Upper Limb Osteology

Humerus:

The head of the humerus is the large rounded end of the bone that articulates with the glenoid fossa of the scapula to form the shoulder joint.  

Just inferior to the head is a constriction, the anatomic neck of the humerus.  This circumferential depression in the bone is the site of attachment of the connective tissue that forms the shoulder joint capsule.

On the anterior surface of the humerus, just inferior to the surgical neck, are the greater and lesser tubercles of the humerus, which are raised, roughened areas of bone where muscles attach.  

Between the tubercles is the intertubercular groove, which the tendon of the long head of the biceps brachii m. passes through.  

Inferior to the tubercles is a circumferential area called the surgical neck of the humerus.  This is a region of the bone that is small in diameter relative to the head and the tubercles, and so is the region of the humerus most often fractured.

On the lateral aspect of the humerus, around the mid-shaft of the bone, is a roughened area for attachment of the deltoid m., the deltoid tuberosity.

Recall that the radial n. and the deep brachial a. pass along the posterior surface of the humerus, and sometimes you can find the groove that they form in the bone, the radial groove.

At the distal end of the humerus the bone starts to widen out laterally and medially, forming the lateral and medial supracondylar ridges, which terminate with the lateral and medial epicondyles.  The ridges and epicondyles are sites of attachment for many of the forearm muscles, with the medial ridge and epicondyle serving mainly as a site for attachment of flexor muscles, and the lateral ridge and epicondyle serving mainly as a site for extensor muscles.  

The smooth articular surfaces of the distal humerus are the trochlea (medially, for articulation with the ulna) and the capitulum (laterally, for articulation with the radius).  

Posteriorly the olecranon fossa is a depression that the olecranon process of the ulna fits into when the elbow is fully extended.

Radius and Ulna:

The radius and ulna are the paired bones that form the skeleton of the forearm, and articulate with the humerus proximally and the carpal bones distally.  The radius and ulna also articulate with one another, which allows pronation and supination of the forearm.  The bones are joined to one another along their length by a thick and inextensible interosseous membrane.

At the proximal end of the radius and ulna, the trochlear notch of the ulna articulates with the trochlea of the humerus, forming the primary joint of the elbow.  A shallow depression in the end of the radius also articulates with the capitulum of the humerus, but that articulation bears little weight.

Elbow flexors attach to raised features on the proximal ends of both the radius and ulna.  The biceps brachii inserts into the bicipital tuberosity of the radius, and the brachialis inserts into the coronoid process of the ulna.

At the elbow the primary articulation is between the humerus and ulna, but at the wrist the primary articulation is between the radius and the scaphoid bone, and to a lesser degree with the lunate bone (2 of the 7 carpal bones).  The carpal bones, or wrist bones, are 7 irregularly shaped bones that collectively bridge the forearm to the hand.  

Viewed in cross-section, the carpal bones form a U-shaped passage, the carpal tunnel, that is roofed over by the transverse carpal ligament (flexor retinaculum).  This is a tight space with 9 muscle tendons and 1 nerve passing though it, and any inflammation in the carpal tunnel puts pressure on the median n. and can lead to sensory and motor deficit in the hand.