Investigation of the mechanical properties of the plantar aponeurosis.

Introduction - The aim of this work was to obtain a preliminary investigation of the mechanical properties of the human plantar aponeurosis based on regional observation, in order to rationally plan a subsequent larger experimental campaign and develop suited constitutive models to characterize the mechanical response of this tissue. Materials and methods - Different in vitro mechanical tests were developed on eleven samples taken from the plantar aponeurosis of human cadaver (man, age 78 years). The samples were tested along the distal–proximal direction. Range of elasticity of the tissue, development of damage phenomena and stress relaxation at different levels of strain were evaluated. Results - The strength of the tissue was found in the order of that proposed in previous works, with peak stress of about 12.5 MPa. The compliance of the plantar aponeurosis was in line with in vivo evaluation. A softening behaviour appeared for tensile strain larger than 12%. In relaxation tests, the stress was reduced of 35–40% in 120 s. The percentage stress relaxation was found independent on the level of the applied strain. Discussion - The evaluation of the mechanical characteristics is fundamental for a subsequent development of numerical models of the plantar aponeurosis. Such approach is helpful to understand its response to overuse, but also to understand the clinical results of different manual and physical therapies that use warm, pressure or stretch to modify this tissue.