Appendicular Skeleton: Structure and Components of Upper and Lower Extremities

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, and includes both the upper and lower body extremities.

• Upper Body Extremities: Includes the pectoral girdle and bones of the arm, forearm, wrist, and hand.

• Lower Body Extremities: Includes the pelvic girdle and bones of the thigh, leg, ankle, and foot.

Major Components of the Appendicular Skeleton

Pectoral Girdle (Shoulder)

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

• Clavicle: Also known as the collarbone.

• Scapula: Also known as the shoulder blade.

Upper Extremity

The upper extremity is composed of several bones that allow for a wide range of motion and dexterity.

• Humerus: The bone of the upper arm.

• Radius and Ulna: The bones of the forearm; radius is on the thumb side.

• Carpals: Eight small bones forming the wrist.

• Metacarpals: Five bones forming the palm.

• Phalanges: Fourteen bones forming the fingers.

Pectoral Girdle

Structure and Articulations

The pectoral girdle consists of the scapula and clavicle, which connect the upper limb to the trunk.

• Attachment: The clavicle attaches medially to the sternum and laterally to the scapula.

• Joints:

  • Sternoclavicular joint: Where the clavicle meets the sternum.

  • Acromioclavicular joint: Where the clavicle meets the scapula.

  • Humeroscapular (shoulder) joint: Where the scapula articulates with the humerus.

• Mobility: The shoulder joint is easily dislocated due to its loose attachment, allowing for a wide range of motion but less stability.

Clavicle

Anatomical Features

The clavicle is a slender, S-shaped bone that serves as a strut between the sternum and scapula.

• Shape: S-shaped and flattened dorsoventrally.

• Inferior Surface: Marked by muscle and ligament attachments.

• Ends:

  • Sternal end: Rounded and articulates with the sternum.

  • Acromial end: Flattened and articulates with the acromion of the scapula.

Scapula

Key Features

The scapula is a triangular bone that overlies the ribs and provides attachment points for muscles and articulation with the humerus.

• Spine: Prominent ridge ending as the acromion process.

• Coracoid Process: Serves as a muscle attachment site.

• Fossae:

  • Subscapular fossa

  • Infraspinous fossa

  • Supraspinous fossa

• Glenoid Fossa: Socket for the head of the humerus, forming the shoulder joint.

Upper Limb Bones

Organization

The upper limb consists of 30 bones per limb, organized into the arm, forearm, wrist, and hand.

• Brachium (Arm): Contains the humerus.

• Antebrachium (Forearm): Contains the radius and ulna.

• Carpus (Wrist): Contains 8 carpal bones arranged in two rows.

• Manus (Hand): Contains 5 metacarpals and 14 phalanges.

Humerus

• Head: Hemispherical, articulates with the glenoid fossa of the scapula.

• Neck: Anatomical neck separates the head from the shaft.

• Tubercles: Greater and lesser tubercles for muscle attachment.

• Deltoid Tuberosity: Site of deltoid muscle attachment.

• Intertubercular Groove: Holds the biceps tendon.

• Capitulum: Articulates with the radius.

• Trochlea: Articulates with the ulna.

• Olecranon Fossa: Receives the olecranon process of the ulna.

• Epicondyles: Medial and lateral, sites for muscle attachment.

Radius and Ulna

• Radius:

  • Disc-shaped head rotates during pronation and supination.

  • Articulates with the capitulum of the humerus.

  • Radial tuberosity for biceps muscle attachment.

• Ulna:

  • Olecranon process forms the elbow.

  • Trochlear notch articulates with the trochlea of the humerus.

  • Radial notch holds the head of the radius.

  • Interosseous membrane connects the radius and ulna along their length.

Carpal Bones

• Function: Form the wrist, allowing flexion, extension, abduction, and adduction.

• Arrangement: Two rows of four bones each.

  • Proximal row: Scaphoid, lunate, triquetrum, pisiform.

  • Distal row: Trapezium, trapezoid, capitate, hamate.

