Fascial Thickness, Pain, and Foot Arch All Linked Together in Plantar Fasciitis
The causes and effects of plantar fasciitis (PF) remain the topic of study and research. The plantar fascia is the fibrous connective tissue under the foot. It goes from the heel along the arch of the foot to the base of the toes.

PF is a painful inflammation of this fascia. It causes heel pain when standing or walking. In this study, three factors are measured and compared to see if they contribute to PF. Ultrasound was used to measure the thickness of the fascia. X-rays were used to measure the shape of the arch. And forces within the foot were measured using a special pressure platform while walking.

Two groups of adults were included. One group had PF just on one side. They reported heel pain when standing or walking that went away with rest. The pain was rated on a scale from zero (no pain) to 10 (most pain). The control group didn't have any symptoms of PF.

After analyzing the data, the authors report that pain was linked with thickness of the fascia, arch angle, and loading on the midfoot in the group with PF. The thickness of the fascia was related to arch angle in both groups.

This is the first study to use ultrasound readings to show that the thickness of the plantar fascia is related to the severity of heel pain in PF. Thicker fascia increases the stiffness of the arch. This puts more pressure on the foot when standing and walking.

Despite these new findings, the researchers still don't know which came first: the changes in the fascial thickness, arch shape, and loading on the foot or the PF. It's possible that pain from PF changes the way the person walks and that's what brings about the change in arch angle and load.

Or it may be that the fascia is thicker but can't handle a normal load so pain develops. The exact relationship between the fascia and the arch still isn't clear. Future studies are needed to sort out which came first and which of the three factors is most important.
References
Scott C. Wearing, PhD, et al. Plantar Fasciitis: Are Pain and Fascial Thickness Associated with Arch Shape and Loading? In Physical Therapy.August 2007. Vol. 87. No. 8. Pp. 1002-1008.