The humerus is the only bone of the upper arm, and has a large number of muscular, ligamentous and bony articulations. It forms a proximal joint with the scapula, and a distal joint with the radius and ulna. As well as forming the bony foundation for the muscles to attach to, the nerve also shares a close anatomical relationship with the nerves of the upper limb, and the vessels. 

The humerus is the bone of the arm and is a part of the appendicular skeleton. It is long and straight, with the head at the proximal end and articulating surfaces at its distal end. The head projects superomedially with respect to the shaft, and is supplied by the anterior and posterior humeral circumflex arteries. These arteries arise from the third part of the axillary artery, and penetrate the joint capsule. The superior, middle and inferior glenohumeral ligaments thicken and support the joint capsule. They provide resistance to translation of the humerus. The coracohumeral ligament limits posterior translation of the flexed, adducted and internally rotated shoulder.

 

The anatomical neck lies directly below the humeral head. The surgical neck lies at the proximal part of the superior shaft. There are two tubercles that arise from its anterolateral surface i.e. the greater and lesser. The lesser is the site of attachment of the infraspinatus and teres minor, and the greater tochanter allows for the attachment of the subscapularis. Between these two tubercles is the intertubercular sulcus, in which the tendon of the long head of biceps brachii lies. This originates from the supraglenoid tubercle and runs in the intertubercular sulcus. The pectoralis major, teres major and latissimus dorsi also insert on the intertubercular groove of the humerus. The pectoralis muscle inserts on the lateral lip, the teres major inserts on the medial lip, and the latissimus dorsi attaches in between. "A lady between two majors!"

 

The shaft of the humerus has a spiral grove, in which the radial nerve and profunda brachii artery run. The distal end of the humerus expands into two condyles with associated articulating surfaces. Just superior to these surfaces are the medial and lateral epicondyles. The ulnar nerve runs behind the medial epicondyle, and the radial nerve runs behind the lateral epicondyle. Above these articulating surfaces are the medial and lateral epicondylar ridges that form the common flexor and common extensor origins respectively. The capitulum is located laterally articulates with the head of the radius. The trochlea (named as it resembles a pulley shape) articulates with the ulna. It is at the humeroulnar joint that flexion and extension of the elbow occur. The humeroradial joint is mainly supportive. The elbow joint complex is supported by the ulnar collateral (lateral epicondyle to the supinator crest if the ulna) and radial collateral (lateral epicondyle to the annular ligament) ligaments.

As the limb buds grow out from the somatic layer of lateral mesoderm, the mesenchyme of the limb buds condenses to form cartilage by six weeks, and partially ossifies by birth. Full ossification is completed in adulthood. 

The anatomical neck sits above the surgical neck. A comes before S.

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