The shoulder is made up of the:
- Clavicle (collarbone)
- Scapula (shoulder blade)
- Humerus (arm bone)
The places where these bones attach form what is called a joint. The clavicle and scapula attach at the acromioclavicular (AC) joint, and the humerus and scapula attach at the glenohumeral (GH) joint.
The scapula and humerus have to work together to move the arm in overhead, behind the back, and lateral directions. Stiffness in a joint can limit movement into one or many of these directions.
Muscle weakness can also interfere with ability to lift and move the arm. Four primary muscles help stabilize the GH joint for fluid movement, as a group called the rotator cuff:
- Supraspinatus
- Infraspinatus
- Teres Minor
- Subscapularis
