WASHINGTON -- The recent approval of a new device to treat knee injuries followed a lobbying campaign that overcame repeated rejections by scientists within the Food and Drug Administration, agency documents show.

The FDA's internal dissent over Menaflex, which targets the most-common knee injury afflicting everyone from high-school athletes to baby boomers, is straining a government agency that oversees a quarter of the U.S. economy. Some senior FDA staff members complained in documents that the handling of Menaflex, made by ReGen Biologics Inc., shows how political and industry pressure can influence scientific conclusions.

At issue isn't just the efficacy of the device -- that remains in dispute -- but the nature of the FDA's own approval process.

In one instance, emails show the FDA's integrity office excising language from a draft letter an FDA lawyer said would "document special treatment for ReGen." (Read the emails.)

Menaflex was approved under fast-track rules that don't require clinical trials needed under a full review. "There's something wrong with how that decision [to go the fast-track route] was made," said Andrew von Eschenbach, who was head of the FDA in December, when Menaflex got the go-ahead. "We fumbled that process."