Help with dissertation!

Hello all,
I am currently struggling to form a solid research title/idea for my dissertation which is in the form of a systematic review which will compare a physiotherapy intervention. I have investigated / scanned the literature with three possible ideas, and so far each time I find that its not feasible due to either the lack of RCTs or, there has recently been a systematic review carried out. Does anyone have any tips of how i can find a gap in the literature? or has anyone over the years ever found that they would of liked more information/evidence about any intervention for a condition? Example: one of the failed ideas investigated was on the conservative management of EXERTIONAL COMPARTMENT SYNDROME which presented no RCTs from the literature.

Would appreciate any of your comments

Thanks