Watched by millions of TV viewers across the country, Madonna opened the Grammy Awards by performing like only she can. But as she danced and gyrated wildly to her latest hit, the super-fit Material Girl was hiding a secret agony from her fans.

Although few would have guessed, she was in excruciating pain from a stomach injury. And first thing the next day she was taken to the hospital for surgery to a hernia that would have had lesser stars confined to bed. An insider said: "The condition was exacerbated greatly by her exercising and rehearsing for Grammy night.

"She endured the pain and confessed to close friends she was in agony. The wild body gyrations she did for a recent video didn't help her condition either."

At 8am the day after the awards, Madonna, 47, had the operation at the Cedar-Sinai Medical Center, Los Angeles.

Scar tissue was removed and the hernia sewn together. She was discharged in the afternoon.

"Madonna's hernia is the result of the weakening of the abdominal wall through having children. Over time it worsened," said an insider. "She'll be tender for a few weeks, but she cracked three ribs and broke her hand and collarbone when she fell while horseback-riding last summer, and made a strong comeback. So her physicians have strong faith in her recuperative powers.

"Madonna knew millions would watch the Grammys and wanted to have the op before the big night. But doctors told her she could not do any strenuous activity for several weeks after the surgery."