LONDON -- World 400 meters hurdles champion Jana Pittman will not defend her title at next month's championships because of a back injury.
The 22-year-old Australian withdrew on Thursday after being diagnosed with a hairline stress fracture in her back last week.
"It's disappointing not to defend my title but rehabilitation is my number one priority to avoid serious long-term injury damage," Pittman told the Athletics Australia Web site.
"I'm looking forward to being fit and ready for the Commonwealth Games next year."
The world championships in Helsinki run from Aug. 6 to 14.
Pittman has been unlucky with injuries at major championships. She finished fifth in last year's Olympic final, 17 days after knee surgery.
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