Relative contributions of plantar fascia and ligaments on the arch static stability: a finite element study.

The plantar fascia (PF) and major ligaments play important roles in keeping the static foot arch structure. Their functions and relative contributions to the arch stability have not been well studied. A three-dimensional finite element foot model was created based on the reconstruction of magnetic resonance images. During balanced standing, four cases after individual releases of the PF, spring ligament (SL), and long and short plantar ligaments (LPL and SPL) were simulated, to compare their biomechanical consequences with the normal predictions under the intact structure. Although the predictions showed the arch did not collapse obviously after each structure sectioning, the internal mechanical behaviors changed considerably. The PF release resulted in the maximal increases of approximately 91%, 65% and 47% in the tensions of the LPF, SPL and SL, produced the largest changes in all bone rotations, and brought an obvious shift of high stress from the medial metatarsals to the lateral metatarsals. The SL release mainly enhanced bone rotation angles and weakened the joint stability of the arch structure. The LPL and the SPL performed the roles of mutual compensation as either one was released. The influence of the LPL on the load distribution among metatarsals was greater than for the SPL and the SL.