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MUSCLES OF THE LEG

BIG PICTURE

The leg consists of the tibia and fibula. The tibia articulates with the femur through the knee joint. Distally, the tibia and fibula articulate with the talus through the ankle joint. The muscles of the leg that act on ankle and foot are organized into three fascial compartments, similar to those of the thigh muscles (Figure 37-1A). The anterior compartment contains muscles that primarily produce dorsiflexion of the ankle and extension of the digits. The posterior compartment contains muscles that primarily produce plantar flexion and inversion at the ankle joint and flexion of the digits. The lateral compartment contains muscles that primarily produce plantar flexion and eversion at the ankle joint.

Figure 37-1:

A. Cross-section of the right leg (viewed from foot to head). B. Movements of the ankle. C. Muscles of the anterior compartment of the leg.

ACTIONS OF THE ANKLE

The primary ankle joints and their associated actions are as follows:

  • Talocrural joint. Consists of articulations between the tibia and talus (tibiotalar joint) and the fibula and talus (talofibular joint) and allows for motion primarily in the sagittal plane (Figure 37-1B):

    • Plantar flexion. Foot moves downwards (standing on tip-toes).

    • Dorsiflexion. Foot moves upwards (standing on heals).

  • Subtalar joint. Formed by articulations between the talus and the calcaneus and allows for motion primarily in the coronal plane:

    • Inversion. Plantar surface of the foot moves to face medially.

    • Eversion. Plantar surface of the foot moves to face laterally.

The terms supination and pronation describe the rolling motion of the heels and feet during normal walking or running. This includes the talocrural, subtalar, and forefoot joints, which permit three simultaneous planes of motion that result in pronation and supination.

  • Pronation. Dorsiflexion, eversion, and forefoot abduction. Pronation occurs as the lateral edge of the heel strikes the ground while walking and running and the foot rolls inward and flattens out to help absorb shock.

  • Supination. Plantar-flexion, inversion, and forefoot adduction. Supination describes the outward rolling motion, which occurs when the calcaneus lifts off the ground during foot take off and most of the body weight is placed onto the lateral surface of the foot. Supination enables the foot to form a rigid structure for propulsion during walking and running.

MUSCLES OF THE ANTERIOR COMPARTMENT OF THE LEG

The anterior compartment of the leg is formed by the deep fascia and contains muscles that primarily dorsiflex the ankle and extend the digits (Table 37-1). It also contains the anterior tibial artery and deep fibular nerve.

TABLE 37-1.Muscles of the Leg

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