Humerus notes

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I now have rich, detailed content from Gray's Anatomy for Students and the THIEME Atlas. Here are comprehensive humerus notes:

The Humerus

The humerus is the single long bone of the arm, articulating proximally with the scapula at the glenohumeral joint and distally with the radius and ulna at the elbow joint.

Proximal End

(Fig. 7.22, Gray's Anatomy for Students)

Head

Half-spherical; projects medially and superiorly to articulate with the glenoid cavity of the scapula.
Covered in hyaline cartilage.

Anatomical Neck

Very short constriction immediately distal to the head, between the head and the tubercles laterally, and between the head and the shaft medially.
Fractures here are rare because the bone is thick at this oblique angle.

Greater Tubercle (lateral)

Three facets on its superior and posterior surface - the "SIT" mnemonic for rotator cuff insertions:

Facet	Muscle
Superior	Supraspinatus
Middle	Infraspinatus
Inferior	Teres minor

Lesser Tubercle (anterior)

Single impression for subscapularis attachment.

Intertubercular Sulcus (Bicipital Groove)

Deep groove separating the lesser and greater tubercles; continues down the proximal shaft.
Transmits the tendon of the long head of biceps brachii.
Muscle attachments to the groove lips:
- Lateral lip - pectoralis major
- Floor - latissimus dorsi
- Medial lip - teres major

Surgical Neck

The horizontal constriction between the expanded proximal humerus (head + tubercles) and the narrower shaft.
Most common fracture site of the proximal humerus (especially in elderly patients falling on an outstretched arm).
The axillary nerve and posterior circumflex humeral artery pass immediately posterior to the surgical neck through the quadrangular space - both are at risk in surgical neck fractures.

Shaft

Right humerus - lateral view (a) and medial view (b) with full labeling

(THIEME Atlas of Anatomy)

Cross-sectional shape

Triangular in cross-section with:

3 borders: anterior, lateral, medial
3 surfaces: anterolateral, anteromedial, posterior

Key landmarks

Feature	Location	Significance
Deltoid tuberosity	Lateral surface, midshaft	Insertion of deltoid muscle
Radial groove (spiral groove)	Posterior surface, passes diagonally	Houses the radial nerve and profunda brachii artery
Coracobrachialis attachment	Medial surface, mid-shaft	Thin vertical roughening

Intermuscular septa

Attach to the medial and lateral borders, dividing the arm into anterior (flexor) and posterior (extensor) compartments.

Distal End

The Condyle (two articular parts)

Part	Shape	Articulates with
Capitulum	Hemispherical, lateral, projects anteroinferiorly, NOT visible from posterior	Radius (head)
Trochlea	Pulley-shaped, medial, extends onto posterior surface, medial edge more pronounced	Ulna

Epicondyles (non-articular, proximal to the condyle)

Medial epicondyle - large, most palpable landmark on medial elbow; bears attachment for anterior compartment forearm muscles; the ulnar nerve passes posterior to it (palpable here; "funny bone")
Lateral epicondyle - less pronounced; attachment for posterior compartment (extensor) forearm muscles

Supracondylar ridges

Both medial and lateral borders expand distally into medial and lateral supraepicondylar ridges.
The lateral ridge is more pronounced and roughened for posterior forearm muscle attachments.

Three Fossae (superior to the condyle)

Fossa	Surface	Relation
Radial fossa	Anterior, above capitulum (least distinct)	Accommodates radial head in elbow flexion
Coronoid fossa	Anterior, above trochlea	Accommodates coronoid process of ulna in flexion
Olecranon fossa	Posterior, above trochlea (largest)	Accommodates olecranon in elbow extension

Nerves Related to the Humerus

(Fig. 7.17, Gray's Anatomy for Students)

Three major nerves are directly related to the humerus:

Nerve	Region	At-risk fracture
Axillary nerve (posterior cord)	Passes around surgical neck posteriorly through quadrangular space	Surgical neck fracture → loss of deltoid function + loss of sensation over "regimental badge" area
Radial nerve	Spirals diagonally in the radial groove (middle third of shaft)	Humeral shaft fracture → wrist drop (loss of wrist + finger extension)
Ulnar nerve	Passes posterior to the medial epicondyle	Medial epicondyle fracture → loss of intrinsic hand muscles, claw hand

Blood Supply to the Humeral Head

Anterior circumflex humeral artery - main supply to humeral head
Posterior circumflex humeral artery - accompanies axillary nerve through quadrangular space

Fractures at the anatomical neck can disrupt both vessels, leading to avascular necrosis of the humeral head.

Torsion of the Humerus

The proximal humerus is rotated relative to the distal end (torsion angle ~16° in adults, decreasing from ~60° at birth).
Assessed by comparing the humeral head axis to the epicondylar axis.
The decrease in torsion angle with growth correlates with repositioning of the scapulae.

Clinical Correlations

Injury	Site	Nerve at risk	Deficit
Fall onto outstretched arm (elderly)	Surgical neck	Axillary nerve	Deltoid paralysis, loss of shoulder abduction
Humeral shaft fracture	Radial groove	Radial nerve	Wrist drop, loss of finger extension
Medial epicondyle fracture	Distal humerus	Ulnar nerve	Claw hand, loss of intrinsic muscles
Supracondylar fracture (children)	Distal humerus	Anterior interosseous nerve / brachial artery	"Danger zone" - can injure brachial artery

Sources: Gray's Anatomy for Students (9780323934237); THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System (9781626237186); Campbell's Operative Orthopaedics 15th Ed 2026 (9780443117633)

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