Shoulder Anatomy: Shoulder Blade, Shoulder Joints, Collarbone (Clavicle)

Your shoulder is the most movable joint in your body. This flexibility allows you to hit a backhand swing, stretch for a top shelf or lift heavy items. The shoulder also helps you position your hand for movements such as waving goodbye or using the mouse on your computer.

With this flexibility, however, can come injury — and a variety of painful problems. The shoulder consists of three bones:

shoulder blade (scapula)
collar bone (clavicle)
upper arm bone (humerus).

Two main joints help your shoulder move easily:

Commonly called the shoulder joint, the glenohumeral joint (def.) helps you move your shoulder forward and backward. It also enables your arm to rotate in a circular manner or move outward.

The glenohumeral joint is composed of the socket on your shoulder blade (glenoid) and the "ball" at the top of your arm bone (the humerus). Uniquely, the ball of the upper arm bone is twice the size of the shoulder blade socket.

One way of picturing this joint is to think of a golf ball on a tee.
The acromioclavicular joint (def.) is located between your shoulder blade (acromion) and your collar bone (clavicle).

In addition, the sternoclavicular joint (def.) is a bridge between the upper extremity and the back of your rib cage (thorax).

Muscles (def.), tendons (def.) and ligaments (def.) also support the shoulder joint. Four tendons make up what is called the rotator cuff (def.).

This complex arrangement of bones, muscles, tendons and ligaments can be injured by an accident or overuse. Disease also can affect the shoulder. When that happens, the pain and lack of mobility can be severe enough to affect your ability to work and enjoy normal activities of daily life.

Learn about common shoulder problems.

Shoulder Anatomy

View the anatomy of the shoulder.

Common Problems

Many shoulder problems are interrelated. For example, tendinitis may be related to a torn rotator cuff. Bursitis may be related to frozen shoulder (adhesive capsulitis.)

Did You Know?

The most movable joint in your body is the shoulder joint.