With a Patella Luxation, the patella or kneecap goes outside its standard track (trochlea) and comes in most cases on the inside. In other cases, the patella ends up on the outside of the knee joint. When the patella slips off, it is no longer possible to put stress on the leg, because the knee joint and elbow work together in a kind of tension saw mechanism.
Patella luxation is a congenital, hereditary defect. The patella runs typically into a groove in the part of the thigh that is part of the knee joint. The fact that the patella runs out of its tracks is caused by faults in the construction of the skeleton. Such as a shallow, sometimes even absent trochlea, a more or less twisted or bent lower leg, or an oblique attachment of the quadriceps.
Depending on the degree to which a kneecap luxuriates, there are different gradations: