Backstreet Boys & NKOTB -- Judge Dismisses $5 Million Brain Trauma Lawsuit

It's official: the New Kids on the Block/Backstreet Boys can't be held responsible for brain trauma -- at least, according to a judge who dismissed the bands from a $5 million lawsuit filed by an injured stagehand ... TMZ has learned.

TMZ broke the story in July ... William Wesley Styron sued NKOTBSB for injuries he allegedly suffered when he fell through a hole in the stage prior to a 2011 concert.

Styron said he fractured his skull and suffered brain trauma from the fall ... and was looking for a cool $5 million from the bands and other parties who he held responsible.

NKOTBSB denied the allegations, claiming it wasn't their fault Styron didn't see the huge hole in front of him ... and it looks like a judge agreed ... ruling that responsibility for the fall lies with the production company who hired him -- not the bands themselves.

The judge promptly dismissed the case against NKOTBSB, finding they "owed no duty to plaintiff that was breached when he was injured."