Even though plantar fasciitis is a relatively common problem, the actual tissue changes are not fully understood. It is theorized to be an inflammatory condition caused by repetitive microtrauma and tensioning at the heel. However, evidence of inflammation was not found in histological samples during surgery. Adding more cloudiness to the picture is that plantar fasciitis often responds favorably to steroid injections, which typically combats the inflammatory process. Therefore, inflammation is part of the puzzle but not the whole puzzle.
The repetitive microtrauma results in microscopic tears at the insertion of the fascia into the heel bone. The micro-tears irritates nerves, muscles, and may cause more inflammation (see above on inflammation.)
It is most commonly caused by a sudden change in activity and often exacerbated by poor footwear selection during tasks, decreased foot, ankle, and hip strength, prior injuries to the big toe or foot, and tightness in the calf muscles. The change in activity may not be planned and it often occurs in those that have careers requiring more time on their feet such as nurses, servers in restaurants, police officers, etc.