Lab Exercise 15 The Lower Extremities

The lower extremities, a marvel of biomechanical engineering, are responsible for our locomotion, balance, and support. Understanding their intricate anatomy is crucial for healthcare professionals, physical therapists, and anyone interested in human movement. This lab exercise provides a comprehensive exploration of the bones, muscles, nerves, and blood vessels of the lower limbs, allowing for a deeper appreciation of their function and interrelationships.

Objectives of the Lab Exercise

The primary goals of this lab exercise are to:

• Identify and describe the major bones of the lower extremity, including their significant landmarks.
• Locate and name the principal muscles of the lower limb, understanding their origins, insertions, actions, and innervations.
• Trace the course of the major nerves and blood vessels of the lower extremity, correlating their paths with the structures they supply.
• Relate anatomical structures to common clinical conditions and injuries affecting the lower limbs.

Materials Required

To effectively participate in this lab exercise, you will need the following materials:

• Anatomical models of the lower extremity (bone models, muscular models, and neurovascular models).
• Anatomical charts and diagrams illustrating the bones, muscles, nerves, and blood vessels of the lower limb.
• Dissected cadaver specimens (if available), offering a real-world view of anatomical structures.
• Textbooks and anatomical atlases for reference.
• Dissection tools (if cadaver specimens are used), including scalpels, forceps, and probes.
• Personal Protective Equipment (PPE): gloves, lab coat, and eye protection.

Part 1: Bones of the Lower Extremity

The bony framework of the lower extremity provides support, attachment points for muscles, and protection for underlying tissues. The lower extremity consists of the following bones:

1. Pelvic Girdle

While technically part of the axial skeleton, the pelvic girdle is crucial for connecting the lower limbs to the trunk. It is formed by three bones that fuse in adulthood:

• Ilium: The largest and most superior part of the hip bone. Key landmarks include the iliac crest, anterior superior iliac spine (ASIS), anterior inferior iliac spine (AIIS), posterior superior iliac spine (PSIS), posterior inferior iliac spine (PIIS), iliac fossa, and greater sciatic notch.
• Ischium: Forms the posteroinferior part of the hip bone. Notable features include the ischial tuberosity (the "sitting bone"), ischial spine, and lesser sciatic notch.
• Pubis: The most anterior part of the hip bone. It features the superior pubic ramus, inferior pubic ramus, pubic symphysis (the cartilaginous joint connecting the two pubic bones), and obturator foramen (a large opening formed by the ischium and pubis).
• Acetabulum: This cup-shaped socket on the lateral aspect of the hip bone articulates with the head of the femur to form the hip joint.

2. Femur

The femur, or thigh bone, is the longest and strongest bone in the human body.

• Head: The rounded proximal end of the femur that articulates with the acetabulum. It contains a fovea capitis, a small pit for the attachment of the ligament of the head of the femur.
• Neck: Connects the head to the shaft. It is a common site for fractures, especially in older adults.
• Greater Trochanter: A large prominence located laterally at the junction of the neck and shaft, serving as an attachment site for several hip muscles.
• Lesser Trochanter: A smaller prominence located medially on the posterior aspect of the femur, also serving as a muscle attachment site.
• Intertrochanteric Line: A ridge located anteriorly connecting the greater and lesser trochanters.
• Intertrochanteric Crest: A ridge located posteriorly connecting the greater and lesser trochanters.
• Shaft: The long, cylindrical body of the femur.
• Linea Aspera: A prominent ridge located posteriorly along the shaft, serving as an attachment site for several thigh muscles.
• Medial and Lateral Condyles: Rounded projections at the distal end of the femur that articulate with the tibia to form the knee joint.
• Medial and Lateral Epicondyles: Located superior to the condyles, these serve as attachment sites for ligaments of the knee joint.
• Intercondylar Fossa: A depression between the condyles posteriorly.
• Patellar Surface: Located anteriorly between the condyles, articulating with the patella (kneecap).

