Keep your joints young - frozen shoulder

“The shoulder joint is made where your arm joins your torso. It is a very mobile joint which allows multi-directional freedom of your arm. In theory, it is a ball and socket joint, though in practice it is hardly that. The ball is there all right: a large round knob, about the size and shape of an ice-cream on a cone, at the top of the long shaft of the upper arm, the humerus. But the arm socket bears little resemblance to its counterpart in the hip. Instead of being a deeply-set bony pocket which encapsulates the ball, as the socket in the pelvis does the head of the thigh bone (femur), the socket of the shoulder joint is a shallow little saucer...

Frozen shoulder
   This most noteworthy affliction of the shoulder is where your joint progressively loses freedom and becomes painful and stiff to the point of rigidity. All movements become difficult but particularly getting on a coat, doing up a bra strap and combing your hair. In extreme cases, it is impossible to get your hand to your trouser pocket.
The problem usually starts insidiously, when the upper arm is achy and you suspect you have pulled a muscle. The arm may be vaguely sore beforehand and then you do something to hurt it, like pulling up the back-door button in the car when there is a momentary flash of pain. The agonising screech subsides with rubbing and soothing and you hope the hovering residual ache will pass. But in fact, your arm is never quite the same.
   Although frozen shoulders vary in painfulness, advanced cases present a severely dysfunctional unit. There is virtually no movement at the shoulder hinge and arm action, such as it is, comes from heaving the scapula about...”

Written by Sara Key, the article describes in detail the shoulder joint, what frozen shoulder is, and continues to provide a sequence of exercises designed to gradually release the joint.