Plantar fasciitis is an injury to connective tissue on the bottom of the foot. To appreciate the Chain Reaction Biomechanics of the CAUSES of plantar fasciitis, the function of this tissue must be understood, particularly as it pertains to human locomotion. The plantar fascia (PF) runs from the medial side of the bottom of the calcaneus, and extends down the length of the foot connecting to the toes. The PF supports the arch of the foot, especially from just before heel rise to toe off.
As the foot lands on the ground, the subtalar joint goes through the triplane motion of pronation (sometimes called eversion because of the motion of the calcaneus in the frontal plane). Pronation of the subtalar joint creates mobility in the midtarsal joint. This mobility allows the foot to adapt to the surface. The arch lowers under the weight of the body and the tissues are loaded. This adapting loading function must very quickly transform into an exploding function (propulsion). The midtasal joint is transformed from a mobile to a stable structure by supination of the subtalar joint. When the subtalar joint is in a supinated position, the foot is stable for propulsion. The PF contributes to this stability. If, in certain circumstances, the subtalar joint does not supinate, then the midtarsal joint stability will be lacking. Without the bony, capsular and muscular support to foot, the PF will be required to handle more stress. The excessive strain that results can produce the clinical symptoms known as plantar fasciitis. The most common consequence is a partial tearing of the PF from the calcaneal attachment.
Many, but not all, of the clients experiencing plantar fasciitis have the “unlocked” foot because of failure of the subtalar joint to adequately supinate prior to the propulsive phase of locomotion. So, as biomechanical detectives, the search for the probable suspects begins. The CAUSE may be anywhere in the body due to the “truth” of the Chain Reaction principle. For this blog, the suspects will be divided into 3 categories: same side leg, opposite side leg, and core/axial skeleton. Some of the most likely suspects will be discussed. Structural foot problems will not be addressed.
SAME SIDE LEG – In the same side leg, the suspects are those dysfunctions that allow excessive pronation of the subtalar joint, or prevent the supination of the subtalar joint.
- Lack of ankle joint dorsiflexion – Insufficient movement of the body over the foot in the sagittal plane leads to deficient eccentric load of the calf in the sagittal plane. The lack of eccentric load makes the econcentric supination of the subtalar joint ineffective.
- Tight calf group – As the body moves forward over the foot, dorsiflexion occurs at the ankle and midtarsal joint. Normally supination reduces midtarsal dorsiflexion, but if the ankle does not have enough dorsiflexion, then the subtalar joint may stay pronated in order to keep the midtarsal dorsiflexion available to the body.
- Weak posterior-lateral hip muscles – When the subtalar joint goes through pronation, the entire lower extremity participates in a tri-plane Chain Reaction that includes adduction and internal rotation of the hip. These motions must be decelerated by the posterior-lateral hip muscles. If the landing Chain Reaction motions are not decelerated, the subtalar joint may go through excessive pronation, making sufficient supination for propulsion difficult to attain.
OPPOSITE SIDE LEG – In the opposite side leg, the suspects are conditions that prevent proper loading of the back leg, or limit propulsion of that leg. Effective propulsion rotates the pelvis towards the front leg. The pelvis rotation causes the front leg to externally rotate, assisting supination of the subtalar joint via a top-down drive.
- Lack of ankle dorsiflexion or tight calf group – Insufficient dorsiflexion limits the load of the calf muscles and inhibits hip extension. When the load prior to heel lift is ineffective, then propulsion will be ineffective.
- Limited hip extension – The greatest power of propulsion comes from the hip flexors muscles. These muscles will be loaded by the motion of hip extension (and internal rotation). Without a good hip load, the propulsion will be less than optimal and the rotation of the pelvis towards the landing leg will be reduced.
- Painful or limited great toe extension – As the heel rises in response to the joint motions and muscle contractions of propulsion, the great toe goes through extension (hallux dorsiflexion). If this toe extension is limited, the power of the propulsion will be “muffled” and pelvis rotation reduced.
CORE / AXIAL SKELETON – In walking, and especially running, the functional abilities of the posterior-lateral hip muscles of the landing leg depend on having a mobile, but stable pelvis at the same time. If the core muscles (both front and back) are not lengthened and loaded, the pelvis will not have mobile-stability, resulting in “functional” weakness of the same side hip muscles.
- Loss of thoracic spine motion – Insufficient thoracic motion, in any of the planes, can result in ineffective loading of the core muscles. Without the core load, pelvic mobile-stability is almost impossible.
- Weak abdominal muscles – If the thoracic motion is available, that motion must be decelerated by the abdominals. Then the energy of deceleration must be transformed into concentric, motion-producing force. Failure of the abdominals to decelerate and/ or accelerate both the trunk and pelvis will negatively affect hip power.
- Upper trapezius fatigue/ tightness – As the trunk goes through motion in all three planes creating the load and explode of the core muscles, the cervical spine is actually experiencing motion. With the head looking forward, the movement of the trunk creates bottom-up motion in the cervical spine. If the trapezius muscles “tighten” with fatigue, either the head will have to rotate from side to side, or the head will remain steady by inhibiting the motion of the thoracic spine (much more likely).
Effective and time-efficient examination of all the probable suspects, while integrated with the rest of the body, is the power of the 3D Movement Analysis and Performance System (3DMAPS). Without an integrated analysis and training / treatment system, determining the CAUSE of plantar fasciitis remains a great challenge.