The 16-year-old reality TV star seems to have injured herself after Khloé fell on top of her, which the elder of the sisters documented in a collage on Instagram.
"This started out calm and ended in a war! Sorry@kyliejenner," wrote Khloé alongside the snapshot.
Kylie responded by posting a picture of herself from hospital, covering half her face with her hand.
"In the hospital thanks to @khloekardashian. (Look at her page for the reason why my mom said 'never thought I would take u to the doctor for a trampoline accident at this age'). This means war Khloe," wrote the injured teen. "Ps. It was painful taking this photo."
Khloé followed up with another photo collage of the duo jumping around and Kylie later clutching her back in pain.
"Kylie this is proof you did it to yourself! Sorry not sorry! Just kidding I am sorry my little bug a boo!! Let the war continue!!!!" she playfully wrote.
The photos didn't stop there, with Khloé posting another image of her and older sister Kim Kardashian, bouncing around and having the time of their life.
"Lady and the tramp...You pick who's who," wrote Khloé to the amusement of her near eight million followers.