To better understand shoulder pain (bilateral), it helps to understand the anatomy of the shoulder joint.

The shoulder joint allows motion between two major bones: the humerus and the scapula. The shoulder joint is a ball and socket joint. A depression in the scapula, known as the glenoid, provides the socket for the head of the humerus. Ligaments and muscles hold the joint together as the bones move.

The clavicle, or collar bone, connects to the scapula at the acromion, which is a bony projection off the scapula. The acromioclavicular ligaments normally surround and secure this joint.

The shoulder bursae are fluid-filled areas in the soft tissues around the shoulder joint where tendons and muscles pass over bony prominences. These fluid-filled sacs serve as a cushion between tendons and bone and lubricate the region with synovial fluid.

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