Ankle Bio mechanics : PART 1

The ankle/foot complex is structurally analogous to the wrist-hand complex of the upper extremity but has a number of distinct differences to optimize its primary role to bear weight. The complementing structures of the foot allow the foot to sustain large weight-bearing.

the bones of the foot are traditionally divided into three functional segments. These are the hindfoot (posterior segment), composed of the talus and calcaneus; the midfoot (middle segment), composed of the navicular, cuboid, and three cuneiform bones; and the forefoot (anterior segment), composed of the metatarsals and the phalanges.

These terms are commonly used in descriptions of ankle or foot dysfunction or deformity and are similarly useful in understanding normal ankle and foot function.

The three motions of the ankle/foot complex that approximate cardinal planes and axes are dorsiflexion/ plantarflexion, inversion/eversion, and abduction/adduction.

Dorsiflexion and plantarflexion are motions that occur approximately in the sagittal plane around a coronal axis. Dorsiflexion decreases the angle between the leg and the dorsum of the foot, whereas plantarflexion increases this angle. 

At the toes, motion around a similar axis is termed extension (bringing the toes up), whereas the opposite motion is flexion (bringing the toes down or curling them). Inversion and eversion occur approximately in the frontal plane around a longitudinal (anteroposterior/A-P) axis that runs through the length of the foot.

Pronation/supination in the foot motions that occur around an axis that lies at an angle to each of the axes for “cardinal” motions of dorsiflexion/plantar flexion, inversion/eversion, and abduction/adduction.

valgus refers to a reduction in the medial angle between two bones (or movement of the distal segment away from the midline); varus refers to the opposite. However, valgus and varus are sometimes used to refer to fixed deformities in the ankle/foot complex, whereas at other times the terms are used to describe or as synonyms for other normal motions.
Valgus and varus are terms that may be used for the ankle/foot complex in several ways, depending on the context.

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