FOOT BIOMECHANICS

Characteristics & Anatomy Of The Foot

The feet are the foundation of support for the pelvis, spine and lower body. They provide the necessary stability to perform daily activities. The foot and ankle form a complex system which consists of 28 bones, 33 joints, 112 ligaments, controlled by 13 extrinsic and 21 intrinsic muscles. The foot is subdivided into the rear-foot, mid-foot & fore-foot and central to the success of the pedal foundation is its “arched structure”. The Arched Structure is a complex of three bony arches: the medial longitudinal arch, the lateral longitudinal arch and the anterior transverse (metatarsal) arch.(Physio-Pedia)

Arches of Foot

The 3 arches of the foot allow the foot to absorb downward forces and act as a rigid lever during gait propulsion:

• Medial Longitudinal Arch: The most obvious arch is seen along the medial aspect of the foot. The navicular bone forms the "keystone" of this large and long arch, which is supported primarily by the plantar fascia and spring ligament. The muscles of the foot and lower leg do not provide support for the medial arch, except during toe-off when walking or while standing on tip-toe.
• Lateral Longitudinal Arch (LLA): This arch is located along the outside of each foot and relies much less on connective tissues for its support. For this reason, proper function of the lateral arch is extremely dependent on the alignment of the cuboid bone, which is frequently found to be in need of adjustment. Proper support for this arch is at least as important as for the other two, but is surprisingly absent in many orthotics.
• Transverse (Metatarsal) Arch: This arch extends from the metatarsal heads back to the tarsal bones, and runs from the medial to the lateral sides of the foot. At its most anterior portion, the metatarsal heads contact the ground. Poor function and loss of this arch will often result in a build-up of thick callus underneath the metatarsal heads. Recurrent "dropped" metatarsal heads and/or irritation of one of the interdigital nerves (a "Morton's neuroma") is also a good indications that this arch is not being supported properly by the plantar fascia. (Dynamic Chiropractic)

Static and Dynamic Support With Orthotics

The structural design of the three-arched plantar vault is very good at supporting weight and carrying heavy loads, while remaining flexible. During normal standing, the load of the body is balanced over the center of the foot, anterior to the ankle. This places the greatest amount of load at the apex of the three arches. This force is then distributed along the "buttresses" of the arches to the heel (which bears 50 percent to 60 percent of body weight) and the metatarsal heads (which bear 40 percent to 50 percent of body weight). Loss of this configuration will result in abnormal force concentrations, which will eventually cause degenerative and symptomatic clinical conditions. (Foot Education) 

During gait, the foot undergoes substantial changes. The arches and connective tissues must sustain the stress of heel strike, then adapt to the ground during stance phase, and finally become a rigid lever to provide an efficient push-off. This must all occur in a coordinated manner, with no glitches or hang-ups. The foot must permit a smooth transfer of the body's center of mass over the leg to conserve energy and keep the work expenditure to a minimum. The heavier a patient is, the greater the stresses on the feet and ankles.

Collapse or dysfunction of any of the arches needs to be addressed with flexible yet stabilizing orthotics that will support the patient's foot both during standing (static support) and throughout the gait cycle (dynamic support), while controlling the impact forces. There is one actual insole that provides “Dynamic” support called SelectFlex which uses a patented arch lifting technology called the PowerLift Arch. The PowerLift Arch provides the wearer with 3 levels to support the arch with dynamic alignment with every step. This unique arch technology dynamically lifts your arch into a comforting sine wave motion that provides up to 89% more arch support with every step.

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