Dictionary

break one's back en · VERB

(alt-of, alternative, idiomatic) Alternative form of break the back of (overburden), when applied to oneself.
alt of break the back of
- They're talkin' bout the night Santa went crazy The night St. Nicholas flipped Broke his back for some milk and cookies Sounds to me like he was tired of gettin' gypped 1996, "Weird Al" Yankovic, “The Night Santa Went Crazy”, in Bad Hair Day:
- See, it's not that I'm a disagreeable person. I just have a motto that I won't break. If I'm asked to do something, I'll break my back to see that it's done. 2008, Stuart Smith, The Mad Ramblings of a Monkey: The Nefarious Project, page 17:
Used other than figuratively or idiomatically: see break, back.

Spelling	Features	Source
broken one's back	Tense=Past, VerbForm=Part	lexicographic
breaking one's back	Tense=Pres, VerbForm=Part	lexicographic
broke one's back	Tense=Past	lexicographic
breaks one's back	Number=Sing, Person=3, Tense=Pres	lexicographic