The human joint consists of the bone and the joint capsule ligament that connects the bones, and there is a layer of cartilage on the surface of the bone. Compared to the underlying bone, cartilage is soft and has a cushioning function for shock; in addition, the normal cartilage surface is smooth, and the synovial fluid makes the friction coefficient between the pairs of bony structures in the joint very small, which is the basis for the flexible movement of the joint. Articular cartilage consists of collagen fibers, interstitial chondrocytes, and matrix, and despite being called cartilage, it is actually quite stiff, depending on the integrity of the collagen fiber architecture. The cartilage on the surface of the joint is transparent cartilage, mainly because it contains less fibers and more matrix than fibrocartilage, and may appear translucent to the naked eye. Compared to fibrocartilage, hyaline cartilage has a lower coefficient of friction, but is more brittle and prone to damage. The collagen fibers of cartilage are distributed horizontally in the most superficial layer, which is more resistant to friction; vertically in the bottom layer, which allows it to withstand certain stresses; and diagonally or interlaced between the superficial and bottom layers, which is the take up between the two layers. The three collagen fibers of cartilage have a calcified layer on the bottom side, which takes over the collagen fibers of cartilage and the bone below. The three layers of cartilage form a dense three-dimensional framework that supports a cushion of both elasticity and stiffness on the bone surface. Softening of cartilage means that the cartilage becomes less rigid and truly soft. Cartilage softening is usually caused by a break in the underlying or intermediate collagen fibers, which weakens the support of the underlying fibers to the surface fibers and creates a significant depression on the cartilage surface when 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 with the exposure of subchondral sclerotic bone. Prior to the advent of MRI, the degree of cartilage degeneration was generally determined intraoperatively. Now, with MRI, the state of cartilage degeneration can be understood without surgical exploration. When cartilage degeneration is present in the patella, it is manifested early on as chondromalacia of the patella. Chondromalacia patellae and chondromalacia patellae are not the same concept. The former refers to a structural change that cannot be called a disease if it does not cause any discomfort. Only when chondromalacia of the patella causes pain and discomfort can it be called a disease, i.e. chondromalacia patellae. The main symptom of chondromalacia patellae is pain on the anterior side of the knee joint, often without any restrictive site, easy to attack when climbing hills, slopes and stairs, difficulty in half squatting and difficulty in power bouncing.