OTTAWA -- Internal Defence Department records show post-traumatic stress as the top diagnosis for hundreds of troops at risk of being forced out of the military because they are too sick or injured for duty.

The documents, obtained by The Canadian Press through the access to information law, underscore the toll the mental-health injury is taking on the Canadian Forces and those who serve in uniform.

They also highlight the importance of proper mental-health services for those still serving in the military, as well as those forced to leave for medical reasons.

Military personnel are required to be physically able to perform their duties and deploy on missions at any given time as a condition for continued employment in the Forces.

Anyone who is unable to meet this so-called Universality of Service principle for medical reasons is given time to recover. If recovery is not possible, they are released from the military.

According to the records, produced by the military's health-services branch, more than 1,300 troops assessed between June 2014 and July 2015 were "at high risk" of never returning to duty.

Of those, PTSD was by far the most common diagnosis, with 290 cases, or about one in every four. That compared to 150 military personnel with back injuries and 124 with knee injuries.

Military health officials saw the same results between January and December 2013, when just over 20 per cent of the 1,217 military personnel at risk of being released had been diagnosed with PTSD, versus 12 per cent with back injuries.

The documents do not provide any explanation for the results, but the question of whether Canadian military personnel are receiving adequate mental-health supports has been a constant theme since the war in Afghanistan.

There have also been concerns about the difficulties which injured troops who are forced from the military face as they attempt to transition into civilian life, particularly if they have a mental-health injury.

National Defence spokesman Dan Le Bouthillier said in an email that caring for military personnel is a top priority and that the Armed Forces are committed to providing the care and support they need.

"Great efforts are made to identify members at risk for mental-health problems and to provide them with assistance in the form of treatment, counselling, and other types of support," he said.

"We have an expert health-care system, but in order for us to help each other, it is essential that all military personnel, like all Canadians, recognize mental-health issues as they develop."

But Michael Blois, former president of the Afghanistan Veterans Association of Canada, said his fear is that troops with PTSD are being forced out more than those with back or knee injuries, because their cases are more complex, not because there are more of them.

"It's much easier to just get them out of the army," said Blois.

"As opposed to having the patience to see what kind of functioning comes back provided the right kind of care is given to them and the right people are available."

Finding ways to keep more personnel suffering from PTSD and other mental-health injuries in uniform would also help address the military's ongoing shortage of personnel, Blois said.

Auditor general Michael Ferguson reported last month that the Canadian Armed Forces is short roughly 4,000 trained people.

Following a report last month that 18 members of the military committed suicide in 2015, Defence Minister Harjit Sajjan promised the government's new defence policy will spare no expense when it comes to supporting the troops.

The policy is expected early next year.

The military has also taken steps to fix the support unit for ill and injured military personnel, which had been plagued with problems stemming from understaffing and poor training for those who work in the unit.