Humerus

The humerus is the single long bone of the upper arm, extending from the shoulder joint superiorly to the elbow joint inferiorly. Its proximal end articulates with the glenoid fossa of the scapula at the glenohumeral joint, and its distal end forms the elbow joint with the radius and ulna. It provides attachment for numerous muscles controlling shoulder, elbow, and forearm movements.

The surgical neck of the humerus is a constricted region just below the greater and lesser tubercles where the proximal humerus meets the shaft. It is a common fracture site in older adults because age-related osteoporosis weakens the bone, and the surgical neck is subject to bending forces during falls on an outstretched hand. The axillary nerve and anterior circumflex humeral artery run nearby and may be injured.

Wrist drop is the inability to extend the wrist and fingers, resulting from radial nerve injury. The radial nerve spirals around the posterior aspect of the humerus in the radial groove at the midshaft level, making it vulnerable to injury with mid-diaphyseal humerus fractures. A complete radial nerve injury causes weakness of wrist and finger extension, loss of grip strength, and sensory changes over the dorsal forearm and hand.

Supracondylar fractures occur just above the elbow joint and are the most common elbow fractures in children aged 5-10 years, typically from a fall on an outstretched hand with the elbow extended. They are clinically important because the anterior interosseous nerve and brachial artery can be injured by displaced bone fragments, potentially causing Volkmann's ischemic contracture—a devastating compartment syndrome of the forearm—if blood flow is compromised.

Several humeral landmarks are clinically important: the greater and lesser tubercles serve as rotator cuff attachment sites; the bicipital groove houses the long head of the biceps tendon; the deltoid tuberosity marks the deltoid insertion; the medial and lateral epicondyles are palpable at the elbow and are sites of origin for forearm flexors and extensors respectively; and the olecranon fossa accommodates the olecranon during elbow extension.