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, support, and interaction with the environment.

• Main Components: Pectoral girdle (shoulder), upper limbs, pelvic girdle (hip), and lower limbs.

• Functions: Facilitates locomotion, manipulation of objects, and supports body weight during movement and sitting.

Pectoral Girdle and Upper Limb

Pectoral Girdle

The pectoral girdle attaches the upper limbs to the trunk and provides mobility and flexibility.

• Bones: Clavicle and scapula (shoulder blade).

• Clavicle: S-shaped bone with acromial end (lateral, articulates with scapula) and sternal end (medial, articulates with sternum).

• Scapula: Flat, triangular bone with key features:

  • Acromion: Articulates with clavicle.

  • Coracoid process: Muscle attachment.

  • Glenoid cavity: Articulates with humerus.

  • Spine, fossae, borders, and angles: Serve as muscle attachment sites and anatomical landmarks.

Upper Limb Bones

• Humerus: Arm bone; articulates with scapula at shoulder and with radius and ulna at elbow.

• Radius and Ulna: Forearm bones; radius is lateral (thumb side), ulna is medial (pinky side).

• Carpal Bones (8): Wrist bones—scaphoid, lunate, triquetral, pisiform, trapezium, trapezoid, capitate, hamate.

• Metacarpal Bones (5): Palm of the hand.

• Phalanges (14): Fingers and thumb; each finger has proximal, middle, and distal phalanges (thumb lacks middle phalanx).

Key Anatomical Features and Clinical Notes

• Articulation and Muscle Attachment: Tubercles, tuberosities, and fossae serve as attachment points for muscles and ligaments.

• Clavicle Fracture: Falling on an outstretched arm transmits force to the clavicle, making it prone to fracture.

• Surgical Neck of Humerus: Named for its frequent involvement in fractures requiring surgical intervention; located just below the tubercles.

• Colle's Fracture: Fracture of the distal radius, common from falls on an outstretched hand.

• Head of Metacarpal: Commonly called the "knuckle."

Pelvic Girdle and Lower Limb

Pelvic Girdle

The pelvic girdle supports the weight of the upper body and protects pelvic organs.

• Bones: Two coxal (hip) bones, each formed by fusion of ilium, ischium, and pubis.

• Pelvis: Composed of two coxal bones, sacrum, and coccyx.

• True vs. False Pelvis:

  • True pelvis: Inferior region, encloses pelvic cavity.

  • False pelvis: Superior region, supports abdominal organs.

• Pubic Symphysis: Joint linking the two coxal bones; contains fibrocartilage disc and ligaments.

• Key Landmarks: Ischial tuberosity (bears weight when sitting), greater sciatic notch, obturator foramen, ischial spine, acetabulum (hip socket).

• Male vs. Female Pelvis: Female pelvis has a wider pubic arch and larger pelvic inlet for childbirth.

Lower Limb Bones

• Femur: Thigh bone; articulates with acetabulum (hip), tibia, and patella.

• Patella: Kneecap; largest sesamoid bone (develops within tendon).

• Tibia: Shin bone; supports most body weight.

• Fibula: Lateral to tibia; stabilizes ankle.

• Tarsal Bones (7): Ankle bones—calcaneus (heel), talus, navicular, cuboid, medial/intermediate/lateral cuneiforms.

• Metatarsal Bones (5): Foot bones.

• Phalanges (14): Toes; similar structure to fingers.

Key Anatomical Features and Clinical Notes

• Sesamoid Bones: Bones embedded in tendons; largest is the patella. Others found in hands and feet.

• Femur Articulations: In adults: acetabulum, tibia, patella. In fetuses: may include additional cartilaginous structures.

• Common Names: Tibia (shin bone), patella (kneecap), calcaneus (heel bone).

• Foot Arches: Formed by tarsal and metatarsal bones; function to distribute weight and absorb shock.

Major Bones and Landmarks: Summary Table

Key Terms and Definitions

• Articulation: A joint where two bones meet.

• Sesamoid Bone: A bone formed within a tendon (e.g., patella).

• Acetabulum: The socket in the pelvis that receives the head of the femur.

• Obturator Foramen: Large opening in the hip bone for nerves and blood vessels.

• Ischial Tuberosity: Part of the pelvis that bears weight when sitting.

Examples and Applications

• Example: A Colle's fracture is a common injury in elderly individuals who fall on an outstretched hand, resulting in a break of the distal radius.

• Application: The difference in male and female pelvis size is crucial in obstetrics for assessing childbirth risk.

Additional info:

• In the fetus, the coxal bone is composed of three separate bones (ilium, ischium, pubis) that fuse in adulthood.

• The arches of the foot are maintained by the shapes of the bones and the strength of ligaments and tendons.