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Discover how your shoulder works.
The shoulder joint has the largest range of motion out of all the joints in the body. This flexibility allows you to hit a backhand swing in tennis or stretch to reach something on a top shelf. The shoulder also helps you position your hands for movements such as waving goodbye or using the mouse on your computer.
The shoulder consists of 3 bones:
- shoulder blade (scapula)
- collar bone (clavicle)
- upper arm bone (humerus)

Two main joints help your shoulder move easily.
Glenohumeral joint
Commonly called the shoulder joint, the glenohumeral joint helps you move your shoulder forward and backward. It also enables your arm to rotate in a circular manner or move outward. The shoulder 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.
Acromioclavicular joint
The acromioclavicular joint is located between your shoulder blade (acromion) and your collar bone (clavicle). The sternoclavicular joint is another joint in this region that isn’t part of the shoulder joint, but is a bridge between the upper extremity and the back of the rib cage (thorax).

Muscles, tendons and ligaments also support the shoulder joint.
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 to enjoy normal activities of daily life.
HELPFUL LINKS

Shoulder Arthroscopy
The diagnosis and treatment of shoulder joint problems have improved greatly since a minimally invasive procedure called arthroscopy was developed. Arthroscopy allows a surgeon to see inside the shoulder and to carry out procedures through tiny incisions.

Shoulder Fracture
Sometimes an injury causes a shoulder bone to break or partially crack. The fracture usually involves the collarbone (clavicle) or the area just below the ball of the upper arm bone (humerus). The cause is often a sudden blow to the shoulder or a bad fall. Pain follows, and the patient may be able to see his or her shoulder bones out of position.

Shoulder Replacement
Whether or not to have shoulder replacement surgery is a difficult decision. Discussing your treatment options with your doctor is essential to helping you decide if this is the right choice for you. Learning more about shoulder replacement surgery can help you to formulate the questions you would like to ask your doctor.