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One Joint Shoulders a Heavy Load

Composed of four muscles and several tendons, the rotator cuff covers the top of the arm bone (humerus) and stabilizes the shoulder. Like the hip, the shoulder, seen here from behind, is a ball-and-socket joint, designed to offer a wide range of movement. The muscles of the rotator cuff help lift and rotate the arm. A torn rotator cuff is a common, painful injury among adults.
Composed of four muscles and several tendons, the rotator cuff covers the top of the arm bone (humerus) and stabilizes the shoulder. Like the hip, the shoulder, seen here from behind, is a ball-and-socket joint, designed to offer a wide range of movement. The muscles of the rotator cuff help lift and rotate the arm. A torn rotator cuff is a common, painful injury among adults. (Getty Images; 3D4medical.com)
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Tuesday, October 7, 2008; Page HE01

I could blame the weightlifting -- the bench presses and overhead military lifts that put the shoulder under pressure. I could blame the arm-twisting I get three times a week from my aikido buddies (are you listening, Jean Luc?).

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Instead I've decided to blame Douglas Engelbart, the man who, perhaps unwittingly, has put a generation of rotator cuffs, shoulders and other body parts at risk. In the 1960s, Engelbart invented the computer mouse, an ingenious device that evolved into a cheap, mass-produced and pretty much unavoidable tool of modern office life. It is, I feel, a likely culprit for the nagging pain that has developed in my right shoulder in the past year or so.

Of course, maybe all the other stuff has had an aggravating role. But when I think about how I have used my right and left arms over the years, the mouse is the most prominent difference between them.

I am by nature left-handed and have spent a lifetime throwing balls, swinging tennis rackets and otherwise favoring my left side when it comes to activity. But I "mouse" with the right hand -- too often with the arm extended and the shoulder twisted in exactly the wrong ways.

Undertrained. Weaker. Overstressed. The right side had all the ingredients for trouble. I am now convinced that hours manipulating the mouse wore down the cartilage in a couple of my shoulder bones, strained some of the small connective muscles in the area and led to the diagnosis I got recently from Jonas Rudzki at Washington Orthopedics and Sports Medicine: arthritis in the acromioclavicular joint and rotator cuff tendinitis.

I turned down the cortisone. The physical therapy is underway.

If you want a surefire way to start a conversation with anyone older than 40, talk about shoulders. Maybe half will have had a problem, and of those who haven't, many can expect to as they age. The symptoms can range from an annoying twinge to a deep throb that interferes with sleep to a loss of motion.

In my case, wear and tear on the AC joint, where the part of the shoulder blade called the acromion meets the clavicle, has worn away the cushion of cartilage between the two bones, the condition known as osteoarthritis. More problematic (at least in my case) is the rotator cuff: a set of four small muscles that help hold the arm in the shoulder socket and stabilize it as it moves.

Why is the shoulder so vulnerable?

It is perhaps the most complicated joint in the body, responsible for the movement of a limb that is designed to go through a wide range of motion in several planes. (To get a sense of the shoulder's diversity, try tracing the same lines in the air with your knee or foot that you can with your hand.)

What's more, it does this while fighting gravity. The hip, for example, also has wide range. But in its case the top of the leg nestles deeply into the socket, and the weight of the body on top of it helps stabilize the whole mechanism. The shoulder, by contrast, has a comparatively shallow socket with connective tissue that is hanging onto a limb that, even at rest, is constantly being tugged on.

Modern life hasn't helped. Even with a desk, computer and chair arrangement that complies with Occupational Safety and Health Administration recommendations, how many of us still hunch over our keyboards? That position prevents the muscles of the upper and middle back from doing their jobs -- part of which is to support the scapula (the shoulder blade) and synchronize it with the motion of the arm. If you use your arms and hands while in this position, the rotator cuff muscles end up under duress.


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