Dara Torres plans to have major surgery on her arthritic left knee at the end of the summer.

The 42-year-old Torres said on a conference call Wednesday that she might not swim the 100-meter freestyle at next week’s U.S. national championships, partly because it’s painful to do a flip turn. She expects to compete in the 50 free, which doesn’t require a turn.

Torres, who won three silver medals at last year’s Beijing Olympics, said she has no cartilage left in the knee and that it swelled up badly when she practiced a few starts Tuesday. She has been unable to do kick sets or weight-training that puts stress on the knee.

Torres had minor surgery on the knee after the Olympics, but it has continued to bother her.

“It hurts some days to walk up and down the stairs,” Torres said. “I need my everyday life back.”

She’ll have another procedure after the world championships – assuming she qualifies at nationals. Then, if the knee fully heals, she again must make a decision about whether to continue competing.

Torres said her coach, who is battling cancer, is back in the hospital because of a blood infection. Michael Lohberg has aplastic anemia but has been able to coach Torres most days in recent months.

Lohberg still hopes to attend nationals in Indianapolis, which start Tuesday. He’s also trying to find somewhere in Rome he can receive the ongoing treatment he needs so he can go to the world championships July 19-Aug. 2.

“He said that he doesn’t care what the doctors say, he’s getting on a plane Sunday,” Torres said.