Kinematic Principles Associated with Full ABD of Shoulder

Question 1

principle 1 (“2 to 1”)

Answer 1

Based on a generalized 2:1 scapulohumeral rhythm, active shoulder abduction of about 180 degrees occurs as a result of simultaneous 120 degrees of GH joint abduction and 60 degrees of scapulothoracic upward rotation

Question 2

principle 2 (“two is better than one”)

Answer 2

The 60 degrees of upward rotation of the scapula during full shoulder abduction is the result of a simultaneous elevation at the SC joint combined with upward rotation at the AC joint

Question 3

principle 3 (“3 steps back”)

Answer 3

The clavicle retracts at the SC joint during shoulder abduction

Question 4

principle 4 (“post-ER”)

Answer 4

The upwardly rotating scapula posteriorly tilts and, less consistently, externally rotates slightly during full shoulder abduction

Question 5

principle 5 (“all by myself”)

Answer 5

The clavicle posteriorly rotates around its own axis during shoulder abduction

Question 6

principle 6 (“somebody come Get HER”)

Answer 6

The GH joint ER during shoulder abduction