Postactivity temperature and perspiration results were also found to improve with the SmartTemp liner. The beginning postactivity rest skin temperature was significantly lower (P = 0.048) when wearing the SmartTemp liner compared with the placebo liner. During the rest period, the mean skin temperature increased 0.4°C and 0.3°C when wearing the placebo and SmartTemp liner, respectively. The mean skin temperature at the end of the 10-minute rest period was significantly lower (P = 0.005) when wearing the SmartTemp liner compared with the placebo liner. Perspiration, while small in quantity, was also significantly (statistically) reduced with the SmartTemp liner during the postactivity rest (Figure 3). Many of the subjects (n = 9) did not sweat with either liner during this period; however, of the seven subjects that did have sweat during this period, only one of these subjects had sweat while wearing the SmartTemp liner (subject 4). The amount of sweat while wearing the SmartTemp liner was less than the amount of sweat this subject produced while wearing the placebo liner.
Inclusion of one subject with bilateral transtibial amputation enabled a unique case study within the larger study, where both treatments could be tested within the same activity period and then tested on the opposite limb during the second activity period. Regardless of the limb the SmartTemp liner was worn on, the temperature increases for both activity periods associated with that limb were lower when wearing the SmartTemp liner compared with the placebo liner. Figure 4A shows the mean start and end temperature for each liner during both activity periods. A reduction in perspiration for the limb wearing the SmartTemp liner was also found during both activity periods compared with the placebo liner (Figure 4B).
In 2005, there were 1.6 million persons living with limb loss in the United States.9 While the anticipated projections for an increasing population of persons with amputations are lower than anticipated,9 the number of amputation cases continues to grow. A major contributing factor to this increase includes the growing health impact of diabetic complications.10 For instance, from 1990 to 2010, the yearly number of amputation cases increased by 22,703 due to diabetic complications alone.11 However, the prevalence of diabetic-related complications resulting in amputation in adults younger than 45 years of age does not surpass amputations due to traumatic injury.12 Recent military conflicts have shed light on a unique subset of the community of persons with amputation in that these individuals are younger and lead highly active lifestyles, which place increased demands on the prosthetic components. Regardless of amputation cause and functional needs, the prosthetic interface is a critical factor to overall success of a prosthetic device.
Heat and perspiration are common complaints among individuals with amputation when using a prosthesis1,13 due to the poor thermal properties of common prosthetic interface materials.7,8 Apart from being uncomfortable for a person with amputation, evidence suggests that warm and moist socket conditions expedite the formation of blisters.3–5 Moist skin may also reduce the adherence between the skin and limb and negatively impact suspension and result in injury of the soft tissues. The most common skin problem clinically presented by individuals with lower-limb amputations is ulcers.14 For individuals with traumatic lower-limb amputations, the incidence of chronic or chronic recurrent ulcers can reach 50%.15 Furthermore, persons with diabetic and dysvascular conditions who have undergone limb amputations are at an increased risk for ulceration. The standard of care for ulcers typically requires disuse of the prosthesis, which negatively impacts rehabilitation efforts and quality of life for the individual. In extreme cases, chronic ulcers necessitate surgical revision of the residual limb. In that light, there is a clear need to improve upon the interface materials traditionally used for prosthetic applications to reduce risk and best protect the comfort and health of individuals with amputation.
