A good analogy for the knee joint is to think about a bowling alley. When you go bowling, the aim is keep the ball in the middle of the lane, away from the edges at all times.
Your knee cap (patella) is also designed to stay dead centre, allowing the force to travel from your upper to lower leg.
Your quadricep (thigh) muscles are primarily responsible for keeping your patella in line.
If your quads become imbalanced – with the muscles on the outside pulling harder than those on the inside – then the patella will get pulled across the joint. Remember our bowling analogy? Think of the force as the bowling ball hits the bumper. When this happens to your knee, you start to irritate your knee joint.
Old school rehab looked at this issue in isolation, and so the rehab was based around isolating the VMO (the smaller quad on the inside of the knee). Now we know rehab needs to be more dynamic. We need to acknowledge the issue of the patella alignment, but also the alignment of the knee, ankle and hip. When we do this, we have a complete solution for knee pain.