The factors affecting plantar fascia thickness and proximal attachment surface area

Plantar fascia is composed of longitudinally arranged collagen fibers that extend from anterior border of calcaneal tuberosity to metatarsophalengeal joints. In healthy subjects thickness of plantar fascia is about 3 mm but it is reported that plantar fascia thickness can arise up to 7 mm in plantar fasciitis. Plantar fascia thickness seems to be relevant in plantar fasciitis, so authors have investigated plantar fascia thickness in both plantar fasciitis patients and healthy normal subjects. Depending on these studies, several reports indicate that plantar fascia thickness is expected to be thinner than 4 mm in healthy subjects, and thicker than 4 mm in the patients with plantar fasciitis. However there are so many healthy people that have plantar fascia be above than 4 mm in those studies. Plantar fascia is a weight bearing structure. Due to its weight bearing property, it seems quite logical to think that plantar fascia thickness is related to weight and BMI and as weight or BMI increase plantar fascia is expected to get thicker. But clinical studies were failed to reveal a strong correlation between plantar fascia thickness and weight or BMI yet as expected. In our study we investigated the effects of weight, height, BMI and the time spent on foot on plantar fascia thickness and proximal attachment area in healthy subjects retrospectively. Plantar fascia thickness and proximal attachment area were calculated from MRI images. It is found that so many healthy subjects have a plantar fascia thicker than 4 mm and plantar fascia thickness is found to be related mildly with height, moderately with weight and BMI but not with the time spent on foot. The length of plantar fascia insertion site on calcaneus in coronal plane and calculated insertion area showed more correlation rate with weight, BMI and length than that of plantar fascia thickness. These findings imply that as weight or BMI increase plantar fascia accommodates to new conditions by increasing its length of insertion site in coronal plane and so by increasing area of insertion site primarily and by increasing its thickness secondarily. The length of plantar fascia insertion site on calcaneus in coronal plane is a new parameter that is not defined up to now. Measuring coronal length of plantar fascia with plantar fascia thickness may be useful in diagnosis of plantar fascia diseases.