. And then it's kind of hard to make sense of what it's actually doing. So if you put it back to the categories that I showed you, it'll make sense. But also, I'm probably guilty of this. Sometimes in practice, when we're talking about knees, we just simplify it to one of those things that I talked about. So I want this patient to get better toe clearance. Let's do a polycentric knee. And then there is this magical, mythical beast called a single axis constant friction knee that doesn't have dedicated stance control. This is something that used to be at a lot of knees, and you could still get a knee that is like this. But in practice, it's very rare that you'd have a knee that has a single axis and has swing control, but doesn't also have a stance control mechanism. So if you understand the categories that I presented, what you can figure out from context, usually at least, when I've seen questions about this kind of setting, you can usually figure out, okay, they're talking about a knee that doesn't have a dedicated stance control mechanism. And if you kind of get that, then that will help you answer questions or work through that. So always try to take it back to these three categories and thinking, okay, I might not know this particular knee, but if I go and look up what the manufacturer says about it, I can figure out how to describe its axis, its swing control, and its stance control. And you can understand most prosthetic knees if you have these concepts. The last thing, I did an amputation rehabilitation fellowship at VA Puget Sound and University of Washington, and I highly recommend that fellowship. There's also some great fellowships at VA Richmond and at Tampa. These are all big regional amputation centers for the VA. So you see a lot of stuff and you work with experts that work with a lot of great prosthetists. And it doesn't mean you have to do 100% amputation rehab forever. It just means that you learn that topic a little bit better, which I really enjoyed. But thank you all for your time. I really appreciate the opportunity. And here's some references. Excellent. Thank you so much. This has been really helpful. I know that sometimes it seems like we learn a lot about sockets and fitting, and then there's everything below that. And that's when we just kind of like, you know, mumble through it. One question. So these microprocessor knees, they have a lot of sensors to kind of guess, as you said, kind of guess at the environment. But much of that sensation appears to be limited to the knee itself. So they're saying like, how much load, what's my angle, and my stomach. What data or sensors are shared between the microprocessor knee and any affiliated ankles? Is that a thing? It's not. So the things I showed you are just, it's just the knee, and some of them have a pylon that goes with it that's also collecting data. And there is one I think it's called the Lynx. There is one out there in the market that's an integrated foot microprocessor hydraulic ankle actually with a microprocessor hydraulic knee. Interesting. Okay. So that could potentially contribute more data to kind of help figure out what's going on in the environment. And taking that one step further, are there any efforts to implement data gathering or sharing from the intact limb? So I know, for example, I think Nike can pair with my iPhone for purposes of running. Can we do that same thing with like near field technology or Bluetooth with the opposite knee and the opposite foot?

data gathering

sharing

intact limb

prosthetic knees

technology

advancements

functionality

performance

prosthetic devices