Your core is the most slept on supports for your knees. Save these for your next workout. With no ACL these are essential for me to stay active at high levels. A strong core builds strength and stability across your whole lower body and the whole chain that supports your knees. It controls movements of the hips and femur to reduce knee pressure, misalignment and stress on the knee joint. These are three of my favorite exercises, with variations to isolate single legs and work imbalances. -planks