Four muscles are holding your arm on
The socket is shallow on purpose. That was the bargain.
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How it works The shoulder is the loosest joint you own. That is not a fault in it. That is the deal. Your hip sits deep in a cup of bone. It gives you very little range… and it almost never comes apart. Your shoulder took the other side of the trade. The socket is a shallow dish, barely a saucer, and the ball of the arm bone is wider than the dish it leans on. That is why you can scratch the middle of your back and swing an axe. And it is why four muscles work all day just to keep the ball where it belongs.
The four They go by the name rotator cuff, which is a poor name, because they do far more holding than rotating. One runs over the top of the joint and helps start the lift. Two run round the back and turn the arm outward. One crosses the front and turns it in. Together they draw the ball into the dish and pin it there while the big muscles do the hauling. So when somebody says a shoulder is wearing out, it is usually not the ball and the dish at all. It is those four tendons… and the gap they have to pass through. The gap Above the ball sits a shelf of bone, the front corner of your shoulder blade. The space between the two runs about half an inch to two thirds of an inch. Through that space go the tendon from the top muscle, parts of two more, the tendon of the biceps, and a slippery sac meant to keep it all from rubbing. Lift the arm and the space narrows. Everything in there gets pressed a little, and in a good shoulder nobody notices. Thicken one of those tendons, or swell that sac, and you notice. In other words the joint is not the problem. The traffic through the gap is. Why it hurts in a band This is the part that puzzles people, and it puzzled me. The pain does not get worse the higher you go. It arrives, and then it often leaves. Roughly 70 to 120 degrees of lift is where the space is tightest. Below it, room. Above it, room again. A doctor calls that a painful arc. It is one of the more useful things about your own pain, because where it starts and stops tells them where to look. And why the night is worst Nearly everyone with a bad shoulder tells the same story. All day it grumbles. At two in the morning it shouts. Some of that is plain enough. Roll onto that side and you press the sore gap under the weight of your own shoulder, with nothing else going on to distract you. Some of it is the arm hanging by your side for hours, which leaves the tendon slack, cold and unloaded. But I will be straight with you. The night pain of a bad shoulder is very well described and not very well explained. What we have is a pattern, and a few things that help… and those are Thursday.
Shoulder pain is common, and it climbs steeply with the years. Under twenty it runs at five to ten people in a hundred. Past eighty it is more than sixty in a hundred. And the first line of treatment, in the textbooks and in the guidelines both, is not a knife and not a needle. It is exercise.
Here is to four muscles doing quiet work, |