Lab Exercise 15 The Lower Extremities

The human body is a marvel of engineering, and the lower extremities play a crucial role in locomotion, balance, and support. Understanding the anatomy and function of the lower extremities is fundamental for anyone in the fields of medicine, physical therapy, or athletic training. This lab exercise will explore the bones, muscles, joints, and nerves of the lower limbs, providing a comprehensive overview of their intricate relationships.

Bones of the Lower Extremities

The skeletal framework of the lower extremity is composed of several key bones, each with unique features and functions. These bones provide structural support, serve as attachment points for muscles, and protect vital structures.

The Pelvic Girdle

• Ilium: The largest and uppermost bone of the pelvis, the ilium forms the superior portion of the hip bone. It features the iliac crest, a prominent ridge that can be palpated along the sides of the waist.
• Ischium: Located inferior and posterior to the ilium, the ischium forms the lower and back part of the hip bone. The ischial tuberosity, a bony prominence on the ischium, is what we sit on.
• Pubis: The most anterior part of the hip bone, the pubis meets its counterpart from the opposite side at the pubic symphysis, a cartilaginous joint.
• Acetabulum: This deep, cup-shaped socket is formed by the ilium, ischium, and pubis. It articulates with the head of the femur to form the hip joint.

The Thigh: 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 to form the hip joint. The fovea capitis is a small pit on the head that serves as an attachment point for a ligament.
• Neck: The narrowed region connecting the head to the shaft of the femur. The femoral neck is a common site for fractures, especially in older adults.
• Greater and Lesser Trochanters: Large bony prominences located at the junction of the neck and shaft of the femur. They serve as attachment points for powerful hip muscles.
• Shaft: The long, cylindrical body of the femur.
• Lateral and Medial Condyles: Rounded projections at the distal end of the femur that articulate with the tibia to form the knee joint.
• Intercondylar Fossa: A deep groove between the condyles on the posterior aspect of the femur.

The Leg: Tibia and Fibula

The tibia, or shin bone, is the larger and more medial of the two bones in the leg. The fibula, a slender bone, runs parallel to the tibia on the lateral side.

• Tibia:
  • Medial and Lateral Condyles: Located at the proximal end of the tibia, these articulate with the femoral condyles to form the knee joint.
  • Tibial Tuberosity: A prominent bony landmark on the anterior surface of the tibia, just below the knee. It serves as the attachment point for the patellar tendon.
  • Anterior Border (Crest): The sharp, palpable ridge along the front of the tibia.
  • Medial Malleolus: The bony prominence on the medial side of the ankle, formed by the distal end of the tibia.
• Fibula:
  • Head: The proximal end of the fibula, which articulates with the lateral condyle of the tibia.
  • Lateral Malleolus: The bony prominence on the lateral side of the ankle, formed by the distal end of the fibula. It provides lateral stability to the ankle joint.

The Foot: Tarsals, Metatarsals, and Phalanges

The foot is composed of a complex arrangement of bones that provide support, flexibility, and propulsion.

• Tarsals: Seven bones that form the posterior part of the foot. These include the talus, calcaneus (heel bone), navicular, cuboid, and three cuneiform bones.
• Metatarsals: Five bones that form the midfoot. They are numbered 1-5, starting from the medial side (big toe).
• Phalanges: Fourteen bones that form the toes. Each toe has three phalanges (proximal, middle, and distal), except for the big toe (hallux), which has only two (proximal and distal).

Muscles of the Lower Extremities

The muscles of the lower extremities are responsible for a wide range of movements, including walking, running, jumping, and maintaining posture. They can be broadly categorized into those acting on the hip, thigh, leg, and foot.

Muscles Acting on the Hip

• Gluteal Muscles:
  • Gluteus Maximus: The largest and most superficial of the gluteal muscles, responsible for hip extension and external rotation.
  • Gluteus Medius: Located deep to the gluteus maximus, the gluteus medius is a powerful hip abductor and stabilizer.
  • Gluteus Minimus: The smallest and deepest of the gluteal muscles, assisting in hip abduction and internal rotation.
• Iliopsoas: A powerful hip flexor composed of the iliacus and psoas major muscles.
• Tensor Fasciae Latae (TFL): Located on the lateral aspect of the hip, the TFL flexes, abducts, and internally rotates the hip. It also contributes to stabilizing the knee.
• Adductor Muscles:
  • Adductor Magnus: The largest and most powerful of the adductor muscles, responsible for hip adduction, flexion, and extension (depending on the portion of the muscle).
  • Adductor Longus: Adducts, flexes, and externally rotates the hip.
  • Adductor Brevis: Adducts and flexes the hip.
  • Gracilis: The most medial of the adductor muscles, also assists in knee flexion and internal rotation.

