The effect of Rest and Exercise on Residual Limb Skin Temperatures

Within the prosthetic socket, elevated residual limb skin temperatures and the accompanying discomfort are known to reduce amputee quality of life (1, 2). Further, the closed thermal environment of the prosthetic socket system traps heat and perspiration, both of which may be related to an increase in the occurrence of skin injuries (3-5). For amputees who experience temperature-related discomfort and increased risk for skin problems, understanding the thermal environment is a fundamental step towards developing new prosthetic socket system designs that could address these issues.

The purpose of this study was to explore the influence of activity on residual limb skin temperature. We measured the residual limb skin temperatures of six transtibial amputees recruited at the Veteran Affairs Puget Sound Health Care System (VAPSHCS) using an approved University of Washington Institutional Review Board protocol. All subjects were in moderate physical condition, independent ambulators, were at least one year post-amputation, and gave informed consent prior to participating. Subjects wore prostheses commonly prescribed at the VAPSHCS (see Table 1) which included Alpha® [*Ohio Willow Wood, Mt. Sterling, OH], Explorer® [*Silipos Inc., Niagra Falls, NY], and Pe-Lite™ [*Durr-Fillauer Medical, Inc., Chattanooga, TN] liners.

Upon arriving in the laboratory, the subjects were asked to sit in a chair and remove their prosthesis. Temperature sensors [*2 mm sensor head diameter, type MA100GG; Thermometrics, Inc., Edison, NJ] the sizes of a grain of rice were held in place with tape at sixteen locations on each subject’s residual limb. The sensors were arranged longitudinally in four columns with four sensors in each column (see Figure 1). The first column was over the tibial crest, the second over the tibialis anterior, the third over the medial gastrocnemius, and fourth was over the lateral gastrocnemius. Sensors were evenly spaced proximally too distally in each column from the transverse plane transecting the tibial tuberosity to the distal end of the limb. After all the sensors were secured, the prosthesis was donned with the sensor wires exiting along the proximal edge of the liner. This process took approximately 15 minutes as subjects became acclimated to the laboratory environment (21.8 ± 0.4° C and 48 ± 9% relative humidity). The experimental protocol consisted of seated resting for 60 minutes, then walking at selfselected speed on a treadmill for 30 minutes, followed by a second seated rest period of 60 minutes. At the beginning of the treadmill walk, the speed of the treadmill was adjusted until the subjects felt confident they could maintain that speed for 30 minutes. This was accomplished within two to three minutes. Data were sampled at 1 Hz for the duration of the protocol (2.5 hours).

The mean results from all six subjects (see Figure 2) suggest that residual limb skin temperatures are strongly influenced by activity level. Immediately after donning, the skin temperature was 31.3 ± 0.6° C. Simply donning the prostheses and resting for 60 minutes resulted in a skin temperature of 31.7 ± 0.9° C, an increase of 0.4° C. During the initial rest period, the skin temperature reached steady-state after approximately 25 minutes. Once treadmill walking began, the skin temperature rapidly increased. After 30 minutes of treadmill walking, the mean skin temperature had increased to 33.9 ± 0.9° C, an increase of 2.2° C, and was still rising. Skin temperatures began to immediately decrease during the second 60 minute rest period, but did not reach steady-state. After 60 minutes of rest, the skin temperature was 33.1 ± 0.7° C, still 1.4° C higher than the pre-walking temperature. The rate of increase during walking was much greater than the rate of decrease during the subsequent rest period.

These results indicate that a rest period of double the duration of the preceding walking period is insufficient to return the skin to its initial temperature and that longer periods may be necessary. Based on evidence that suggests amputees perform numerous short duration (three minutes or less) walking bouts throughout the day (6), substantially longer rest periods may need to be interspersed to obviate the cumulative effect of heat from sequential activities.

Differences in liner and socket systems may also affect skin temperatures (see Figure 3); however, a limitation of this interim report is the small size of the sample population. The group 1 participant (subject 1) wore a Pe-Lite liner and experienced a skin temperature increase of 1.3° C during the initial rest period, an increase of 1.9° C during exercise, and a decrease of 1.0° C during the final rest period. The results from the group 2 participant (subject 2) suggest there is no difference between the Alpha and Explorer liners in retaining heat (within-subject comparison). Averaging the results shows the subject experienced a skin temperature increase of 1.1° C during the initial rest period, an increase of 2.3° C during exercise, and a decrease of 0.8° C during the final rest period. The results from the group 3 participants (subjects 3 and 4) may be strongly influenced by co-morbidities, as both subjects had vascular issues arising from diabetes. Their skin temperatures increased during the initial rest period like other subjects (1.0° C), but did not increase nearly as much during exercise (0.7° C). This result may be due more to complications from diabetes and the inability to thermoregulate properly than to the prosthetic socket material (thermoplastic rather than carbon fiber). Interesting, the group 4 participants (subject 5 and 6) decreased during the initial rest period (0.3° C). Their results also showed the greatest increase during exercise (2.9° C) which may be due to the 9mm of material (either 9mm Alpha or 3mm Alpha plus 6mm sock) between the skin and the socket. The differences between liner and socket systems noted above are tentative; additional subjects are being recruited to make a statistical analysis possible.

In summary, a common complaint of lower extremity amputees is that excessive residual limb skin temperatures reduce their quality of life. In addition to being uncomfortable, this warm environment may result in the increased occurrence of skin problems such as friction blisters and ulcers. The data presented here indicate that donning and walking on a prosthesis results in elevated skin temperatures. Further, the elevated skin temperatures produced during walking remain long after activity cessation. Additional participants are necessary to generate statistical differences between prosthetic prescriptions. We conclude that residual limb skin temperature is strongly influenced by activity level and may also be dependent on the patient’s prosthetic prescription. Consideration of heat transfer properties in the design of prosthetic socket and liner systems may result in the development of more comfortable prosthetic systems.

This research was supported by the Department Veterans Affairs, Veterans Health Administration, Rehabilitation Research and Development Service, Merit Review A3289R.

Table 1: Participant prescription, self-selected walking speed, and etiology. Subjects in Group 2 and 4 were tested with a repeated measures design. Both subjects in group 3 had infectionrelated amputations but were also dysvascular; all other subjects were of traumatic etiology.

Figure 1: Representative image of sensor placement on the residual limb. The lines on the residual limb were drawn to help guide sensor placement.	Figure 2: Residual limb skin temperature (mean: solid line, ± 1 standard deviation: dotted lines) for donning followed by 60 minutes of rest, 30 minutes of treadmill walking, and an additional 60 minutes of rest.

Figure 3: Effect of differences in liner and socket systems on residual limb skin temperatures. See Table 1 for patient prescription.

References

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2. Legro MW, Reiber G, del Aguila M, Ajax MJ, Boone DA, Larsen JA, et al. Issues of importance reported by persons with lower limb amputations and prostheses. J Rehabil Res Dev 1999;36(3):155-63.

3. Naylor PFD. Experimental friction blisters. British Journal of Dermatology 1955;67:327-342.

4. Naylor PFD. The skin surface and friction. British Journal of Dermatology 1955;67:241-248.

5. Akers WA, Sulzberger MB. The friction blister. Military Medicine 1972;137(1):1-7.

6. Klute GK, Berge JS, Orendurff MS, Czerniecki JM. Lower limb amputee activity uneffected by shock-absorbing pylon or C-Leg knee. In: Proceedings of the International Society of Biomechanics XXth Congress; 2005 August 1-5, 2005; Cleveland, OH; 2005.