Metacarpals and Phalanges

• Metacarpals: Five bones forming the palm; each has a base, shaft, and head.

• Phalanges: Fourteen bones forming the fingers.

  • Thumb (pollex): Proximal and distal phalanx.

  • Other fingers: Proximal, middle, and distal phalanx.

Pelvic Girdle and Lower Extremity

Major Components

• Pelvic Girdle: Formed by two hip bones (ilium, ischium, pubis).

• Lower Extremity: Includes femur, tibia, fibula, tarsals, metatarsals, and phalanges.

Pelvic Girdle

• Pelvis: Consists of the pelvic girdle and sacrum; supports the trunk and protects internal organs.

• Sacroiliac Joint: Where each hip bone joins the vertebral column.

• Pubic Symphysis: Anterior joint formed by fibrocartilage between pubic bones.

• Acetabulum: Socket for the head of the femur.

• Ilium: Features include iliac crest, iliac fossa, and greater sciatic notch (contains sciatic nerve).

• Pubis: Composed of body, superior and inferior ramus.

• Ischium: Includes ischial tuberosity (bears body weight), ischial spine, and lesser sciatic notch.

Comparison of Male and Female Pelvis

Feature	Female Pelvis	Male Pelvis
Weight	Lighter	Heavier
Shape	Shallower, pubic arch >100°, round/oval inlet	Upper pelvis nearly vertical, heart-shaped inlet
Coccyx	Less vertical	More vertical

Sciatica

Sciatica is pain radiating from the buttock down the leg, often reaching the feet and toes. It is commonly caused by compression or irritation of the sciatic nerve.

Femur and Patella

Femur

• Head: Nearly spherical, articulates with the acetabulum.

• Neck: Constricted region below the head.

• Trochanters: Greater and lesser, serve as muscle attachment sites.

• Linea Aspera: Posterior ridge for muscle attachment.

• Condyles and Epicondyles: Medial and lateral, found distally.

Patella

• Shape: Triangular sesamoid bone.

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

Tibia and Fibula

Tibia

• Function: Main weight-bearing bone of the leg (medial).

• Head: Broad superior end with two flat articular surfaces.

• Condyles: Medial and lateral, roughened for muscle attachment.

• Tibial Tuberosity: Palpable below the patella.

• Medial Malleolus: Distal expansion forming the inner ankle.

Fibula

• Function: Slender lateral bone, stabilizes the ankle but does not bear significant weight.

• Head: Proximal end.

• Lateral Malleolus: Distal expansion forming the outer ankle.

• Interosseous Membrane: Connects the fibula to the tibia.

Ankle and Foot

Tarsal Bones

• Function: Support body weight and allow movement.

• Talus: Most superior tarsal bone, forms ankle joint with tibia and fibula.

• Calcaneus: Forms the heel, attachment for Achilles tendon.

• Other Tarsals: Navicular, cuboid, medial/intermediate/lateral cuneiforms.

Metatarsals and Phalanges

• Metatarsals: Five bones forming the foot; metatarsal I is proximal to the great toe (hallux).

• Phalanges:

  • Great toe: Proximal and distal phalanx.

  • Other toes: Proximal, middle, and distal phalanx.

Foot Arches

• Medial Longitudinal Arch: Runs from heel to hallux.

• Lateral Longitudinal Arch: Runs from heel to little toe.

• Transverse Arch: Runs across the middle of the foot.

• Function: Arches absorb stress and are held together by short, strong ligaments.

• Flat Feet (Pes Planus): Condition where the sole of the foot is flat on the ground due to collapsed arches.

Summary Table: Major Bones of the Appendicular Skeleton

Region	Main Bones
Pectoral Girdle	Clavicle, Scapula
Upper Extremity	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges
Pelvic Girdle	Ilium, Ischium, Pubis
Lower Extremity	Femur, Tibia, Fibula, Tarsals, Metatarsals, Phalanges

Additional info: The notes have been expanded with academic context, definitions, and logical organization for clarity and completeness.