What’s What with a Bionic Shoulder?

Some friends I saw a couple of weeks after my shoulder replacement wanted to know what part of my shoulder was “me.” I realized that we’re all pretty hazy about anatomy. For instance, who knew that the shoulder joint is part of the shoulder blade (scapula), not the collarbone (clavicle), which is the bone from which we hang our tote bags, briefcases and pocketbooks?

Specifically, at the end of the scapula is a shallow “socket” called the glenoid. At the end of the upper arm bone, the humerus, is a “ball” that rotates in that shallow socket.

Both ball and socket are cushioned by cartilage. When the cartilage goes, as with arthritis, damage ensues.

The scapula actually protects the shoulder joint. A “bony projection” angles up and curves forward to meet the end of the collarbone, making a “roof” over the joint. (That little bony hillock most of the way down your shoulder, so handy for anchoring a shoulder strap, is the end of the clavicle, where it meets the scapula.) Another, lower and shorter, projection extends partway over the joint under the clavicle.

So what’s replaced?

All of that protective shoulder structure remains; what’s replaced is just the ball and socket—the part that’s bracketed top and bottom by grayish-white in the image directly above. The new “ball,” made of cobalt and chromium, is attached to a long stem that fits down into the hole in the center of the humerus. At the top of this stem, titanium mesh enables the bone to grow right into it. (One hopes.) The new “socket” is polyethylene, attached to the scapula with a titanium mesh piece that also allows bone to grow into it.

If you’re really curious, you can get a look at the device on the Biomet website: on the right, under “Additional Information,” click on  “Comprehensive® Shoulder System – Product Brochure.” Note that there are a number of different shoulder implant systems,  made by different manufacturers. The one used in my shoulder was co-developed by my surgeon, Dr. David Dines of Hospital for Special Surgery.


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2 Responses to “What’s What with a Bionic Shoulder?”

  1. Joseph Says:

    Hi.I have lost a cartilage on my right shoulder, how long will your implants last. Thanks

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