Lady Gaga cancels shows over injured hip

Lady Gaga has cancelled the rest of her tour dates because of a hip injury.

Live Nation Global Touring said the pop star had a tear in her right hip that needs surgery, followed by a recovery period.

Her website showed 21 dates until March 20 remaining on her Born This Way Ball tour schedule. Fans who have already bought tickets will receive a refund.

Lady Gaga postponed four dates on Tuesday, a day after experiencing difficulties during her concert in Montreal, Canada.

The singer's show is high energy with non-stop dancing. She told fans on Twitter that she had hurt herself while performing some time ago.

She wrote: "I hid it from my staff, I didn't want to disappoint my amazing fans. However after last nights performance I could not walk and still can't."

A news release on Tuesday said the 26-year-old singer, whose real name is Stefani Germanotta, was suffering from synovitis, an inflammation of the joints. But tests yesterday showed she had a labral tear in her right hip.

The labrum is a layer of muscle that helps holds the ball-shaped hip joint in place. The news release said the surgery would require strict downtime.

The tour, in support of her second album Born This Way, began last April in Asia and was one of 2012's highest grossing.

Pollstar reported that it made more than 161 million dollars in 2012 with an average attendance of more than 31,000, making it the fifth-highest grossing tour.