Cutaneous Sensitivity Across Regions of the Foot Sole and Dorsum are Influenced by Foot Posture

Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p < 0.001). Touch sensitivity also significantly increased in postures where the skin was compressed (p = 0.001). Regional differences in spatial acuity were found on the foot sole (p = 0.002) but not dorsum (p = 0.666). Spatial acuity was not significantly altered by posture across the foot sole and dorsum, other than an increase in sensitivity at the medial arch in the dorsiflexion posture (p = 0.006). Posture*site interactions were found for stretch sensitivity on the foot sole and dorsum in both the transverse and longitudinal directions (p < 0.005). Stretch sensitivity increased in postures where the skin was pre-stretched on both the foot sole and dorsum. Changes in sensitivity across locations and postures were believed to occur due to concurrent changes in skin mechanics, such as skin hardness and thickness, which follows our previous findings. Future cutaneous biofeedback interventions should be applied with an awareness of these changes in skin sensitivity, to maximize their effectiveness for foot sole and dorsum input.

Remote Subthreshold Stimulation Enhances Skin Sensitivity in the Lower Extremity

Foot sole skin interfaces with the ground and contributes to successful balance. In situations with reduced sensitivity in the glabrous foot skin, stochastic resonance (SR) improves skin sensitivity by adding tactile noise. Some situations, however, involve an interface comprised of hairy skin, which has higher thresholds for sensitivity. For example, in lower extremity amputation the residual limb is comprised of hairy leg skin. The main objective of this study was to determine if SR improves skin sensitivity in hairy skin, and whether a specific intensity of noise is most effective. Secondary objectives were to compare the effect between locations, ages and modalities. In 60 healthy participants a vibrotactile (test) input was delivered at the lower extremity concurrently with a second, noisy stimulus applied more proximally. The presence of a remote SR effect was tested in 15 young participants using electrotactile noise at the calf. Secondary objectives were tested in separate groups of 15 subjects and differed by substituting for one of the three variables: vibrotactile noise, heel site, and with older participants. A forced-choice protocol was used to determine detection ability of the subthreshold vibration test input with varying noise levels applied simultaneously (0, 20, 40, 60, 80, and 100% of perceptual threshold). An SR effect was identified when increased detection of the input was obtained at any level of noise versus no noise. It was found that all four test groups demonstrated evidence of SR: 33–47% of individuals showed better detection of the input with added noise. The SR effect did not appear consistently at any specific noise level for any of the groups, and none of the variables showed a superior ability to evoke SR. Interestingly, in approximately 33% of cases, threshold values fluctuated throughout testing. While this work has provided evidence that SR can enhance the perception of a vibrotactile input in hairy skin, these data suggest that the ability to repeatably show an SR effect relies on maintaining a consistent threshold.

Comparison of skin sensitivity following breast reconstruction with three different techniques: Autologous fat grafting, DIEP flap and expander/implant1

BACKGROUND: Autologous fat grafting (AFG) has been established over the past two decades as an additive technique during and after breast reconstruction. Complete reconstruction of the breast mound with AFG alone represents an exceptional technique that has been published mostly in case reports or in studies with limited cases. The purpose of this study is to investigate the influence of three different techniques for breast reconstruction on the recovery of skin sensitivity at the reconstructed breast. METHODS: The study included 30 patients after mastectomy following breast cancer. Three groups were examined: A) breast reconstruction by autologous fat grafting (AFG), B) breast reconstruction by deep inferior epigastric artery perforator flap (DIEP) and C) breast reconstruction by expander/implant (TE). Biometric data were compared; sensitivity tests were performed using Semmes-Weinstein monofilaments. The non-operated, healthy contralateral breasts of the patients were used as a reference. RESULTS: While the traditional reconstruction techniques by microsurgical anastomosed perforator flap or expander/implant showed a strongly decreased or completely missing sensitivity of the skin, the tests after reconstruction by AFG represented high values of sensory recovery, which came close to the reference group of non-operated breasts. CONCLUSION: To our knowledge, this is the first study to compare skin sensitivity after AFG-based reconstruction to established techniques for breast reconstruction. We could demonstrate in a limited group of patients, that breast reconstruction by autologous fat grafting can achieve higher values of skin sensitivity compared to traditional techniques.

Gender, ethnic and other features of skin sensitivity

We considered the current problem of determining pain sensitivity of different sections of the human body to find the most painless and safe zones for different medical procedures. The study involved 3 groups of students, 8 people in each group. In the first group were Russian boys, in the second – Russian girls, in the third – African girls aged 18–22 years. We carried out studies in 8 areas of the body, which are most often used in medicine for injecting: cheek, shoulder, forearm, wrist, underarm, shin behind (under the knee), iliac and gluteal areas. These areas are most commonly used for various medical procedures. We determined objective differences of sensitivity thresholds of different body sections. As the threshold increases (decrease in sensitivity), these are: underarm, forearm, iliac region, lower leg behind, gluteal region, shoulder. There were no pronounced sexual features of pain sensitivity among boys and girls 18–20 years old. We revealed ethnic features of skin sensitivity. The overall sensitivity of African students is higher than that of Russians. Taking into account the features of tactile and pain sensitivity will reduce the negative sensations of patients during pain-provoking procedures.