While working with a post surgical ACL patient that has +2 laxity and graft pain, I was reminded of something Dr. Allen and I were talking about while discussing this case.
One of the primary goals post ACL is stated as improving range of motion, particularly getting to full extension. If you look at the mechanics of the anterior cruciate ligament, you'll see that placing the knee in full extension places this ligament under stretch. We often will try to increase range of motion by hyper extending the knee, or using it as a fulcrum, which can cause undue stretch to this ligament. This means the burden of oweness is on the musculature surrounding the joint to provide stability, similar to what we are seeing in my patient.
I asked him to perform a one legged stand keeping his knee over his second metatarsal and just hold it. I then had him perform a mini squat, but rather than a traditional knee forward squad I had him do a potty squat (tibia remains vertical, while flexion occurs at the knee by moving the femur and glutes backward). Note that his foot is in a tripod position and his toes are up. (see video here) He was able to maintain good control of the knee for about the first 10° of flexion and then his motion started to degrade. Our goal will be to keep him in a range of motion where he has good neuromotor (find the first 10° of motion) and expand upon that. We remember from our principles of exercise that isotonic exercises (like a potty squat) have a physiological overflow of 15° on each side of the point of application. If I can get him to flex to 10° and be in control, I'm actually getting effects up to 25° flexion.
Simple? Yes. Important? Incredibly! If you can't control the range of motion that you have, why should you have more? Remember in your rehab procedures, keep it in a safe range.