Humerus

Humerus

Also known as: arm bone, upper arm bone, surgical neck, radial groove, medial epicondyle

The long bone of the arm, articulating with the scapula at the shoulder and with the radius and ulna at the elbow. Three major nerves are in direct contact with it — axillary, radial and ulnar.

Show on body map Muscles — Posterior View

Overview

Length≈30–36 cm in adults

Nutrient foramenDirected toward the elbow (distal)

Proximal end: the hemispherical head faces medially, upward and backward to the glenoid; it is separated from the tubercles by the anatomical neck (capsule attachment). The greater tubercle (laterally) receives supraspinatus, infraspinatus and teres minor; the lesser tubercle (anteriorly) receives subscapularis. Between them, the intertubercular sulcus (bicipital groove) carries the tendon of the long head of biceps beneath the transverse humeral ligament; its lips receive pectoralis major (lateral), teres major (medial) and latissimus dorsi (floor) — "the lady between two majors". The surgical neck, the narrow region below the tubercles, is the commonest fracture site and is in contact with the axillary nerve and posterior circumflex humeral artery.

Shaft: the deltoid tuberosity lies laterally at mid-shaft; behind it the radial (spiral) groove carries the radial nerve and profunda brachii artery. Distal end: the bone flattens into a wide condyle with the medial and lateral supracondylar ridges and epicondyles. The articular surfaces are the pulley-shaped trochlea (with the ulna) and the rounded capitulum (with the radial head). Above them, the coronoid fossa and radial fossa anteriorly and the deep olecranon fossa posteriorly receive the processes of the forearm bones in flexion and extension. The ulnar nerve runs in a groove behind the prominent medial epicondyle (the "funny bone"), which is the common flexor origin; the lateral epicondyle is the common extensor origin.

Location: Arm, between the shoulder and the elbow.

Parts & subdivisions

Head
Articulates with the glenoid cavity.
Anatomical neck
Encircles the head; capsular attachment.
Surgical neck
Below the tubercles; axillary nerve and posterior circumflex humeral artery.
Greater and lesser tubercles
Rotator cuff insertions (SIT on greater, subscapularis on lesser).
Intertubercular sulcus
Tendon of the long head of biceps.
Deltoid tuberosity
Insertion of deltoid.
Radial groove
Radial nerve and profunda brachii artery.
Medial epicondyle
Common flexor origin; ulnar nerve passes behind.
Lateral epicondyle
Common extensor origin.
Trochlea and capitulum
Articulate with the ulna and radius respectively.
Olecranon, coronoid and radial fossae
Receive the olecranon in extension and the coronoid process and radial head in flexion.

Anatomy

Arterial supply: Nutrient artery from the brachial artery (or profunda brachii); anterior and posterior circumflex humeral arteries (head).
Articulations: Scapula (glenohumeral joint), ulna (humero-ulnar joint), radius (humeroradial joint).
Ossification: Primary centre in the shaft ≈week 8. Secondary centres: head (≈birth–6 months), greater tubercle (≈1–2 y), lesser tubercle (≈4–5 y) — fuse into one proximal epiphysis that unites with the shaft ≈18–20 y (the "growing end"); distal centres CRITOE: Capitulum ≈1, Radial head ≈3–5, Internal (medial) epicondyle ≈5–7, Trochlea ≈7–9, Olecranon ≈9–11, External (lateral) epicondyle ≈11–13 years.

Function

Lever for movements of the arm at the shoulder
Forms the upper surfaces of the elbow joint
Attachment for rotator cuff, deltoid, pectoralis major, latissimus dorsi, brachialis, triceps and forearm muscles

Clinical significance

Surgical neck fracture

Common in elderly osteoporotic people after falls; may injure the axillary nerve (paralysed deltoid and teres minor, numbness over the "regimental badge" area).

Mid-shaft fracture

Fracture at the radial groove damages the radial nerve: wrist drop (paralysed wrist and finger extensors) with sensory loss on the dorsum of the first web space; triceps is usually spared because its branches arise higher.

Supracondylar fracture

Commonest elbow fracture in children (5–7 years), usually extension-type from a fall on the outstretched hand. The distal fragment displaces posteriorly, endangering the brachial artery and median nerve (anterior interosseous branch); untreated ischaemia causes compartment syndrome and Volkmann ischaemic contracture. Cubitus varus ("gunstock" deformity) may follow malunion.

Medial epicondyle injury

Fractures or chronic traction ("Little League elbow") may injure the ulnar nerve: claw hand and hypothenar wasting.

Mnemonics

Elbow ossification centres

"CRITOE" (≈1-3-5-7-9-11 years): Capitulum, Radial head, Internal epicondyle, Trochlea, Olecranon, External epicondyle.

Nerves in contact with the humerus

"ARM": Axillary (surgical neck), Radial (radial groove), Median (supracondylar region); plus Ulnar (behind the medial epicondyle).

Test yourself

A mid-shaft fracture of the humerus is most likely to injure which nerve, producing which sign?

Axillary nerve — loss of shoulder abduction
Ulnar nerve — claw hand
Median nerve — ape hand
Radial nerve — wrist drop

Answer: Radial nerve — wrist drop

The radial nerve lies in the radial (spiral) groove on the posterior shaft. Injury there paralyses the wrist and finger extensors (wrist drop) with sensory loss over the dorsal first web space; triceps is usually spared.