Temperature measurement over the transtibial residual limb
In line with previous studies [5, 8, 10, 17], uneven temperature distribution over TRL was found. In this study, the highest temperature was recorded at middle part of the anteromedial (Z2) location of TRL. The lowest temperature was recorded at the distal part of the anteromedial (Z3) location of TRL. Contrary to the intact limb [23], the locations of the highest and lowest temperature sites over the TRL are close probably due to shortened length of the limb (decreased surface area) and compromised muscular and vascular tissues after amputation. Previous research with small sample sizes and diverse study designs on TRL skin temperature is conflicting. Peery et al. evaluated skin temperature of five TRLs and reported that proximal anterior region of the residual limb was the coldest site and the posterior region of the residual limb was the warmest site [8]. Klute et al. examined residual limb skin temperature of nine transtibial amputees and found that skin over the tibialis anterior, i.e. anterolateral location of the residual limb, at the middle level between the proximal and distal ends had the warmest temperature while the posteromedial location at the distal level of the residual limb had the coldest temperature [5]. Ghoseiri and collegues measured residual limb skin temperature in a single transtibial amputee and found that the middle part of the anterolateral region of the TRL showed the highest skin temperature, whereas the distal part of the posterior region of the residual limb showed the lowest skin temperature [17]. Therefore, in spite of some common findings regarding the warmest and coldest regions of the TRL, there is no general consensus, which indicate the need for further research.
It was reported that spotted higher skin temperature compared to the adjacent parts is a predictor of skin damage [24]. Therefore, provision of a constant temperature, thermoregulation, by keeping a relatively constant temperature as well as heating or cooling mechanisms could ensure optimal physiological health and function [25]. Thermoregulation can be induced internally (e.g. by changes in the blood flow during vasodilation or vasoconstriction) [26] or externally (e.g. thermoregulatory systems and exercise maneuvers) [22]. With respect to the external thermoregulation, the pattern of temperature distribution over the TRL may be useful for selecting appropriate thermoregulatory strategies both in and out of the prosthesis. Challenges in developing a thermoregulatory system include management of the size, weight, cost, and required power of the system to work efficiently when applied as a prosthetic component [5, 22]. Therefore, for both in and out of prosthesis approaches, the distinct skin temperature measurements based on column and row could help in the selection of the best attachment sites of thermoregulatory systems. Our findings revealed that the anteromedial and posteromedial columns of the residual limb were the warmest and coldest regions, respectively, while the anterior part of the TRL had higher temperature compared to the posterior part. Furthermore, the proximal and middle circumferential rows had higher temperature compared to the distal row. Therefore, to provide a thermal equilibrium out of the prosthesis, a cooling mechanism may be required for the proximal and middle rows of the anterior part of the residual limb, while a heating mechanism may be necessary for the distal and posterior parts of the residual limb.
In this study, the skin temperature of the TRL averaged 27.7 ± 0.8 °C, ranging from 27 to 31 °C. However, the reported average temperature of the TRL was 29.1 ± 0.6 °C [17], 29.5 ± 0.9 °C [10], 31.0 ± 1.5 °C [5] and 31.4 ± 1.3 °C [8]. These variations could be related to differences in study designs and recording methods. Thermal standards in non-amputees are based on both environmental (e.g. air temperature, air velocity, radiant temperature, and relative humidity) and personal factors (e.g. activity level, metabolic rate, weighted average of skin temperature, and clothing insulation) [26, 27]. In people with amputation the residual limb skin temperature is generally greater than in non-amputees because of the decreased surface area of the body and changes in blood circulation, as well as the volume and shape of the residual muscles [18, 28]. Interestingly, the distal residual limb temperature in unilateral amputees is cooler than the corresponding site on the contralateral intact side [18]. Therefore, all personal factors differ from non-amputee people and thermal standards available for intact persons cannot be used for people with amputation.
Relationship of the average residual limb temperature with demographic and clinical characteristics of participants
Statistical analysis indicated small non-significant relationships between the average residual limb temperature and participants’ demographic and clinical characteristics. This finding was promising as we recorded temperature without prosthesis at the rest condition, which excludes the potential heating effects of prosthetic socket on the skin temperature and thermal discomfort [11]. We found that the middle part of the anteromedial region of the residual limb had over 2 °C temperature difference with the mean temperature of the residual limb; therefore, this site may have higher vulnerability to thermal discomfort and skin irritation. With increasing age, thermal sense may be decreased and some older persons may not detect up to 4 °C of temperature change [29]. However, thermal sense quantification differs from skin temperature recording and was beyond the scope of the present study. Although the present study had no focus on participants thermal comfort, Klute et al. reported an increase of 2 °C can cause thermal discomfort in people with amputation [5]. In contrast, Diment and colleagues noted that thermal discomfort in lower limb prosthetic users is not directly related to the skin temperature [30]. Similar to localized TRL skin temperature, there is no consensus about thermal comfort in people with amputation. The interaction of residual limb temperature with demographic and clinical characteristics has direct effect of quality of life of amputees and needs further investigation probably around residual limb tissue characteristics.
Study Limitations
Several aspects may threaten then internal and external vailidity of this study. Evaluating residual limb temperature is difficult because the thermistors are connected to a computer or microcontroller using small and breakable wires, likely leading to small sample sizes in the previous temperature measurement studies in amputees [5, 8, 10, 17]. The small sample size and purposive sampling of male veteran amputees may limit generalizability to other amputees. Future studies may assess thermoregulatory mechanisms such as skin perfusion or thermal receptor activation. Skin and tissue thickness was not assessed in this study, which may influence results. Future research may use muscluloskeletal ultrasound to quantify soft tissue thickness of the residual limb.