All the joints in the body are self-lubricating, but the method of lubrication is far better that anything humans have ever invented.
Human lubrication in machines consists of three
basic types:

Hydrodynamic, where the oil film is picked up and transferred by the moving parts of the machine.
Hydrastatic, where the oil is forced, under pressure, into
the space between moving parts (or non-moving parts).

Boundary lubrication, where the oil is attached to the
surfaces of moving parts.


           But bones don't work like man-made machines. Bone
           joints roll and slide, and they do not fit together
           closely. The ends of the bones have a layer of
           cartilage on them, with a space between them
          filled with synovial fluid, which is like blood
    plasma  without the proteins.
Bone lubrication used not one of the three types
used by man-made machines, but is based instead
on another principle altogether. It works this way:
as the surfaces of the joint press against each
other, and slide across each other, the synovial fluid is released or soaked up by the cartilage, according to the load.
This means that the joints have as much or as little 'oil'as they need. This design makes bone-lubrication far superior to any
          man-made lubrication design.
God's design allows for bone growth, bone repair, and bone maintenance, plus the ability for joints to move in many directions, and to a far greater degree that most man-made joints are able.
© 2006 ChristArt, Inc.