3. Patella

The patella, or kneecap, is a sesamoid bone embedded within the tendon of the quadriceps femoris muscle. It protects the knee joint and improves the mechanical advantage of the quadriceps muscle.

• Anterior Surface: Rough and convex.
• Posterior Surface: Articulates with the patellar surface of the femur.
• Apex: The inferior point of the patella.
• Base: The superior aspect of the patella.

4. Tibia

The tibia, or shin bone, is the larger of the two bones of the lower leg. It is located medially.

• Medial and Lateral Condyles: Located at the proximal end, articulating with the femoral condyles to form the knee joint.
• Tibial Tuberosity: A prominence on the anterior aspect of the proximal tibia, serving as the attachment site for the patellar ligament.
• Anterior Border (Crest): A sharp ridge running along the anterior aspect of the tibial shaft, easily palpable beneath the skin.
• Medial Malleolus: A bony prominence at the distal end of the tibia, forming the medial "ankle bone."
• Fibular Notch: A depression on the lateral aspect of the distal tibia where the fibula articulates.

5. Fibula

The fibula is the smaller of the two bones of the lower leg, located laterally. It is primarily involved in ankle joint stability and muscle attachment.

• Head: The proximal end of the fibula, articulating with the lateral condyle of the tibia.
• Lateral Malleolus: A bony prominence at the distal end of the fibula, forming the lateral "ankle bone."

6. Bones of the Foot

The foot is comprised of three groups of bones: tarsals, metatarsals, and phalanges.

• Tarsals: There are seven tarsal bones:

  • Talus: Articulates with the tibia and fibula to form the ankle joint.
  • Calcaneus: The heel bone, the largest tarsal bone.
  • Navicular: Located on the medial side of the foot, between the talus and the cuneiforms.
  • Cuboid: Located on the lateral side of the foot, between the calcaneus and the fourth and fifth metatarsals.
  • Cuneiforms (Medial, Intermediate, and Lateral): Located between the navicular and the metatarsals.

• Metatarsals: There are five metatarsal bones, numbered 1-5 from medial to lateral. Each metatarsal consists of a base, shaft, and head.

• Phalanges: The phalanges are the bones of the toes. Each toe has three phalanges (proximal, middle, and distal), except for the great toe (hallux), which has only two (proximal and distal).

Part 2: Muscles of the Lower Extremity

The muscles of the lower extremity are responsible for a wide range of movements, including walking, running, jumping, and maintaining posture. They are generally divided into groups based on their location and primary function.

1. Hip Muscles

• Gluteal Muscles:
  • Gluteus Maximus: The largest and most superficial of the gluteal muscles. Originates from the ilium, sacrum, and coccyx, and inserts onto the gluteal tuberosity of the femur and the iliotibial tract. It is a powerful hip extensor and external rotator. Innervated by the inferior gluteal nerve.
  • Gluteus Medius: Located deep to the gluteus maximus. Originates from the ilium and inserts onto the greater trochanter of the femur. It is a primary hip abductor and medial rotator. Innervated by the superior gluteal nerve.
  • Gluteus Minimus: The deepest of the gluteal muscles. Originates from the ilium and inserts onto the greater trochanter of the femur. It assists the gluteus medius in hip abduction and medial rotation. Innervated by the superior gluteal nerve.
• Deep Lateral Rotators: A group of six muscles located deep to the gluteus maximus that primarily function to externally rotate the hip. These include:
  • Piriformis: Originates from the sacrum and inserts onto the greater trochanter of the femur. Can compress the sciatic nerve in some individuals, leading to piriformis syndrome.
  • Obturator Internus: Originates from the obturator membrane and surrounding bone, and inserts onto the greater trochanter of the femur.
  • Obturator Externus: Originates from the obturator membrane and surrounding bone, and inserts onto the greater trochanter of the femur.
  • Gemellus Superior: Originates from the ischial spine and inserts onto the greater trochanter of the femur.
  • Gemellus Inferior: Originates from the ischial tuberosity and inserts onto the greater trochanter of the femur.
  • Quadratus Femoris: Originates from the ischial tuberosity and inserts onto the intertrochanteric crest of the femur.
• Iliopsoas: A powerful hip flexor composed of two muscles:
  • Iliacus: Originates from the iliac fossa and inserts onto the lesser trochanter of the femur.
  • Psoas Major: Originates from the lumbar vertebrae and inserts onto the lesser trochanter of the femur.
• Adductor Group: Located on the medial aspect of the thigh, these muscles primarily adduct the hip.
  • Adductor Longus: Originates from the pubic bone and inserts onto the linea aspera of the femur.
  • Adductor Brevis: Originates from the pubic bone and inserts onto the linea aspera of the femur.
  • Adductor Magnus: The largest of the adductor muscles, originating from the pubic bone, ischial tuberosity, and ischial ramus, and inserting onto the linea aspera and adductor tubercle of the femur. It has both adductor and hamstring functions.
  • Gracilis: The most medial of the adductor muscles, originating from the pubic bone and inserting onto the medial surface of the tibia (pes anserinus). It also assists in knee flexion and medial rotation.
  • Pectineus: Originates from the pubic bone and inserts onto the pectineal line of the femur. It assists in hip flexion and adduction.

