- The shoulder joint, also known as the glenohumeral joint, is a synovial triaxial (polyaxial) joint.
- It is formed by the glenoid fossa of the scapula meeting the head of the humerus.
- It allows motion in all three cardinal planes:
- flexion/extension in the sagittal plane.
- abduction/adduction in the frontal (coronal) plane.
- lateral rotation/medial rotation (external/internal rotation) in the transverse (horizontal) plane.
- The glenohumeral (GH) joint is the most mobile joint of the human body.
- When the humerus moves at the glenohumeral joint, there is a coupled action of movement of the scapula at the scapulocostal joint. This coupling of joint actions is called scapulohumeral rhythm.
- With scapulohumeral rhythm, there is also a coupling of movement of the clavicle at the sternoclavicular joint.