The Appendicular Skeleton

Overview

The appendicular skeleton consists of 126 bones that form the limbs and their attachments to the axial skeleton. It is essential for movement and manipulation of the environment. The appendicular skeleton is divided into the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

The Pectoral Girdle

Structure and Function

The pectoral girdle attaches the upper limbs to the axial skeleton and provides mobility and flexibility to the shoulder region. It consists of two bones on each side: the clavicle and the scapula.

• Clavicle (Collar Bone):

  • Sternal end: Articulates with the manubrium of the sternum.

  • Acromial end: Articulates with the acromion of the scapula.

• Scapula (Shoulder Blade):

  • Borders: Superior, medial, and lateral borders define the shape.

  • Glenoid cavity: Articulates with the head of the humerus.

  • Acromion: Lateral projection for muscle attachment.

  • Coracoid process: Attachment for ligaments and muscles.

  • Spine: Prominent ridge on the posterior surface.

  • Fossae: Supraspinous, infraspinous, and subscapular fossae serve as muscle attachment sites.

  • Other features: Suprascapular notch, superior/inferior angles, infraglenoid tubercle.

Upper Limb

Regions and Bones

Each upper limb contains 30 bones, divided into the arm, forearm, and hand.

Arm (Shoulder to Elbow)

• Humerus:

  • Head: Fits into the glenoid cavity of the scapula.

  • Surgical neck: Common fracture site.

  • Greater and lesser tubercles: Muscle attachment sites.

  • Intertubercular sulcus: Groove for tendon of biceps brachii.

  • Deltoid tuberosity: Attachment for deltoid muscle.

  • Distal features: Trochlea, capitulum, medial/lateral epicondyles, coronoid/olecranon/radial fossae, lateral supracondylar ridge.

Forearm (Elbow to Hand)

• Ulna (Medial):

  • Olecranon: Forms the elbow's point.

  • Coronoid process, trochlear notch, radial notch, styloid process.

• Radius (Lateral):

  • Head: Articulates with the capitulum of the humerus.

  • Radial tuberosity, ulnar notch, styloid process.

  • Colle’s fracture: Break in the distal radius, often from falls.

Hand

• Carpals (Wrist): Eight bones arranged in two rows.

  • Scaphoid (most commonly fractured), lunate (most frequently dislocated), hamate, capitate, trapezoid, trapezium, pisiform, triquetrum.

  • Scaphoid and lunate articulate with the radius.

• Metacarpals (Palm): Five long bones numbered I (thumb) to V (pinky).

  • Boxer’s fracture: Break of the fifth metacarpal.

• Phalanges (Fingers): Fourteen bones per hand.

  • Each finger: Proximal, middle, and distal phalanges (thumb lacks middle phalanx).

Pelvic Girdle

Structure and Function

The pelvic girdle attaches the lower limbs to the axial skeleton and supports the weight of the upper body. It is formed by two coxal (hip) bones, each resulting from the fusion of three bones: ilium, ischium, and pubis.

• Ilium: Superior region; features include iliac fossa, crest, anterior/posterior superior/inferior iliac spines, greater sciatic notch, auricular surface.

• Ischium: Posterior, L-shaped; includes ischial tuberosity, lesser sciatic notch, ischial spine, ischial ramus.

• Pubis: Anterior, V-shaped; features obturator foramen, pubic tubercle, superior/inferior pubic rami, acetabulum, articular surface at pubic symphysis.

Pelvic Structure and Sex Differences

• Pelvic outlet: Inferior opening of the pelvis.

• Sex determination: Female pelvis is lighter, shallower, rounder, with a wider arch and larger opening; male pelvis is heavier, taller, narrower, with a smaller opening.

Lower Limb

Regions and Bones

Each lower limb contains 30 bones, divided into the thigh, leg, and foot.

Thigh (Hip to Knee)

• Femur:

  • Head: Articulates with the acetabulum of the pelvis.

  • Fovea capitis, neck, greater/lesser trochanters, patellar surface, lateral/medial condyles and epicondyles, linea aspera, popliteal surface, gluteal tuberosity, intercondylar fossa.

• Patella (Kneecap):

  • Apex, facet.

Leg (Knee to Ankle)

• Tibia (Medial):

  • Medial/lateral condyles, medial malleolus, anterior border, inferior articular surface, tibial tuberosity, intercondylar eminence, fibular notch.

• Fibula (Lateral):

  • Head, lateral malleolus.

Foot

• Tarsals (Ankle): Seven bones.

  • Talus (articulates with leg), calcaneus, navicular, cuboid, medial/intermediate/lateral cuneiforms.

• Metatarsals: Five bones numbered I (big toe) to V (little toe).

• Phalanges (Toes): Fourteen bones per foot; each toe has proximal, middle, and distal phalanges (big toe lacks middle phalanx).

Right vs Left Identification

Determining Sidedness of Bones

Many bones of the appendicular skeleton are paired and can be distinguished as right or left based on anatomical landmarks and orientation. For example, the humerus, scapula, clavicle, hand, femur, tibia, foot, and patella all have features that allow for identification of their side in the body.

Summary Table: Major Bones of the Appendicular Skeleton

Additional info: The appendicular skeleton is crucial for locomotion and manipulation. Knowledge of bone landmarks is essential for clinical assessment, injury diagnosis (e.g., Colle’s and boxer’s fractures), and forensic identification (e.g., sex determination from pelvis).