The Appendicular Skeleton

The Appendicular Skeleton

Overview

• The appendicular skeleton comprises the pectoral girdle, upper limbs, and lower limbs.

• Total bones involved: 206 bones in the human body consist of 80 bones in the appendicular skeleton and 126 bones in the axial skeleton.

Detailed Breakdown of Bones in the Appendicular Skeleton

• Pectoral girdle

  • Components:

  • Clavicles (2 bones)

  • Scapulae (2 bones)

• Upper limbs

  • Components:

  • Humerus (2 bones)

  • Radius (2 bones)

  • Ulna (2 bones)

  • Carpal bones (16 bones)

  • Metacarpal bones (10 bones)

  • Phalanges (28 bones)

• Pelvic girdle

  • Components:

  • Hip bones (2 bones)

• Lower limbs

  • Components:

  • Femur (2 bones)

  • Patella (2 bones)

  • Tibia (2 bones)

  • Fibula (2 bones)

  • Tarsal bones (14 bones)

  • Metatarsal bones (10 bones)

  • Phalanges (28 bones)

The Pectoral Girdle

• Also known as the shoulder girdle

• Major characteristics:

  • Provides great mobility due to the shallow glenoid fossa.

  • Considered an unstable joint due to its shallow glenoid fossa.

  • Functions include:

  • Connecting the arms to the body.

  • Positioning the shoulders.

  • Providing a base for arm movement.

• Components:

  • Clavicles

  • Scapulae

• Connects with the axial skeleton only at the manubrium.

The Clavicle

• Anatomy:

  • Lateral (Acromial) end: Articulates with acromion.

  • Medial (Sternal) end: Connects to the manubrium of the sternum.

The Scapula

• Anatomy:

  • Consists of three corners:

  • Superior angle

  • Inferior angle

  • Lateral angle (head)

  • Glenoid cavity: Articulates with the humerus, forming the glenohumeral joint (shoulder joint).

The Upper Limbs

• The Humerus

  • Commonly referred to as the arm bone.

  • Characteristics:

  • Longest upper arm bone.

  • Articulates with the pelvic girdle.

• Anatomy of the Humerus:

  • Greater tubercle: Lateral of the head, forms the tip of the shoulder.

  • Lesser tubercle: Anterior and medial, separated from the greater tubercle by the intertubercular groove.

  • Head: Rounded surface that articulates within joint capsule.

  • Anatomical neck: Margin of the joint capsule.

  • Surgical neck: Narrow metaphysis, a common site for fractures.

  • Medial and lateral epicondyles: Sites for muscle attachment.

  • Condyle: Articulates with the ulna and radius. Articular regions include:

  • Trochlea: For ulna articulation.

  • Capitulum: For radius articulation.

  • Coronoid fossa: Articulates with the coronoid process of the ulna.

The Ulna and Radius

• Ulna:

  • Articulates with the humerus and has a significant role in forming the elbow joint.

  • Contains key features like the olecranon (form of the elbow) and the coronoid process which articulate with the humeral condyle.

• Radius:

  • Round radial head for articulation with the humerus and the ulna.

  • Features such as the neck, radial tuberosity, and styloid process which stabilize the wrist joint.

• Interosseous membrane: Connects the ulna and radius along their lengths.

Wrist & Hand

• Carpals:

  • Total of 8 bones, divided into:

  • Four proximal carpal bones.

  • Four distal carpal bones.

• Metacarpals:

  • Numbered I through V, beginning at the thumb.

  • Articulate with carpals at the base and with phalanges at the heads.

• Phalanges:

  • Total of 14 bones; composed of:

  • 2 in the thumb (pollex) - proximal and distal only.

  • Proximal, middle, and distal in other fingers.

Proximal Carpal Bones

• Scaphoid: Near styloid process.

• Lunate: Medial to scaphoid.

• Triquetrum: Medial to lunate.

• Pisiform: Anterior to triquetrum.

Distal Carpal Bones

• Trapezium: Lateral side.

• Trapezoid: Medial to trapezium.

• Capitate: Largest carpal bone.

• Hamate: Medial and distal.

The Pelvic Girdle

• Structure: Comprised of 2 coxal (hip) bones.

• Each coxal bone is formed from three fused bones:

  • Ilium: Most prominent; connects with sacrum at the sacroiliac joint, and features the iliac crest.

  • Ischium: Weight-bearing bone we sit upon; contains sciatic notches for vessel and nerve passage.

  • Pubis: Contains the obturator foramen and the pubic symphysis.

• Acetabulum: Socket for the head of the femur.

Differences in Male and Female Pelvises

• Female Pelvis:

  • Broader, adapted for childbearing.

  • True pelvis cavity is broad and shallow, allowing greater capacity.

  • Pubic angle is greater than 100°.

• Male Pelvis:

  • Tilted forward less, ilia are more vertical; adapted for a heavier build.

  • True pelvis cavity is narrow and deep.

  • Pubic angle is less than 90°.

The Lower Limb

• Femur: Largest and strongest bone in the body, articulating with the acetabulum at the hip joint.

  • Contains:

  • Neck

  • Greater and lesser trochanters

  • Lateral and medial condyles

  • Patellar surface at the anterior side.

• Patella:

  • Also called the kneecap; a sesamoid bone formed within the tendon of the quadriceps femoris.

  • Base attaches to the quadriceps femoris, while the apex attaches to the patellar ligament.

The Lower Leg

• Comprises two parallel long bones:

  • Tibia: The shinbone, weight-bearing.

  • Articulates with femur at the knee joint via lateral and medial condyles.

  • Fibula: Does not form part of the knee joint; articulates only with the tibia.

The Foot

• Composed of:

  • 7 tarsal bones.

  • 5 metatarsal bones (I - V).

  • 14 phalanges, arranged as proximal, middle, and distal.

  • The hallux has 2 phalanges (proximal and distal).

The Ankle

• Also referred to as the tarsus, consists of seven tarsal bones:

  • Talus: Carries weight from tibia across trochlea.

  • Calcaneus: Forms the heel, transferring weight from the talus to the ground.

  • Cuboid: Articulates with calcaneus.

  • Navicular: Articulates with the talus and three cuneiform bones: medial, intermediate, and lateral.