Muscles Acting on the Thigh (Knee)

• Quadriceps Femoris: A group of four muscles located on the anterior aspect of the thigh, responsible for knee extension.
  • Rectus Femoris: Also flexes the hip.
  • Vastus Lateralis:
  • Vastus Medialis:
  • Vastus Intermedius: Located deep to the rectus femoris.
• Hamstrings: A group of three muscles located on the posterior aspect of the thigh, responsible for knee flexion and hip extension.
  • Biceps Femoris:
  • Semitendinosus:
  • Semimembranosus:
• Sartorius: The longest muscle in the body, crossing both the hip and knee joints. It flexes, abducts, and externally rotates the hip, and flexes and internally rotates the knee.

Muscles Acting on the Leg (Ankle and Foot)

These muscles are primarily located in the leg and act on the ankle and foot to produce movements such as plantarflexion, dorsiflexion, inversion, and eversion.

• Anterior Compartment:
  • Tibialis Anterior: Dorsiflexes and inverts the foot.
  • Extensor Hallucis Longus: Extends the big toe and dorsiflexes the foot.
  • Extensor Digitorum Longus: Extends the lateral four toes and dorsiflexes the foot.
  • Fibularis (Peroneus) Tertius: Dorsiflexes and everts the foot.
• Lateral Compartment:
  • Fibularis (Peroneus) Longus: Everts and plantarflexes the foot.
  • Fibularis (Peroneus) Brevis: Everts and plantarflexes the foot.
• Superficial Posterior Compartment:
  • Gastrocnemius: Plantarflexes the foot and flexes the knee.
  • Soleus: Plantarflexes the foot.
  • Plantaris: Assists in plantarflexion of the foot and knee flexion (weak).
• Deep Posterior Compartment:
  • Tibialis Posterior: Inverts and plantarflexes the foot.
  • Flexor Hallucis Longus: Flexes the big toe and plantarflexes the foot.
  • Flexor Digitorum Longus: Flexes the lateral four toes and plantarflexes the foot.
  • Popliteus: Unlocks the knee joint by laterally rotating the femur on the tibia (or medially rotating the tibia).

Intrinsic Muscles of the Foot

These muscles are located entirely within the foot and are responsible for fine motor movements of the toes, supporting the arches of the foot, and providing sensory feedback. There are several layers of intrinsic foot muscles, including:

• Dorsal Muscles: Extensor hallucis brevis, extensor digitorum brevis.
• Plantar Muscles: Abductor hallucis, flexor hallucis brevis, adductor hallucis, abductor digiti minimi, flexor digiti minimi brevis, quadratus plantae, lumbricals, plantar interossei, dorsal interossei.

Joints of the Lower Extremities

Joints are the connections between bones, allowing for movement and providing stability. The lower extremities contain several major joints, each with unique characteristics and ranges of motion.

Hip Joint

The hip joint is a ball-and-socket joint formed by the articulation of the head of the femur with the acetabulum of the pelvis. It is a highly stable joint due to the deep socket and strong ligaments.

• Movements: Flexion, extension, abduction, adduction, internal rotation, external rotation, circumduction.
• Ligaments: Iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament, ligamentum teres (ligament of the head of the femur).

Knee Joint

The knee joint is a complex hinge joint formed by the articulation of the femoral condyles with the tibial condyles, and the patella with the femur. It is stabilized by ligaments, menisci, and muscles.

• Movements: Flexion, extension, and slight rotation when the knee is flexed.
• Ligaments: Anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL).
• Menisci: Medial meniscus, lateral meniscus – fibrocartilaginous structures that deepen the articular surfaces and provide shock absorption.

Ankle Joint

The ankle joint, also known as the talocrural joint, is a hinge joint formed by the articulation of the distal ends of the tibia and fibula with the talus.

• Movements: Dorsiflexion and plantarflexion.
• Ligaments: Deltoid ligament (medial), anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), posterior talofibular ligament (PTFL) (lateral).

Subtalar Joint

The subtalar joint, also known as the talocalcaneal joint, is located between the talus and calcaneus.

• Movements: Inversion and eversion of the foot.

