They needed bigger rumps for their bump and grind.

Several strippers were among those who paid a Bronx woman up to $1,500 a pop for dangerous silicone injections to plump up their posteriors, a prosecutor said at her sentencing yesterday.

Whalesca Castillo, 38, got a year in the slammer for her underground cosmetic-surgery racket, which she brazenly continued even after getting busted last year.

Manhattan federal prosecutor Sarah Lai said Castillo, who agreed to cough up $100,000 in crooked earnings, preyed on low-income women who “resorted to this treatment” after Castillo told them it was safe.