Muscles of the Lower Extremity

Muscles of the Lower Extremity: Attachments, Functions, and Innervation

A Brief Description of Muscle Actions

• Muscle Attachments:

  • Muscles have two attachment sites:
  • Proximal Attachment (Origin): Fixed point where the muscle originates.
  • Distal Attachment (Insertion): Movable point where the muscle attaches, usually resulting in joint movement.

• Types of Muscle Contractions:

  • Concentric Contraction:
  • Occurs when a muscle shortens.
  • Involves one attachment point remaining fixed while the other moves toward it.
  • Example: Lifting a cup of water to the mouth (biceps) or extending the leg when kicking a ball (quadriceps).
  • Eccentric Contraction:
  • Occurs when a muscle resists being lengthened.
  • The force of gravity or an external load pulls the attachment points away from each other; the muscle gradually lengthens while continuing to exert force.
  • Example: Lowering a hand weight after a bicep curl or descending during a squat (quadriceps preventing knee buckling).

• Importance of Muscle Actions:

  • Balance between concentric and eccentric actions is vital for coordinated activities (e.g., walking, running, etc.).
  • Muscle groups often work in pairs (e.g., biceps and triceps) to allow smooth movement.

• Learning Muscle Functions:

  • Knowing origins and insertions helps visualize both concentric and eccentric actions.
  • Philosophy: "Don’t memorize if you don’t have to, but rather Make It Make Sense!"

Muscles of The Anterior Thigh

• Iliopsoas:

  • Proximal Attachments: Transverse processes, lateral bodies, and intervertebral discs of T12-L4.
  • Distal Attachments: Lesser trochanter of the femur.
  • Function: Hip flexion; external rotation from abduction position.
  • Innervation: L2-L4 ventral rami, femoral nerve.

• Sartorius:

  • Proximal Attachments: Anterior superior iliac spine (ASIS).
  • Distal Attachments: Proximal medial tibia.
  • Function: Flexes, abducts, laterally rotates thigh; flexes and internally rotates leg at knee.
  • Innervation: L2-L3, femoral nerve.

• Quadriceps:

  • Muscle Components: Rectus femoris, vastus medialis, vastus lateralis, vastus intermedius.
  • Proximal Attachments:
  • Rectus femoris: Anterior inferior iliac spine (AIIS), superior rim of acetabulum.
  • Vastus medialis: Lower intertrochanteric line, medial lip of linea aspera.
  • Vastus lateralis: Upper intertrochanteric line, anterior/inferior greater trochanter, greater gluteal tuberosity.
  • Vastus intermedius: Anterior/lateral regions of upper 2/3 of femur.
  • Distal Attachments: Base of patella and tibial tuberosity via patellar ligament.
  • Function: Flexes thigh at hip joint, extends leg at knee.
  • Innervation: L2-L4, femoral nerve.

Muscles of the Medial Thigh

• Pectineus:

  • Proximal Attachments: Pectineal line on superior pubic ramus.
  • Distal Attachments: Pectineal line on posterior femur.
  • Function: Flexes, adducts, and internally rotates thigh.
  • Innervation: Femoral nerve (may also receive from obturator nerve), (L2-L4).

• Adductor Brevis:

  • Proximal Attachments: Anterior surface of inferior pubis ramus.
  • Distal Attachments: Proximal 1/3 of linea aspera of femur.
  • Function: Adducts, flexes, internally rotates thigh.
  • Innervation: Obturator nerve (L2-L4).

• Adductor Longus:

  • Proximal Attachments: Anterior surface of body of pubis.
  • Distal Attachments: Middle 1/3 of linea aspera of femur.
  • Function: Adducts, flexes, internally rotates thigh.
  • Innervation: Obturator nerve (L2-L4).

• Adductor Magnus:

  • Proximal Attachments:
  • Anterior Head: Ischial ramus.
  • Posterior Head: Ischial tuberosity.
  • Distal Attachments: Entire linea aspera; adductor tubercle of femur.
  • Function: Adducts thigh (anterior head) and also extends the thigh (posterior head).
  • Innervation: Obturator nerve and tibial nerve (L2-S1).

• Gracilis:

  • Proximal Attachments: Lower body of pubis, inferior pubic ramus.
  • Distal Attachments: Proximal medial surface of tibia (posterior to sartorius attachment).
  • Function: Adducts and flexes thigh; flexes and medially rotates leg at knee.
  • Innervation: Obturator nerve (L2-L4).

