The phrase "remain a concern" is correct and usable in written English. You can use it when something is still a worry or problem, either in the present or in the future. For example: "With the economic growth slowing, inflation will remain a concern in the coming months.".
The knees, of course, remain a concern.
Issues of supervision remain a concern at the firms".
But the political atmosphere is bound to remain a concern of the selection committee.
As in Europe, America's high debt and deficit remain a concern.
In America, as in Europe, high debt and deficit remain a concern.
But falling standards and conditions in the state system remain a concern.
As with last year's trip to the US the pitches remain a concern.
Awesome tool! I started using it one year ago and I never had to look for another app
Ha Thuy Vy
MA of Applied Linguistic, Maquarie University, Australia