Plantar fasciitis - causes
One of the most interesting findings about plantar fasciitis is that the condition is an overuse syndrome specific to an aging yet active patient population. I can't recall ever seeing a case of plantar fasciitis in a child under the age of 20. And nor do you see plantar fasciitis in the elderly. The vast majority of cases of plantar fasciitis that I treat are in patients who are between the ages of 35 and 65 years of age. These folks are typically active, not necessarily runners or athletes (although some are). Usually, these are patients who enjoy working in the yard on weekends, they go for walks and haven't slowed down in their lives at all. They really share no common denominator in terms of their chosen employment or level of physical activity. I see plantar fasciitis in patients who are office workers, factory workers, lawyers, and pizza shop owners.
Plantar fasciitis - tissue elasticity
What these patients do have in common is a loss of tissue elasticity. Tissue elasticity is that ability of tissue to accept a load, perform a task and heal within a 24hr period so that you're ready to repeat the same activity the next day. To illustrate this point, let's use a really simple example. When you're in your 20's you're able to be active and participate in so many things. You may be on the local softball team. You play soccer with your kids and you can go out and work all day in the yard. But as you get into your 40's and 50's things start to change. Last year you got injured playing softball so you bailed out on the team knowing that you just don't have the stamina and ability to heal like you used to. Your kids are in high school and now you go watch their games instead of actually playing with them. And yard work? It's not getting any easier. After a big Sunday in the yard, you're stiff until Tuesday or Wednesday. All of this is due to a loss of tissue elasticity. You just cannot rebound as quickly as you used to be able to. And that's part of the key to understanding plantar fasciitis. The injury that causes plantar fasciitis is simple enough - walking. With each step, the calf muscle delivers a force through the Achilles tendon into the heel, and the plantar fascia carries the force to the ball of the foot where the 'action of walking' takes place. The injury to the plantar fascia that caused plantar fasciitis is actually due to the inherent mechanical stress placed on the fascia with simple walking. The tissue elasticity of the fascia has decreased to a degree that it is susceptible to injury from a benign activity like simple walking. Not recognizing the fact that we are recreating the injury each day, we continue with our normal activities and wonder why we ever got plantar fasciitis in the first place and why it won't go away. An important part of treating plantar fasciitis is breaking into that cycle of re-injury. That cycle of re-injury is what we call an overuse syndrome.
I became very interested in this topic about 20 years ago and did a fair amount of original research on lower extremity biomechanics. My goal was to quantify the amount of force that was generated by the calf and delivered to the foot during gait. I called the project CT band syndrome, CT referring to calf-to-toes. The topic proved to be somewhat challenging from the standpoint that the leg ankle and foot are in a constant state of change during gait. The leg, ankle, and foot are a lever that functions in the sagital plane. Think of other examples of levers that you may use in your daily life. A pry bar is a good example. If you want to move a rock in your yard, you find a small rock that you place adjacent to the large rock to use a fulcrum. So the long arm of the pry bar is the effort arm and the short arm is the resistance arm. The small rock is the fulcrum. If we translate this lever knowledge to the CT band, the calf is the effort arm, the ankle is the fulcrum and the foot is the resistance arm. Levers need to function in one plane. Think of how that pry bar works. The pry bar cannot be curved or in an S shape. It needs to be straight and move in one direction (a single plane.) The same holds true for the CT band. Although I think the CT band concept is interesting and I did publish in a peer-reviewed journal, the topic never really gained much traction in the literature. For those of you who are bio-engineers, you might want to take a peek at these links to better understand the mechanical aspects of CT band syndrome and how it relates to plantar fasciitis.
Simply put, plantar fasciitis is due to mechanical load applied through the CT band that results in an injury to the insertion of the plantar fascia on the plantar aspect of the heel. When we talk about treatment, you'll see how weakening the force of the calf is key to breaking into the overuse syndrome of plantar fasciitis.
Plantar fasciitis - contributing factors
What are some of the contributing factors to plantar fasciitis? Put your bio-engineer hat back on for a second and think about the concept of work. Work is the amount of action that a structure performs. And when something contributes to or increases the amount of work or the duration of work performed, it has the potential to contribute to the problem. The work that the CT band performs is to deliver force from the calf to the ball of the foot. Think of walking as a controlled forward fall. The CT band slows that forward fall. And in running the CT band actually pushes off, rapidly pushing your center of mass forward. The more bodyweight that the CT band has to manage, the more work it has to perform. As such, obesity is a contributing factor to plantar fasciitis. Other contributing factors include age, increased duration of time spent on the feet and any condition that would result in loss of tissue elasticity. The primary contributing factor that causes loss of tissue elasticity is age.
Most importantly, remember that plantar fasciitis is an overuse syndrome caused primarily by the calf muscle. Contributing factors include age and obesity.
Additional topics in this blog series include -
Plantar fasciitis | History
Plantar fasciitis | Differential diagnosis of heel pain
Plantar fasciitis | Conservative methods of care
Plantar fasciitis | Surgical treatment
Plantar fasciitis | Additional treatment methods
Plantar fasciitis | Surgical complications