Friday, December 28, 2012

Normal shoulder, shoulder arthritis

The Normal Shoulder

This is a cross-section of a normal left shoulder provided by my friend Chris Jobe. Front is up and the side of the body is to the right. The ball shaped object in the middle is the head of the humerus. The triangular object at the lower left is the glenoid socket. The reddish tissue on either side of the glenoid represent the rotator cuff muscles that hold the ball in the glenoid socket. The reddish tissue above and to the right of the humeral head is the deltoid muscle.

One can see how shallow the glenoid socket is - this allows of a great range of motion of the shoulder, but also puts the joint at risk for dislocation. Even though it is shallow, the glenoid concavity is critical to the stability of the joint. Note the thin layers of cartilage covering the joint surfaces of the humeral head and glenoid. It is this cartilage that enables smooth motion of the normal shoulder. It is this cartilage that is destroyed in shoulder arthritis.

The Arthritic Shoulder

The normally smooth surface of the humeral head provides an almost frictionless joint with the socket.

In arthritis, the surface is rough, devoid of cartilage, and surrounded by bone spurs, rendering the joint stiff and painful.


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