You want to open the files as an Image Sequence. You can only do this if the files are named sequentially (e.g., myfile000.jpg, myfile001.jpg, myfile002.jpg, etc.) Here's how:
Choose File | Import | Media...
Select only the first file in the sequence
Check the box Open still image sequence at the bottom of the window
Press Open
In the next window set the framerate to90.000
Press OK
You should now have a clip in the Project Media of your new video composed of 90fps images.