The surface of the patella is covered with a layer of cartilage, which is soft compared to the underlying bone and has the function of cushioning shock and protecting the joint; in addition, the normal cartilage surface is smooth and, together with the synovial fluid, the coefficient of friction between the pairs of bone structures in the joint is small, which is the basis for the flexible movement of the joint. Articular cartilage consists of collagen fibers, interstitial chondrocytes, and matrix, and is actually very hard despite being called cartilage. The cartilage on the surface of the joint is hyaline cartilage, which has a low coefficient of friction, but is brittle, hard and easily damaged. Softening of cartilage means that the cartilage has become less hard and is actually softer. Cartilage softening is generally caused by the breakage of the underlying or intermediate collagen fibers, which weakens the support of the underlying fiber framework to the superficial fibers and creates a significant depression when the cartilage surface is pressed. In vitro, there are no direct measures of cartilage stiffness. Cartilage chondromalacia is actually an intraoperative diagnosis, as it can only be explored during surgery. Articular cartilage softening is the earliest manifestation of joint degeneration. In clinical practice, there are four stages of articular cartilage degeneration: the first stage is the softening of the articular cartilage; the second stage is the appearance of cartilage surface roughness or cracks; the third stage is the partial loss of thickness due to cartilage wear; and the fourth stage is the total cartilage exfoliation and the exposure of subchondral sclerotic bone. Currently, the state of cartilage degeneration can be understood by MRI without surgical exploration. Only when the chondromalacia of the patella causes pain and discomfort can the disease be called chondromalacia patellae. The main symptom of chondromalacia patella is pain on the anterior side of the knee joint, often with no limiting site, easy onset when climbing hills, slopes and stairs, difficulty in half squatting and difficulty in power bouncing. Because chondromalacia patella has no diagnostic, therapeutic or prognostic significance, many scholars now advocate abandoning the designation chondromalacia patellae.