The humerus is a long bone of the upper limb, which extends from the shoulder to the elbow.
The proximal aspect of the humerus articulates with the glenoid fossa of the scapula, forming the glenohumeral joint. Distally, at the elbow joint, the humerus articulates with the head of the radius and trochlear notch of the ulna.
In this article, we shall look at the anatomy of the humerus – its bony landmarks and clinical correlations.
The proximal humerus is marked by a head, anatomical neck, surgical neck, greater and lesser tubercles and intertubercular sulcus.
The upper end of the humerus consists of the head. This faces medially, upwards and backwards and is separated from the greater and lesser tubercles by the anatomical neck.
The greater tubercle is located laterally on the humerus and has anterior and posterior surfaces. It serves as an attachment site for three of the rotator cuff muscles – supraspinatus, infraspinatus and teres minor – they attach to superior, middle and inferior facets (respectively) on the greater tubercle.
The lesser tubercle is much smaller, and more medially located on the bone. It only has an anterior surface. It provides attachment for the last rotator cuff muscle – the subscapularis.
Separating the two tubercles is a deep groove, known as the intertubercular sulcus. The tendon of the long head of the biceps brachii emerges from the shoulder joint and runs through this groove.
The edges of the intertubercular sulcus are known as lips. Pectoralis major, teres major and latissimus dorsi insert on the lips of the intertubercular sulcus. This can be remembered with the mnemonic “a lady between two majors”, with latissimus dorsi attaching between teres major on the medial lip and pectoralis major laterally.
The surgical neck runs from just distal to the tubercles to the shaft of the humerus. The axillary nerve and circumflex humeral vessels lie against the bone here.
Clinical Relevance: Surgical Neck Fracture
The surgical neck of the humerus is a frequent site of fracture – usually by a direct blow to the area, or falling on an outstretched hand.
The key neurovascular structures at risk here are the axillary nerve and posterior circumflex artery.
Axillary nerve damage will result in paralysis to the deltoid and teres minor muscles. The patient will have difficulty performing abduction of the affected limb. The nerve also innervates the skin over the lower deltoid (regimental badge area), and therefore sensation in this region may be impaired.
The shaft of the humerus is the site of attachment for various muscles. Cross section views reveal it to be circular proximally and flattened distally.
On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the deltoid tuberosity.
The radial (or spiral) groove is a shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity. The radial nerve and profunda brachii artery lie in this groove. The following muscles attach to the humerus along its shaft:
- Anteriorly – coracobrachialis, deltoid, brachialis, brachioradialis.
- Posteriorly – medial and lateral heads of the triceps (the spiral groove demarcates their respective origins).
Clinical Relevance: Mid-Shaft Fracture
A mid-shaft fracture of the humerus risk damage to the radial nerve and profunda brachii artery (as they are tightly bound in the radial groove).
The radial nerve innervates the extensors of the wrist. In the event of damage to this nerve (either direct or as a consequence of swelling), the extensors will be paralysed. This results in unopposed flexion of the wrist, known as ‘wrist drop’.
There can also be some sensory loss over the dorsal (posterior) surface of the hand, and the proximal ends of the lateral 3 and a half fingers dorsally.
The lateral and medial borders of the distal humerus form medial and lateral supraepicondylar ridges. The lateral supraepicondylar ridge is more roughened, providing the site of common origin of the forearm extensor muscles.
Immediately distal to the supraepicondylar ridges are extracapsular projections of bone, the lateral and medial epicondyles. Both can be palpated at the elbow. The medial is the larger of the two and extends more distally. The ulnar nerve passes in a groove on the posterior aspect of the medial epicondyle where it is palpable.
Distally, the trochlea is located medially, and extends onto the posterior aspect of the bone. Lateral to the trochlea is the capitulum, which articulates with the radius.
Also located on the distal portion of the humerus are three depressions, known as the coronoid, radial and olecranon fossae. They accommodate the forearm bones during flexion or extension at the elbow.
The proximal region of the humerus articulates with the glenoid fossa of the scapula to form the glenohumeral joint (shoulder joint).
Distally, at the elbow joint, the capitulum of the humerus articulates with the head of the radius and the trochlea of the humerus articulates with the trochlear notch of the ulna.
Clinical Relevance: Supracondylar Fracture
A supracondylar fracture is a fracture of the distal humerus just above the elbow joint. The fracture is typically transverse or oblique, and the most common mechanism of injury is falling on an outstretched hand. It is more common in children than adults.
In this type of injury, the brachial artery can be damaged; either directly, or via swelling following the trauma. The resulting ischaemia can cause Volkmann’s ischaemic contracture – uncontrolled flexion of the hand – as flexor muscles become fibrotic and short.
There also can be damage to the anterior interosseous nerve (branch of the median nerve), ulnar nerve or radial nerve. The anterior interosseous nerve can be tested by asking the patient to make an ‘okay’ sign, testing for weakness of flexor pollicis longus.
The Gartland classification is used for these fractures:
- Type 1 is minimally displaced
- Type 2 is displaced with but with an intact posterior cortex
- Type 3 is completely off-ended.
Type 1 can usually be managed conservatively with an above elbow cast whereas types 2 and 3 typically require surgical fixation with crossed, bi-cortical k-wires.