Introduction: How a Prosthetic Leg Is Made!
Third Prize in the
Full Spectrum Laser Contest
Being an amputee is difficult, no two ways about it.
No matter what the circumstances behind an amputation are for a person, the loss of a limb is almost always a traumatic, strange, and depressing thing to endure and accept. Fortunately the field of orthotics, prosthetics, and physical therapy have advanced tremendously to allow amputees the best quality of life possible through advances in technology and education.
If you've had your leg, or part of your leg amputated you are most commonly an AKA (above the knee/trans-femoral amputation) or a BKA (below the knee/trans tibial amputation) both legs require a few different methods and less or more steps to make.
This instructable will focus on a Below the knee leg because it has the least amount of steps, I will show some various fabrication methods and components along the way.
This is a picture driven Instructable, so follow along with the boxes in the pictures. I took many photos of many different legs while at work so they don't all follow the same project, but the method is the same for my particular O&P practice. Please note that there are a vast number of components and methods out there and each O&P practitioner and/or lab have their own recipe for success, so what you are about to read is not the only way it's done or the "end all beat all", it's just the way we do it at my particular practice. In this field there are many ways to skin the proverbial cat and all that matters is patient care and satisfaction.
The goal of this instructable is to give a glimpse into what we as O&P technicians do to give patients their lives back as best as possible. Even most patients have no idea of the work involved in making their new limb.
I work at a small O&P company in Sacramento. We are lucky to have our own in-house lab which allows us to meet patient needs in a matter of days as opposed to conventional practices forced send out all their work resulting in a 3 week average wait for a patient.
I'm entering this in the Full Spectrum Laser contest, we can do a lot of good things for our patients with the prizes so please vote!
Step 1: Initial Stages of a Leg: the Diagnostic Socket.
The first step in getting a new leg is to be evaluated by your doctor, given a prescription for a prosthesis, then make an appointment with a Prosthetist.
Your prosthetist will need to provide you with a temporary socket to go over your limb. This is used to give your new leg a "test run" so to speak.
Your Prosthetist will first take a cast of your residual limb and hand it off to his or her technician, we technicians fill it with plaster to form a "positive" mold. From that a diagnostic socket (or check socket) is formed from a clear PETG plastic that we bake in an infra-red oven. In the industry this plastic is also commonly called Vivak.
Your practitioner can then use this to test fit a socket to your residual limb. They can also attach components to allow you to stand and walk in it, the plastic's clarity and low melting point allow your practitioner to see where you're feeling pressure and use a torch or heat gun (not while you're wearing it of course) to gently soften the plastic and relieve the areas of pressure. Foam padding can also be added to the interior of this socket if needed.
At the time you have your residual limb cast the practitioner will discuss with you what methods to use in holding you in your new leg.
These methods are typically:
Suction: A one way expulsion valve installed into your socket allows air to be pushed out when inserting your limb, but does not let air back in and holds you in place.
Vacuum: Similar to suction but a pump of some sort sucks air out while you wear your leg creating a negative atmosphere holding you in your socket. This pump can be a piston style device that continuously draws atmosphere as you walk/step and substitutes your pylon (the pipe that makes your leg longer). The vacuum can also be provided by an electronic, removable pump if so desired.
Pin System: You wear a silicone liner over your residual limb which has a serrated pin at the distal (bottom) end that clicks into a lock bolted into the bottom of your socket.
The method chosen will decide what, if any, modifications will need to be made to your positive mold prior to pulling plastic, to make your diagnostic socket. Once the best fit is attained, the socket returns to the lab to begin making your definitive!
Step 2: The Definitive Begins: Single Stage Lamination
After your prosthetist makes the necessary modifications to your diagnostic socket, it returns to the lab and we begin to fabricate your definitive socket.
For pin systems and suction systems we do a single stage lamination. This means our fabric layup goes on all at once and resin is poured only once to finish the socket. We do a single stage lam for suction sockets using a three prong adapter with a plastic liner, but I'll show that in the next step.
We use a variety of fabrics in our layup. They are:
Nylon Stocking: These provide a smoother interior and exterior texture post lamination, we use them as the first and last layers for this reason.
