Real World Reading: Prosthetic Limbs
Read the short article below, in its entirety, and then answer the corresponding questions on the following page.
A prosthesis (plural: prostheses) is a device that replaces a missing body part in order to restore the functionality of the body part in an artificial way. The first replacement body parts are believed to have been rudimentary wooden structures made by the Egyptians, as they have unearthed 3,000-year-old mummies with prostheses made out of wood and leather. Modern prosthetic technology is now far more advanced than simply wooden peg legs. The advancements especially in the last several decades with the development of 3D printing and the ability to use lightweight but strong materials like polypropylene plastic and carbon fiber have completely revolutionized the way prostheses work today. Prostheses also includes more than just artificial limbs – any artificial replacement falls into this category, including fingers, eyes, ears, and noses!
Despite the wide range in prostheses, they are most commonly associated with artificial limbs used after surgical removal of an arm, hand, leg or foot, called an amputation. There are many reasons for amputation such as diagnosis of a cancerous tumor in a limb’s muscle or bone or a severe infection that is unresponsive to antibiotic treatment, but the most common reason is due to circulatory issues in a limb as the result of the narrowing (or damaging) of essential arteries. Amputation is also being explored as a treatment option for patients suffering from nervous system disorders such as CRPS, or complex regional pain syndrome.
When an amputation is done to prepare a lost limb for an artificial replacement, all damaged tissue must be removed as well as any bones in the amputated limb. The remaining bone must be smoothed out and any blood vessels or nerves that went into the removed bone must be sealed off. The muscles and skin around the new stump, or residual limb, must also be shaped in preparation for a prosthesis to eventually be attached. It is important that enough muscle is left behind to cover and attach to the end of the limb (whether it be bone or tendon) so that it can remain a functioning muscle and provide necessary cushioning for the prosthesis.
Patients often stay in the hospital for 1-2 weeks after an amputation surgery and some can begin being measured and fit for their new prosthesis anywhere from 2-3 weeks later. Every prosthetic limb has three main components – the pylon, socket, and suspension system. The pylon is the “skeleton” of the limb and provides the main structural support, just like a bone would. The socket is the part of the artificial limb that connects to the patient’s residual limb, and its structure is incredibly significant as it transmits forces applied to limb to the rest of the patient’s body. Lastly, the suspension system keeps the prosthesis attached to the body and can be a combination of harnesses, straps, and sleeves. Recently, suction has been used as the primary suspension mechanism with a simple seal holding the artificial limb in place.
Every prosthesis must be custom fit and built specifically for the patient’s body. The most critical part of the prosthesis is the socket where the residual limb will attach. Getting the right fit can be tricky as the area is often very swollen after surgery. However, if too much time is lost between surgery and fitting the new limb, the muscles in the residual limb can start to atrophy and shrink, affecting the fit of the socket. Once a prosthesis is correctly fit and built for the patient, lots of physical therapy is to be expected moving forward. Most patients need anywhere from 6 months to a year in rehabilitation support in order to master using their new limb to accomplish nearly all of the same functions of life as they could have prior to surgery.
1. What organ systems must be understood in detail by the medical doctors and bioengineers who develop amputation techniques in preparation for prostheses? Explain why for each system.
2. Why do you think smoothing out the remaining bone in the limb is an important part of the amputation process?
3. What are artificial limbs currently made out of? Why are these current materials much improved from those used in the past?
4. Despite the similarities in all prosthetic limbs, there are also many differences, especially with regards to where the prosthesis will be located. For example, a different type of artificial limb is needed after a transfemoral amputation vs. a transtibial amputation vs. a transhumeral amputation. Just looking at these three terms, predict the difference in the types of amputations and the structure of the prosthetic limb each would require.
5. Consider a prosthetic limb designed for an upper limb versus a lower limb. Based on what you know so far in this course, what similarities do you think the prostheses would have in design? What differences in structure would be necessary in order for each limb to accomplish its specific functions? Justify your answers with reasoning.