THE Northern Territory Corrections Commissioner says an extraordinary number of his staff have been assaulted on the job, including 11 so badly injured they can never work again.

Mark Payne hit back at last week’s Four Corners program into abuse at the Don Dale juvenile detention centre, saying many of the examples aired had already been addressed by previous investigations.

Many of the children in detention were troubled and were there for a reason, he told Sky News on Tuesday.

“We’ve had 15 of our officers over the past couple of years who have been assaulted to the extent that they’ve had to leave work,” he said, adding that many assaults went unreported.

“People who have been so damaged, so injured, with broken eye sockets, broken bones, even spinal injuries... 11 of those individuals have never been able to return to the workplace.”

Commissioner Payne said he had told staff to reconsider walking around in public in their uniforms, following threats made to officers.

“Many of them are quite fearful of reprisals,” he said.

“Some have been the victim of reprisals.”

Commissioner Payne also defended the previous use of restraint chairs, insisting they were used to prevent youths from hurting themselves.