2. Thigh Muscles

• Quadriceps Femoris: Located on the anterior aspect of the thigh, these muscles are powerful knee extensors.
  • Rectus Femoris: The only quadriceps muscle that crosses the hip joint. Originates from the AIIS and inserts onto the tibial tuberosity via the patellar tendon. It also assists in hip flexion.
  • Vastus Lateralis: Originates from the greater trochanter and linea aspera of the femur and inserts onto the tibial tuberosity via the patellar tendon.
  • Vastus Medialis: Originates from the linea aspera of the femur and inserts onto the tibial tuberosity via the patellar tendon. The Vastus Medialis Obliquus (VMO) is the most distal portion and is important for patellar tracking.
  • Vastus Intermedius: Located deep to the rectus femoris. Originates from the anterior and lateral surfaces of the femur and inserts onto the tibial tuberosity via the patellar tendon.
• Hamstrings: Located on the posterior aspect of the thigh, these muscles primarily flex the knee and extend the hip.
  • Biceps Femoris: Has two heads:
    • Long Head: Originates from the ischial tuberosity and inserts onto the fibular head.
    • Short Head: Originates from the linea aspera of the femur and inserts onto the fibular head.
  • Semitendinosus: Originates from the ischial tuberosity and inserts onto the medial surface of the tibia (pes anserinus).
  • Semimembranosus: Originates from the ischial tuberosity and inserts onto the medial condyle of the tibia.
• Sartorius: The longest muscle in the body. Originates from the ASIS and inserts onto the medial surface of the tibia (pes anserinus). It flexes, abducts, and externally rotates the hip, and also flexes and medially rotates the knee.

