To better understand rotator cuff tendinitis, it helps to understand the anatomy of the shoulder joint.

The rotator cuff is part of the shoulder joint. This joint allows motion between two major bones: the humerus and the scapula. The shoulder joint is a ball and socket joint. A depression off the scapula, known as the glenoid, provides the socket for the head of the humerus. Ligaments and muscles stabilize the joint during use.

The rotator cuff consists of four muscles and tendons that surround the top and back of the shoulder. These tendons hold the head of the humerus in the glenoid.

The rotator cuff tendon is composed of:

• Supraspinatus tendon
• Infraspinatus tendon
• Teres minor tendon
• Subscapularis tendon

These four muscles normally act to raise the arm up and away from the body. This motion is called abduction.

Anatomy examples:

• The shoulder joint viewed from the front
• The shoulder joint viewed from the back
• The shoulder joint viewed from the top, showing rotator cuff
• Muscles of the shoulder from the front
• Muscles of the shoulder from the back
• The acromioclavicular joint