Bones of the Shoulder Girdle
The bony structures of the shoulder include the pectoral girdle and one arm bone. These bones have some interesting landmarks, including various bumps and projections. The shoulder and arm bones can be broken or dislocated by traumatic injuries.
The pectoral girdle
The two bones of the shoulder, the clavicle and the scapula, comprise the pectoral girdle.
The clavicle, or collarbone, lies horizontally at the root of the neck. It’s a long, thin bone that curves outward at the middle of your body and curves inward on the end where it goes to the shoulder. It’s easy to see and palpate in most people.
The clavicle articulates with the manubrium and with the scapula, so it’s described as having two ends: the sternal end, which attaches to the manubrium, and the acromial end, which joins the scapula. The conoid tubercle is found on the bottom of the acromial end of the clavicle.
The clavicle is a common site for fractures (in fact, it’s the most commonly fractured bone in the body), which usually happens when a person stretches out her hand to prevent a fall. When the hand contacts a hard surface, the force goes through the arm and up into the shoulder to the clavicle. Falling directly on the shoulder may result in a fracture, too.
The scapula is easy to locate on the upper back; it’s the large bone that runs on the surface of the 2nd and 7th ribs. It has a flat, triangle-shaped body. The anterior surface of the body faces the ribs and has a large subscapular fossa (indentation).
The posterior surface has a horizontal projection near the top called the spine of the scapula that ends at the top of the shoulder at the acromion. The spine divides the posterior surface of the scapula into a supraspinous fossa and an infraspinous fossa.
The pear-shaped glenoid cavity is located at the upper and outer part of the scapula. The coracoid process is located just above the glenoid cavity, and it projects forward and upward.
The arm contains one sturdy bone, the humerus. The spherical-shaped head is at the proximal end of the humerus, which joins the shoulder girdle. Just below the head you find the anatomic neck, which is a slightly narrower portion of the bone. Greater and lesser tubercles are right below the anatomical neck and are separated by the intertubercular sulcus (bicipital groove). The shaft, or the longer middle portion of the humerus, joins the proximal part at the surgical neck. The shaft has two important landmarks, the deltoid tuberosity and the spiral groove.