The chairman of the Joint Chiefs of Staff wants to know if there is a limit to the number of concussions that servicemembers can suffer before they become nondeployable.

"There clearly are situations where individuals are exposed to numerous explosions and numerous potential [concussions], and I think the question is, is there a limit, or should there be a limit," Adm. Mike Mullen said Friday during his visit to Fort Campbell, Ky.

Of the troops suffering from traumatic brain injury and psychological injuries who are treated at Fort Campbell, about 77 percent improve to the point where they can return to duty, while 23 percent do not, Army medical officials said.

Mullen plans to ask his staff whether limiting the number of concussions servicemembers can receive while deployed can reduce the number of troops whose resulting injuries prevent them from returning to duty.

Earlier in the day, Mullen asked doctors if there was such a limit when he visited the TBI Resilience and Recovery Center at Fort Campbell.

"The problem is, sir, I can tell you we have people in treatment with five and seven, and they respond wonderfully, no sequelae. We have people with one or two, they're having great difficulty, so where that number is, I can't tell you at this point," said Dr. Bret Logan, a psychiatrist and director of the center.

The NFL limits the number of concussions players can receive in a season, said Dr. (Col). Richard Thomas, commander of the hospital at Fort Campbell.

"I think we do need to have some kind of threshold number, whatever that is, and we don't have that," Thomas said.

In a separate matter, Mullen said he uses the acronym "PTS" instead of "PTSD" when referring to combat stress because he feels the word "disorder" is degrading.

Mullen stressed the need to eliminate the stigma attached to psychological wounds.

"I've had too many young -- mostly, but not exclusively -- soldiers and Marines, they're not happy with the term 'disorder,' " Mullen said. "I understand 'disorder' is a medical term, and I understand why it's there, but I just choose not to use it."

Learn more about Traumatic Brain Injury.