The Court of Arbitration for Sport (CAS) ruled on Monday that Leeper's prostheses gave him a competitive advantage over other athletes and that the 400 metre runner could not use them in events such as the world championships and Olympics.
"The panel ... concluded that the running-specific prostheses used by Blake Leeper indeed gave him an overall competitive advantage in the 400 metres event over an athlete not using such a mechanical aid," said Lausanne-based CAS.
"They enabled him to run at a height that was several inches taller than his maximum possible height if he had intact biological legs."
Leeper, 31, who was born without legs below the knees, finished fifth in the 400 meters at the U.S. championships last year but was barred from competing at the subsequent world championships in Doha.
Before reaching its final decision, CAS said it had accepted Leeper's argument that the burden of proof should fall on World Athletics rather than the athlete, and said the rules should be changed.
World Athletics welcomed the ruling which it said was based on extensive expert evidence.
"(The) rules permit competitive use of aids such as prosthetics if they do not give the user an artificial competitive advantage over those not using such aids," it said.
"World Athletics met its burden of proving that Mr Leeper's prostheses give him an artificial competitive advantage."
It said it would review its rules so that the burden of proof no longer fell on the athletes in such cases in the future. (Writing by Brian Homewood Editing by Christian Radnedge)