Appendicular Skeleton: Shoulder, Arm, Hip, and Leg – Study Guide

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 divided into the upper extremity (shoulder and arm) and the lower extremity (hip and leg). Understanding the structure and function of these bones is essential for comprehending human movement and anatomy.

Shoulder and Arm (Upper Extremity)

Clavicle

• Clavicle: Also known as the collarbone, it connects the upper limb to the trunk.

• Sternal end: The medial, rounded end that articulates with the manubrium of the sternum.

• Acromial end: The lateral, flattened end that articulates with the acromion of the scapula.

Scapula

• Acromion process: Lateral extension forming the highest point of the shoulder.

• Coracoid process: Anterior projection for muscle attachment.

• Glenoid cavity (fossa): Shallow socket that articulates with the head of the humerus.

• Superior border: Uppermost edge of the scapula.

• Medial (vertebral) border: Edge closest to the vertebral column.

• Lateral (axillary) border: Edge closest to the armpit.

• Spine: Prominent ridge running across the posterior surface.

• Superior angle: Uppermost angle of the scapula.

• Inferior angle: Lowermost angle of the scapula.

• Supraspinous fossa: Depression above the spine.

• Infraspinous fossa: Depression below the spine.

• Right vs. Left Scapula: The glenoid cavity always faces laterally; the spine is posterior.

Humerus

• Head: Rounded proximal end that fits into the glenoid cavity.

• Anatomic neck: Slight constriction immediately below the head.

• Surgical neck: Common fracture site, below the tubercles.

• Deltoid tuberosity: Rough area for deltoid muscle attachment.

• Medial epicondyle: Bony projection on the distal, medial side.

• Lateral epicondyle: Bony projection on the distal, lateral side.

• Olecranon fossa: Posterior depression for the olecranon of the ulna.

• Coronoid fossa: Anterior depression for the coronoid process of the ulna.

• Capitulum: Lateral condyle that articulates with the radius.

• Trochlea: Medial condyle that articulates with the ulna.

• Greater tubercle: Lateral projection for muscle attachment.

• Lesser tubercle: Anterior projection for muscle attachment.

• Intertubercular groove (sulcus): Groove between the tubercles for the biceps tendon.

• Right vs. Left Humerus: The head faces medially; the olecranon fossa is posterior.

Forearm: Ulna and Radius

• Ulna:

  • Head: Distal end of the ulna.

  • Olecranon process: Prominent, proximal projection forming the elbow.

  • Coronoid process: Anterior projection at the proximal end.

  • Trochlear notch: Deep notch that articulates with the trochlea of the humerus.

  • Styloid process: Distal, pointed projection.

  • Radial notch: Lateral depression for articulation with the head of the radius.

• Radius:

  • Styloid process: Distal, lateral projection.

  • Head: Proximal, disc-shaped structure that articulates with the capitulum of the humerus.

  • Ulnar notch: Distal depression for articulation with the ulna.

Wrist and Hand

• Carpals: Eight small bones arranged in two rows forming the wrist.

• Metacarpals: Five bones numbered I–V from thumb (lateral) to little finger (medial).

• Phalanges: Fourteen bones in the fingers; each finger has proximal, middle, and distal phalanges, except the thumb (pollex), which has only proximal and distal.

Hip and Leg (Lower Extremity)

Hip Bone (Os Coxae/Innominate)

• Ilium, Pubis, Ischium: The three bones that fuse to form each hip bone.

• Iliac crest: Superior border of the ilium.

• Anterior superior/inferior iliac spine: Projections on the anterior ilium.

• Posterior superior/inferior iliac spine: Projections on the posterior ilium.

• Greater/Lesser sciatic notch: Indentations for nerve passage.

• Acetabulum: Deep socket for the head of the femur.

• Superior/Inferior pubic ramus: Branches of the pubis.

• Symphysis pubis: Cartilaginous joint uniting the two pubic bones.

• Ischial spine/tuberosity: Projections for ligament and muscle attachment.

• Obturator foramen: Large opening for nerves and blood vessels.

• Greater (false) pelvis: Area above the pelvic brim.

• Lesser (true) pelvis: Area below the pelvic brim.

• Pelvic inlet/outlet: Openings at the top and bottom of the true pelvis.

• Right vs. Left Os Coxa: The acetabulum faces laterally; the pubic symphysis is anterior.

Femur

• Head: Proximal, rounded end that fits into the acetabulum.

• Fovea capitis: Small pit in the head for ligament attachment.

• Neck: Constricted region below the head.

• Greater/Lesser trochanter: Large projections for muscle attachment.

• Medial/Lateral condyle: Distal, rounded surfaces that articulate with the tibia.

• Intertrochanteric crest: Ridge between the trochanters on the posterior side.

• Linea aspera: Ridge along the posterior shaft for muscle attachment.

• Right vs. Left Femur: The head faces medially; the linea aspera is posterior.

Patella

• Patella: The kneecap; a sesamoid bone embedded in the quadriceps tendon.

Tibia and Fibula

• Tibia:

  • Medial/Lateral condyle: Proximal surfaces that articulate with the femur.

  • Intercondylar eminence: Raised area between the condyles.

  • Tibial tuberosity: Anterior projection for patellar ligament attachment.

  • Medial malleolus: Distal projection forming the inner ankle.

  • Right vs. Left Tibia: The tibial tuberosity is anterior; the medial malleolus is medial.

• Fibula:

  • Lateral malleolus: Distal projection forming the outer ankle.

  • Head: Proximal end of the fibula.

Ankle and Foot

• Tarsals: Seven bones forming the ankle, including the calcaneus (heel bone) and talus (articulates with tibia).

• Metatarsals: Five bones numbered I–V from medial (big toe) to lateral (little toe).

• Phalanges: Fourteen bones in the toes; each toe has proximal, middle, and distal phalanges, except the big toe (hallux), which has only proximal and distal.

Comparative Anatomy: Male vs. Female Pelvis

Pelvic Differences

The male and female pelvis differ in several anatomical features, reflecting adaptations for childbirth in females.

Feature	Male Pelvis	Female Pelvis
Coccyx	Less flexible, curves more anteriorly	More flexible, straighter
Sacrum	Narrower, more curved	Wider, less curved
Pubic Arch Angle	Less than 90°	Greater than 90°
Greater Sciatic Notch	Narrower	Wider
Pelvic Inlet/Outlet	Smaller, heart-shaped	Larger, oval-shaped
Ischial Spines	Project more medially	Project less medially

Key Terms and Applications

• Proximal, Medial, Distal: Used to describe the location of phalanges in both hand and foot.

• Numbering of Metacarpals/Metatarsals: I–V, starting from the thumb/big toe side.

• Clinical Application: Knowledge of bone markings is essential for identifying fracture sites and understanding muscle attachments.

Additional info: The study of the appendicular skeleton is foundational for understanding movement, diagnosing injuries, and performing physical examinations in clinical practice.