Temperature control with a prosthetic limb

As warm-blooded mammals, our bodies are constantly working to maintain our normal core temperature of 37.0 degree Celsius. In a comfortable situation, when we are relaxing in an air-conditioned room, our bodies control this temperature without us even noticing. Walking outside in the heat of summer however is a different matter entirely. In both of these situations, our bodies are producing and loosing heat through several different mechanisms.

The major heat sources in our bodies are the muscles and the liver. While the heat generated by the liver remains relatively consistent, the heat generated by our muscles is directly dependent on how active we are at the time. At the same time as heat is being produced, our body is losing heat in three main ways. Heat is constantly radiating off us in the form of invisible infrared beams, through convection (heating up the surrounding air) and through evaporation of sweat on our skin and as moisture when we breath.

Back in our comfortable cool room, all the above processes (thermos-production and heat loss) balance each other without excessive effort. By leaving the indoors and walking into the afternoon sun, our muscles work producing more internal heat and the surrounding temperature increases. In this situation, our heat loss through infrared emission and convection becomes significantly less efficient at reducing our body temperature. This leaves us with evaporation and our bodies response is to increase sweat production. If we further increase our physical activity or the ambient temperature, the situation will become more stressful for our body resulting in uncomfortable sensations.

Amputation complicates this situation even more. Any lower limb amputation leads to additional energy consumption when walking which means additional heat production from the muscles. Scientific research has found that this energy consumption is higher for those individuals with higher levels of amputation. This means that a person with a short above knee amputation will use much more energy than someone with a partial foot.

Another complicating factor to be aware of is that all socket style prostheses cover up the skin. The three ways that heat is lost from the body (radiation, convection and evaporation) are blocked by the materials covering the stump such as: liners, stump socks and the socket.

Ways to reduce the problem.

There are several ways that a prosthesis can be designed and different coping strategies that can be adopted by the wearer in order to reduce the heat stress on their body.

• Prosthetic Socket: The prosthetic socket should be correctly fitted to provide a firm yet comfortable connection between the body and prosthesis. The better this connection, the more control the wearer has over the prosthesis and less energy is needed to walk.
• Fixation methods (how the prosthesis is held on). Similar with the socket, fixation should be reliable while only covering as much skin as is needed.
• Alignment of the prosthesis: An incorrectly aligned prosthesis results in muscles being used more (producing more heat) in order to maintain balance.
• Prosthetic components: There are thousands of different types of prosthetic components (knees, feet, etc) because everyone is different. Because of the differences in physical abilities, body weights and lifestyles, prosthetic components need to be appropriate for the individual wearer. By selecting the best components, a prosthetist may be able to reduce energy expenditure and heat production for the user. A very rough example of this can be choosing light weight components for low active amputees and heavier but highly functional components for very active users.
• Skin/prosthesis interface: Prosthetic interfaces have changed dramatically in the last 30 years with the more recent advances focusing on temperature management within the prosthetic liner. Modern materials are available which absorb and store excess heat away from the stump allowing it to stay cooler for a longer period of time.
• Pay additional attention to the condition of your stump during the hot season.
• Wash and dry your stump daily (in the morning and before bed).
• Talk to your prosthetist about specific skin creams and lotions to reduce the effect of sweat, irritation and damage to the skin.
• If you use socks directly against your skin, make sure you have access to clean dry socks that can be changed during the day if required.
•  If it is possible, try to limit hard physical labor or activity on days that are especially hot.
• When out and about, try to keep in the shade as much as possible.
• Drink enough water. If you live or work in extremely hot regions, consult your medical specialist (GP) regarding drinks containing electrolytes.

What can I do?

•  Check your skin before and after limb use
•  If something feels uncomfortable during use; take the prosthesis off and check your skin. If something is concerning you, consult your prosthetist for advice.

Australia is a notoriously hot environment and it can be difficult to avoid situations when we are unprotected from overheating. With advances in modern prosthetics, your specialist can offer individual solutions to your situation. Their professional solution in combination with the tips and strategies we describe in this article, can help reduce the risk of overheating and limit the negative effects of high temperatures.

ArtLimb is a non-profit, independent project dedicated to sharing knowledge and discussing information about artificial limbs.

If you are interested in reading more information about prosthetics, please visit ArtLimb online at www.artlimb.com