Patellar luxation occurs when the knee cap dislocates and is both painful and a cause of chronic lameness and arthritis. It can be traumatic and associated with cruciate ligament rupture or is seen as an inherited defect in certain small breeds of dogs like Yorkshire terriers. It is often bilateral (both legs affected) and is occasionally also seen in cats. Correction of patellar luxation is a routine and relatively basic orthopedic procedure.