Hand Therapy & Occupational Fitness Center of Santa Barbara

The Shoulder & Repetitive Strain Injuries

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Anatomy

The shoulder is a unique joint in the body. It has a great deal of mobility in order to allow us to reach and perform activities away from our body. The cost of this mobility is a lack of stability. Most of the stabilizing forces at the shoulder are muscular and ligamentous rather than bony. These soft tissues that provide the shoulder motion and stability can be at risk for repetitive strain injuries.

The shoulder is composed of three bones: the clavicle (collar bone), the scapula (shoulder blade), and the humerus (long bone of the upper arm). The rotator cuff surrounds the shoulder and provides muscular stability for the humeral head. The shoulder blade controls shoulder motion. Nine of the fifteen muscles that attach to the scapula provide this motion.

RSI

With computer, desk, assembly or other types of hand intensive work, the neck and shoulders round forward and the upper arm tends to rotate inward. The chest muscles become tight. The muscles of the back weaken and stretch. The upper trapezius (the big, bulky muscles that make up the top of the shoulder) try to compensate by working harder than they should. Muscle knots and tension develop. The arms feel tired and weak. Eventually, this muscular imbalance can cause a tendonitis in the rotator cuff (supraspinatus) or in the biceps where it attaches to the humerus. Or the fluid cushion (bursa) between the rotator cuff and the shoulder bones can become inflamed (bursitis).

Poor posture can be the primary factor in developing shoulder pain. Other activities that tend to cause problems are prolonged or repetitive overhead reaching (such as when lifting binders or books down from shelves above the computer) or holding the arms elevated while typing, using the mouse, or performing other hand work. Tichauer (1978, The Biomechanical Basis of Ergonomics) discovered that a chair height that was 3 inches too low for a worker caused excessive shoulder movements and reduced productivity by as much as 50%.

RSI Prevention for Shoulder Pain

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