3. Lower Leg Muscles

• Anterior Compartment: Located on the anterior aspect of the lower leg, these muscles primarily dorsiflex the ankle and extend the toes.
  • Tibialis Anterior: Originates from the lateral condyle and anterior surface of the tibia, and inserts onto the medial cuneiform and first metatarsal. It is the primary dorsiflexor of the ankle and also inverts the foot.
  • Extensor Hallucis Longus: Originates from the middle portion of the fibula and inserts onto the distal phalanx of the great toe. It extends the great toe and also assists in ankle dorsiflexion.
  • Extensor Digitorum Longus: Originates from the lateral condyle of the tibia and anterior surface of the fibula, and inserts onto the dorsal aponeurosis of the lateral four toes. It extends the lateral four toes and also assists in ankle dorsiflexion.
  • Fibularis (Peroneus) Tertius: Often considered part of the extensor digitorum longus. Originates from the distal fibula and inserts onto the base of the fifth metatarsal. It assists in ankle dorsiflexion and eversion.
• Lateral Compartment: Located on the lateral aspect of the lower leg, these muscles primarily evert the foot.
  • Fibularis (Peroneus) Longus: Originates from the proximal fibula and inserts onto the medial cuneiform and first metatarsal. It everts the foot and also plantarflexes the ankle.
  • Fibularis (Peroneus) Brevis: Originates from the distal fibula and inserts onto the base of the fifth metatarsal. It everts the foot and also assists in ankle plantarflexion.
• Superficial Posterior Compartment: Located on the superficial posterior aspect of the lower leg, these muscles primarily plantarflex the ankle.
  • Gastrocnemius: Has two heads:
    • Medial Head: Originates from the medial epicondyle of the femur.
    • Lateral Head: Originates from the lateral epicondyle of the femur. Both heads insert onto the calcaneus via the Achilles tendon. It is a powerful plantarflexor of the ankle and also assists in knee flexion.
  • Soleus: Located deep to the gastrocnemius. Originates from the proximal tibia and fibula and inserts onto the calcaneus via the Achilles tendon. It is a powerful plantarflexor of the ankle and is particularly important for posture and balance.
  • Plantaris: A small muscle located between the gastrocnemius and soleus. Originates from the lateral epicondyle of the femur and inserts onto the calcaneus via the Achilles tendon. Its function is minimal.
• Deep Posterior Compartment: Located on the deep posterior aspect of the lower leg, these muscles primarily plantarflex the ankle and flex the toes.
  • Tibialis Posterior: Originates from the interosseous membrane and adjacent tibia and fibula, and inserts onto the navicular, cuneiforms, cuboid, and metatarsals. It plantarflexes the ankle and inverts the foot.
  • Flexor Digitorum Longus: Originates from the posterior tibia and inserts onto the distal phalanges of the lateral four toes. It flexes the lateral four toes and also assists in ankle plantarflexion.
  • Flexor Hallucis Longus: Originates from the posterior fibula and inserts onto the distal phalanx of the great toe. It flexes the great toe and also assists in ankle plantarflexion.
  • Popliteus: Located posterior to the knee joint. Originates from the lateral condyle of the femur and inserts onto the posterior tibia. It unlocks the knee by laterally rotating the femur on the tibia (or medially rotating the tibia on the femur).

4. Intrinsic Foot Muscles

These muscles are located entirely within the foot and are responsible for fine motor control of the toes and supporting the arches of the foot. They are divided into dorsal and plantar groups. Due to their complexity, they are often studied in more advanced anatomy courses.

Part 3: Nerves of the Lower Extremity

The nerves of the lower extremity provide motor innervation to the muscles and sensory innervation to the skin. The major nerves originate from the lumbar and sacral plexuses.

1. Lumbar Plexus

The lumbar plexus is formed by the ventral rami of spinal nerves L1-L4, with contributions from T12 and L5. Major nerves arising from the lumbar plexus that innervate the lower extremity include:

• Femoral Nerve: The largest nerve of the lumbar plexus. It innervates the iliacus, pectineus, sartorius, and quadriceps femoris muscles. It also provides sensory innervation to the anterior thigh and medial leg.
• Obturator Nerve: Innervates the adductor muscles of the thigh (adductor longus, adductor brevis, adductor magnus, gracilis, and obturator externus). It also provides sensory innervation to the medial thigh.
• Lateral Femoral Cutaneous Nerve: Provides sensory innervation to the lateral thigh.

2. Sacral Plexus

The sacral plexus is formed by the ventral rami of spinal nerves L4-S4. Major nerves arising from the sacral plexus that innervate the lower extremity include:

• Sciatic Nerve: The largest nerve in the body. It is composed of two divisions:
  • Tibial Nerve: Innervates the hamstring muscles (except the short head of the biceps femoris), the gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus. It also provides sensory innervation to the posterior leg and plantar surface of the foot.
  • Common Fibular (Peroneal) Nerve: Divides into the superficial and deep fibular nerves.
    • Superficial Fibular Nerve: Innervates the fibularis longus and fibularis brevis muscles. It also provides sensory innervation to the lateral leg and dorsal surface of the foot (except between the great toe and second toe).
    • Deep Fibular Nerve: Innervates the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles. It also provides sensory innervation to the skin between the great toe and second toe.
• Superior Gluteal Nerve: Innervates the gluteus medius, gluteus minimus, and tensor fasciae latae muscles.
• Inferior Gluteal Nerve: Innervates the gluteus maximus muscle.
• Posterior Femoral Cutaneous Nerve: Provides sensory innervation to the posterior thigh and popliteal region.
• Pudendal Nerve: Primarily innervates the perineum, but also provides some innervation to the external rotators of the hip.

