What Is a Prosthetic Socket: Function and Fititng

Prosthetic sockets are devices that join your residual limb to the prosthesis. Each prosthetic socket is unique as it is made for the individual who will be wearing it. As you can imagine, one of the most important parts of a prosthetic socket is ensuring that it fits comfortably so that it helps amputees and allows them to live a functional and full life. At PrimeCare Orthotics & Prosthetics, we excel in the art and science of personalized socket manufacturing, creating bespoke devices tailored to your needs. In this article, we&#;ll provide a comprehensive understanding of how they work.

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What Is a Prosthetic Socket?

A socket is an interface between a residual limb (stump) and a prosthetic device. This custom-made sleeve fits snugly around the end of the residual limb. It creates a suction seal that allows the prosthesis to distribute an amputee's weight and facilitates their movement, making it fluid and comfortable.

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Sockets are custom-made to fit the individual amputee's residual limb and may have various features to provide support, stability, and comfort.

Some of the most common features of prosthetic sockets include:

• &#;A suction seal: This helps to create a secure fit between the socket and the residual limb.&#;
• A liner: This is a soft, cushioned layer that distributes pressure and reduces friction.&#;
• A suspension system: This keeps the prosthesis in place and prevents too much socket rotation and slippage.&#;
• Adjustment features: These features allow the prosthetist to make fine-tuning adjustments to the socket fit.

What Are Prosthetic Sockets Made Of?

Today&#;s prosthetic sockets are made of modern plastic and silicone materials as they offer a good mixture of comfort and functionality for the patient. It&#;s also common to see materials such as aluminum, stainless steel, carbon, and titanium in prosthetic connective componentry. The use of these materials is relatively new as more research and technology help to modernize and improve the prosthetic socket design. Some of the first lower-limb sockets were made from wood and leather.

How Do Prosthetic Sockets Work?

During the fitting process, you&#;ll work directly with a prosthetist to create a check (test) socket. This is a clear socket that helps the prosthetist understand if any areas cause too much pressure or redness. If you try your check socket and you are having issues with its comfortability or wearability, it can easily be modified to better suit the shape of your limb. The prosthetic socket shouldn&#;t just fit properly, but also have adequate load transmission to ensure stability and control for the patient.

Most Common Prosthetic Socket Type

While there are different options when it comes to prosthetic socket types, most use the PTB SC (Patellar Tendon Bearing Supracondylar) socket for lower-limb amputations. With this type of design, the weight bearing takes place at the patellar tendon which is located underneath the patella. This is often used across the world as the most basic design for fitting medium and long stumps. One upside to this type of socket is that the design doesn&#;t result in blood circulation problems or atrophy.

Other types of prosthetic sockets used in prosthetic design:

• &#;Total Surface-Bearing (TSB) sockets with gel interfaces offer pressure distribution across the entire limb surface, benefiting those with scar tissue or chronic skin issues.&#;
• Hydrostatic weight-bearing sockets, a variation of TSB, promote tissue elongation and reduce skin breakdown risks.&#;
• Ischial Containment (I.C.) sockets are common in above-knee designs, encapsulating the ischium within the socket for enhanced comfort and stability.&#;
• Marlo Anatomical Sockets provide increased hip motion range and discreetness under clothing for female above-knee amputees.
• For upper-limb sockets, both body-powered and externally powered systems are utilized, with socket design critical for maintaining control and suspension throughout the range of motion.

The Importance of a Good Amputee Socket Fitting

The correct amputee socket fitting is essential for the comfort and function of prosthetic legs and arms. Adjusting the fit of a prosthesis to the correct level of comfort is vital for the following:

• Comfort: The right socket reduces pressure and friction on the residual limb, preventing pain and discomfort, which is essential for those with sensitive skin or prone to developing pressure sores.
• Functionality: A snug socket allows amputees to use their prostheses effectively and comfortably, making walking, running, and participating in activities easier.
• Confidence: A well-fitted socket ensures amputees feel confident and independent, improving their quality of life.

If you are an amputee, it is essential to work with a qualified prosthetist to ensure that you have a well-fitted, weight-bearing socket. They will rectify any prosthesis fit issues to achieve the best possible results from your prosthetic device.

The Prosthesis Fitting Process &#; What to Expect

We're often asked, "When is a prosthesis fitted after amputation?"

Regardless of whether it's an above-the-knee or below-knee amputation prosthesis fitting, the process for a new amputee only begins after the swelling in the residual limb has subsided, and the suture line has healed, which usually takes four to six weeks after surgery.

