The plantar fascia is a thick, fibrous, connective tissue band which extends along the bottom of the foot. The structural make up of the plantar fascia consists of collagen, elastin, glycosaminoglycans and water. The primary cells are fibroblasts, which synthesize collagen. The primary component of the fascia is type I collagen which adds to the strength of the structure. Elastin is a protein which gives the fascia some elasticity as well as increasing it’s function in dynamic arch support when walking. Glycosaminoglycans, GAGs, are long chains of repeating sugar units that attract water and add resiliency to the ligamentous structure.
When the fascia is torn, generally due to repetitive stress and microtrauma, the collagen fibers unravel and separate. To better understand the process, think of the collagen fibers as long ropes. A rope is a bunch of threads woven together, then twisted to provide strength. In the image to the right, the ropes represent the longitudinal arrangement of collagen fibers in the plantar fascia. When there is a tear, the rope unravels and frays. This is essentially what happens within the plantar fascia on a microscopic level. The initial response by the body is to send cells to the injured area to heal the tissue. This initially causes inflammation. The body attempts to clean up the injured area and repair the damaged tissue. This process may continue uneventfully as new collagen is synthesized to bridge the gap between the torn tissue. Unfortunately, most cases of plantar fasciitis go undiagnosed in the early stages. The injury and repair process tends to cycle with repeated microtrauma impairing the healing process. The plantar fascia then progresses to a deteriorated state as the structural components undergo degeneration. This means that instead of new collagen bridging the gap and adding strength to the fascia, the collagen starts to uncoil and fragment.
In a normal repair process, the collagen degradation and collagen synthesis occur simultaneously. Collagen is being broken down and built up at the same time, but the rate of new collagen formation exceeds the rate of breakdown. When the plantar fascia starts to deteriorate, the rate of collagen breakdown exceeds the rate of build up. There is also a loss of new small blood vessels to the injured site and this decreases the number of cells and growth factors within the area to aid in healing. This impairs the body’s ability to clean up waste products in the area. In a normal healing process, specialized cells aid in cleaning up injured tissue and waste products. Without adequate blood supply to the area, these specialized cells are also in short supply. The injured area will have uncoiled collagen, protein fragments, dead cells and other waste products. At this point, there are few to no inflammatory cells. The condition is no longer termed plantar fasciitis because “itis” means inflammation. The most appropriate term for this condition is plantar fasciosis.
Diagnosis and treatment information on plantar fasciitis/fasciosis.
View our five part series on plantar fasciitis, plantar fasciosis and plantar fascia structure.
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