T
he foot serves several important biomechanical functions. It forms a rigid lever
arm to propel us in any direction. It mainly performs this in the terminal phase of
gait through assistance of the hallux. It provides terrain adaptability to perform
activities on uneven surfaces, absorbs shock through dissipating ground reaction
forces (GRF) which occurs at initial contact phase. Finally, the foot acts as the
body’s support for static and dynamic weight-bearing positions.
Of the five phases of gait, the push off and propulsion phase
is critical for human locomotion. The foot begins as a shock
absorbing lever in the initial contact phase, and then becomes rigid
through supination for propulsion. However, Caravaggi and Pataky,
found that the Plantar Aponeurosis could begin contracting in early
stance phase. It is important that the foot moves in this manner
that provides a stable support and lever on to continue forward.
However, there are several degrees that humans can uniquely
compensate that can have prolonged impact on the foot and other
portions of the body over time.
Of the 26 bones in the foot there are 17 that are the most important
when it comes to walking. Listed from posterior to anterior they are
the Calcaneus, the Talus, the five transverse Metatarsal Heads, and
the distal phalanges. Another component that is equally important
for gait propulsion is the plantar aponeurosis and the Plantar Fascia.
The plantar fascia can be split into two portions. Plantar fascia is
deep to the sole of the foot and is thinner on the lateral and medial
portions. The collagen fibers run parallel to the direction of pull. It
is a passive structure and can transmit mechanical stress throughout
the body. The plantar fascia is directly touching the calcaneal
tuberosity and with insufficient biomechanical control, can cause
various chronic pathologies to form. Towards midline of the sole
of the foot, it becomes thicker and becomes white and illuminant
in color. This portion is known as the plantar aponeurosis . The
aponeurosis contributes to propulsion of the body through the gait
cycle. They are two very important elements of foot functional
anatomy.
The “windlass mechanism” is a mechanical model that provides a
thorough explanation of these biomechanical factors and stresses.1
Generally, the windlass p ɽ٥