Articular cartilage damage
Articular cartilage is a layer of smooth tissue that covers the bones which come into contact in many joints. It is a very important and amazing structure which has many roles, but acts as shock absorber to protect the underlying bone. It has the lowest coefficient of friction of any natural or man-made material. If there was no articular cartilage the bone surfaces would rub against one another and wear away, leading to pain and arthritis.
Sometimes focal defects occur, after trauma, sometimes the cartilage is damaged by inflammatory conditions, and sometimes tissue breaks off causing loose bodies that may float around the knee.
Often damage to the articular cartilage and loose bodies need surgical treatment.
Ask your doctor / specialist for more information