What is scalloping of the knees? what causes it?

More info is needed to narrow my answer. Maybe you are referring to scalloping of the endosteum which is part of the bone. Endosteal scalloping is an imaging finding that a radiologist can see on XR, CT, and MRI. It indicates a disturbance of the bone and can occur around the knee (eg. femur/tibia) & can be seen w/ benign and cancerous (malignant) processes. U need to get more info from ur doctor