Humerus · What Is It, Location, Function, and More

The humerus is located in the upper arm, between the shoulder joint and the elbow joint. The shoulder joint, also known as the glenohumeral joint, is a ball and socket joint where the ball is the humeral head and the socket is the glenoid fossa of the scapula. The joint is supported by ligaments and surrounded by the four rotator cuff muscles and their tendons: the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles originate on the scapula and insert on the humeral head, allowing for a large range of motion in the shoulder. 

The proximal humerus is the part of the bone closest to the shoulder joint and is most prone to fracture. Below the head of the humerus is the anatomical neck of the humerus, followed by the greater and lesser tubercles, which are small projections of the bone that serve as attachment points for muscles of the shoulder. Underneath the tubercles is the surgical neck, a transition area between the proximal humerus and the bone shaft that is structurally weaker than the surrounding bone. Proximal humerus fractures most often occur in the surgical neck, especially in older individuals with osteoporosis who have undergone a bad fall. These fractures are often treated surgically if displaced, hence the name "surgical" neck. 

The proximal humerus is connected through the bone shaft to the distal humerus. The distal humerus articulates at the elbow joint to the radius and ulna, the two arm bones that make up the forearm.  

The humerus provides structural support and serves as an insertion point for many important muscles. The pectoralis major (i.e., “pecs”) and latissimus dorsi (i.e., “lats”) muscles attach at the intertubular sulcus, or groove, in the head of the humerus, and work to help rotate the humerus. Several other muscles that provide motion for the arm and upper body attach to the humerus, these include the deltoids, brachioradialis, coracobrachialis, pronator teres, teres major, brachialis, and common flexor and extensor tendons. Finally, the rotator cuff muscles at the shoulder connect to the humerus to stabilize the glenohumeral joint, which is freely movable, but also highly unstable and prone to dislocation, as well as rotator cuff injury. Injuries to the rotator cuff are common in individuals over 60 years of age.  

Various arteries and veins travel along the humerus bone. The brachial artery, the major blood vessel of the upper arm, runs along the length of most of the humerus bone. At the elbow joint, it divides into the radial and ulnar arteries which supply blood to the forearm. The basilic vein also travels close to the humerus and helps drain parts of the hand and forearm. 

Moreover, nerves of the brachial plexus travel along the humerus. The radial nerve follows a similar path to the humerus, rotating along the bone midway down the humeral shaft. Fractures in this region can cause damage to the radial nerve, causing inability to extend the wrist (i.e., wrist drop). The ulnar nerve travels along the distal end of the humerus, near the elbow. When one refers to hitting their “funny bone,” they are actually referring to striking the ulnar nerve.