HUMERUS ANATOMY

GENERAL CHARACTERISTICS

• The humerus is the longest and largest bone of the upper limb
• Divided into three main parts:
  • Body (shaft)
  • Proximal epiphysis (upper end)
  • Distal epiphysis (lower end)
• Forms part of the shoulder joint and elbow joint
• Plays a crucial role in arm movement

PROXIMAL EPIPHYSIS (UPPER END)

• Includes the head, which forms the ball of the ball-and-socket shoulder joint
• Articulates with the glenoid cavity of the scapula
• Features the greater and lesser tubercles, as well as the intertubercular sulcus (bicipital groove)
• These structures provide attachment sites for muscles and contribute to shoulder stability and movement

Head of the Humerus

• Structure:
  • Rounded, ball-like
• Function:
  • Articulates with the glenoid cavity of the scapula
  • Forms the ball-and-socket shoulder joint, enabling a wide range of motion

Anatomical Neck

• Location:
  • Below the head
• Function:
  • Separates the head from the greater and lesser tubercles
  • Attachment point for the capsule of the shoulder joint

Surgical Neck

• Location:
  • Below the tubercles
• Clinical Significance:
  • Common site of fractures, especially in older adults
  • Fractures here may damage nearby nerves or blood vessels

Greater Tubercle

• Structure:
  • Protrusion with a convex upper surface and three indentations
• Attachment Points:
  • Highest point: Supraspinatus muscle
  • Middle indentation: Infraspinatus muscle
  • Lowest indentation (2-5 cm down): Teres minor muscle

Lesser Tubercle

• Structure:
  • Smaller bony projection on the front part of the humerus
• Function:
  • Attachment point for a muscle in the rotator cuff
  • Aids in internal rotation of the arm

Intertubercular Sulcus (Bicipital Groove)

• Location:
  • Between the greater and lesser tubercles
• Function:
  • Passage for the long tendon of the Biceps brachii muscle
  • Attachment site for muscles

Crest of the Greater Tubercle

• Structure:
  • Bony ridge extending downward from the greater tubercle
• Function:
  • Attachment site for the Pectoralis major muscle

Crest of the Lesser Tubercle

• Structure:
  • Ridge extending downward from the lesser tubercle
• Function:
  • Attachment site for the Teres major muscle
  • Aids in internal rotation and extension of the arm

DISTAL EPIPHYSIS (LOWER END)

• Forms part of the elbow joint
• Includes two key articular surfaces: the capitulum and the trochlea
• These structures facilitate articulation and movement at the elbow

Articular Surfaces

Capitulum

• Location: Lateral side of the humeral condyle
• Function:
  • Articulates with the head of the radius
  • Allows rotation and flexion of the forearm at the elbow joint

Trochlea

• Location: Medial side of the humeral condyle
• Structure: Pulley-like articular surface
• Function:
  • Articulates with the semilunar notch of the ulna
  • Allows hinge movements like bending and extending the forearm

Condyle of the Humerus

• Structure:
  • Large, rounded structure at the distal end near the elbow
  • Divided into capitulum and trochlea by a smooth ridge
• Function:
  • Connects the humerus to the elbow joint

Fossae

Olecranon Fossa

• Location: Posterior aspect of the distal humerus
• Function:
  • Accommodates the olecranon process of the ulna during forearm extension

Coronoid Fossa

• Location: Anterior surface above the trochlea
• Function:
  • Receives the coronoid process of the ulna during forearm flexion

Radial Fossa

• Location: Anterior surface above the capitulum
• Function:
  • Accommodates the head of the radius during forearm flexion

Epicondyles

Medial Epicondyle

• Structure:
  • Prominent bony projection on the medial side
• Function:
  • Attachment point for the ulnar collateral ligament and flexor muscles of the forearm

Groove for Ulnar Nerve

• Also known as the sulcus for the ulnar nerve
• Location: Behind the medial epicondyle
• Function:
  • Houses the ulnar nerve, often referred to as the "funny bone"

Lateral Epicondyle

• Structure:
  • Smaller, tuberculated bony projection on the lateral side
• Function:
  • Attachment point for extensor muscles and ligaments of the forearm

BODY (SHAFT)

• The shaft has a cylindrical shape
• Composed of compact bone that is thicker in the center and tapers toward the ends
• Encloses a large medullary canal
• Features three surfaces: anteromedial, anterolateral, and posterior
• Features three borders: anterior, lateral, and medial
• Toward the distal end, displays the supracondylar ridges

Surfaces

Anteromedial Surface

• Direction:
  • Faces forward and upward in the upper part, then turns inward and downward
• Function:
  • Provides attachment sites for muscles

Anterolateral Surface

• Direction:
  • Directed outward with a smooth, rounded contour
• Features:
  • Covered by the deltoid muscle
• Deltoid Tuberosity:
  • Location: Rough, triangular elevation about halfway down the humerus
  • Function: Attachment site for the deltoid muscle, aiding arm movement

Posterior Surface

• Covered by:
  • Lateral and medial heads of the Triceps brachii
• Function:
  • Responsible for extending the forearm at the elbow
• Radial Groove (Sulcus nervi radialis):
  • Runs obliquely across the posterior surface
  • Transmits a nerve and artery to the posterior arm compartment

Borders

Anterior Border

• Location:
  • Extends from the greater tubercle to the coronoid fossa
• Function:
  • Separates the anteromedial and anterolateral surfaces

Lateral Border

• Location:
  • Extends from the greater tubercle to the lateral epicondyle
• Function:
  • Separates the anterolateral and posterior surfaces

Medial Border

• Location:
  • Extends from the lesser tubercle to the medial epicondyle
• Function:
  • Separates the anteromedial and posterior surfaces

Supracondylar Ridges

Lateral Supracondylar Ridge

• Location:
  • Lower portion of the lateral border
• Function:
  • Attachment site for the lateral intermuscular septum

Medial Supracondylar Ridge

• Location:
  • Lower third of the medial border
• Function:
  • Provides attachment for muscles contributing to forearm movement and stability

Supracondylar Process

• Location:
  • Small bony projection occasionally found on the anteromedial surface above the medial epicondyle