Shaping Covers and Applying Skin

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There are many different types of prosthetic leg covers and fabrication materials. You need to know upfront what your end result should be before you make a decision about components. Depending on the circumstances, you may be following the prosthetist's directions, or you may be working directly with the patient, who is providing feedback firsthand. Is fit and function the criteria, or does the client care more about the shape and cosmesis? Are there specific components of the device that may be difficult to camouflage? For example, if a shuttle button that sticks out on the lateral side will displease the patient, relocate it to the medial side and try to hide it. Thinking ahead about the project will save your company time and money in replicated or revised work.

Other factors to consider are whether the cover should be removable or permanent, as this will impact the way you approach producing the final product. The type of cover will also determine what you use as an interface; two possible choices are a laminated sleeve or a glued fabric sleeve.

Prior to fabricating a cosmetic cover for a transfemoral prosthetic leg, you will have to determine whether to make it discontinuous or in one piece so that the prosthetic knee mechanism is not visible. While there may be concern regarding inhibition of knee motion with a one-piece cover, that will not be an issue if it is prepped and installed properly; it must be hollowed out correctly so flexion and extension are not affected. Fortunately, we've developed an elaborate testing procedure to determine in advance if you have prepped the cover properly to allow for this movement: it's called measuring!

In all seriousness, to ensure a good fit, one of the most important steps is to make sure you hollow out the distal two-thirds of the foam that covers the socket. If you stretch the foam cover circumferentially over the socket to make it fit, you eliminate its ability to stretch lengthwise. Once you have hollowed out the foam properly and placed it on the prosthesis, make a mark on the knee center and another mark four inches above and below the knee on the anterior side while the leg is in full extension. Then, flex the prosthesis 90 degrees and measure between the marks; the marks should be equal. Each leg is different in its requirements, but I usually start at 1-inch stretch when flexed. You may need to hollow out the shin section or the thigh section to make the sections equal.

We've all seen one-piece cosmetic covers for a transfemoral prosthetic limb that have torn at the knee. Every one that we have tested demonstrated that the failure resulted because the foam could not stretch. Usually the underlying foam tears and then the skin tears. Because the foam could not stretch, it was doomed from the start. Very few splits are caused by the patient falling on the knee.

Next, add the skin coating. Again, you will have more options if you have made key decisions in advance such as whether to use a removable skin sleeve or sprayed-on skin. Sprayed-on skin produces by far the best cosmetic finish. For a transtibial prosthesis, we can pull a nylon hose on it, glue it down, spray the skin onto the leg, and smooth it. However, a nylon cannot be pulled over a one-piece cover for a transfemoral prosthesis to use for the skin because it will bond to the foam and inhibit the foam's ability to stretch over the knee lengthwise. This means you must smooth the foam with a sanding sleeve or foam finisher before you apply the skin coating. The skin-coating product you choose for this application has to be able to stretch. We have used Stretch EZ with success.

There are a couple of additional considerations before finalizing your skin coating: mobile internal components and vacuum exhaust ports. If you have components that rotate, you must accommodate for that internally. If you don't, the components will squeak, and putting a skin over the prosthesis will not help. Instead, the skin amplifies the noise. Choose carefully what type of foam you use over a rotating component because some are more likely than others to cause squeaking. Vacuum exhaust ports can also create issues if not treated properly. If you cover the ports with foam and then apply a skin coating to the prosthesis, it will inflate like a balloon—the exhausted air has to go somewhere. To address the issue of exhaust from vacuum ports and still create an attractive cover, we use an exhaust hose line and bury it in the foam. You can hide where it comes out either in the foot shell or by drilling a small hole in the proximal edge, provided that you give it some space for the air to escape.

Fabricating cosmetic covers can be a fun and rewarding part of the prosthetic process to return a client to a sense of normalcy.

Ronnie N. Graves, BOCPO, LPO, CO, CTP, is the owner of Prosthetics Research Specialists, Bushnell, Florida, and has worked in the O&P industry for 33 years. He specializes in hard-to-fabricate devices and teaches fabrication techniques. Graves is also president of Sumter Disaster Animal Response Team, Bushnell, a non-profit organization that specializes in assisting in animal rescue, particularly in disaster situations.

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