Question
1 am 44yrs old.  i surfed regularly in my youth for around 12 years, but
havent surfed for the past 15yrs or so. 12 months ago i sustained a fractured
LHS rib whilst lying and paddling a surfboard. no impact or reason. simply
lying on the board and paddling. it happened soon after paddling.

this year, 12 months later, the same thing happened, but on the OTHER SIDE
(rhs this time).  i got my xray results today and it confirmed a rib fracture.  i
was just paddling the longboard, no impact, and soon after starting to
paddle, PING, sudden pain in the rib area. GRRR!

mid year, i went skiing and had plenty of falls that would have damaged other
bones if my bones were becoming brittle.  

the only other relevant (possibly?) info is that 3 years ago, 12 months before
the first surfing injury, i had a fall at work and landed heavily on the corner of  
some boxes of tinned food, causing i suspect rib fractures on the Lhs. (i
didn't get it checked, suspecting a fracture, but figuring there's nothing to
treat it with.)  it was very painful, and took a long time many many weeks to
heal, consistent with a fracture (i have experience now!).  prior to this injury, i
have never had any rib problems.

basically i don't want to give up on surfing.  but i can't continue to break ribs
every summer!  it seems ridiculous to me that this can happen.  could there
be other causes i should be getting checked for?

Answer
I would suggest you see your primary physician to rule out any medical problems that could be causing the fractures.  it is quite possible that you had fractured it in the fall against the box, and it hadn't healed correctly.  The paddling motion uses some of the larger muscles (Trapezius for one) and if it wasn't healed correctly, could have caused it to refracture.