Lesson 6: Joints of the Shoulder Girdle and Scapular Motion

The scapula (shoulder blade) and shoulder girdle are comprised of two joints, the acromioclavicular joint (AC joint) and sternoclavicular joint (SC joint), and analysis of the motion usually refers to a false joint known as the scapulothoracic joint. The scapulothoracic joint is not a true joint because there are no joint capsules or ligaments connecting the scapula to the thoracic spine or rib cage. The scapula is held to the thorax by scapular muscle activity, and the joints connecting the clavicle (collar bone) to the scapula and sternum.

The name of the joint actions of the scapula are different than the joint actions commonly used for other synovial joints of the body. The eight additional joint actions for describing scapulothoracic motion include protraction, retraction, depression, elevation, upward rotation, downward rotation, anterior tipping, and posterior tipping. Note, these joint actions correspond to the planes of motion and recruitment of muscles. For example, the concentric phase of a wide-grip (conventional) pull-up is an example of shoulder adduction and scapular downward rotation, downward rotation is a frontal plane motion that is the result of pectoralis minor, rhomboid, and levator scapulae recruitment. Another example, the concentric phase of a shoulder press is an example of upward rotation and elevation of the scapula, both actions occurring in the frontal plane; however, to achieve a full range of motion at the shoulder joint (glenohumeral joint) the scapula will also posteriorly tip, which is a sagittal plane motion.

Sports medicine professionals (personal trainers, fitness instructors, physical therapists, massage therapists, chiropractors, occupational therapists, athletic trainers, etc.) must be aware of the shoulder girdle and scapula joint actions for detailed analysis of human movement, and the development of sophisticated exercise programs and therapeutic (rehabilitation) interventions. Further, this course is essential knowledge for future courses discussing scapular muscles (e.g. the serratus anterior), shoulder muscles (e.g. rotator cuff), upper arm muscles (e.g. biceps brachii), and vertebral column muscles (e.g. rhomboids). In addition, this knowledge is fundamental to more complex topics like scapular kinematics (relationship between scapular motion, the glenoid cavity, and the humeral head), role in injury (e.g. shoulder pain, shoulder impingement syndrome, rotator cuff strain/tear, frozen shoulder - you don't always need rotator cuff repair), and sports performance (e.g. throwing, shooting, punching, lifting).

Caption: The bones, boney landmarks, and ligaments of the shoulder joint