Kneecap Dislocation
A dislocation of the kneecap occurs when the patella comes completely out of its groove on the end of the thigh bone (femur), and comes to rest on the outside of the knee joint. Kneecap dislocations usually occur as a significant injury the first time the injury occurs, but the kneecap may dislocate much more easily thereafter.
Source: Verywell Health