Patellar Luxation, or “slipped stifles,” is a common condition in small dogs. Patellar Luxation is caused when the thigh bone (femur), the kneecap (patella), and the calf (tibia) are not correctly aligned. This condition can cause an abnormal gait. However, it is present at birth and does not usually happen until much later. This condition can lead to arthritis. Severe cases of Patellar Luxation can require surgery.