Low-cost methodology for skin strain measurement of a flexed biological limb

Abstract

*Objective:* The purpose of this manuscript is to compute skin strain data from a flexed biological limb, using portable, inexpensive, and easily-available resources. *Methods:* We apply and evaluate this approach on a person with bi-lateral transtibial amputations, imaging left and right residual limbs in extended and flexed knee postures. We map 3D deformations to a flexed biological limb using freeware and a simple point-and-shoot camera. Mean principal strain, maximum shear strain, as well as lines of maximum, minimum, and non-extension are computed from 3D digital models to inform directional mappings of the strain field for an unloaded residual limb. *Results:* Peak tensile strains are ~ 0.3 on the anterior surface of the knee in the proximal region of the patella, whereas peak compressive strains are ~ -0.5 on the posterior surface of the knee. Peak maximum shear strains are ~ 0.3 on the posterior surface of the knee. The accuracy and precision of this methodology are assessed for a ground truth model. The mean point location distance is found to be 0.08 cm, and the overall standard deviation for point location difference vectors is 0.05 cm. *Conclusion:* This low-cost and mobile methodology may prove critical for applications such as the prosthetic socket interface where whole-limb skin strain data are required from patients in the field outside of traditional, large-scale clinical centers. *Significance:* Such data may inform the design of wearable technologies that directly interface with human skin.