VAIL, Colo. -- Olympic champion Chloe Kim said she'll need surgery after breaking her ankle at the Burton U.S. Open this weekend.

Kim got off her snowboard gingerly following her first run in Saturday's halfpipe final, but she finished all three rounds of the contest.

Later, she said on Twitter that she had broken the ankle and would need surgery.

Kim, 18, finished second to Maddie Mastro, who became the first woman to land a double crippler -- a double backflip above the halfpipe -- in competition.

The victory snapped Kim's eight-contest winning streak. Kim, who won the gold medal at the Pyeongchang Olympics last year, will enroll at Princeton in the fall.