Bones - Humerus Flashcards
Where is the humerus located?
What type of bone is it?
Proximally it forms the glenohumeral joint with the glenoid fossa.
Distally, it forms the elbow joint by articulating with the head of the radius and the trochlear notch of the ulna.
It is a long bone.
What are the bony landmarks of the proximal humerus?
The proximal humerus is marked by a head, anatomical neck, surgical neck, greater and lesser tubercles and intertubercular sulcus.
1) Head - faces medially, upwards and backward. Separates from the greater and lesser tubercles by the anatomical neck.
2) Greater tubercle - located laterally on the humerus and has anterior and posterior sufaces.
Serves as an attachment site for three rotator cuff muscles:
1) Supraspinatus (attaches to superior facet)
2) Infraspinatus (attaches to middle facet)
3) Teres minor (attaches to inferior facet)
3) Lesser tubercle - much smaller and located more medially on the bone. It only has an anterior surface.
Provides attachment for the last rotator cuff muscle - the subscapularis.
4) Intertubercular sulcus - a groove that separates the two tubercles.
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 of the lips of the intertubercular sulcus. This can be remembered with a mnemonic ‘a lady between two majors’, with the latissimus dorsi attaching between teres major on the medial lip and pectoralis major laterally.
5) 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
This is a frequent site of fracture - usually by 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 difficultly 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.
What are the features of the shaft of the humerus?
This is the site of attachmet for various muscles. The cross-section of the humerus is circular proximally and flattened distally.
1) Deltoid tuberosity - roughed area located on the lateral surface of the humeral shaft.
2) Radial (spiral) groove - a shallow depression running diagonallly 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 -
1) Coracobrachialis
2) Deltoid
3) Brachialis
4) Brachioradialis
Posteriorly -
1) Medial and lateral heads of the triceps (the spiral groove demarcates their respective origins.
Clinical relevance: mid-shaft fracture
A mid-shaft fracture risks 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 three and a half fingers dorsally.
What are the bony landmarks of the distal end of the humerus?
1) Supraepicondylar ridges - there are two - medial and lateral. The lateral is more roughed, providing the site of common origin of the forearm extensor muscles.
2) Epicondyles - immediately distal to the supraepicondylar ridges. Both can be palpated at the elbow. The medial is the large of the two. The ulnar nerve passes in a groove on the posterior aspect of the medial epicondyle where is is more palpable.
3) Trochlea - located distally and medially - extends onto the posterior aspect of the bone.
4) Capitulum - lateral to the trochlea. This articulates with the radius.
5) Coronoid fossa - located superior to the trochlea
6) Radial fossa - located superior to the capitulum
7) Olecranon process - located on the posterior surface of the distal humerus.
5, 6, and 7 accomodate the forearm during flexion and extension of the forearm.
What are the articulations of the humerus?
Proximally - glenhumeral joint
Distally - elbow joint - capitulum of the humerus articulates with the head of the radius and the trochlea of the humerus articulares with the trochlear notch of the ulna.
Clinical relevance: supracondylar fracture
This 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 sweliing following trauma. Resulting ischaemia can cause Volkman’s ischaemic contracture - uncontrolled flexion of the hand - as flexor muscles become fibrotic and short.
There can also 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 fracture:
1) Type 1 is minimally displaced
2) Type 2 is displaced with but with an intact posterior cortex
3) Type 3 is completely off-ended
Type 1 can usually be managed conservatively with an above elbow cast whereas type 2 and 3 typically require surgical fixation with cross bi-cortical k-wires.
