Britney Spears' knee injury has caused the cancellation of her Onyx Hotel Tour.

The tour was scheduled to resume on June 22 in Hartford, Connecticut. But following arthroscopic surgery to repair severe damage to her joint, which occurred after a fall during a video shoot last week (see [article id="1488285"]"Britney Busts Knee, Complicating Video Shoot And Tour"[/article]), Spears will be out of commission for at least four months. Doctors are advising her to stay off her knee and keep it in a hard brace for at least six weeks, after which she'll require a minimum of eight to 12 weeks of physical therapy, according to her spokesperson (see [article id="1488319"]"Brit-Knee Spears Update: An Expert Weighs In"[/article]).

The canceled tour includes 35 dates all across the U.S. After she recovers, Spears hopes to make up the shows, although it's not clear when that will take place. Refunds will be available at point of purchase, according to the tour's promoter, Clear Channel.

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Click for photos of Britney's fall

Spears had already completed a five-week U.S. tour and a six-week European trek earlier this year. In March, the singer postponed two shows because of a knee injury suffered onstage (see "Britney Spears Cancels Show After Injuring Knee"[/article]), and four years ago Spears underwent surgery after twisting her knee during a dance rehearsal.