• Obturator Externus:

  • Proximal Attachments: External surface of the obturator membrane, inferior pubic ramus, ischial ramus.
  • Distal Attachments: Trochanteric fossa of the femur.
  • Function: Externally rotates thigh at hip joint.
  • Innervation: Obturator nerve (L3-L4).

Muscles of the Gluteal Region

• Tensor Fascia Lata:

  • Proximal Attachments: Outer surface of iliac crest (just posterior to ASIS).
  • Distal Attachments: Iliotibial band.
  • Function: Flexes, abducts, internally rotates thigh.
  • Innervation: Superior gluteal nerve (L4-S1).

• Gluteus Maximus:

  • Proximal Attachments: Outer ilium, posterior gluteal line, aponeurosis of erector spinae, gluteus medius, posterior surface of sacrum, coccyx, sacrotuberous and posterior sacroiliac ligaments.
  • Distal Attachments: Iliotibial band and gluteal tuberosity.
  • Function: Extends and externally rotates thigh; upper fibers abduct, lower fibers adduct thigh.
  • Innervation: Inferior gluteal nerve (L5-S2).

• Gluteus Medius:

  • Proximal Attachments: Outer surface of ilium above anterior gluteal line.
  • Distal Attachments: Lateral greater trochanter of femur.
  • Function: Abducts the thigh; anterior fibers medially rotate and flex hip, while posterior fibers laterally rotate and extend hip.
  • Innervation: Superior gluteal nerve (L4-S1).

• Gluteus Minimus:

  • Proximal Attachments: Outer surface of ilium between anterior and inferior gluteal lines.
  • Distal Attachments: Antero-lateral greater trochanter of femur.
  • Function: Abducts the thigh; medially rotates and flexes hip.
  • Innervation: Superior gluteal nerve (L4-S1).

• Piriformis:

  • Proximal Attachments: Anterior sacrum.
  • Distal Attachments: Superior greater trochanter.
  • Function: Laterally rotates thigh and can cause hip abduction.
  • Innervation: Nerve to the piriformis (S1-S2).

• Obturator Internus:

  • Proximal Attachments: Internal surface of obturator membrane, inferior pubic ramus, ischial ramus.
  • Distal Attachments: Medial greater trochanter (anterior and superior to trochanteric fossa).
  • Function: Laterally rotates thigh.
  • Innervation: Nerve to obturator internus (L5-S2).

• Superior Gemellus:

  • Proximal Attachments: Dorsal surface of ischial spine.
  • Distal Attachments: Tendon of obturator internus.
  • Function: Laterally rotates thigh.
  • Innervation: Nerve to obturator internus (L5-S2).

• Inferior Gemellus:

  • Proximal Attachments: Ischial tuberosity.
  • Distal Attachments: Tendon of obturator internus.
  • Function: Laterally rotates thigh.
  • Innervation: Nerve to the quadratus femoris (L4-S1).

• Quadratus Femoris:

  • Proximal Attachments: Lateral ischial tuberosity.
  • Distal Attachments: Middle of intertrochanteric crest of femur (quadrate tubercle).
  • Function: Laterally rotates thigh.
  • Innervation: Nerve to quadratus femoris (L4-S1).

Muscles of the Posterior Thigh

• Semimembranosus:

  • Proximal Attachments: Posterior ischial tuberosity.
  • Distal Attachments: Posterior medial tibial condyle.
  • Function: Extends thigh, internally rotates hip; flexes and internally rotates leg.
  • Innervation: Tibial nerve (L4-S2).

• Semitendinosus:

  • Proximal Attachments: Posterior ischial tuberosity, sacrotuberous ligament.
  • Distal Attachments: Proximal medial surface of tibia (posterior to sartorius attachment).
  • Function: Extends thigh, internally rotates hip; flexes and internally rotates leg.
  • Innervation: Tibial nerve (L4-S2).

• Biceps Femoris:

  • Components: Long head and short head.
  • Proximal Attachments: Long head - posterior ischial tuberosity, part of sacrotuberous ligament; Short head - lateral linea aspera (inferior to gluteal tuberosity).
  • Distal Attachments: Head of fibula.
  • Function: Long head - extends thigh, laterally rotates hip; both heads flex and externally rotate leg.
  • Innervation: Long head - tibial nerve (L5-S3); Short head - common fibular (peroneal) nerve (L5-S2).

