The United States is home to over 2 million people living with limb loss or limb difference. Those who choose to utilize a prosthetic device are likely to agree unanimously: the process of acquiring a prosthetic limb is not a case of one-size-fits-all. Instead, each individual undergoes a lengthy process of preparation, measuring, casting, designing, and finally prosthesis fabrication, all before actually receiving their device for training and use. However, the techniques used to create devices can vary based on the resources, time, and budget. Here we will explore a few of the most common techniques that help bring prosthetic devices from the labs to the streets.
Water immersion is one form of residual limb measuring that is particularly helpful for capturing volumetric changes. In this technique, a residual limb is placed into a tank, and water is added. By measuring the depth and displacement of the water, prosthetists can obtain the limb’s segmental volume and total volume.
Pros of this technique: cost-effective, timely
Cons of this technique: not a portable approach due to equipment required
Computer-aided designs, or CAD, systems are becoming more prevalent as technology in this field advances. This technique consists of a hand-held device that scans a residual limb, creating a 3-D computerized image of the limb.
Pros of this technique: most reliable, portable
Cons of this technique: length of time required to complete measurements, costly
Circumferential measurement is the most “old-fashioned” of the techniques for residual limb assessment. This technique requires nothing more than a simple measuring tape and consistent landmarks. Scientists have created a formula, referred to as Sitzia after its creator, to calculate the limb's total volume based on landmarked measurements.
Pros of this technique: portable, cost-effective
Cons of this technique: low reliability due to variability in identifying bony landmarks
Research on the various techniques found the CAD hand-held scanner described in surface scanning above to be the most reliable technique for measuring a residual limb. The measured variability between the CAD system and the others was minimal. However, small changes in this population can be the difference between skin breakdown or a healthy residual limb. Regardless of what the research on measuring shows, most of the challenges are known to come when training and learning to use the prosthetic limb. So, while fitting and fabrication are essential aspects of being aware of, they are just one step in the process of acquiring a prosthetic limb.