Introduction
Custom orthotics are designed to support and align specific foot types. They are typically more expensive than OTC (over-the-counter) orthotics because of the time, material, and design process involved in building one. They must be precise and accurate when used to treat specific foot types. This article will focus on the process of making a custom orthotic.
Taking a Cast of the Foot
A cast is a negative impression of a foot, and when done right, it captures a foot's curves, shape, and contour. Casting techniques have developed from the use of plaster to 3D scanners. There are various methods of creating a cast, but the most common are plaster casting impressions, foam box impressions, and computer-modeled casts:
Plaster Casting Impression
Plaster casting is one of the earliest casting techniques for making orthotics. It is favored because it is non-weight-bearing — that is, the patient lies on their back, and the practitioner casts the plaster on the foot. Non-bearing casting techniques are typically more accurate, ensuring that orthotics fit perfectly around the patient's feet.
Plaster Casting Process
A: Instruct the patient to lie on his back and remain still. Patients can also lie on their chest or kneel on a chair with their toes pointed to the ground.
B: Dip each portion of plaster in water and squeeze gently.
C: Wrap the plaster on the heel, arch, and toes, ensuring that the foot remains neutral and does not push outward or inward.
D: Wait for the plaster to dry, and carefully remove the mold.
Plaster casting gives an almost precise cast of the feet, making it excellent for creating comforting and agile custom-made orthotics. However, the process can be messy, plus the plaster may break if transported.
Foam Box Impression Cast
Foam box impression is a technique in which the patient pushes their foot through soft foam to form the foot's shape. The procedure is done with the help of a pedorthist, who ensures that only minimal force is used and the patient keeps the foot still. The process takes less time than plaster casting and isn’t as messy; however, the semi-weight position of the foot means that small movements may lead to casts that are inconsistent with the shape of the foot.
Foam Box Impression is less messy but might not be as accurate as plaster casting. Albeit, foam box impression has its advantages:
A: Excellent for people with painful foot protrusions. Plaster casting involves considerable pressure, which increases the pain of protrusions.
B: Foams are usually much softer and take considerably lesstime, making the procedure less painful and quicker.
C: Foam box casting is appropriate for restless patients like children. The pedorthist can push their foot in and out within seconds.
Computer-Modeled Scanning
3D scanning is a technologically driven foot-casting technique. Depending on the device, the casting method can be weight-bearing or non-weight-bearing. Weight-bearing devices involve standing on the scanner, which takes several pictures of your foot.
3d scanning isn't really 3D. It's just a system where multiple pictures of your foot from multiple angles are shot, and then the algorithm combines all the pictures to create a near-perfect impression of the foot. 3D casting can also be done through special 3D capture tablets and devices.
Advantages of Computer-Modeled Scanning
A: Easy casting process: The process is simple because it's technologically driven.
B: No transportation: Unlike plaster casting and foam box technique, where the cast is transported to an orthotic laboratory, 3D casts can be printed into an orthotic immediately.
C: The quality of the printer determines the quality of the orthotic device.
Immediate production of orthotics.
D: Digitally created models cannot be damaged. The pedothrist saves them to a local device or the cloud.
E: Several copies of the same orthotic can be produced within a short period.
Building an Orthotic From a Cast
After obtaining a 3D model of a patient's foot, the model or cast is usually sent to an orthotic laboratory. However, you can build your own orthotic device with the right materials and tools
.
The material you use depends on the purpose of the orthotic. Accommodative orthotics need very soft material like gel and plastic. People with flat feet who want to prevent overpronation of the feet need more rigid materials to hold their feet in one place.
To build your first orthotic device,
A: Clean the mold: If you use a foam box, expect visible foam threads over the mold. Use an iron brush to wipe off the foam. Use curved rasps to take off the edges and smooth off imperfections.
Practitioner Cleaning a Mold: Image Source: https://www.youtube.com/watch?v=eFQGisZM1wU
B: Make necessary markings on the mold, which will be transferred to the orthotic material.
C: Cut the material (in this case, plastic) to the needed size. Cut off the corner of the plastic where the heel will sit to prevent creasing. The size of the orthotic determines the size of the plastic. Orthotic sizes include full-length, half-length, and full-quarter length.
Practitioner Cutting the Material for the Orthotic. Image Source:
https://www.youtube.com/watch?v=eFQGisZM1wU
D: Place the plastic in an oven and wait till it changes color. At the same time, place the cast in the vacuum device.
Plastic Being Placed in the Oven for Softening. Image Source:
https://www.youtube.com/watch?v=eFQGisZM1wU
D: Transfer the plastic from the oven to the cast. Close the vacuum device, sucking out the air and letting the plastic wrap seamlessly over the cast.
Vacuuming Process. Image Source:
https://www.youtube.com/watch?v=eFQGisZM1wU
E: Your orthotic is ready. File to remove excesses. You can also glue a heel pad or other accessory to the device.
Producing Orthotics Using 3D Technology
3D technology has reshaped the way we produce orthotics. Depending on the machine, the 3D scanning process can take up to three minutes. Patients need to stand still throughout the scan. The result is usually more detailed, showing the patient's gait, pronation, and pressure points. Printing can be done immediately, and you can print multiple orthotic devices at once.
Conclusion
Orthotic devices are often built in orthotic laboratories, and the process begins with taking a perfect or near-perfect cast of the patient’s foot. The time you spend building an orthotic device depends on factors like the technique used for casting and printing, building materials, and the need for attachments like heel pads. The best custom-made orthotics perfectly fit and do exactly what they were created for. For example, an orthotic custom-made to correct improper body alignment should be rigid, unlike soft orthotics that accommodate the foot.
