Trauma to the knee can tear the menisci (pads of connective tissue that act as shock absorbers and also enhance stability). Cartilage injuries and tears can often occur with sprains. Treatment may involve wearing a brace during an activity to protect the knee from further injury. Surgery may be needed to eliminate the tear.
Injury to the knee can cause damage to the articular lining cartilage in the knee joint, or sometimes to both the cartilage and the bone.
If the injury is restricted to the cartilage, it will not show up in a plain X-ray; it may be noted on an MRI. An arthroscopy (using a special instrument to look inside the joint) can thoroughly identify it.