Joints of the Foot

The foot contains numerous small joints between the tarsal bones, metatarsals, and phalanges, allowing for flexibility and adaptation to uneven surfaces.

• Tarsometatarsal Joints: Joints between the tarsal bones and the metatarsals.
• Metatarsophalangeal Joints (MTP): Joints between the metatarsals and the proximal phalanges.
• Interphalangeal Joints (IP): Joints between the phalanges of each toe (proximal interphalangeal (PIP) and distal interphalangeal (DIP)).

Nerves of the Lower Extremities

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

Lumbar Plexus

The lumbar plexus is formed by the ventral rami of spinal nerves L1-L4, with contributions from T12 and L5.

• Femoral Nerve: Innervates the quadriceps femoris, sartorius, and iliacus muscles. Provides sensory innervation to the anterior thigh and medial leg.
• Obturator Nerve: Innervates the adductor muscles of the thigh. Provides sensory innervation to the medial thigh.
• Lateral Femoral Cutaneous Nerve: Provides sensory innervation to the lateral thigh.

Sacral Plexus

The sacral plexus is formed by the ventral rami of spinal nerves L4-S4.

• Sciatic Nerve: The largest nerve in the body, it arises from the sacral plexus and splits into the tibial and common fibular (peroneal) nerves.
  • Tibial Nerve: Innervates the muscles of the posterior compartment of the leg (gastrocnemius, soleus, tibialis posterior, flexor hallucis longus, flexor digitorum longus) and the intrinsic muscles of the foot. 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 brevis muscles. Provides sensory innervation to the lateral leg and dorsum of the foot.
    • Deep Fibular Nerve: Innervates the muscles of the anterior compartment of the leg (tibialis anterior, extensor hallucis longus, extensor digitorum longus, fibularis tertius). Provides sensory innervation to the web space between the big toe and the second toe.
• Superior Gluteal Nerve: Innervates the gluteus medius, gluteus minimus, and tensor fasciae latae muscles.
• Inferior Gluteal Nerve: Innervates the gluteus maximus muscle.
• Pudendal Nerve: Primarily innervates structures in the perineum and is not directly involved in innervation of the lower limb muscles, but its branches provide sensory innervation to the skin of the perineum.

Common Injuries and Conditions of the Lower Extremities

Understanding the anatomy and function of the lower extremities is essential for diagnosing and treating various injuries and conditions.

• Hip Fractures: Commonly occur in older adults due to osteoporosis.
• Hip Bursitis: Inflammation of the bursae around the hip joint, causing pain and stiffness.
• Knee Ligament Injuries (ACL, MCL, PCL, LCL): Often result from sports-related trauma.
• Meniscal Tears: Can occur due to twisting or traumatic injuries to the knee.
• Patellofemoral Pain Syndrome: Pain around the kneecap, often caused by malalignment or overuse.
• Ankle Sprains: Ligament injuries resulting from inversion or eversion of the ankle.
• Achilles Tendinitis/Rupture: Inflammation or tearing of the Achilles tendon, which connects the calf muscles to the heel bone.
• Plantar Fasciitis: Inflammation of the plantar fascia, a thick band of tissue on the bottom of the foot, causing heel pain.
• Shin Splints (Medial Tibial Stress Syndrome): Pain along the shinbone, often caused by overuse.
• Stress Fractures: Small cracks in the bone, commonly occurring in the tibia or metatarsals, due to repetitive stress.
• Peripheral Neuropathy: Nerve damage in the lower extremities, often caused by diabetes or other medical conditions, leading to pain, numbness, and weakness.

Clinical Significance

A thorough understanding of the lower extremities is critical for healthcare professionals. It informs diagnosis, treatment, and rehabilitation strategies for a wide range of conditions affecting mobility and quality of life. Whether it's a sports injury, a chronic condition like osteoarthritis, or a neurological disorder impacting motor function, a solid grasp of lower limb anatomy and biomechanics is indispensable.

Conclusion

The lower extremities are a complex and interconnected system of bones, muscles, joints, and nerves that work together to enable movement, support the body, and maintain balance. A comprehensive understanding of the anatomy and function of the lower extremities is essential for anyone in the fields of medicine, physical therapy, or athletic training. By studying the bones, muscles, joints, and nerves, we gain valuable insights into the intricate mechanisms that allow us to walk, run, jump, and perform countless other activities. This knowledge is crucial for diagnosing and treating injuries and conditions, ultimately improving the lives of patients and enhancing their ability to move and function optimally.