The kneecap, also known as the patella, can move up, down, or left or right in normal people, but the range of movement is generally small, especially the left and right range of movement is much smaller than the up and down range of movement. Only when the knee joint is straight or hyperextended, the quadriceps muscle is relaxed and the patella can move slightly to the left or right at this time. If the knee joint is flexed, then the patella is unable to move left or right. If the patella is able to move widely, especially to the left and right, then it is likely to be a patellar dislocation and patellar ligament laxity, which is usually seen as a sequel to some trauma. The best treatment for this condition is surgery to reset the patella.