7. Preventing excessive dorsiflexion bending moments on metatarsals. The plantar fascia acts to prevent excessive dorsiflexion of the metatarsals during weight bearing. If the plantar fascia is not intact, it can increase the stress on the metatarsals, even leading to stress fractures of the third metatarsal. 8. Passively stabilizing the proximal phalanx of digits in the sagittal plane. One function of the plantar fascia is to passively plantarflex the digits into the ground during weight bearing. Without this, there may be toe deformities such as floating toe and hammertoe. 9. Reducing ground reaction forces on the metatarsal heads during late mid stance and propulsion. The digital purchase force that results from the passive plantar flexion of the digits into the ground allows the digits to share the load with the metatarsal heads, reducing stress on the metatarsal heads. Plantar plate tears and metatarsalgia may result without a functioning plantar fascia. 10. Helping absorb and release elastic strain energy during running. The elastic properties of the plantar fascia allow this structure to store up to 17 joules of energy, effectively reducing the amount of energy required to run. The plantar fascia does much more than simply support the longitudinal arch. A patient that has ruptured the plantar fascia or had a plantar fasciotomy may struggle with significant deficits in the foot. These may include overworking of the deep posterior compartment muscles, overuse of the plantar intrinsic muscles, increased stress on the plantar ligaments, dorsal and mid-foot pain, stress fractures of the third metatarsal, floating toe and
hammertoe, plantar plate tears or metatarsalgia, and increased energy required to run. To a smaller extent, these can also be affected with plantar fasciitis. These issues will cause significant difficulty with normal gait patterns. The potential for these deficits highlights the importance of conservative treatments for this condition, in order to allow the plantar fascia to stay intact and maintain the normal gait pattern for the patient. Figure 1: Forces of the Foot
Note . Used with permission from Dr Kevin Kirby, DPM.
RISK FACTORS
It is estimated that 1% of the US population will have a diagnosis of plantar fasciitis with 3.2 million new cases of plantar fasciitis every year (Nahin, 2018). Each case can cause difficulty with mobility, specifically walking and running, which can interfere with the ability of many patients to complete their jobs and causing some to miss work. Unfortunately, there is no single treatment that works for every patient, so it is important to educate patients on all the possible risk factors and contributing factors to minimize further aggravation. The risk factors for plantar fasciitis are explored in detail below. However, the level of risk between these will vary, and some more recent research states that some are not true risk factors at all. Obesity : Is found to be a significant predisposing risk factor for plantar fasciitis. An obese person is 1.4-times more likely to develop plantar fasciitis than someone whose BMI is 25 or less (Tanamas, Wluka, & Berry, 2012). Someone who is obese is likely have an altered gait pattern, specifically shorter steps, causing decreased ankle plantarflexion and increased pronation secondary to increased step width. The added weight puts stress on the plantar fascia, making it more likely to respond with dysfunction. Decreased ankle dorsiflexion : One study found that people who had 0° or less of dorsiflexion had an odds ratio of 23.3 of having plantar fasciitis compared to the group of people who had 10° or more of active dorsiflexion. This study concluded that decreased ankle dorsiflexion was the single-most important risk factor in predicting plantar fasciitis (Patel and DiGiovanni, 2011). Excessive time standing : Nearly every website that speaks of plantar fasciitis will list time standing as a risk factor to plantar fasciitis. However, research shows only a small correlation between these two. Further research is needed to establish this as a true risk factor (Waclawski et al., 2015). Change in training patterns : Running is a sport that is closely associated with plantar fasciitis. Interestingly, a recent study of elite runners showed only 12% had a plantar fasciitis injury while 56% had an Achilles tendon overuse injury. Another study
showed a close relationship between gastrocnemius contracture and plantar fasciitis. It is possible that the increase in plantar fasciitis in runners is more closely related to the Achilles injuries than to running itself (Knobloch et al., 2008). Flat feet : There is a relationship between flat feet and plantar fasciitis, though the exact cause of the symptoms is unknown. An older study published in 2004 showed that when people with flat feet were compared to those with a normal arch, 42% of those with flat feet had plantar fasciitis compared to only 8% of the normal arch group having plantar fasciitis symptoms (Chang, 2004). This study also found a significant thickening of the fascia in people with flat feet, and other studies have pointed to a link between fascia thickening and plantar fasciitis. Female gender : Many articles list being female as a risk factor to developing plantar fasciitis, though some research contradicts this claim. It has also been suggested that wearing improper footwear, specifically high heels, contributes to the cause of plantar fasciitis. This may be one factor in some studies that show females with a higher incidence of injury, as males typically do not wear heels. Ultimately, there is no greater risk to having plantar fasciitis simply by being female (Riddle et al., 2003). Tight calf muscles : In a study published in Foot & Ankle International, it was found that 83% of patients with plantar fasciitis had decreased ankle dorsiflexion due to tight calf musculature, 57% (145 of 254) had an isolated contracture of the gastrocnemius, 26% (66 of 254) had a contracture of the gastrocnemius-soleus complex, and 17% (43 of 254) did not have a dorsiflexion limitation (Patel & DiGiovanni, 2011). Age : Being over age 40 is considered a risk factor by many; however, some studies suggest that age is not truly the risk factor, but rather the decline in ankle dorsiflexion that often occurs with age. High arches : Some small studies have found a correlation between high arches, a supinated foot, and plantar fasciitis. This is not as highly researched as the incidence of flat feet with plantar fasciitis (Golightly et al., 2014).
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