Appendicular Skeleton

Overview

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton. It is essential for movement and manipulation of the environment.

• Pectoral Girdle: Clavicle and scapula

• Upper Limbs: Humerus, radius, ulna, bones of the wrist and hand

• Pelvic Girdle: Hip bones (ilium, ischium, pubis)

• Lower Limbs: Femur, tibia, fibula, bones of the ankles and feet

Pectoral Girdle

Clavicle

The clavicle, or collarbone, is a slender S-shaped bone that connects the upper limb to the trunk.

• Articulates medially with the manubrium of the sternum and laterally with the acromion of the scapula.

• Serves as a strut to keep the scapula in position so the arm can hang freely.

• Located above the first rib.

• Key landmarks: acromial extremity, sternal extremity, conoid tubercle, costal tuberosity.

Scapula

The scapula, or shoulder blade, is a flat, triangular bone located in the upper back.

• Articulates with the humerus at the glenoid cavity (glenohumeral joint) and with the clavicle at the acromioclavicular joint.

• Major processes: coracoid process and acromion (for muscle attachment).

• The spine on the posterior surface ends as the acromion process.

• Key borders and angles: superior, medial, lateral borders; superior, inferior, lateral angles.

Upper Limbs

Humerus

The humerus is the long bone of the upper arm, extending from the shoulder to the elbow.

• The head of the humerus articulates with the scapula at the glenoid cavity.

• The distal condyle articulates with the bones of the forearm (radius and ulna).

• Important structures:

  • Greater tuberosity (lateral prominence for muscle attachment)

  • Medial and lateral epicondyles (sites for muscle attachment)

  • Trochlea (articulates with ulna) and capitulum (articulates with radius)

  • Olecranon fossa, coronoid fossa, radial fossa (depressions for forearm bones during movement)

Radius and Ulna

The radius and ulna are the two long bones of the forearm.

• In anatomical position, the ulna is medial to the radius.

• Ulna: Proximal end forms the olecranon (elbow), articulates with the humerus at the trochlea, and with the radius at the radial notch.

• Radius: Proximal end articulates with the capitulum of the humerus and the head of the ulna; distal end articulates with the carpal bones of the wrist.

• Key features: styloid process (distal projection for ligament attachment).

Wrist and Hand

The wrist and hand are composed of multiple small bones that allow for a wide range of motion and dexterity.

• Carpals: 8 bones forming the wrist.

• Metacarpals: 5 bones forming the palm.

• Phalanges: 14 bones forming the fingers (2 in the thumb, 3 in each finger).

Pelvic Girdle

Structure and Function

The pelvic girdle consists of two hip bones (coxal bones), each formed by the fusion of three bones: ilium, ischium, and pubis.

• The acetabulum is the deep socket on the lateral surface that articulates with the head of the femur.

• Key bone markings: ischial spine, pubic ramus, pubic tubercle, greater sciatic notch.

• The right and left pubic bones meet at the pubic symphysis (anterior joint).

• The pelvic girdle, sacrum, and coccyx together form the pelvis.

• Pelvis is divided into the greater (false) pelvis and lesser (true) pelvis, separated by the pelvic brim.

Lower Limbs

Femur

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

• Proximal head articulates with the acetabulum of the hip bone.

• Key features: greater and lesser trochanters (muscle attachment), medial and lateral condyles (articulate with tibia), intercondylar fossa, patellar surface.

Patella

The patella, or kneecap, is a triangular sesamoid bone embedded in the quadriceps tendon.

• Protects the knee joint and improves leverage of the thigh muscles.

• Base is superior; apex is inferior.

Tibia and Fibula

The tibia and fibula are the two bones of the lower leg.

• Tibia: Larger, medial bone; bears most of the body’s weight.

• Key features: medial and lateral condyles (articulate with femur), tibial tuberosity (attachment for patellar ligament), medial malleolus (ankle prominence).

• Fibula: Slender, lateral bone; not involved in knee joint but stabilizes the ankle.

• Key features: head, shaft, lateral malleolus (ankle prominence).

Ankle and Foot

The ankle and foot are composed of multiple bones that provide support and flexibility for movement.

• Tarsals: 7 bones in the ankle, including the talus (articulates with tibia and fibula) and calcaneus (heel bone).

• Metatarsals: 5 bones forming the arch of the foot.

• Phalanges: 14 bones forming the toes (2 in the big toe, 3 in each other toe).

Summary Table: Major Bones of the Appendicular Skeleton

Clinical and Nursing Considerations

• Understanding the structure and function of the appendicular skeleton is essential for assessing injuries, growth, and development.

• Common clinical issues: fractures (e.g., clavicle, femur), dislocations (shoulder, hip), and developmental abnormalities.

• Growth and development: Many bones of the appendicular skeleton ossify from multiple centers and fuse during adolescence.