Ankle and Foot; structure, function and joints

STRUCTURE AND FUNCTION OF THE ANKLE AND FOOT

The bones of the ankle and foot consist of the distal

tibia and fibula, 7 tarsals, 5 metatarsals, and 14 phalanges

STRUCTURAL RELATIONSHIPS AND MOTIONS

Anatomical Characteristics

The leg is structurally designed to transmit the ground reaction forces from the foot upward to the knee joint and femur, and adapt as needed to provide stability to or allow motion of the ankle. The resulting motions in the ankle and foot are defined using primary plane descriptors and triplanar descriptors.

Ankle and Foot


Leg

The tibia and fibula make up the leg. These two bones are bound together by an interosseous membrane along the shafts of the bones, by strong anterior and posterior inferior tibiofibular ligaments that hold the distal tibiofibular articulation together, and by a strong capsule that encloses the proximal tibiofibular articulation. Unlike the radius and ulna in the upper extremity, the tibia and fibula do not rotate around each other, but there is slight movement between the two bones that allows greater movement of the ankle joints.

Foot

The foot is divided into three segments: the hindfoot, midfoot, and forefoot.

Hindfoot. The talus and calcaneus make up the posterior segment.

Midfoot. The navicular, cuboid, and three cuneiforms make up the middle segment.

Forefoot. Five metatarsals and 14 phalanges make up the anterior segment. Each toe has three phalanges except for the large toe, which has two.

Motions of the Foot and Ankle Defined

Primary Plane Motions

Although motions in the foot and ankle do not occur purely in the cardinal planes, they are still defined as follows.

Sagittal plane motion around a frontal (coronal axis).

Dorsiflexion is movement in a dorsal direction which decreases the angle between the leg and dorsum of the foot, and plantarflexion is movement in a plantar direction. Motion occurring at the toes may also be called dorsiflexion or extension, and plantarflexion or flexion.

Frontal plane motion around a sagittal (anteroposterior)

axis. Inversion is inward turning of the foot and eversion is outward turning. Normally, an inward and outward motion is described by the terms abduction and adduction, but because the foot is at a right angle to the leg, the terms abduction and adduction are not used here.

Transverse plane motion around a vertical axis. Abduction is movement away from the midline, and adduction is movement toward the midline.

Triplanar Motions

Triplanar motion occurs around an oblique axis at each articulation of the ankle and foot. The definitions are descriptive of the movement of the distal bone on the proximal bone. When the proximal bone moves on the stabilized distal bone, as occurs in weight bearing, the motion of the proximal bone is opposite, although the relative joint motion is the same as defined.

Pronation. Pronation is a combination of dorsiflexion, eversion, and abduction. During weight bearing, pronation of the subtalar and transverse tarsal joints causes the arch of the foot to lower, and there is a relative supination of the forefoot with dorsiflexion of the first and plantarflexion of the fifth metatarsals. This is the loose-packed or mobile position of the foot and is assumed when the foot absorbs

the impact of weight bearing and rotational forces of the rest of the lower extremity and when the foot conforms to the ground.

Supination. Supination is a combination of plantarflexion, inversion, and adduction. In the closed-chain, weightbearing foot, supination of the subtalar and transverse tarsal joints with a pronation twist of the forefoot (plantarflexion of the first and dorsiflexion of the fifth metatarsals) increases the arch of the foot and is the close-packed or stable position of the joints of the foot. This is the position the foot assumes when a rigid lever is needed to propel the body forward during the push-off phase of ambulation.

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