唔小心拗到條腰骨，英文點講?

It would depend who you were telling it to, as in your friends, your parents, your doctor or your teacher.

But the conversation would sound like this in general:

" I was just (moving stuff around) and all of a sudden i sprained my backbone. "

2007-06-21 12:06:14 補充：
Regardless if you wanna listen to me or not, the other response i saw above does not sound like english to me, neither would the person be able to articulate what you would be trying to say...

I twisted my backbone accidentally.

唔小心拗到條腰骨，英文點講?

I have twisted my spine by carelessness.

Has gotten a cut not carefully the back