Upper limb anatomy

Shoulder girdle

• Clavicle: first bone to ossify, mainly intramembranous; its medial epiphysis fuses last (mid-twenties), so a smooth fleck there in a young adult is normal. After a midshaft fracture, sternocleidomastoid lifts the medial fragment and the weight of the arm drags the lateral fragment down. A clavicle riding high above the acromion means the coracoclavicular ligament is torn.
• Os acromiale: unfused acromial centre on the axillary view; causes impingement.
• Proximal humerus: a fracture through the anatomical neck cuts the supply to the head (avascular necrosis); a surgical neck fracture (or anterior dislocation) endangers the axillary nerve and posterior circumflex humeral artery in the quadrangular space: weak abduction beyond the first 15° (deltoid), and numbness over the lower deltoid (regimental badge area, upper lateral arm).
• Anterior dislocation: on the scapular Y view the head lies in front of the Y, beneath the coracoid. It leaves a Hill-Sachs dent on the posterolateral head and a Bankart tear of the anteroinferior labrum (recurrence). The inferior capsule has no cuff support.
• Posterior dislocation (seizure, electric shock): arm locked in internal rotation; easily missed on the AP film, so an axillary view is needed.

Muscles that move the scapula and arm

• Rotator cuff: supraspinatus, infraspinatus, teres minor, subscapularis. Teres major is not part of it.
• The long head of biceps passes through the shoulder joint, enclosed in a synovial sleeve, to the supraglenoid tubercle.
• Pectoralis major inserts on the lateral lip of the intertubercular groove. Its main artery is the pectoral branch of the thoracoacromial artery, which is why the pectoralis major myocutaneous flap for head and neck reconstruction is based on the thoracoacromial vessels.

Rotator cuff and tendons on imaging

• Supraspinatus tears about 1 cm proximal to its insertion, a zone of relatively poor blood supply; it catches under the acromion between 60° and 120° of abduction (painful arc).
• On arthrography, contrast passing from the joint into the subacromial–subdeltoid bursa means a full-thickness cuff tear. A subscapularis tear lets the long head of biceps slip medially out of the groove.
• Calcific tendinitis: dense hydroxyapatite deposit in the cuff. SLAP tear (throwers): contrast enters the superior labrum at the biceps anchor.
• Distal biceps rupture (weightlifter, sudden pop at the front of the elbow): the tendon pulls off the radial tuberosity, the belly bunches up (Popeye bulge) and supination with the elbow flexed is weak. Brachialis also flexes the elbow but inserts on the coronoid process and ulnar tuberosity and does not supinate.

Brachial plexus and nerve injuries

• The plexus is named by its relation to the axillary artery: cords (lateral, medial, posterior) surround the second part of the axillary artery, behind pectoralis minor. Roots and trunks lie in the neck; divisions behind the clavicle; branches around the third part.
• Supination: biceps (musculocutaneous) and supinator (radial nerve, deep branch), so loss needs injury to both.

• Ulnar paradox: at the elbow the injury paralyses the ulnar half of flexor digitorum profundus as well as the lumbricals, so the fingers cannot flex strongly and the claw is mild. At the wrist FDP still works, so the unopposed long flexors plus extensors pull harder into a claw.
• Root values: biceps jerk C5–C6, supinator (brachioradialis) jerk C5–C6, triceps jerk C7 (C6–C7). A C5/C6 disc compresses the C6 root: weak elbow flexion and wrist extension, reduced biceps and supinator jerks, numb thumb and index finger. A C6/C7 disc compresses C7 (triceps, middle finger).

Elbow

• Ossification centres appear in a fixed order: capitellum (about 1 year), radial head, medial epicondyle, trochlea, olecranon, lateral epicondyle (about 10–11 years). A trochlear centre with no medial epicondyle in its usual place after a reduced dislocation means the avulsed medial epicondyle is trapped in the joint.

• Terrible triad: posterior dislocation with radial head and coronoid fractures. Throwers tear the anterior band of the ulnar collateral ligament.
• Supracondylar fracture endangers the brachial artery (Volkmann ischaemic contracture) and median nerve (often its anterior interosseous branch).
• A thin oblique lucent line in the humeral shaft cortex, directed towards the elbow, is a nutrient canal, not a fracture.

Forearm, wrist and hand

• The distal radius normally has a palmar tilt of about 11°. Colles: dorsal tilt; Smith: palmar displacement. Galeazzi: distal radius fracture with distal radioulnar dislocation. Monteggia: proximal ulna with radial head dislocation.
• Children: torus (buckle) fracture because metaphyseal bone is porous and elastic; Salter–Harris II is the commonest growth-plate injury.
• Carpal bones: proximal row scaphoid, lunate, triquetrum, pisiform. Capitate and hamate ossify first. Bone age is read from a left hand and wrist film. Scaphoid is the commonest carpal fracture; lunate the commonest carpal dislocation.

• Boxer's fracture of the 5th metacarpal neck. Mallet finger: avulsion of the terminal extensor tendon. Skier's thumb: a retracted ulnar collateral ligament trapped outside the adductor aponeurosis (Stener lesion) will not heal.
• Rheumatoid arthritis: periarticular osteopenia, symmetrical joint space loss, marginal MCP and PIP erosions. Enchondroma: lytic phalangeal lesion with endosteal scalloping.

Arteries and veins

• Subclavian artery lies behind scalenus anterior, the vein in front; proximal stenosis reverses vertebral flow (steal).
• Axillary artery: outer border of the first rib to the lower border of teres major; three parts defined by pectoralis minor. Its largest branch, the subscapular, runs along the lateral border of the scapula; the scapular anastomosis keeps the arm alive if the artery is tied above it.
• Brachial artery divides at the neck of the radius in the cubital fossa, medial to the biceps tendon.
• At the wrist the radial artery lies between brachioradialis and flexor carpi radialis tendons (pulse, cannulation; Allen test checks ulnar flow), then crosses the snuffbox floor. The ulnar artery lies lateral to flexor carpi ulnaris and crosses the hook of hamate (hypothenar hammer).
• Superficial palmar arch (mainly ulnar) lies level with the distal border of the extended thumb; the deep arch (mainly radial) is more proximal.
• Cephalic vein: deltopectoral groove, pierces the clavipectoral fascia into the axillary vein. Basilic vein: medial, larger and straighter, joins the brachial veins to form the axillary vein, so it is preferred for a PICC line.
• Effort thrombosis: axillosubclavian vein compressed between the clavicle and first rib in repetitive overhead work.

Remember On a child's elbow film, check the fat pads, the anterior humeral line and the radiocapitellar line every time.

Exam trap Posterior shoulder dislocation is missed on a single AP view; get an axillary view.

Exam trap Ulnar nerve injury at the wrist gives a worse claw than at the elbow, because profundus is spared.

How FCPS asks about this

• Surgical neck fracture, weak abduction, numb lateral arm: axillary nerve (deltoid and teres minor).
• Mid-shaft humeral fracture with wrist drop: radial nerve in the spiral groove.
• Cannot supinate: musculocutaneous (biceps) and radial (supinator) nerves.
• Popeye bulge after lifting: distal biceps rupture from the radial tuberosity.
• Part of plexus around the second part of the axillary artery: cords.
• Triceps jerk root: C7; C5/C6 disc compresses C6 (weak elbow flexion, numb thumb).
• Pectoralis major flap blood supply: thoracoacromial artery.