Upper Limb, NEET PG & INI-CET Anatomy MCQs

Explanation

The upper trunk is formed by C5 and C6, and traction that widens the head-to-shoulder angle stretches it at Erb point. Loss of the deltoid, supraspinatus, infraspinatus and biceps leaves the limb adducted, medially rotated, extended and pronated. C8 and T1 injury instead produces a claw hand from intrinsic muscle paralysis.

Explanation

The axillary nerve winds around the surgical neck, so a fracture there is its classic injury site. It supplies deltoid, the main abductor beyond the first 15 degrees, and gives the upper lateral cutaneous nerve of the arm to the regimental badge area. Supraspinatus, supplied by the suprascapular nerve, initiates abduction, which is why the first few degrees are preserved.

Explanation

The radial nerve lies directly against bone in the spiral groove of the humeral shaft, so mid-shaft fractures injure it. It supplies all the extensors of the wrist and fingers, and losing them gives wrist drop. Its cutaneous territory includes the dorsal skin of the first web space, which is the small area most reliably affected.

Explanation

The ulnar nerve passes in a groove behind the medial epicondyle, where it is subcutaneous and easily struck. It supplies most intrinsic hand muscles, and losing the lumbricals to the fourth and fifth digits leaves the metacarpophalangeal joints extended and the interphalangeal joints flexed. Sensation over the medial one and a half digits is also ulnar territory.

Explanation

The long thoracic nerve arises from the C5, C6 and C7 roots and runs superficially on serratus anterior along the chest wall, which puts it at risk during axillary surgery. Serratus anterior holds the medial border of the scapula against the thorax and protracts it. Without it the medial border lifts away, most obviously when the arm pushes forward against resistance.

Explanation

The palmar cutaneous branch of the median nerve leaves the trunk about 5 cm proximal to the wrist and crosses superficial to the flexor retinaculum rather than through the tunnel. Compression under the retinaculum therefore spares the skin of the thenar eminence while affecting the lateral three and a half digits. Preserved thenar sensation with numb fingers is a useful sign that the lesion is at the tunnel rather than higher.

Explanation

The scaphoid forms the floor of the anatomical snuffbox, so tenderness there after a fall on the outstretched hand suggests its fracture. Its nutrient vessels enter near the distal pole and run backwards through the bone, so a waist fracture cuts off the proximal fragment. That retrograde supply is why avascular necrosis and non-union are common and why suspected fractures are immobilised even with normal initial films.