I have had a torn meniscus myself, as well as several clients. We do very light spring tension for footwork on the reformer, as well as the chair. I focus on the pulling in motion using the hamstrings instead of a heavy push out with the quads. Keeping the feet and ankles strong and flexible is helpful as well. I do trotting and use the foot corrector and a half foam roller to rock forward and back on to improve flexibility and balance. Some of them seem more comfortable doing the standing work. I avoid the long springs and feet in straps and just stick with closed chain exercises.
Best to you!