The plantar aponeurosis (plantar fascia) serves to elevate and stabilize the medial longitudinal arch during stance. It also augments the transformation of the foot from a mobile adaptor at heel contact to a more rigid lever at heel-off and during the propulsive phase of gait.2-4
Hicks provided experimental evidence of the biodynamic role of the plantar fascia during gait.5 He referred to the tensioning of the plantar fascia as a “windlass mechanism.” This mechanism results in elevation (supination) of the foot as a coupling influence of digital dorsiflexion (especially hallux) acting upon the subtalar joint axis, leading to supinatory force being directed across the subtalar and oblique axis of the midtarsal joints.
Other structures, including the adipose heel cup and ligament and Achilles tendon, contribute to the function of the plantar fascia. The adipose heel cup serves to dissipate the initial impact and shear load of heel contact. However, due to the arrangement of septal fibers and the blending of the heel cup ligament with the plantar fascia, the adipose heel cup may also serve to dampen occasional peaks to the linear load, which would otherwise be dissipated by the less elastic plantar fascia. The fibers of the Achilles tendon insertion serve to increase tension in the proximal fibers of the plantar fascia via its periosteal attachment during stance and gait.
Today, we recognize the importance of the plantar fascia not only as it serves to tension the longitudinal arch but also as it acts to elevate and stabilize the medial longitudinal arch in static stance. When functioning appropriately, the plantar fascia effectively augments the structural integrity of the longitudinal arch.5 When the plantar fascia and windlass mechanism malfunction, the foot fails to adequately transform to a more stable appendage. This exposes the plantar fascia and associated structures to greater eccentric loads, which may increase the potential for overuse injuries.