General things you can expect during the fitting process:

• Your physician will prescribe a prosthesis once the limb has healed. They and your insurance company (or other payers) will determine the timing of the fitting.
• As a prosthetic user, your prosthetist will discuss your rehabilitation goals and expectations for everyday life, so they can customize your device to fit your lifestyle and daily needs.  

The fitting process can take several weeks or even months, as your prosthetist will need to adjust the socket and other components as your residual limb changes shape and size. Be patient and work closely with your prosthetist to ensure you have a well-fitting prosthesis that meets your needs.

&#; Fitting the Temporary Socket

The next step in the fitting process is creating a temporary socket. New amputees receive a temporary prosthesis for a few months as their residual limb continues to reduce in size and mature.

However, those who have worn a prosthesis before have a much shorter fitting process &#; a few days to a few weeks.

Below are some of the things you can expect during this stage of the prosthetic socket fitting process:

• Your prosthetist will create test sockets to see how your residual limb responds to them.
• Other components are added as you start to stand and walk or use your arm and hand. The temporary prosthesis does not usually have a cosmetic covering, as adjustments will need to be made continually as the residual limb decreases in size.
• Physical therapy is an integral part of your recovery and rehabilitation process. Your physical therapist will design a rehabilitation plan that suits your lifestyle goals. Some people may also need to have occupational therapy.

Remember that the temporary prosthesis may not be perfect, but it will allow you to start using your prosthesis and regain your independence.

As your residual limb changes shape and size, your prosthetist will adjust the prosthetic design. At PrimeCare, we monitor your progress with an app that provides important data for the final fitting.

Eventually, you will have a permanent prosthesis that meets your needs.

&#; Fitting the Final (Definitive) Prosthesis

The final stage of the fitting process is the definitive prosthesis. This is the permanent prosthesis you will use in the long term.

Your prosthetist determines the timing of casting for the definitive prosthesis. For new amputees, it is usually done several months after surgery to allow the residual limb to heal and stabilize in size and shape. However, experienced prosthetic users may undergo casting more quickly as they are accustomed to the process and adjustments.

Here are some of the things you can expect during this stage of the fitting process:

• Your prosthetist will create a final custom socket and attach all other prosthesis components to it.
• There will be options for a cosmetic covering.
• The creation and fitting of the definitive prosthesis will require several visits and can take a few weeks to complete.

The terms "final" or "definitive" prosthesis are not necessarily absolute, meaning no prosthetic leg or arm will last forever. A prosthesis can last anywhere from two to five years, depending on daily usage and activity level.

In some cases, the prosthesis may need repairs. At other times, only single components may require replacement rather than creating an entirely new prosthesis.

Tips for Fitting a Prosthesis Socket

It's normal for your residual limb volume to fluctuate during rehabilitation. To prevent pain and discomfort and improve the fit of your prosthesis, you should:

&#; Get the Right Liner

If your socket is too loose, switch to a thicker liner to create a snug fit and reduce the amount of movement within the socket. You may also need to reduce the number of plies (layers of fabric) in your prosthetic sock.

If your socket is too tight, switch to a thinner liner to reduce the pressure on your residual limb. You may also need to add a thin sock to take up extra volume within the socket.

Some specific recommendations:

• If you have an above-the-knee prosthetic, switch to a 9mm liner, and reduce the number of plies in your prosthetic sock by 10-15. This usually helps knee amputees manage any rotation they may have been experiencing in their prosthetic leg.
• If you have a below-the-knee prosthetic, switching to a 9mm liner can make it easier to bend your knee, as the liner still features a 3mm thickness in the back, which avoids knee flexion restrictions.

It is important to note that these are just general recommendations. The best way to determine which liner thickness is right for you is to consult your prosthetist. They will be able to assess your needs and make a recommendation based on your situation.

&#; Consider a Gel Sheath

Consider using a gel sheath or sock if your prosthetic socket feels loose. You can wear this thin, flexible sleeve over or under your prosthetic liner.

Here's how a gel sheath can improve your prosthetic fit:

• Increases cushioning: Extra cushioning between the liner and the residual limb reduces pressure and prevents skin irritation.
• Reduces friction: A gel sheath reduces friction between the liner and the residual limb, which prevents the liner from slipping or bunching up.
• Improves suspension: Better suspension creates a more snug fit between the liner and residual limb.
• Absorbs moisture: Moisture absorption prevents skin irritation and keeps the limb cool and dry.
• Customized fit: Customization ensures a comfortable and functional fit.

Talk to your prosthetist to determine if a gel sheath suits you.

Quality Care with PrimeCare Orthotics & Prosthetics

For any further questions regarding prosthetic sockets, or if you're ready to take the next step toward enhancing your mobility, our compassionate team is here to assist you. At PrimeCare Orthotics & Prosthetics, we are dedicated to empowering our patients with mobility and confidence.

