Muscles Crossing the Hip and Knee Joints: Movements of the Thigh and Leg chapter 10 part 4

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The Muscular System: Muscles of the Thigh and Leg

Overview of Muscles Crossing the Hip and Knee Joints

The muscles crossing the hip and knee joints are essential for movements of the thigh and leg, including walking, running, and jumping. These muscles are grouped anatomically and functionally into anterior, medial, and posterior compartments, each with distinct actions and innervations.

Anterior muscles: Flex the femur at the hip and extend the leg at the knee (foreswing of walking).
Posterior muscles: Extend the thigh and flex the leg (backswing of walking).
Medial muscles: Adduct the thigh.
All groups are enclosed by the fascia lata.

Table summarizing muscles crossing the hip and knee joints

Anterior Compartment Muscles

The anterior compartment contains muscles that primarily flex the hip and extend the knee. The quadriceps femoris is the most prominent muscle group in this compartment.

Iliopsoas (iliacus and psoas major): Prime mover of hip flexion.
Tensor fasciae latae: Assists in hip flexion and abduction.
Rectus femoris: Flexes thigh at hip and extends leg at knee.
Quadriceps femoris: Consists of four heads (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius); all insert into the quadriceps tendon, patella, and tibial tuberosity. Powerful knee extensor.

Anterior and medial muscles of the thigh and leg

Muscle	Description	Origin & Insertion	Action	Nerve Supply
Rectus femoris	Superficial muscle of anterior thigh	O: Iliac spine; I: Patella/tibial tuberosity	Extends leg, flexes thigh	Femoral nerve
Vastus lateralis	Lateral thigh muscle	O: Femur; I: Patella/tibial tuberosity	Extends leg, stabilizes knee	Femoral nerve
Vastus medialis	Medial thigh muscle	O: Femur; I: Patella/tibial tuberosity	Extends leg, stabilizes patella	Femoral nerve
Vastus intermedius	Deep to rectus femoris	O: Femur; I: Patella/tibial tuberosity	Extends leg	Femoral nerve

Quadriceps femoris muscle group

Medial Compartment Muscles

The medial compartment muscles are primarily responsible for adduction of the thigh and also contribute to medial rotation. These muscles are important in movements that press the thighs together.

Adductor magnus, longus, brevis: Adduct and medially rotate thigh.
Pectineus: Adducts, flexes, and medially rotates thigh.
Gracilis: Adducts thigh, flexes and medially rotates leg.
Innervated mainly by the obturator nerve.

Medial compartment muscles of the thigh

Muscle	Description	Origin & Insertion	Action	Nerve Supply
Adductor magnus	Large muscle, medial thigh	O: Ischial/pubic rami; I: Femur	Adducts, flexes, medially rotates thigh	Obturator/sciatic nerves
Adductor longus	Medial thigh muscle	O: Pubis; I: Femur	Adducts, flexes, medially rotates thigh	Obturator nerve
Adductor brevis	Short, medial thigh muscle	O: Pubis; I: Femur	Adducts, flexes, medially rotates thigh	Obturator nerve
Pectineus	Flat, anterior thigh muscle	O: Pubis; I: Femur	Adducts, flexes, medially rotates thigh	Femoral/obturator nerves
Gracilis	Long, thin, medial thigh muscle	O: Pubis; I: Tibia	Adducts thigh, flexes leg	Obturator nerve

Posterior Compartment Muscles

The posterior compartment muscles, including the hamstrings, are responsible for extension of the thigh and flexion of the leg. These muscles are crucial for activities such as running and jumping.

Hamstrings: Biceps femoris, semitendinosus, semimembranosus; extend thigh and flex leg.
Innervated by the sciatic nerve.
Common sports injury: "pulled hamstring".

Posterior compartment muscles of the thigh

Muscle	Description	Origin & Insertion	Action	Nerve Supply
Biceps femoris	Lateral hamstring muscle	O: Ischial tuberosity/femur; I: Fibula/tibia	Extends thigh, flexes leg	Sciatic nerve
Semitendinosus	Medial hamstring muscle	O: Ischial tuberosity; I: Tibia	Extends thigh, flexes leg	Sciatic nerve
Semimembranosus	Deepest hamstring muscle	O: Ischial tuberosity; I: Tibia	Extends thigh, flexes leg	Sciatic nerve

Hamstring muscles of the posterior thigh

Lateral Rotators and Abductors

Lateral rotators and abductors of the thigh stabilize the hip and allow for complex movements such as rotation and abduction. These muscles are important for balance and mobility.

Gluteus maximus: Extends and laterally rotates thigh.
Gluteus medius and minimus: Abduct and medially rotate thigh.
Piriformis, obturator externus/internus, gemellus: Laterally rotate thigh.

Lateral rotators and abductors of the hip

Muscle	Description	Origin & Insertion	Action	Nerve Supply
Gluteus maximus	Largest gluteal muscle	O: Ilium/sacrum/coccyx; I: Femur	Extends, laterally rotates thigh	Inferior gluteal nerve
Gluteus medius	Middle gluteal muscle	O: Ilium; I: Femur	Abducts, medially rotates thigh	Superior gluteal nerve
Gluteus minimus	Smallest gluteal muscle	O: Ilium; I: Femur	Abducts, medially rotates thigh	Superior gluteal nerve
Piriformis	Pyramidal muscle	O: Sacrum; I: Femur	Laterally rotates thigh	Sacral nerves
Obturator externus/internus	Flat, triangular muscles	O: Obturator foramen; I: Femur	Laterally rotates thigh	Obturator nerve
Gemellus (superior/inferior)	Small, twin muscles	O: Ischial spine/tuberosity; I: Femur	Laterally rotates thigh	Sacral nerves

Muscles of the gluteal region

Summary Table: Actions of Muscles Acting on the Thigh, Leg, and Foot

The following table summarizes the actions of major muscles acting on the thigh, leg, and foot, including their roles in flexion, extension, abduction, adduction, rotation, and movements at the knee and ankle joints.

Summary table of muscle actions on thigh, leg, and foot

Compartmentalization of Thigh and Leg Muscles

Muscles of the thigh and leg are organized into compartments separated by connective tissue. Each compartment contains muscles with similar functions and innervation.

Anterior compartment of thigh: Extends leg, flexes thigh; innervated by femoral nerve.
Medial compartment of thigh: Adducts thigh; innervated by obturator nerve.
Posterior compartment of thigh: Flexes leg, extends thigh; innervated by sciatic nerve.
Anterior compartment of leg: Dorsiflexes foot; innervated by deep fibular nerve.
Lateral compartment of leg: Everts foot; innervated by superficial fibular nerve.
Posterior compartment of leg: Plantar flexes foot; innervated by tibial nerve.

Compartments of the thigh Compartments of the leg

Key Terms and Concepts

Origin: The fixed attachment point of a muscle.
Insertion: The movable attachment point of a muscle.
Prime mover (agonist): Muscle primarily responsible for a specific movement.
Antagonist: Muscle that opposes the action of the prime mover.
Synergist: Muscle that assists the prime mover.
Fascia lata: Deep fascia enclosing the thigh muscles.

Clinical Relevance

Pulled groin: Injury to overstretched adductor muscles.
Pulled hamstring: Common sports injury involving posterior thigh muscles.

Summary

The muscles crossing the hip and knee joints are essential for locomotion and stability. Understanding their anatomy, actions, and innervation is crucial for comprehending human movement and diagnosing musculoskeletal injuries.