Muscles of the Lateral Leg

• Fibularis (Peroneus) Longus:

  • Proximal Attachments: Head and proximal 2/3 of lateral fibula.
  • Distal Attachments: Lateral surface of medial cuneiform, lateral base of 1st metatarsal.
  • Function: Eversion of foot at subtalar joint; weakly plantarflexes foot at talocrural joint.
  • Innervation: Superficial fibular (peroneal) nerve (L4-S1).

• Fibularis (Peroneus) Brevis:

  • Proximal Attachments: Distal 2/3 of lateral fibula.
  • Distal Attachments: Tuberosity of 5th metatarsal.
  • Function: Everts foot at subtalar joint; weakly plantarflexes foot at talocrural joint.
  • Innervation: Superficial fibular (peroneal) nerve (L4-S1).

Muscles of Anterior Leg

• Tibialis Anterior:

  • Proximal Attachments: Lateral tibial condyle, proximal 2/3 of lateral tibia surface, interosseous membrane.
  • Distal Attachments: Medial and plantar surfaces of medial cuneiform, base of 1st metatarsal.
  • Function: Dorsiflexion of foot at talocrural joint; inverts foot at subtalar joint.
  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

• Extensor Digitorum Longus:

  • Proximal Attachments: Lateral condyle of tibia, proximal 2/3 of medial fibula, interosseous membrane.
  • Distal Attachments: By four tendons to dorsal surface of middle and distal phalanges of digits 2-5.
  • Function: Extends digits 2-5; dorsiflexion of foot; eversion at subtalar joint.
  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

• Fibularis (Peroneus) Tertius:

  • Proximal Attachments: Distal 1/3 of medial fibula, interosseous membrane.
  • Distal Attachments: Dorsal base of 5th metatarsal.
  • Function: Eversion of foot at subtalar joint.
  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

• Extensor Hallucis Longus:

  • Proximal Attachments: Middle medial fibula, adjacent interosseous membrane.
  • Distal Attachments: Dorsal base of distal phalanx of great toe.
  • Function: Extends great toe; dorsiflexes foot at talocrural joint.
  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

Muscles of the Posterior Leg

• Gastrocnemius:

  • Proximal Attachments: Via two heads to posterior surface of medial and lateral femoral condyles.
  • Distal Attachments: Calcaneal tuberosity via Achilles’ tendon.
  • Function: Plantarflexes foot; flexes leg at knee joint.
  • Innervation: Tibial nerve (S1-S2).

• Soleus:

  • Proximal Attachments: Posterior surface of fibular head, proximal 1/3 shaft, posterior tibia near soleal line.
  • Distal Attachments: Calcaneal tuberosity via Achilles’ tendon.
  • Function: Plantarflexes foot at talocrural joint.
  • Innervation: Tibial nerve (L5-S2).

• Plantaris:

  • Proximal Attachments: Most inferior aspect of lateral supracondylar line of femur, oblique popliteal ligament of knee.
  • Distal Attachments: Joins medial aspect of Achilles’ tendon to calcaneal tuberosity.
  • Function: Plantarflexes ankle; flexes leg at knee joint.
  • Innervation: Tibial nerve (L4-S1).

• Popliteus:

  • Proximal Attachments: Lateral aspect of femoral condyle via intracapsular tendon.
  • Distal Attachments: Posterior surface of proximal tibia above soleal line.
  • Function: Initiates knee flexion from extended position; causes either external rotation of femur on tibia or internal rotation of tibia on femur.
  • Innervation: Tibial nerve (L4-S1).

• Flexor Digitorum Longus:

  • Proximal Attachments: Posterior surface of middle 1/3 of tibia (medial to tibialis posterior).
  • Distal Attachments: Via four tendons to plantar surface of distal phalanges of digits 2-5.
  • Function: Flexes digits; plantarflexes foot; inverts foot.
  • Innervation: Tibial nerve (L5-S1).

• Flexor Hallucis Longus:

  • Proximal Attachments: Distal 2/3 of posterior fibula, interosseous membrane.
  • Distal Attachments: Plantar surface of distal phalanx of great toe.
  • Function: Flexes great toe; assists in plantarflexion and inversion of foot.
  • Innervation: Tibial nerve (L5-S2).

• Tibialis Posterior:

  • Proximal Attachments: Proximal 2/3 of posterior tibia, fibula, adjacent interosseous membrane.
  • Distal Attachments: Navicular tuberosity, all three cuneiforms, cuboid, bases of metatarsals 2-4.
  • Function: Plantarflexes foot; inverts foot.
  • Innervation: Tibial nerve (L5-S1).

