Muscles of the Lower Limb: Structure, Function, and Compartmentalization

Muscles of the Body: Lower Limb

Girdles and Limbs: Overview

The lower limb muscles are organized into compartments based on their anatomical location and function. These muscles are essential for movement, stability, and posture, and are grouped into anterior, medial, lateral, and posterior compartments of the thigh and leg, as well as intrinsic muscles of the foot.

Muscles of the Thigh

Anterior and Medial Muscles of the Thigh

The anterior and medial compartments of the thigh contain muscles responsible for flexion, extension, and adduction of the hip and knee. The quadriceps femoris is the primary extensor of the knee, while the medial compartment muscles adduct the thigh.

• Quadriceps femoris: Composed of four heads (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius), all inserting at the quadriceps tendon. Powerful knee extensors.

• Sartorius: Flexes, abducts, and laterally rotates the thigh; flexes the knee.

• Iliopsoas (Iliacus + Psoas major): Major hip flexor.

• Medial compartment muscles: Adductor longus, adductor brevis, adductor magnus, pectineus, gracilis. Responsible for thigh adduction.

Muscles of the Posterior Gluteal Region and Lateral Rotators

The posterior gluteal muscles and lateral rotators originate from the pelvis or sacrum and are involved in extension, abduction, and lateral rotation of the thigh.

• Gluteus maximus: Main extensor of the hip.

• Gluteus medius and minimus: Abduct and medially rotate the thigh.

• Lateral rotators: Piriformis, obturator externus/internus, superior/inferior gemellus, quadratus femoris. Laterally rotate the thigh.

Muscles of the Posterior Compartment of the Thigh

The posterior compartment contains the hamstring muscles, which are responsible for hip extension and knee flexion.

• Biceps femoris

• Semitendinosus

• Semimembranosus

Muscles of the Leg

Anterior Compartment of the Leg

The anterior compartment muscles dorsiflex the foot and extend the toes. They are crucial for walking and balance.

• Tibialis anterior: Dorsiflexes and inverts the foot.

• Extensor digitorum longus: Extends toes and dorsiflexes foot.

• Extensor hallucis longus: Extends big toe and dorsiflexes foot.

• Fibularis tertius: Dorsiflexes and everts the foot.

Lateral Compartment of the Leg

The lateral compartment muscles evert the foot and assist in plantar flexion.

• Fibularis longus

• Fibularis brevis

Posterior Compartment of the Leg

The posterior compartment is divided into superficial and deep groups. These muscles are responsible for plantar flexion and toe flexion.

• Superficial muscles (Triceps surae): Gastrocnemius, soleus, plantaris. Plantar flex the foot.

• Deep muscles: Popliteus, flexor digitorum longus, flexor hallucis longus, tibialis posterior. Flex toes and invert the foot.

Intrinsic Muscles of the Foot

Overview and Function

The intrinsic muscles of the foot are responsible for toe movement and maintaining the arches of the foot. They are organized into layers on the dorsal and plantar aspects.

• Dorsal aspect: Extensor digitorum brevis.

• Plantar aspect: Multiple layers including flexor digitorum brevis, abductor hallucis, abductor digiti minimi, flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis, plantar and dorsal interossei.

Key Functions and Clinical Relevance

• Flexion and extension: Allow movement of toes for walking and balance.

• Abduction and adduction: Spread and bring together toes, important for stability.

• Arch support: Muscles help maintain the structural integrity of the foot arches, preventing flatfoot.

Summary Table: Major Muscles of the Lower Limb

Compartment	Major Muscles	Primary Actions
Anterior Thigh	Quadriceps femoris, Sartorius, Iliopsoas	Knee extension, hip flexion
Medial Thigh	Adductor longus, Adductor brevis, Adductor magnus, Pectineus, Gracilis	Thigh adduction
Posterior Thigh	Biceps femoris, Semitendinosus, Semimembranosus	Hip extension, knee flexion
Gluteal Region	Gluteus maximus, medius, minimus, lateral rotators	Hip extension, abduction, lateral rotation
Anterior Leg	Tibialis anterior, Extensor digitorum longus, Extensor hallucis longus, Fibularis tertius	Dorsiflexion, toe extension
Lateral Leg	Fibularis longus, Fibularis brevis	Eversion, plantar flexion
Posterior Leg	Gastrocnemius, Soleus, Plantaris, Popliteus, Flexor digitorum longus, Flexor hallucis longus, Tibialis posterior	Plantar flexion, toe flexion, inversion
Foot	Extensor digitorum brevis, Flexor digitorum brevis, Abductor hallucis, Abductor digiti minimi, Flexor hallucis brevis, Adductor hallucis, Flexor digiti minimi brevis, Interossei	Toe movement, arch support

Additional info:

• Muscle origins and insertions are critical for understanding their actions. For example, the quadriceps femoris originates from the pelvis and femur and inserts into the patella via the quadriceps tendon.

• Clinical relevance includes injuries such as strains, tears, and compartment syndrome, which affect muscle function and mobility.