Three Phases of Shoulder ABDUCTION Movement
The first phase of abduction: 0-60″
The muscles involved are essentially the deltoid and the supraspinatus, which form functional couple at the level of the shoulder joint. It is in this joint that the movement of abduction starts. This first phase ends near 90′,when the shoulder’locks’ as a result of the greater tuberosity hitting the superior margin of the glenoicl cavity. Lateral rotation and a slight flexion of the humerus displace the greater tuberosity posteriorly and delay this mechanical block. Thus abduction combined with 30′ flexion and taking place in the plane of the scapula is the trlle physiological movement of abduction
The second phase of abduction: 60-120′
As the shoulder is lockecl, abduction can only proceed with participation of the shoulder girdle. The movements afe these:. A’swing’of the scapula with anticlockwise rotation (for the right scapula), causing the glenoid cavity to face more superiody. The
range of this movement is 60′. Axial rotation mechanically linked at the stefno-costo-clavicular and the acromioclavicular joints, each joint contributing up to 30′.
The muscles involved in this second phase are these :
. serrants anterior
These muscles form a functional couple of abduction at the level of the scapulo-thoracic ‘joint’.This movement is checked at about 150″ (90′ + 60′ due to rotation of the scapula) by the resistance of the stretched adductors: latissimus dot”si and pectoralis majcn.
The third phase of abduction: 120-180″
To allow the limb to reach the vertical position, movement of the spinal column becomes necessary. If only one arm is abclucted,lateral bending of the spinal column produced by the contfalateral spinal muscles (6) is adequate. If both arms are
abductecl, they can come to lie parallel vertically only by being maximally flexed. For the vertical position to be reached, exaggeration of the lumbar lordosis is necessary and this is achieved by the action of the spinal muscles. This division of abduction into three phases is, of collrse, artiflcial; in fact, these various combinations of muscular movements fun into one another. Thus it is easy to observe that the scapula begins to’swing’before the arm has reached 90′ abduction; likewise, the spinal column begins to bencl before 150″ abduction is reachecl.
At the end of abcluction all the muscles are in a
state of contraction.