Patella luxation (floating or dislocated kneecap) is a common condition that the kneecap is dislocating and slips out of its normal position. There are 4 grades described according to the time the kneecap spends in the abnormal position.

Patients are presented with a history of intermittent limping in the back leg with a characteristic sudden carrying of the limb up for a few steps ("skip") and then using it again.