The results of the double-blind clinical trial support the use of the SmartTemp liner to reduce skin surface temperature and perspiration within the prosthetic liner. The authors attribute this result to the increased latent heat of the SmartTemp material, which provides a pathway to remove heat away from the residual limb, thereby reducing perspiration. Indeed, the SmartTemp liner resulted in a consistently lower residual limb skin temperature compared with the placebo liner and was particularly effective at reducing or even eliminating perspiration within the liner. Localized cooling of the skin surface has shown to impact sweat rate through the delay of cutaneous vasodilation.16,17 In addition, it has been suggested that local cooling may mitigate neurotransmitter release associated with perspiration.17 Peery et al.18 suggests that a change in temperature of 1°C or 2°C is clinically significant. The results in this study support the hypothesis of Peery et al.18 The average temperature change for the placebo treatment of 1.2°C (31.2°C–30.0°C) is within the range specified by Peery et al.18 and resulted in higher average perspiration compared with results for the SmartTemp treatment. The average temperature increase for the SmartTemp treatment of 1°C (30.4°C–29.4°C) is near the lower boundary of the range suggested by Peery et al.18 Qualitative reports from persons with amputation wearing the SmartTemp system in the field over longer periods report a perceived reduction in residual limb perspiration during activities of daily living even though the PCM may become saturated (i.e., has reached the limit of heat capacity where all PCM has undergone a change in physical state) during the course of wearing the liner. These qualitative reports suggest that establishing a pathway for heat to move out of the socket may result in reduced perspiration beyond local cooling. Further research is warranted in this regard.
Previous work19 found temperature increased on average 3.1°C during a 30-minute continuous walk and an average maximum of 34°C. Another study found an average temperature increase of 1.7°C during a 10-minute walking activity.16 While individual patients from this the current study had temperature increases similar to these studies, the average temperature increases in the current study for both the placebo and SmartTemp liners are lower than that in the previous studies. The authors believe the difference in activities had the biggest impact on this outcome. The activity of walking may be more vigorous than riding a stationary bike as in this protocol. The stationary bike ride was chosen for this study over a walking task as an additional safety measure to reduce the risk of thermocouple wire failure and to limit subject withdrawal due to difficulty completing the task. Other factors that may have had an impact are the subject population and the season during data collection. The study by Klute et al.19 also found that skin surface temperatures varied depending on the location measured, suggesting that the development of location-specific technology would be advantageous to regulate subject-specific areas that could benefit from additional heat removal. The results of this work also found that skin surfaces temperatures for each of the sites varied among individual subjects with no clear trends presented. This suggests that any attempts to optimize interface design would need to be done on an individual basis. Further research is needed to better understand these differences.
The testing protocol sought to determine the amount of sweat produced during activity and postactivity periods separately. This required the socket system to be doffed immediately after activity and redonned before collecting postactivity temperatures. Interestingly, the temperatures associated with wearing the placebo liner reduced during this period (31.2°C at the end of activity and 30.8°C at the start of postactivity) while the temperatures associated with wearing the SmartTemp remained the same. This may be an indication of the SmartTemp liner not only storing but also releasing thermal energy and protecting against thermal fluctuations.
The design of clinical research trials that includes blinding of subjects and researchers is not a trivial endeavor when investigating prosthetic devices. Often, it is very difficult to camouflage the appearance or function of a prosthetic component to the individual with amputation, researcher, or both parties. In this study, a placebo liner was successfully made that replicated the appearance and feel of a real SmartTemp liner. Qualitative feedback was collected from the subjects by asking which of the two liners they believed to be the real SmartTemp liner. Surprisingly, 65% of persons with unilateral transtibial amputations correctly chose the real SmartTemp liner. However, the bilateral subject correctly chose the real SmartTemp liner for both activities when asked the same question. This result for unilateral subjects may be influenced by the long break between activity periods, the mind-set of performing the activity for the first or second time, and the ability to perceive changes in temperature. The latter point could be particularly relevant for four subjects that did not perspire with either liner as well as the four to five additional subjects who had very little perspiration (approximately <0.01 g). However, analyzing the responses of the unilateral subjects did not reveal any trend related to treatment order and correct/incorrect responses.
The SmartTemp liner is the first commercially available liner to address the prominent problem of excessive heat and perspiration for persons with amputation using a prosthesis. The results presented demonstrate the ability of the liner to reduce temperature and perspiration before and after a 25-minute exercise period and 10-minute postactivity rest period, and corroborate clinical feedback from individuals with amputations and prosthetists. Further work is needed to fully understand the impact this liner will have on the health of the residual limb by reducing factors that accelerate injuries to the soft tissues.
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Keywords:© 2015 by the American Academy of Orthotists and Prosthetists.
phase change material; prosthesis; socket; interface; heat; amputation; lower limb