Biomechanical and mechanical behavior of the plantar fascia in macro and micro structures.

Plantar fascia (PF) is a heterogeneous thickness structure across plantar foot. It is important significance to investigate the biomechanical behavior of the medial, middle and lateral PF regions. To investigate the non-uniform macro/micro structures of the different PF regions, the uniaxial tensile test of PF strips were performed to assess the mechanical behavior of PF. A scanning electron microscope (SEM) was used to visualize and measure the micro morphology of PF associated with collagen fibers. A three-dimensional foot finite element (FE) model was developed to quantify the tensile behavior of the internal PF. The elastic modulus of the lateral PF component (1560 MPa) was observed, followed by the medial (701 MPa), the central (1100 MPa) and the lateral (714 MPa) portions in the central component. Elongation of the central portion (0.192) was lower than the medial (0.223) and the lateral (0.227) portions. The corresponding SEM images showed that the fibers of the central portion were more densely packed and thicker compared to the ambilateral portions in the central component. While the FE model prediction also suggested that the greater elastic modulus of the central PF portion had lower strain (0.192) versus the ambilateral portions. Therefore, the lower elongation and greater elastic modulus at the central portion of PF would probably have a high risk of PF injury. The findings showed a relation between the mechanical tension and fibrous morphology of PF. This information would have a better understanding of the PF pathophysiology diseases related to tear and injury of PF.