Upper Limb Joints
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Direct answer
Four short muscles hold the head of the humerus against the glenoid — supraspinatus, infraspinatus, teres minor and subscapularis, the SITS of the rotator cuff — and the deltoid beside them is served by the axillary nerve, which is the nerve stretched in an anterior shoulder dislocation. At the elbow, the annular ligament that rings the radial head is the structure a toddler's pulled elbow escapes, and the ulnar nerve behind the medial epicondyle is the nerve of supracondylar fracture complications. The wrist adds the two most-tested small anatomy facts of the limb: the carpal tunnel carries the median nerve and nine tendons, and the scaphoid — the commonest fractured carpal bone, tender in the anatomical snuffbox — suffers avascular necrosis of its proximal pole because its blood supply enters distally and runs retrogradely.
What you must remember
- Rotator cuff: supraspinatus initiates abduction (first 15 degrees) and is the commonly torn tendon in impingement; infraspinatus and teres minor laterally rotate; subscapularis medially rotates; supraspinatus and infraspinatus share the suprascapular nerve, teres minor takes the axillary, subscapularis the subscapular nerves.
- Shoulder dislocation: anterior is commonest (glenoid labrum stripped — Bankart lesion; posterolateral humeral head impaction — Hill-Sachs lesion); the axillary nerve is injured, giving deltoid weakness and anaesthesia over the regimental badge area.
- Pulled elbow: the radial head subluxates out of the annular ligament in a preschooler yanked by the arm; the arm is held pronated and flexed, and reduction is by supination and flexion.
- Supracondylar territory: the median nerve and brachial artery lie anterior to the elbow and are endangered by extension-type supracondylar fractures in children — the source of Volkmann's ischaemic contracture; the ulnar nerve grooves behind the medial epicondyle.
- Carpal tunnel: the median nerve with the four flexor digitorum superficialis, four flexor digitorum profundus and flexor pollicis longus tendons within the flexor retinaculum tunnel; nocturnal paraesthesia, thenar wasting, and Phalen and Tinel signs.
- Anatomical snuffbox: bounded laterally by abductor pollicis longus and extensor pollicis brevis, medially by extensor pollicis longus; the floor is the scaphoid and trapezium; its contents are the radial artery pulse and the origin of the cephalic vein.
- Distal radius fractures: a Colles fracture from a fall on the outstretched hand displaces the distal fragment dorsally, giving the dinner-fork deformity; a Smith fracture displaces volarly (reverse).
One fall, three ages, three fractures
A fall on the outstretched hand produces different injuries at different ages, and the reasoning is biomechanical rather than arbitrary. In a child, the metaphyseal bone of the distal humerus fails first, so the extension-type supracondylar fracture results — and because the brachial artery and median nerve lie in front of the joint, the pulse and the median territory must be checked explicitly before and after reduction; a missed compartment syndrome of the forearm becomes Volkmann's ischaemic contracture. In a young adult, the force travels to the carpus: the scaphoid bridges the two rows of the carpus and takes the load, so waist fractures are easy to miss on initial radiographs — snuffbox tenderness with a normal film still warrants a cast and repeat imaging, because the dorsal and volar vessels enter the distal half and the proximal pole is left bloodless, heading to avascular necrosis and non-union. In an older woman with osteoporotic bone, the distal radius metaphysis gives way as a Colles fracture. The same hand may then swell within the restricted tunnel at the wrist — haemorrhage plus oedema raising pressure on the median nerve — which is why carpal tunnel symptoms after a wrist injury are not dismissed.
Fracture-nerve pairs NBE recycles
The screening examination trades on fixed pairs: surgical neck of humerus — axillary nerve; midshaft humerus — radial nerve with wrist drop; medial epicondyle — ulnar nerve; supracondylar — median or anterior interosseous with brachial artery; posterior dislocation of the shoulder and the quadrangular space — axillary again. Reversed stems are commoner still: a wrist drop after a fracture names the radial nerve, and a claw hand worse with a medial epicondyle injury names the ulnar. The distractor pair most often harvested is Colles versus Smith — remember dinner-fork dorsally for Colles, and garden-fork volarly for Smith.
Frequently asked questions
Which muscles form the rotator cuff and which nerves supply the lesser-known pair?
Supraspinatus, infraspinatus, teres minor and subscapularis; teres minor is axillary-nerve supplied while subscapularis takes the subscapular nerves.
Why does the proximal fragment of a fractured scaphoid undergo avascular necrosis?
Because the scaphoid's blood vessels enter its distal half and run retrogradely, a waist fracture cuts off supply to the proximal pole.
What passes through the carpal tunnel?
The median nerve and nine tendons — flexor digitorum superficialis and profundus (four each) and flexor pollicis longus — beneath the flexor retinaculum.
What is a pulled elbow, and how is it reduced?
Subluxation of the radial head out of the annular ligament in a young child, reduced by supination and flexion of the elbow.
What are the boundaries and contents of the anatomical snuffbox?
Abductor pollicis longus and extensor pollicis brevis laterally, extensor pollicis longus medially, scaphoid and trapezium in the floor, with the radial artery and cephalic vein origin within.