Reigning women's 400m hurdles world champion Jana Pittman has withdrawn from the upcoming world athletics titles with a back injury.

Pittman was diagnosed with a hairline stress fracture in the L5 vertebrae last week and made the decision to pull out rather than risk further injury.

"It's disappointing not to defend my title but rehabilitation is my No.1 priority to avoid serious long-term injury damage," she said.

"I'm looking forward to being fit and ready for the Commonwealth Games next year."

It's the second time in as many years that Pittman's preparation for a major championships has been cruelled by injury.

She hurt her knee in the leadup to the 2004 Olympics and although she made it to the start-line in Athens, Pittman could only finish fifth in the final.

Pole vault medal hope Paul Burgess and 1500m runner Sarah Jamieson have also been forced out of the Australian team for the August 6-14 championships in Helsinki with calf injuries.

And leading Australian distance runner Benita Johnson has had blood tests after finishing a disappointing 13th in the 5,000m at a grand prix meet in Athens earlier this week.

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