A luxating patella, sometimes called a trick knee, is a condition in which the

patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as ...

, or kneecap, dislocates or moves out of its normal location. Patellar luxation is a common condition in dogs, particularly small and miniature breeds. The condition usually becomes evident between the ages of 4 and 6 months. It can occur in

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s, as well, especially

domestic short-haired cat A domestic short-haired cat is a cat possessing a coat of short fur, not belonging to any particular recognised cat breed. In Britain they are sometimes colloquially called moggies. Domestic short-haired cats are distinct from the British Shortha ...

s. It also occurs in humans, where it can be associated with damage to the

anterior cruciate ligament The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. The two ligaments are also called "cruciform" ligaments, as they are arranged in a crossed formati ...

.RINTABLEAnterior Cruciate Ligament Surgery"> There have been several reports of patella luxation in other species such as miniature pigs, alpacas, llamas, cattle and goats.

Causes

Rarely, it can be caused by some form of

blunt trauma Blunt trauma, also known as blunt force trauma or non-penetrating trauma, is physical traumas, and particularly in the elderly who fall. It is contrasted with penetrating trauma which occurs when an object pierces the skin and enters a tissue ...

, but most frequently, it is a developmental,

congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...

defect. In congenital cases, it is frequently bilateral. The condition can also be inherited through genetics. This can also be caused by obesity.

Diagnosis

Diagnosis is made through palpation of the knee, to see whether it slips inside the joint more than would normally be expected. Often, a dog owner might be told that his or her pet has "loose knee", but this is not a medical term, and it is not correct to use it interchangeably with luxating patella. Luxating patella cannot be present without the knee being loose, but a loose knee is not necessarily slipping out of the joint. Even with luxating patella, symptoms such as intermittent limping in the rear leg might be mild or absent. Physical examination and manual manipulation are the preferred methods for diagnosis. More extreme cases can result in severe lameness.

Osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the ...

typically develops secondarily. The four recognized diagnostic grades of patellar luxation include, in order of severity:

Grade I

* Grade I - the patella can be manually luxated but is reduced (returns to the normal position) when released.

Grade II

* Grade II - the patella can be manually luxated or it can spontaneously luxate with

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

of the stifle joint. The patella remains luxated until it is manually reduced or when the animal extends the joint and derotates the

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...

in the opposite direction of luxation.

Grade III

* Grade III - the patella remains luxated most of the time, but can be manually reduced with the stifle joint in extension. Flexion and extension of the stifle results again in luxation of the patella.

Grade IV

* Grade IV - the patella is permanently luxated and cannot be manually repositioned, with up to 90° of rotation of the proximal tibial plateau. The femoral trochlear groove is shallow or absent, with displacement of the

quadriceps The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...

muscle group in the direction of luxation.

Treatment

Grades II, III, and IV require

surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pa ...

to correct, if the animal has difficulty walking. The surgery required is governed by the type of abnormality present, but often involves a sulcoplasty, a deepening of the trochlear sulcus where the patella sits, a realignment of the attachment of the patella tendon on the tibia, and tightening or releasing of the capsule on either side of the patella, according to which side the patella is slipping. Some grade IV conditions may require more involved surgery to realign the femur and/or tibia. A therapeutic dosage of glucosamine can be used as a preliminary treatment to strengthen ligaments and the surrounding tissues of the joint and can delay or prevent surgery. 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.

Dog & cat breeds affected

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, Maltese,

Jack Russell Terrier The Jack Russell Terrier is a small terrier that has its origins in fox hunting in England. It is principally white-bodied and smooth, rough or broken-coated and can be any colour. Small tan and white terriers that technically belong to ot ...

s, Yorkshire Terriers, Pomeranians,

Pekingese The Pekingese (also spelled Pekinese) is a breed of toy dog, originating in China. The breed was favored by royalty of the Chinese Imperial court as a companion dog, and its name refers to the city of Peking (Beijing) where the Forbidden City i ...

, Patterdale Terriers,

Chihuahua Chihuahua may refer to: Places * Chihuahua (state), a Mexican state **Chihuahua (dog), a breed of dog named after the state **Chihuahua cheese, a type of cheese originating in the state **Chihuahua City, the capital city of the state **Chihuahua Mu ...

Cavalier King Charles Spaniel The Cavalier King Charles Spaniel is a British breed of toy dog of spaniel type. Four colours are recognised: Blenheim (chestnut and white), tricolour (black/white/tan), black and tan, and ruby; the coat is smooth and silky. The lifespan is u ...

s, Papillons,

Boston Terrier The Boston Terrier is a breed of dog originating in the United States of America. This "American Gentleman" was accepted in 1893 by the American Kennel Club as a non-sporting breed. Color and markings are important when distinguishing this breed f ...

Plummer Terrier The Plummer Terrier is a working terrier. It was originally bred by Brian Plummer to hunt vermin, especially rats. The breed, while unrecognized by any kennel club, is known for its rugged determination and hardiness. Origins and history I ...

s and

Teddy Roosevelt Terrier The Teddy Roosevelt Terrier is a small to medium-sized American hunting terrier. It is lower-set, with shorter legs, and is more muscular with heavier bone density than the related American Rat Terrier. Much diversity exists in the history of ...

s. 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, a defect in hind limb conformation is generally agreed to be the underlying cause.Patellar Luxation, canine and feline (cat and dog) veterinary factsheets

References

External links

{{DEFAULTSORT:Luxating Patella Cat diseases Dog musculoskeletal disorders Patella