Longstanding cases of plantar fasciitis often demonstrate more degenerative changes than inflammatory changes, in which case they are termed plantar fasciosis. The suffix "osis" implies a pathology of chronic degeneration without inflammation. Since tendons and ligaments do not contain blood vessels, they do not actually become inflamed. Instead, injury to the tendon is usually the result of an accumulation over time of microscopic tears at the cellular level.
The plantar fascia is a thick fibrous band of connective tissue originating on the bottom surface of the calcaneus (heel bone) and extending along the sole of the foot towards the toes. It has been reported that plantar fasciitis occurs in two million Americans a year and in 10% of the U.S. population over a lifetime. It is commonly associated with long periods of weight bearing. Among non-athletic populations, it is associated with a high body mass index. The pain is usually felt on the underside of the heel and is often most intense with the first steps of the day. Another symptom is that the sufferer has difficulty bending the foot so that the toes are brought toward the shin (decreased dorsiflexion of the ankle). A symptom commonly recognized among sufferers of plantar fasciitis is an increased probability of knee pains, especially among runners.