A kneecap that twists when it slides from side to side may be a problem with patellar movement. The kneecap sliding from side to side is usually a movement of the patella, which is normal. The knee joint is composed of the tibia, the lower end of the femur, and the patella and other bony mechanisms, and the corresponding ligaments, menisci and other tissues, is the largest and most complex joint in the human body. The patella is a round bone located above the knee joint. Under normal circumstances, there is a certain degree of mobility in the human patella, which can slide from side to side and is not immobile. If the kneecap is hit by an external force or the joint capsule is loosened, causing damage to the joint capsule, ligaments and other tissues, resulting in abnormal movement of the patella such as semi-dislocation or complete dislocation, and the phenomenon of the kneecap sliding from side to side and twisting, then this is an abnormal condition and requires treatment.