Luxating patella | |
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Other names | Trick knee, subluxation of patella, floating patella, floating kneecap |
Patellar luxation on radiograph: Left before, right after reduction; after reduction, the patella is still displaced. | |
Specialty | Orthopedics |
A luxating patella, sometimes called a trick knee, is a condition in which the patella, or kneecap, dislocates or moves out of its normal location. It can be associated with damage to the anterior cruciate ligament. [1]
Patellar luxation is a common condition in dogs, particularly small and miniature breeds. [2] The condition usually becomes evident between the ages of 4 and 6 months. It can occur in cats, as well, especially domestic short-haired cats. [3]
There have been several reports of patella luxation in other species such as miniature pigs, alpacas, llamas, cattle and goats. [4]
Rarely, it can be caused by some form of blunt trauma, but most frequently, it is a developmental, congenital defect. In congenital cases, it is frequently bilateral. The condition can also be inherited through genetics. This can also be caused by obesity.
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. [5]
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 typically develops secondarily. [5]
The four recognized diagnostic grades of patellar luxation include, in order of severity: [5]
Grades II, III, and IV require surgery 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. [6]
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.
Most cases of patellar luxation are medial, and this is frequently a congenital problem in toy- and miniature-breed dogs. [7] Breeds showing a predisposition for medial patellar luxation include miniature and toy Poodles, Maltese, Jack Russell Terriers, Yorkshire Terriers, Pomeranians, Pekingese, Patterdale Terriers, Chihuahuas, Cavalier King Charles Spaniels, Papillons, Boston Terriers, Plummer Terriers and Teddy Roosevelt 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, a defect in hind limb conformation is generally agreed to be the underlying cause. [8]
In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body. The knee is a modified hinge joint, which permits flexion and extension as well as slight internal and external rotation. The knee is vulnerable to injury and to the development of osteoarthritis.
The Jack Russell Terrier is a British breed of small terrier. It is principally white-bodied and smooth-, rough- or broken-coated, and can be any colour.
The Chinese Crested Dog is a hairless breed of dog. Like most hairless dog breeds, the Chinese Crested Dog comes in two varieties, without hair and with hair, which can be born in the same litter: the hairless and the powderpuff.
The Yorkshire Terrier, also known as a Yorkie, is a British breed of toy dog of terrier type. It is among the smallest of the terriers and indeed of all dog breeds, with a weight of no more than 3.2 kg/7 pounds. It originated in the nineteenth century in the English county of Yorkshire, for which it is named. The coat is tan on the head and dark steel-grey on the body; no other colour is accepted by either The Kennel Club or the Fédération Cynologique Internationale.
Attenuated patella alta is an extremely rare condition affecting mobility and leg strength. It is characterized by an unusually small knee cap (patella) that develops out of and above the joint. Typically, as the knee cap sits in the joint, it is stimulated to growth by abrasion from the opposing bones. When not situated properly in the joint, the knee cap does not experience such stimulation and remains small and undeveloped. Note that the cartilage under and around the kneecap is eight times smoother than ice, so "abrasion" may not be the best term.
The posterior cruciate ligament (PCL) is a ligament in each knee of humans and various other animals. It works as a counterpart to the anterior cruciate ligament (ACL). It connects the posterior intercondylar area of the tibia to the medial condyle of the femur. This configuration allows the PCL to resist forces pushing the tibia posteriorly relative to the femur.
The English Miniature Bull Terrier is a breed with origins in the extinct English White Terrier, the Dalmatian and the Bulldog. The first existence is documented in 1872 in The Dogs of British Island.
Ectopia lentis is a displacement or malposition of the eye's crystalline lens from its normal location. A partial dislocation of a lens is termed lens subluxation or subluxated lens; a complete dislocation of a lens is termed lens luxation or luxated lens.
The knee examination, in medicine and physiotherapy, is performed as part of a physical examination, or when a patient presents with knee pain or a history that suggests a pathology of the knee joint.
The stifle joint is a complex joint in the hind limbs of quadruped mammals such as the sheep, horse or dog. It is the equivalent of the human knee and is often the largest synovial joint in the animal's body. The stifle joint joins three bones: the femur, patella, and tibia. The joint consists of three smaller ones: the femoropatellar joint, medial femorotibial joint, and lateral femorotibial joint.
Cruciate ligaments are pairs of ligaments arranged like a letter X. They occur in several joints of the body, such as the knee joint, wrist joint and the atlanto-axial joint. In a fashion similar to the cords in a toy Jacob's ladder, the crossed ligaments stabilize the joint while allowing a very large range of motion.
The patellar tendon is the distal portion of the common tendon of the quadriceps femoris, which is continued from the patella to the tibial tuberosity. It is also sometimes called the patellar ligament as it forms a bone to bone connection when the patella is fully ossified.
TPLO, or tibial-plateau-leveling osteotomy, is a surgery performed on dogs to stabilize the stifle joint after ruptures of the cranial cruciate ligament.
The unhappy triad, also known as a blown knee among other names, is an injury to the anterior cruciate ligament, medial collateral ligament, and meniscus. Analysis during the 1990s indicated that this 'classic' O'Donoghue triad is actually an unusual clinical entity among athletes with knee injuries. Some authors mistakenly believe that in this type of injury, "combined anterior cruciate and medial collateral ligament disruptions that were incurred during athletic endeavors" always present with concomitant medial meniscus injury. However, the 1990 analysis showed that lateral meniscus tears are more common than medial meniscus tears in conjunction with sprains of the ACL.
Canine hydrotherapy is a form of hydrotherapy directed at the treatment of chronic conditions, post-operative recovery, and pre-operative or general fitness in dogs.
Tibial Tuberosity Advancement (TTA) is an orthopedic procedure to repair deficient cranial cruciate ligaments in dogs. It has also been used in cats. This procedure was developed by Dr. Slobodan Tepic and Professor Pierre Montavon at the School of Veterinary Medicine, University of Zurich, in Zurich, Switzerland beginning in the late 1990s.
Sulcoplasty is an orthopedic surgical procedure performed on a groove (sulcus) or indentation present on particular bones. In veterinary surgery it is often employed to remedy a displaced kneecap by deepening the trochlear sulcus, the groove on which the patella normally sits.
The triple tibial osteotomy is a surgical procedure used to treat dogs that have completely or partially ruptured the cranial cruciate ligament in one or both of their stifles. The cranial cruciate ligament connects the femur with the tibia, which functions to stabilise the canine stifle joint from the forces put on it during exercise and weight bearing.
A patellar dislocation is a knee injury in which the patella (kneecap) slips out of its normal position. Often the knee is partly bent, painful and swollen. The patella is also often felt and seen out of place. Complications may include a patella fracture or arthritis.
Simitri Stable in Stride is a three part modular surgical implant used during surgery performed on dogs to stabilize the stifle joint (knee) after rupture of the cranial cruciate ligament (CrCL) which is analogous to the anterior cruciate ligament (ACL) in humans.