Classification and external resources
Luxating patella (or trick knee, subluxation of patella, or floating patella), is a condition in which the patella, or kneecap, dislocates or moves out of its normal location. The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The International Statistical Classification of Diseases and Related Health Problems 10th Revision ( ICD -10) is a coding of diseases and signs symptoms abnormal findings M00-M99 - Diseases of the Musculoskeletal system and Connective tissue (M00-M25 Arthropathies (M00-M03 Infectious arthropathies The patella or kneecap is a thick triangular Bone which articulates with the Femur and covers and protects the knee joint
Patellar luxation is a common condition in dogs, particularly small and miniature breeds. The dog ( Canis lupus familiaris) is a domesticated Subspecies of the gray wolf, a Mammal of the Canidae family of the order The condition usually becomes evident between the ages of 4 to 6 months. It also occurs in cats, especially the Domestic Shorthair. WikipediaManual of Style (spelling, articles should conform to one overall spelling style of English typically the one most linked to the article topic (if it is geographic A domestic shorthaired cat (DSH is a Cat fancy term used to describe a shorthaired Cat that does not have a Pedigree or belong to a recognized Cat 
Most cases of patellar luxation are medial and this is frequently a congenital problem in toy and miniature breed dogs. Breeds showing a predisposition for medial patellar luxation include miniature and toy poodles, Yorkshire terriers, Pomeranians, Pekingese, Chihuahuas and Boston Terriers. Large breed dogs are also affected and the Labrador retriever seems particularly predisposed. Patellar luxation is less common in cats than in dogs. Predisposed breeds include the Devon Rex and the Abyssinian. Although the specific cause of patellar luxation is unknown in these cases, it is generally agreed that a defect in hind limb conformation is the underlying cause. 
Diagnosis is made through palpation of the knee. X-rays are necessary in some cases. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. The luxating patella often causes no or very slight symptoms. There may be intermittent limping in the rear leg. Osteoarthritis can develop secondarily. Osteoarthritis ( OA, also known as degenerative Arthritis, degenerative joint disease) is a clinical syndrome in which low-grade inflammation
There are four diagnostic grades of patellar luxation, each more severe than the previous:
Grades III and IV, as well as most grade II cases, require surgery to correct, if the animal has difficulty walking. Surgery (from the χειρουργική cheirourgikē, via chirurgiae meaning "hand work" is a medical specialty that uses operative manual and instrumental The surgery involves a sulcoplasty, a deepening of the trochlear sulcus that the patella sits in. Sulcoplasty is an orthopedic surgical procedure performed on a Sulcus, which is a groove or indentation present on particular bones
Additional help can be given with the use of pet ramps, stairs, or steps. These can help the animal travel from one place to another, especially up and down, without adding any pain or damage to the patella.