Nyglass Stocking: This fabric is a blend of nylon and fiberglass. It isn't as structurally rigid as conventional fiberglass is, but it is light, stretches well and provides good structure when used in combination with other materials.
Spectracarb: This is a composite fabric of carbon fiber and spectra, this stuff is so tough you can't cut it with scissors and it dulls utility knives in an instant. Because of its toughness it serves as the "backbone" of our layup and makes up the middle layers. For more info on spectra check out this link.
Carbon Fiber: This one requires no introduction. It is light weight and strong, enough said. We will sometimes use carbon fiber exclusively, and other times use it as the interior and exterior of a socket with spectracarb in the middle for added structure. For our purposes, the fiber is tubular rather than in a sheet. The weave is similar to a Chinese finger trap and allows for a snug layup and reflection.
The materials are almost always the same but the quantities of said materials will vary based on a patient's weight and activity level. The more materials used and the more resin involved to laminate it, the more sturdy the socket will be, but it will be heavier and vice versa. Ideally we aim for a finished thickness of about 3/16" with the socket as light and strong as possible.
Step 3: Definitive Socket: Two Stage Lamination.
Two stage laminations are required for vacuum and suction suspension systems.
This means we first pull a thin vivak liner over the positive cast to offer a smooth interior which helps to draw and maintain vacuum/suction. It only takes a scratch the width of a hair to compromise these systems so we take extra care to ensure the plaster mold is baby smooth before pulling the plastic liner. The smoothness of the plastic interior when finished guarantees the sockets success.
After the liner is pulled we place it in the lamination station, sand the surface, and do a layup of just nylon and nyglass and in some cases two layers of spectracarb. Suction sockets normally only require a single stage lamination, but can sometimes require two.
Resin is poured with some pigment and left to cure for about an hour or two. The curing process gives off a lot of heat and it can be sanded as soon as it becomes cool to the touch. We never cut out a socket unless it has cured for at least 8 hours, sanding and grinding at this stage are still safe however.
This initial layup allows for a solid platform to affix a plate to allow an interface for the vacuum system and the rest of the components to complete the leg.
Once the plate is epoxied to the socket we sometimes use bondo to blend it in to the overall shape of the leg, otherwise we simply just proceed with the secondary fabric layup. The plate has a groove around its circumference which allows us to tie it off to reflect it instead of twisting it.
If the patient brings us a cool T-shirt to laminate to the exterior of their socket it gets prepared and stretched on as the last layer prior to pouring resin.
I donated my treasured instructables shirt for this how-to. It's for a good cause and now it's immortalized! Hopefully I'll win another one.
Step 4: Assembly: Finishing Your Leg
After the socket is finished your prosthetist or their technicians will attach the necessary components to complete your leg. These components will be pyramids and various adapters for those pyramids, pylons (pipes made of titanium or aluminum) to make your leg long enough, any vacuum or pin systems to hold you in your leg, a foot that suits your activity level to afford you the best quality of life, and a foot shell for cosmetic aesthetics and to fill the inner space of a shoe.
The following pictures show a rough breakdown of the assembly including a foot shell.
There are many components available, much more than I'm showing. Each selection is chosen on a case by case basis, this field is truly all about custom work. Good O&P practitioners really try to go above and beyond to help their patients and don't quit until you are comfortable. Amputees and their practitioners should form a good working relationship, we strive to earn patients for life and we technicians see work for the same patients cross our paths constantly. This is great because while we techs don't always get introduced to the patients, we get the satisfaction of knowing our patients trust us to return for care and they're satisfied with the work that we do.
Being a patient loyal to a practitioner is vastly different from being a patient of a family doctor. Amputees will see their prosthetist twice a year at the least. Some patients see their prostheitst a few times a week if they are a new amputee, or if their bodies change in a way that doesn't allow them to fit into their socket (think weight gain, loss, or discomfort), and of course malfunctions.
It's a lot like having a mechanic you keep going back to because you really like them and you know does good honest work.
Step 5: Final Notes and Details Not Mentioned.
Come and pay us a visit!
I hope you all enjoyed my instructable shedding some light into a lesser known aspect of the medical field. This is a great profession if you want to make a career out of being a maker, every day is different and demands clever thinking and use of materials you have on hand. It is extremely fun and rewarding to do, it rarely feels like a job.
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Please be positive and constructive.