How a Prosthetic Leg Is Made!




About: I'm a total geek when it comes to tools and craft supplies. Never let me in a hardware or craft store without a leash, I'll just run off.....

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!

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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.

So who get's what componentry?  Who get's the carbon fiber running blade, or the top of the line bionic ankle or knee?
The unknown factor for most of us is a diagnosis for amputees called a K-level.

 K-level basically allows for insurance to pay for commensurate components based on how active your lifestyle is; meaning you will or won't get a carbon fiber running blade or bionic knee or ankle if your lifestyle does or doesn't justify a need for it.  They are all decided on a commensurate lifestyle basis.

The below video is from a Youtube channel I subscribe to, it is done by a gal named Christina, she's known on Youtube as the amputeeOT.
She does a great job of enlightening the rest of us on what it's like to be an amputee, the OT stands for Occupational Therapist which is her profession. 
Therapy is essential for amputees, it can be difficult adapting to a new prosthesis.  Physical and occupational therapy help in getting you on your way to accomplishing your goals of hiking that trail you've always wanted to do, or just to get back into the normal swing of life.  Check out her channel if you'd like to know more.

With a 3D printer we can make an infinite number of our own components and devices to help our patients.  Being self sufficient as a small business with an in house lab is a huge money saver, but we need the equipment.  Patient care and satisfaction afford us to stay in business and the addition of a laser cutter and printer will give us the ability to so much more than what we are currently able to do. 
Medical care is expensive we all know this,  If you haven't seen or heard of the amazing prosthetic hands being made, here's a video showing how effective they are.  I'd be thrilled to be able to make these for patients for a fraction of what conventional prosthetic hands cost.

Once again this is being entered in the full spectrum laser contest so please vote for me and for all the patients at Anchor O&P in Sacramento!
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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    35 Discussions


    5 years ago

    I am a dbtk amputee. I am very handy and workshop orientated. Do you think these instructions would be enough information and tips to make my own sockets since I could not afford them from a medical institution? I have to get around walking on my knees and it starts to wear me out so fast.

    4 replies

    Reply 5 years ago on Introduction

    hi, I'm missing half a leg as well and their damn expensive considering the price of the materials involved. The market price around here is about 6000 euros. Perhaps that's justified by the work hours involved, but the thing is I don't have a job, and therefore on the up-side I've got lot's of time, so I'm converting it back into money so to speak. I'm walking on a prosthesis I got in 1998 and it's kinda falling apart. So I'm looking into repairing it (something that is out of the question with the prosthetists), and making a new one. I can't offer a tutorial since I haven't completed anything yet, but we can exchange thoughts if you'd like.


    Reply 3 years ago

    Hi, i have also lost my leg and am wanting to manufacture my own socket due to the rediculous pricing in the medical field. I have a number of ideas on how to accomplish this but id like to talk to other people for more information.


    Reply 5 years ago on Introduction

    I'm very sorry to hear that.
    Unfortunately I haven't provided enough information or tips for someone untrained to make their own sockets. This was only a rough outline of what's involved in the process, we work closely with practitioners as a team to fine tune any details. If done incorrectly or with the wrong materials, serious health issues or injury could result.
    I'd recommend calling around to your local O&P shops and see if they offer free consultations. They will be able to tell you about any financial strategies you may not know of.
    Cheers and good luck to you.



    Reply 5 years ago on Introduction

    Now if you win cause I voted for you I get to fly on out and have you 3-D print me a NEW LEG right????

    My prosthetist doesn't believe me when I say that this IS the way all of these things will be done in the future. In fact I see a day not that far off where our actual biological LEGS will be 3-D printed---new meaning to "I Made It At Tech Shop"!!!!

    I have seen some of the steps used in making legs--my guy is very good at showing this stuff---but some I had not seen. Very interesting. Am going to have my guy look this over---might be useful to new or even older amps.

    AS to K-Levels---the ins co's like to "downgrade" them and keep you at a lower level as it is generally much cheaper; but then you can't move on. I am not using Cheetah legs and never will but a basic foot was causing me to NOT be able to use ramps etc. I had two valved ankles that FAILED--I won't mention the Co here--and now have one (from a different maker) that works and I can do more.

    Now if we could only get this socket fine tuned! It's an all day deal to go see my "Leg Guy" as it is an hour drive one way and at least an hour or more visit. I love him but---I know it frustrates him as well when we can't get things in order.

    I do find the whole argument that "Socialized Medicine" is WRONG to be a bit odd when you consider that here in the USA we have to FIGHT to even GET a prothesis==I know I did!---and yet in England they are "entitled" to three faux legs--a work leg a sport leg and a dress leg. Now if I am wrong on this you Brits please let me know!!!!!

    And if anyone knows WHERE to donate old but very useable leg pieces and bits--please let me know!!!!

    After my leg was amp'ed our ins co balked at getting me a prosthetic---they approved the amp but apparently had NO plans on getting me walking again. My husband works for a Home Improvement Store and went to the plumbing aisle and got several plungers and took them to the Managers Office and showed them to some visiting VIP's and asked--Which one do you think I should buy for my wife? Gee funny but we DID get approval after that---


    3 years ago

    Thanks for posting. It is fascinating to see how prosthetic legs are made. I have to admit, though, that it doesn't look as difficult as I thought it would be. I'm not saying it looks easy, but that it is fairly strait forward. About how long does it take to complete the entire process?


    5 years ago on Introduction

    Awesome write up! I have a neighbor that lost his leg and we have spent a lot of time together discussing prosthetics. It's a fascinating field to say the least.

    1 reply

    I used extra parts lying around the shop to demonstrate. None of the hardware or components are brand new. By law every patient gets brand new componentry when they get a new leg.


    5 years ago on Introduction

    Awesome tutorial; The vivak sheet part look fun!

    We have a parrot at the sanctuary who came to us with a severed leg from a fight with another bird, I would like to set it up with a prosthetic in the future... I've been playing with some ideas and a friend on facebook was helping me with a gear mechanism that would help it grasp [allowing it to be mobile and perhaps one day climb along its perch again.]

    Thank you again for this tutorial, ill reference it in the future. :)

    1 reply

    5 years ago on Introduction

    Hi Pat Have heard on the BBC about the possibilities for 3D printing bringing prosthetics to those who need them in unfortunate parts of the world. As someone who wears stilts at work at least once a week for 40 years, and a compulsive tinkerer, I am interested in adapting some of the techniques for prosthetics to a better fitting more ergonomic stilt. Any ideas? I don't have a 3D printer or much of a workshop, but I bet there is some market for retrofitting stilts for construction workers, though I suppose the costs through accredited prosthetic shops would be too much for a non-medical need

    2 replies

    Reply 5 years ago on Introduction

    I'm not familiar with stilts or how you wear them, but I would suggest looking intoorthotics. If they strap to your legs then that would be the better avenue to research.


    5 years ago on Introduction

    Oh thank you so much for posting this! I'm looking at going into prosthetics for a career. I've been researching the field but everything written has been very vague so it's nice to see something this detailed. I'm voting for you so good luck and thanks again for the post!!

    1 reply