Obviously the plantar fascia itself is isolated in the foot and is the source of the pain you feel. But, that is only part of your pain picture. One of the main actions of the foot is to transmit and disperse weight effectively up into the lower limb. If there are alignment or restriction concerns in the knee or hip for example, then the load is increased on the foot itself, including overload to the plantar fascia. It is very common to see plantar fasciitis develop after an ankle sprain or knee sprain, as the loading onto the plantar fascia is significantly altered with the injury related gait changes. Another common trigger is poorly fitting and unsupportive shoes, especially when combined with a new or increased exercise plan. The plantar fascia needs some degree of external support from a shoe to help it manage repetitive impact sports such as running.