The Shoulder Girdle ” Part Two

The development of problems with shoulder movement involves a common pattern of abnormal movement involving shrugging the shoulder to some extent, moving the neck to the same side and a winging of the scapula away from the ribs. This abnormal movement pattern forces the shoulder to endure the development of pathologies such as rotator cuff tears and impingement. As the arm is used normally the body’s preparation process engages the core stability system to stiffen the spine and ensures the scapula is prepared for the forces by pulling it in to the trunk.

Once the scapula is stable against the chest wall by the action of the serratus anterior muscles this gives a stable base for the rotator cuff muscles to work from, allowing them to act without being disadvantaged. This also allows the correct actions in the neck and surrounding muscles and prevents the abnormal movement pattern developing. As in all joints the accessory muscles play a major role in the normal functioning of the shoulder joint, where these movements are particularly important. Accessory movements are small gliding and sliding motions which occur in concert with larger, more obvious movements.

A seal balancing a ball on the tip of its nose is how the interaction between the humeral ball and scapular socket has been described. The seal (the scapula) has to keep the ball (the humeral head) correctly and precisely centred over its nose ( the socket). The scapula has the job of successfully centring the large arm ball on the socket in all normal activities. If the ball is centred quickly and accurately this increases the precision and strength of arm movements. The shoulder has small muscles to control the arm and the arm is a long lever which generates a lot of force, with the added problem that the scapular muscles are working at poor angles.

A millimetre or so can make a big difference in the accuracy of placing the humeral head and so to the efficiency of movement which results, provided the head can slide and glide. These small and unseen corrections happen in frequently used actions such as lifting the arm above the head. A small glide of the head downwards initially allows the main moving muscles to get into the best position to be at their strongest. Loss of accessory movements leads to abnormal movement, increased muscle strain and develops into joint stiffness and pain.

All joints use accessory movements to accomplish normal motion for the joint in order to position themselves so their major moving muscles can work most efficiently. Without these very small inside movements the moving muscles strain to accomplish their goals, leading to pain and stiffness. The inability to position the scapula accurately and strongly is a common problem and may be the basis for many shoulder problems. The serratus anterior and lower trapezius, the main stabilising muscles of the scapula, may become under active and the upper trapezius, between the shoulder and the neck, overactive.

The scapular muscles have a different functional technique to those of the rotator cuff. The muscles which connect the scapula and the thorax are postural muscles and function by holding position for an extended period. The muscles of the rotator cuff, attached via the scapula, work in a different way, being short acting muscles which move quickly into action when required then relax until the next activity. The scapular muscles can step in to accomplish a movement if the rotator cuff muscles become weaker, leading to a process whereby the larger, less precise, muscles do much of the movements, gradually inhibiting and weakening the cuff.

If there is gradual weakness in the subtler, more finely controlled muscles of the shoulder and cuff, an abnormal movement rhythm can develop in the scapula as the stronger muscles take over. In normal activities people usually perform the same action repeatedly, mostly with the arm near the body and with muscle activity in short ranges. We typically perform actions involving drawing objects inwards towards the body rather than pushing things away, increasing the likelihood of the anterior muscles shortening and becoming stronger and the back muscles lengthening and losing strength.