My New Leg

Okay, the photo is a cheap shot. Yes, my footshell is clearly worn out, but that’s not why I need a new leg. That’s purely a cosmetic problem, and one I’m too lazy to fix. My current foot is a model called the Renegade, which is manufactured by a company called Freedom Innovations. It’s a great foot, but the footshells are poorly designed and the toes break off after a couple months. I went into my prosthetics shop and ordered replacement footshells a couple times, but then gave up. I’m just too busy to be dealing with this on a regular basis. But I would like to be able to take my shoes off in public without looking raggedy. I’ve been an amputee long enough that it doesn’t occur to me there’s anything weird about walking around barefoot with a prosthesis. But I do want it to look sharp, not broken down. It’s one of those small things that matter.

The first reason I need a new leg — and this is more functional than cosmetic — is that the vertical compression on my foot seems to bottom out too easily. Vertical compression refers to how much the foot will compress when you apply a load to it, or how much shock absorption you feel when taking a step onto the foot. Like many other carbon fiber “energy storing” feet, the Renegade has a heel designed to compress and absorb shock when you put weight on it. And the keel, or forward part of the foot, is designed to provide some spring as you roll over the foot and off the toes. Essentially, you’re walking on a spring: you compress the spring when you step onto it, and the spring stores the energy and then releases it when you step off.

Ideally, this whole process of taking a step should feel very smooth and fluid. When I land on my prosthetic foot, I like to feel some “give” as the heel absorbs my weight. But if the heel compresses too much, it feels as though I’m stepping into a hole, and if it doesn’t compress enough, it feels jarring — especially if stepping off a curb or when carrying a weight. When I roll over the foot and off the toes, I like to feel some spring or bounce. But if the keel is too soft and doesn’t provide enough spring, it feels like I’m falling off the foot rather suddenly. And if the keel is too stiff, it feels like my foot is too long and I’m being catapulted over it. If you’re a fast walker like me, this also gives you the disconcerting feeling of being launched out of a slingshot every time you step off the foot because it provides too much spring.

Ideally, I want to feel like walking is an unconsciously cooperative effort between me and my prosthesis — not like I’m lugging it around behind me, and not like it’s taking me for a quick, bouncy spin around the block.

I really do like the Renegade’s keel. It’s not too springy and not too mushy, and feels smooth when I roll over and step off it. In fact, it’s so nice that I really take it for granted, which is exactly what you want in a prosthetic foot: to not have to consciously think about it. But when I said above that the vertical compression bottoms out, I mean that I can feel the heel compress all the way and then stop when I step down, which is a jarring feeling. This happens sometimes, usually when walking quickly or carrying additional weight.

There may be a few reasons for this:

• I walk very quickly sometimes, which loads the foot more heavily.
• I’m often carrying one of my kids, which increases my body weight about 20-25%, or a child and bag of groceries, which increases my body weight even more.
• I’ve been stomping around on this foot for a few years now and seem to remember the heel had a better loading response when it was newer. Does carbon fiber lose its kinetic properties over time?

Amputees do often have to carry children (or grandchildren), groceries, luggage, gardening and building supplies, and so on. Feet are designed for various body weights (a person weighing 300 pounds needs a stiffer foot than I do at 150 pounds) but not for extreme variation in one person’s body weight. If I start walking quickly, or pick up a child weighing 30 pounds, or lift two heavy bags of groceries, my foot fails to respond to the sudden extreme increase in body weight and/or load. I suspect this is a general limitation of prosthetic feet, not of the Renegade in particular, but I’m still curious to see if I find something with a smoother loading response when walking, especially with a load.

But the most important reason I need a new leg is that my stump changed shape over the winter, and my socket doesn’t fit as well as it used to. While footshells, feet, and many other modular components of prostheses can be replaced, the socket is the most crucial part of a prosthesis: it is the interface between one’s stump and the rest of the prosthesis. It is custom made for each prosthesis, requires a lot of skill and labor to fit well, and can’t simply be swapped out without replacing the entire prosthesis.

Stumps are an artificial body part themselves and, unlike feet, are not designed to bear weight. Trust me, putting much weight on the end of one’s tibia (or other sensitive areas of a stump) really, really hurts. So the trick with sockets is to comfortably support the amputee’s weight in the right places, fit it closely enough to provide proprioception to the closest joint and accurately enough to help the amputee walk well, yet allow enough padding to be comfortable.

The most common socket design for below-knee amputees (currently, in America, at least) is called patellar-tendon bearing (PTB), meaning that it supports most of your weight on the patellar tendon, the strong tendon connecting your kneecap to your tibia, or shinbone. PTB sockets also support some weight in the popliteal area, behind your knee and are supposed to be “total contact,” meaning they fit closely to the entire surface of the stump to prevent movement and wobble inside the socket.

This is a challenge for prosthetists to do well. If the socket is too tight, or too loose, or too long, or too short, or suffers from any one of a host of potential inaccuracies, it will hurt. And if it hurts, why wear it? And, even under the best of circumstances, it’s a challenge for amputees to become accustomed to prostheses. Encasing your stump in a 7mm thick silicone liner and a cloth sock, stuffing it into a snug carbon fiber shell, and then walking on it takes some getting used to — particularly for new amputees.

And, getting back to my current problem, stumps may be artificially created body parts, but they are still body parts. And like the rest of your body, they change shape depending on your diet, how much fluid and/or salt you intake, your level of physical exercise, the weather, your age, and other contextual factors. My stump has changed shape over the years as my calf muscles have gradually atrophied (without an ankle, not much need for muscles to control it), and it changes shape from day to day, and even over the course of a day, depending on the factors above.

This past winter, my stump went through a series of drastic changes in shape and atrophied further. I lost the “total contact” fit in my socket because my stump was smaller and didn’t fit so accurately. This, in turn, caused my knee (the patellar tendon and popliteal area) to support more of my weight, which both caused my prosthesis to feel slightly loose and lead to skin irritations and sores on the sides of my knee and behind it. The end result was that I spent too much of last winter feeling a little cranky and walking with a limp. Those problems have since resolved themselves, but the socket fit is still not as accurate as I would like it to be.

Had my prosthetist known about this, he probably would have been cranky, himself, that I didn’t drop into the shop to have him make adjustments to the socket to resolve the problem. He’s a great clinician as well as a superb craftsman and, like any good prosthetist, is concerned for his patients’ comfort. But I was super busy this past winter and kept procrastinating taking a day off to go into San Francisco and deal with it, figuring, “Oh, I need a new leg, anyway. I’ll just make some phone calls and take care of it next week…”. But after all these years I really should know better, which reminds me of…

Lesson #1: If your prosthesis hurts, call your prosthetist. It may not be comfortable 100% of the time, but it should never hurt.

But now my COBRA health insurance will run out on June 1 and I really need to get moving on getting a new leg, which highlights good general advice:

Lesson #2: Don’t procrastinate, especially important health care stuff.