Humerus

What is the humerus

A type of long bone that connects the upper limbs to the shoulder girdle.

Located between and articulates with the shoulder and elbow joints

diagram

how to tell which view

Anterior - bicipital groove, coronoid fossa, radial fossa and capitilum

Posterior - olcraneon fossa

Features of the proximal end

• Head of humerus - rounded covered in cartilage

• Anatomical neck - adjoining the head, distal to the articular surface and proximal to tuberosities. Location of growth plate.

• Surgical neck - imaginary horizontal line across proximal shaft, distal to the tuberosity. Common fracture site

• Greater tuberosity - posterolaterally the supraspinatus tendon is attached to the superior aspect

• Lesser tuberosity - anteriorly, tendon of the subscapularis muscle is attached

• Bicipital groove - between tuberosities

proximal extremity

• articulates with glenoid cavity to form glenohumeral joint

• synovial ball and socket joint

articulations

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.

Features of shaft (diaphysis)

Cylindrical in cross section, flattened and wider at distal extremity. Has 3 key features;

• deltoid tuberosity on antero lateral surface, attaches to deltoid muscle

• spiral groove runs obliquely, forwards and downwards transmits radial nerve

• nutrient foramen located on antero-medial surface, allows small blood vessels to pass through medullary cavity

Features of distal end

• 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 (superior to capitulum) and medial epicondyles (superior to trochlea). Both can be palpated at the elbow. The medial is the larger of the two and extends more distally.

• Capitulum - lateral condyle. Rounded, articulates with head of radius

• Trochlea - medial condyle. Lateral to the trochlea is the capitulum, which articulates with the radius

distal features continued

• capitulum - smaller or 2 articular surfaces, articulates with radial head

• trochlear - larger of distal articular surfaces, pulley shaped and articulates with trochlear notch of ulna

• radial and coronoid fossae - 2 smaller depressions on anterior surface, located immediately above capitulum and trochlear

• olecranon fossa - deep depression on posterior aspect of lower humerus, located above trochlear and accomodates olcranon process of ulna during extension of elbow

• ulnar groove - marked groove between medial end of trochlear and medial epicondyle, transmits ulnar nerve

distal - depressions

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.

Ossification

Shaft - one centre, 8th/9th week intraterine

Upper end;

• one centre in head - 6 months

• one centre in greater tuberosity - 2 years

• one centre in lesser tuberosity - 5th year

• all centres unite to form one epiphysis at year 6 and fuse with shaft at 20 years

Lower end;

• one centre in capitulum - 2 years

• one centre in medial epicondyle - 5th year

Trauma and pathology of humerus

• fracture of surgical neck

• fracture of humeral shaft

• supracondylar fracture

• condylar fracture

• bone metastases

• malignant bone tumours

Surgical neck fracture

• Cause is FOOSH, usually in elderly

• Treatment usually is a sling

Shaft fracture

• Middle third; spiral, oblique or comminuted

• Cause - FOOSH, direct blow or high velocity injuries

• Sling or cast

• risk damage to radial nerve, leading to unopposed flexion of the wrist, known as wrist drop

Supracondylar fracture

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 FOOSH. It is more common in children than adults.

The brachial artery can be damaged. The resulting ischaemia can cause uncontrolled flexion of the hand – as flexor muscles become fibrotic and short.

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.