Symptoms such as pain, swelling, stiffness, lack of movement, and grinding in the knee can suggest that knee cartilage is no longer smooth. X-rays are a common way of diagnosing diseased cartilage in the knee. The X-rays show the bones around the joint. The cartilage layer cannot be seen on X-rays, and shows up as a space between the femur and tibia bones.
In a healthy knee, this space is about a quarter of an inch thick. When joint space taken up by cartilage is destroyed by arthritis, X-rays will show joint-space narrowing. With significant cartilage loss, the bones may touch each other; doctors call this finding “bone-on-bone” on the X-rays.
Over time, cysts and bone spurs may form around the knee. Left untreated, the leg can get so deformed that it appears to be either bow-legged or knock-kneed.
MRI scans are a special X-ray study that can diagnose diseased cartilage somewhat more accurately and at an earlier point than plain X-rays. Another method includes actually looking inside the knee during a procedure called “knee arthroscopy.” This involves the surgeon placing a small camera in the knee and inspecting the cartilage.