The vastus medialis muscle in your knee - just like every other muscle in your body - requires proper strength to function correctly. This muscle keeps your kneecap perfectly aligned as you move.
However, due to natural muscle weakening over time, your vastus medialis becomes too weak to do its job - which leads to kneecap misalignment. This causes grinding, cartilage damage, and ultimately bone-on-bone pain.
But there's another problem making it worse.
Your cartilage - just like every other tissue in your body - requires nutrients to stay healthy. These nutrients are delivered through synovial fluid that flows in and out of the cartilage.
However, when your kneecap is misaligned, it can't move properly, which blocks this essential fluid flow. This starves your cartilage of the nutrients it needs to repair itself.
In other words, your cartilage is literally dying because it's not getting the nourishment it needs from synovial fluid.