Why does cold weather make joints sore?

There is a psychological link:
people who claim the weather
affects their joints do feel
more pain than those who
don’t make these claims.
If weather sensitivity was a
purely physical phenomenon,
then people would be affected
whether they believed that the
variability was related to the
weather or not. But a 2007
study also found that every
10°C drop in temperature
resulted in worse arthritis
pain. This may be because
cold weather causes changes
in the fluid that lubricates
each joint.