The shoulder is a ball-and-socket joint that enables you to move your arm in almost any direction. The shoulder is often compared to a golf ball sitting on a tee (Figure 1). The head of the humerus (upper arm bone) is the ball, and a circular concavity (glenoid) in the shoulder bone (scapula) is the socket. A soft-tissue rim called the labrum surrounds and deepens the glenoid, making it more concave. The head of the humerus is coated with articular cartilage, and the shoulder joint has a thin, inner lining that produces an oil-like substance called synovial fluid for smooth movement. The surrounding muscles and tendons provide stability and support.
The shoulder joint is often compared to a golf ball on a tee.
- A golf ball sitting on a tee
- The head of the humerus sitting on the glenoid
- Both images superimposed