Shoulder Anatomy

All About Shoulder Pain

Anatomy

The shoulder joint is a modified ball and socket joint. The ball is at the top of the Humerus (arm bone), whilst the socket is a shallow cup on the end of the scapula (shoulder blade). This is a good design to give mobility to the shoulder joint but it makes it inherently unstable, and dislocation is common. To improve the stability of the shoulder a cuff of four muscles (called the rotator cuff) braces the joint as well as a complex plethora of tough internal ligaments. Surrounding the Gleno-humeral joint (shoulder joint) is a bag called the CAPSULE. When the arm is raised above the head, this CAPSULE is fully stretched; when the arm is lowered to the side, the capsule hangs down in a small pouch-like sack.