The Shoulder Girdle-part 2


by Jonathan Blood-Smyth - Date: 2009-10-07 - Word Count: 683 Share This!

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.

For the rotator cuff muscles to function properly from their base the scapula must be held firmly as a stable point against the chest wall, otherwise they will suffer from a mechanical disadvantage and work abnormally. With normal scapular function the shoulder can work and avoid the unwanted extra movements of the neck and shoulder girdle. Accessory movements, as in all joints, play an important role in joint function. Accessory sliding and gliding movements occur naturally with the more normal movements of the joints .

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.

The accuracy of placement of the head is vital and a millimetre or so can make a difference to the quality of movement involved, with the head able to slide or glide as it needs to. This kind of subtle, internal adjustment occurs in common movements such as raising the arm above the head, which is preceded by a small downward glide of the head on the socket. This allows the main shoulder movement muscles to exert the maximum force they need for strength. If accessory movements are lost this can force the muscles to work under strain, causing pain and stiffness in the joint.

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 rotator cuff muscles are functionally different in action from those muscles which give the scapula stability against the chest wall. The scapulothoracic muscles are designed to do low level holding of a posture for a time. The cuff muscles, however, typically act in a different way by acting quickly to perform a particular movement and then go into relaxation while they wait for the next required action. If weakness develops in the muscles of the rotator cuff then the scapular muscles can be recruited to complete the movement. Gradual domination of the scapular activity over the cuff activity can occur by inhibition.

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.

Related Tags: back pain, pain management, sciatica, back pain relief, back injury, frozen shoulder, piriformis syndrome, injury management

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