We&#;ve aided over 30,000 individuals and specialize in lower- and upper-limb prosthetics, other prosthetic components, and customized socket shapes tailored to your needs. Contact us today to learn more about how we can support you on your journey.

The process of moulding a socket is often seen as an art and requires great skill of a prosthetist. The socket needs to conform perfectly to the patient&#;s stump so that it feels comfortable but still offers the necessary support.

One way to create a prosthetic socket is by using the bubble-forming method: a thermoplastic socket material is heated in an infrared or convection oven until it starts to drop into a bubble-like shape. The bubble is then pulled over a positive mould of the patient&#;s stump and is left to harden completely. This method results in a socket that neatly conforms to the patient&#;s contours and gives the prosthesis a secure fit.

Follow along as we take you through all the steps of moulding a prosthetic socket using the bubble-forming method.

Step 1: Create a foam or plaster positive mould

Before you can start moulding any prosthetic socket, you need a good positive mould. Read our 5 tips on forming and positioning the perfect positive mould here.

For more Prosthetic equipment speed Socket Routerinformation, please contact us. We will provide professional answers.

Step 2: Prepare and heat the thermoplastic sheet

1. Preheat your convection or infrared oven (for this article we are using an infrared oven) at the correct temperature. The diagram below gives an overview of all Orfit&#;s socket materials and the corresponding heating temperatures. We also recommend reading our blog post about the ideal heating technique for Orfitrans Stiff.

(Click to enlarge)

2. Remove the protective foil on both sides of the thermoplastic sheet, there is one on all Orfitrans products. This protective foil helps to prevent scratches on the material and protects against the absorption of moisture, but once you are ready to mould it is very important to remove it. Otherwise, the Orfitrans sheet will not drop in the oven.

3. Wedge the thermoplastic sheet firmly into a supporting frame.

4. Place the frame on a support rack and make sure that there is enough space for the bubble to form and drop in the oven.

5. Place the sheet into the oven and allow the bubble to form. We usually recommend to let the bubble drop 2/3 the length of the socket.

6. Take the sheet out of the oven with heat-resistant gloves.

Step 3: Pull the sheet over the positive mould

1. Turn the bubbled sheet upside down with the convex side pointing upwards.

2. Before you start moulding, take a look at the different sides of your positive mould. The socket shape usually has shorter and longer sides and you will need more thermoplastic material to cover the longer sides. You can position the bubble slightly off-centre over the top of the positive mould.

3. Take account of the stiffness of your thermoplastic sheet:
   • Stiff materials: Use light pressure to pull the material down. Do this very slowly and make sure that you do not twist the material &#; keep the sheet straight.
   • Soft materials: Support the material and make sure it does not drop too quickly.
     Give the thermoplastic the chance to conform to the mould in smooth and fluid movements in order to avoid bulging and unevenness.

4. Let the sheet drop to the proximal sides of the mould.

5. Activate the vacuum very slowly to reach a vacuum pressure of 0,2 bar.

6. Then, let it drop further down to the edges of the vacuum baseplate.

7. Optionally, you can lightly press the thermoplastic material against the positive mould, while wearing your gloves, to let the sheet conform even more.

8. Let the thermoplastic sheet cool down entirely on the positive mould. The longer you can leave it to cool down the better, as this will guarantee that the socket keeps its shape. We usually recommend a cooling time of 24 hours.

Step 4: Remove the socket from the positive mould

When the socket has cooled down, saw off the material just above the proximal edge of the socket. Now you can slide the socket off or break out your positive mould.

Step 5: Finish the prosthetic socket

1. Sand the edges of the socket with a router socket machine fitted with sanding rolls. Begin with a grit of 40 and then switch to a grit of 80.

2. Use silicone polishing cones to give the edges a nice finish. Make sure to install your milling machine to a maximum of rpm. A higher amount of revs will generate too much heat and could potentially melt the material.

3. Lightly reheat the edges with a heat gun to make them perfectly smooth.

Now your socket is completely finished and ready to be fitted to your patient.

We hope that this overview will help you to fabricate highly conforming prosthetic sockets that are as comfortable as they are supportive.

Written by Marc Blij

Marc studied in Brussels and London and is a certified Orthotist and Prosthetist.

After working in an O&P lab at the Universities of Louvain and Brussels, he decided to set up his own O&P lab in Antwerp. For over 30 years, he ran his own practice, together with his wife.

Since , Marc works at the Orfit Industries headquarters in Wijnegem (Belgium) as a Product and Educational Specialist in Orthotics & Prosthetics and Physical Rehabilitation.

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