London Olympics | Oscar Pistorius

Oscar Pistorius sprints toward the finish line in the first round of the 400 meters. The double amputee from South Africa finished second in his heat to qualify for the semifinals.  (Wally Skalij / Los Angeles Times)

Dominican Republic’s Luguelin Santos leads South Africa’s Oscar Pistorius in a men’s 400-meter qualifying heat on Saturday in London.  (David J. Phillip / Associated Press)

South Africa’s Oscar Pistorius, running on carbon-fiber prosthetics, qualified for the next round in the 400-meter race.   (Wally Skalij / Los Angeles Times)

Oscar Pistorius, who finished second in his 400-meter heat to advance to the semifinals at the London Olympics on Saturday, was born without a fibula in either leg.  (Paul Gilham / Getty Images)

Luguelin Santos of Dominican Republic shakes hands with Oscar Pistorius of South Africa after finishing first and second, respectively, in their heat of the 400-meter qualifying on Saturday.  (Michael Steele / Getty Images)