Part 4: Blood Vessels of the Lower Extremity

The blood vessels of the lower extremity supply oxygenated blood to the tissues and return deoxygenated blood back to the heart.

1. Arteries

• External Iliac Artery: A continuation of the common iliac artery, it becomes the femoral artery as it passes under the inguinal ligament.
• Femoral Artery: The main artery of the thigh. It gives rise to the deep femoral artery (profunda femoris artery) and continues distally as the popliteal artery.
• Deep Femoral Artery (Profunda Femoris Artery): The largest branch of the femoral artery, supplying blood to the deep muscles of the thigh.
• Popliteal Artery: A continuation of the femoral artery, located posterior to the knee joint. It divides into the anterior and posterior tibial arteries.
• Anterior Tibial Artery: Supplies blood to the anterior compartment of the leg. It becomes the dorsalis pedis artery as it crosses the ankle joint.
• Dorsalis Pedis Artery: Located on the dorsal surface of the foot, it supplies blood to the foot and toes.
• Posterior Tibial Artery: Supplies blood to the posterior compartment of the leg. It gives rise to the fibular (peroneal) artery.
• Fibular (Peroneal) Artery: Supplies blood to the lateral compartment of the leg.
• Medial and Lateral Plantar Arteries: Branches of the posterior tibial artery that supply blood to the plantar surface of the foot.

2. Veins

The veins of the lower extremity return deoxygenated blood to the heart. They are divided into superficial and deep veins.

• Superficial Veins: Located superficial to the deep fascia.
  • Great Saphenous Vein: The longest vein in the body, running from the medial malleolus to the femoral vein in the groin.
  • Small Saphenous Vein: Runs from the lateral malleolus to the popliteal vein behind the knee.
• Deep Veins: Located deep to the deep fascia, accompanying the arteries. They have the same names as the corresponding arteries:
  • Femoral Vein
  • Deep Femoral Vein
  • Popliteal Vein
  • Anterior Tibial Vein
  • Posterior Tibial Vein
  • Fibular (Peroneal) Vein
  • Dorsalis Pedis Vein
  • Medial and Lateral Plantar Veins

Part 5: Clinical Considerations

Understanding the anatomy of the lower extremities is essential for diagnosing and treating a wide range of clinical conditions. Here are a few examples:

• Hip Fractures: Common in older adults, often involving the femoral neck. Can disrupt blood supply to the femoral head, leading to avascular necrosis.
• Knee Injuries: Include ligament tears (ACL, MCL, LCL, PCL), meniscal tears, and patellar dislocations.
• Ankle Sprains: Result from excessive inversion or eversion of the ankle, damaging ligaments.
• Compartment Syndrome: Increased pressure within a muscle compartment, compromising blood supply and nerve function. Requires prompt treatment to prevent permanent damage.
• Sciatica: Pain radiating along the sciatic nerve, often caused by a herniated disc or piriformis syndrome.
• Deep Vein Thrombosis (DVT): Blood clot formation in a deep vein, often in the lower leg. Can lead to pulmonary embolism, a life-threatening condition.
• Plantar Fasciitis: Inflammation of the plantar fascia, a thick band of tissue on the bottom of the foot.

Conclusion

This lab exercise has provided a comprehensive overview of the anatomy of the lower extremities. By studying the bones, muscles, nerves, and blood vessels, you have gained a deeper appreciation for the intricate design and function of these essential structures. This knowledge will serve as a foundation for understanding human movement, diagnosing clinical conditions, and providing effective healthcare. Remember to continue your studies and explore the vast resources available to further enhance your understanding of the human body.