Joint movements usually are accompanied by a relative
compression (approximation) or distraction (separation) of
the opposing joint surfaces.

These relative compressions or distractions affect the
level of congruity of the opposing surfaces

The position of maximum congruity of the opposing joint
surfaces is termed the close-packed position of the joint.
The position of least congruity is termed the open-packed
position.

Thus, movements toward the close-packed position of a
joint involve an element of compression, whereas
movements out of this position involve an element of
distraction.