Notes on Clavicle, Scapula, Humerus, Radius, Ulna, Carpal Bones & Metacarpal Bones

Notes on Clavicle, Scapula, Humerus, Radius, Ulna, Carpal Bones & Metacarpal Bones

Clavicle :

The clavicle is commonly fractured by falling on the outstretched hand (indirect violence). The most common site of fracture is the junction between the two curvatures of the bone, which is the weakest point.

The lateral fragment is displaced downwards by the weight of the limb as trapezius muscle alone is unable to support the weight of upper limb.

The clavicles may be congenitally absent, or imperfectly developed in a disease called cleidocranial dysostosis. In this condition, the shoulders droop, and can be approximated anteriorly in front of the chest.

Scapula:

Paralysis of the serratus anterior causes Swinging’ of the scapula. The medial border of the bone becomes unduly prominent, and the arm cannot be abducted beyond 90 degrees.

Humerus:

The common sites of fracture of humerus are the surgical neck, the shaft, and the supracondylar region.

Supracondylar fracture is common in young age. It is produced by a fall on the outstretched hand. The lower fragment is mostly displaced backwards, so that the elbow is unduly prominent, as in dislocation of the elbow joint.

The three bony points of the elbow form the usual equilateral triangle. This fracture may cause injury to the median nerve. It may also lead to Volkmann’s ischaemic contracture caused by occlusion of the brachial artery.

The humerus has a poor blood supply at the junction of its upper and middle thirds. Fractures at this site show delayed union or nonunion.

The head of the humerus commonly dislocates inferiorly.

Radius

The radius commonly gets fractured about 2 cm above its lower end (Coles fracture). This fracture is caused by a fall on the outstretched hand. The distal fragment is displaced upwards and backwards, and the radial styloid process comes to lie proximal to the ulnar styloid process.

A sudden powerful jerk on the hand of a child may dislodge the head of the radius from the grip of the annular ligament. This is known as subluxation of the head of the radius (pulled elbow). The head can normally be felt in a hollow behind the lateral epicondyle of the humerus.

Ulna:

The ulna is the stabilising bone of the forearm, with its trochlear notch gripping the lower end of the humerus. On this foundation, the radius can pronate and supinate for efficient working of the upper limb.

The shaft of the ulna may fracture either alone or along with that of the radius. Cross-union between the radius and ulna must be prevented to preserve pronation and supination of the hand.

Dislocation of the elbow is produced by a fall on the outstretched hand with the elbow slightly flexed. The olecranon shifts posteriorly and the elbow is fixed in slight flexion.

Normally in an extended elbow, the tip of the olecranon lies in a horizontal line with the two epicondyles of the humerus; and in the flexed elbow the three bony points form an equilateral triangle. These relations are disturbed in dislocation of the elbow.

Fracture of the olecranon is common and is caused by a fall on the point of the elbow. Fracture of the coronoid process is uncommon, and usually accompanies dislocation of the elbow.

Madelung’s deformity is dorsal subluxation (displacement) of the lower end of the ulna, due to retarded growth of the lower end of the radius.

Carpal Bones

Fracture of the scaphoid is quite common. The bone fractures through the waist at right angles to its long axis. The fracture is caused by a fall on the outstretched hand, or on the tips of the fingers. This causes tenderness and swelling in the anatomical snuff box, and pain on longitudinal percussion of the thumb and index finger.

The residual disability is more marked in the midcarpal joint than in the wrist joint. The importance of the fracture lies in its liability to nonunion and avascular necrosis of the body of the bone.

Normally, the scaphoid has two nutrient arteries, one entering the palmar surface of the tubercle and the other the dorsal surface of the body. Occasionally (13% of cases) both vessels enter through the tubercle or through the distal half of the bone. In such cases, fracture may deprive the proximal half of the bone of its blood supply leading to avascular necrosis.

Dislocation of the lunate may be produced by a fall on the acutely dorsiflexed hand with the elbow joint flexed. This displaces the lunate anteriorly, also leading to carpal tunnel syndrome-like features.

Metacarpal Bones

Fracture of the base of the first metacarpal is called Bennett’s fracture. It involves the anterior part of the base, and is caused by a force along its long axis. The thumb is forced into a semiflexed position and cannot be opposed. The fist cannot be clenched.

The other metacarpals may also be fractured by direct or indirect violence. Direct violence usually displaces the fractured segment forwards. Indirect violence displaces them backwards.

Tubercular or syphilitic disease of the metacarpals or phalanges in a child is located in the middle of the diaphysis rather than in the metaphysis because the nutrient artery breaks up into a plexus immediately upon reaching the medullary cavity.

In adults, however, the chances of infection are minimised because the nutrient artery is replaced (as the major source of supply) by periosteal vessels.

When the thumb possesses three phalanges, the first metacarpal has two epiphyses one at each end. Occasionally, the first metacarpal bifurcates distally. Then the medial branch has no distal epiphysis, and has only two phalanges. The lateral branch has a distal epiphysis and three phalanges. Total digits are six in such case.

Anatomical snuff box is a triangular depression on the posterolateral aspect of the wrist joint. It is bounded by abductor pollicis longus, extensor pollicis brevis laterally and extensor pollicis longus medially. In its floor are scaphoid and trapezium.

Relation of capsular attachments and epiphyseal lines: If epiphyseal line, i.e. site of union of epiphysis and metaphyseal end of diaphysis, is intracapsular, the infections of the joints are likely to affect the metaphysis, the actively growing part of the bone especially in young age.

Fracture of distal phalanx of middle finger is commonest. It is treated by splinting the injured phalanx to the adjacent normal finger. This is called “buddy splint”.