Intrinsic Muscles of the Plantar Foot

• Abductor Hallucis:

  • Proximal Attachments: Medial process of calcaneus, plantar fascia, and flexor retinaculum.
  • Distal Attachments: Medial aspect of base of proximal phalanx of great toe.
  • Function: Abducts and flexes the 1st digit.
  • Innervation: Medial plantar nerve (L4-S1).

• Flexor Digitorum Brevis:

  • Proximal Attachments: Medial process of calcaneal tuberosity, plantar fascia.
  • Distal Attachments: Middle phalanges of digits 2-5.
  • Function: Assists flexor digitorum longus in digit flexion.
  • Innervation: Medial plantar nerve (L4-S1).

• Abductor Digiti Minimi:

  • Proximal Attachments: Processes of calcaneal tuberosity, plantar base of 5th metatarsal, plantar aponeurosis.
  • Distal Attachments: Lateral side of proximal phalanx of 5th digit.
  • Function: Abducts and flexes the 5th digit.
  • Innervation: Lateral plantar nerve (S1-S2).

• Quadratus Plantae:

  • Proximal Attachments: Two heads from medial and lateral calcaneal surfaces below tuberosity.
  • Distal Attachments: Lateral border of flexor digitorum longus tendon.
  • Function: Stabilizes tendons of flexor digitorum longus.
  • Innervation: Lateral plantar nerve (S1-S2).

• Lumbricals:

  • Proximal Attachments: Tendons of flexor digitorum longus.
  • Distal Attachments: Dorsal digital expansion of digits 2-5.
  • Function: Flexes metatarsophalangeal joints; extends interphalangeal joints.
  • Innervation: 1st lumbrical - medial plantar nerve (L4-S1); 2nd to 4th lumbricals - lateral plantar nerve (S1-S2).

• Flexor Hallucis Brevis:

  • Proximal Attachments: Plantar surface of cuboid, lateral cuneiform, parts of tibialis posterior tendon.
  • Distal Attachments: Medial and lateral aspects of base of proximal phalanx of 1st digit.
  • Function: Flexes great toe at MTP joint.
  • Innervation: Medial plantar nerve (L4-S1).

• Adductor Hallucis:

  • Heads:
  • Oblique Head: Plantar bases of 2nd to 4th metatarsal.
  • Transverse Head: Ligaments supporting MTP joints (3rd-5th).
  • Distal Attachments: Lateral aspect of proximal phalanx of great toe.
  • Function: Adducts and flexes great toe at MTP joint.
  • Innervation: Lateral plantar nerve (S1-S2).

Intrinsic Muscles of Plantar Foot (cont)

• Flexor Digiti Minimi:

  • Proximal Attachments: Plantar base of 5th metatarsal.
  • Distal Attachments: Lateral base of proximal phalanx 5th digit.
  • Function: Flexes little toe at MTP joint.
  • Innervation: Lateral plantar nerve (S1-S2).

• Plantar Interossei:

  • Proximal Attachments: Medial sides of metatarsals 3-5.
  • Distal Attachments: Medial bases of proximal phalanges (digits 3-5).
  • Function: Adducts digits 3-5; aids in flexion of MTP joints.
  • Innervation: Lateral plantar nerve (S1-S2).

• Dorsal Interossei:

  • Proximal Attachments: Adjacent sides of metatarsals 1-5.
  • Distal Attachments:
  • 1st: Medial base of proximal phalanx of 2nd digit.
  • 2nd-4th: Lateral bases of proximal phalanges of 2nd-4th digits.
  • Function: Abducts digits 2-4; aids in flexion of MTP joints.
  • Innervation: Lateral plantar nerve (S1-S2).

Intrinsic Muscles of the Dorsum of the Foot

• Extensor Digitorum Brevis:

  • Proximal Attachments: Distal-lateral aspect of calcaneus.
  • Distal Attachments: Blends with tendons of extensor digitorum longus for digits 2-4.
  • Function: Aids in extension of digits 2-4.
  • Innervation: Deep fibular nerve (L4-S1).

• Extensor Hallucis Brevis:

  • Proximal Attachments: Distal-lateral aspect of calcaneus.
  • Distal Attachments: Base of proximal phalanx of great toe.
  • Function: Extends great toe at MTP joint.
  • Innervation: Deep fibular nerve (L4-S1).