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Chapter 8: The Appendicular Skeleton

Overview of Appendicular Skeleton

  • The appendicular skeleton is made up of:
    • Upper limb bones
    • Lower limb bones
    • Bones of the hands and feet
    • Bones that anchor the limbs to the axial skeleton
Key Figures
  • Figure 8.1: Illustration of a dancer highlighting the appendicular skeleton.
  • Figure 8.2: Diagram contrasting the axial and appendicular skeletons:
    • Axial Skeleton: Comprises the skull, vertebral column, and thoracic cage.
    • Appendicular Skeleton: Consists of the pectoral and pelvic girdles, limb bones, and bones of hands and feet.

Components of the Appendicular Skeleton

Pectoral Girdle
  • Composed of:
    • Clavicle: Collarbone
    • Scapula: Shoulder blade
Upper Limb
  • Includes:
    • Humerus: Bone of the upper arm
    • Radius: Lateral bone of the forearm
    • Ulna: Medial bone of the forearm
    • Carpals: Bones of the wrist
    • Metacarpals: Bones of the hand (palm)
    • Phalanges: Bones of the fingers
Pelvic Girdle
  • Comprised of:
    • Coxal Bones: Hip bones
    • Sacrum: Part of the axial skeleton
Lower Limb
  • Incorporates:
    • Femur: Thigh bone
    • Patella: Knee cap
    • Tibia: The larger weight-bearing bone in the lower leg
    • Fibula: The slender bone in the leg
    • Tarsals: Ankle bones
    • Metatarsals: Bones of the foot
    • Phalanges: Bones of the toes

Pectoral Girdle

Clavicle
  • Structure:
    • An S-shaped, somewhat flattened bone.
    • Sternal End: Rounded head for articulation with the sternum.
    • Acromial End: Flattened end connecting to the scapula.
    • Conoid Tubercle: A roughened tuberosity near the acromial end for ligament attachment.
  • Function:
    • Braces shoulder, holding the upper limb away from the body’s midline.
    • Most frequently fractured bone in the body.
Scapula
  • Structure:
    • A triangular plate that posteriorly overlies ribs 2 to 7.
  • Main Features:
    • Spine: Ridge on the posterior surface.
    • Acromion: Extension of the spine; forms the apex of the shoulder; articulates with the clavicle.
    • Coracoid Process: Shaped like a bent finger; provides attachment for tendons of the biceps brachii.
    • Glenoid Cavity: A shallow socket that articulates with the head of the humerus, forming the glenohumeral joint.

Upper Limb

Regions of the Upper Limb
  • Brachium (Arm Proper): Contains the Humerus.
  • Antebrachium (Forearm): Contains the Radius and Ulna.
  • Carpus (Wrist): Composed of Carpals.
  • Manus (Hand): Includes Metacarpals and Phalanges (fingers).
Humerus
  • Characteristics:
    • The sole bone of the upper arm.
  • Landmarks:
    • Head: Articulates with glenoid cavity of scapula.
    • Great and Lesser Tubercles: Sites for muscle attachment.
    • Bicipital Groove: Pathway for a tendon of the biceps.
    • Trochlea: Articulates with the trochlear notch of ulna.
    • Capitulum: Articulates with the radial head of radius.
    • Epicondyles: Medial and lateral, with the medial known as the "funny bone" due to proximity to the ulnar nerve.
    • Fossae: Olecranon, coronoid, and radial fossae accommodating processes of radius and ulna.
Forearm (Radius and Ulna)
Ulna
  • Location: Medial side of forearm.
  • Landmarks:
    • Trochlear Notch: Articulates with trochlea of humerus.
    • Coronoid Process: Projects to help form the elbow joint.
    • Olecranon Process: Forms the bony point of the elbow.
    • Interosseous Membrane: Connective tissue uniting the ulna and radius.
Radius
  • Location: Lateral side of forearm.
  • Landmarks:
    • Head: Disc-shaped, allowing rotation (pronation/supination).
    • Neck: Barest part between the head and tuberosity.
    • Radial Tuberosity: Attachment site for biceps muscle.
    • Styloid Process: Can be palpated near the thumb.

Carpal Bones

  • Total of 8 wrist bones arranged into two rows:
    • Proximal Row: Scaphoid, Lunate, Triquetrum, Pisiform.
    • Distal Row: Trapezium, Trapezoid, Capitate, Hamate.

Metacarpals and Phalanges

Metacarpals
  • 5 bones forming the palm of the hand, numbered I-V:
    • Metacarpal I: Proximal to the base of thumb (pollex).
    • Metacarpal V: Proximal to the base of little finger.
Phalanges
  • Bone arrangement:
    • Thumb (Pollex): Consists of 2 phalanges (proximal, distal).
    • Fingers: Each has 3 phalanges (proximal, middle, distal).

Pelvic Girdle

Structure
  • Composed of:
    • Two Coxal Bones and the Sacrum (part of the vertebral column).
  • Function:
    • Supports the trunk on the lower limbs and protects pelvic organs.
Key Features
  • Sacroiliac Joint: Connects the hip bone to the vertebral column.
  • Interpubic Disc: Joins the two pubic bones composed of fibrocartilage.
  • Pubic Symphysis: A joint formed by the interpubic disc and adjacent parts of the pubic bones.
  • Iliac Crest: Superior crest of the hip bone.
  • Acetabulum: The hip socket where the femur articulates.
  • Obturator Foramen: A large hole below the acetabulum.

Lower Limb

Regions of the Lower Limb
  • Femoral Region: Extends from hip to knee (contains femur and patella).
  • Crural Region: Extends from knee to ankle (contains tibia and fibula).
  • Tarsal Region: Connects the crural region to the foot (contains tarsal bones).
  • Pedal Region: Contains the bones of the foot (7 tarsal bones, 5 metatarsals, and 14 phalanges).
Femur and Patella
Femur
  • Characteristics:
    • The longest and strongest bone in the body.
  • Landmarks:
    • Head: Hemispherical, articulates with acetabulum of pelvis.
    • Greater and Lesser Trochanters: Sites for muscle attachment.
    • Condyles: Medial and lateral, articulate with superior surface of tibia at the knee.
    • Epicondyles: Medial and lateral, attachment points for muscles and ligaments.
Patella
  • Structure:
    • A triangular sesamoid bone embedded in the tendon of the knee.
    • Base: Broad superior portion.
    • Apex: Pointed inferior portion articulating with femur.
Tibia and Fibula
Tibia
  • Also known as the shin bone; the larger, weight-bearing bone of the leg.
  • Landmarks:
    • Medial Malleolus: Bony knob on the inside of the ankle.
Fibula
  • A slender bone, does not bear weight, located on the lateral side of the leg.
  • Landmarks:
    • Lateral Malleolus: Bony knob on the outer side of the ankle.

Bones of the Foot

Structure

  • The components of the foot are grouped as follows:

    • Tarsal Bones: 7 arranged into proximal and distal groups.
    • Proximal Row: Talus, calcaneus, navicular.
    • Distal Row: Medial, intermediate, lateral cuneiforms, cuboid.
    • Metatarsals: 5 bones similar to metacarpals.
    • Phalanges: 14 bones in toes (2 in the big toe, 3 in other toes).

  • Specific bones include:

    • Calcaneus: Largest tarsal bone, forms the heel, attachment point for Achilles tendon.
    • Talus: Most superior tarsal bone, forming the ankle joint with tibia and fibula.