The spring tension on pilates equipment really helped to strengthen the muscles that support my knees without straining the joint.
I had injury that left my knee in a constant state of hyperextension and it was very painful in the back of my knee.
I have to consciously exercise with it slightly bent and the springs on the reformer and chair are a great way to strengthen both the hamstrings and the quads that help to stabilize my knee.
If you have a chance to find an equipment instructor near you I would highly recommend it for any kind of knee arthritis, replacement, cartilage tears, etc.
