Title: Luxating patella

{{Infobox medical condition (new) 
| name            = Luxating patella 
| image           = Patellaluxation.jpg 
| caption         = Patellar luxation on radiograph: Left before, right after reduction; after reduction, the patella is still displaced. 
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| field           = [[Orthopedics]]
| synonyms        = Trick knee, subluxation of patella, floating patella, floating kneecap
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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]].&lt;ref&gt;{{cite web |url=http://www.kneeandshoulder.md/print/print_acl.html |title=The Knee and Shoulder Centers - [PRINTABLE] Anterior Cruciate Ligament Surgery |access-date=2007-11-27 }}&lt;/ref&gt;

Patellar luxation is a common condition in [[dog]]s, particularly small and miniature breeds.&lt;ref&gt;{{cite journal |last1=Engdahl |first1=Karolina |last2=Bergström |first2=Annika |last3=Höglund |first3=Odd |last4=Hanson |first4=Jeanette |title=The epidemiology of patellar luxation in an insured Swedish dog population |journal=Preventive Veterinary Medicine |date=September 2023 |article-number=106034 |doi=10.1016/j.prevetmed.2023.106034 |url=https://www.sciencedirect.com/science/article/pii/S0167587723001988|doi-access=free }}&lt;/ref&gt; The condition usually becomes evident between the ages of 4 and 6 months. It can occur in [[cat]]s as well, especially [[domestic short-haired cat]]s.&lt;ref name=Ettinger_1995&gt;{{cite book|author1=Ettinger, Stephen J. |author2=Feldman, Edward C. |title=Textbook of Veterinary Internal Medicine|edition=4th |publisher=W.B. Saunders Company|year=1995|isbn=0-7216-6795-3}}&lt;/ref&gt;

There have been several reports of patellar luxation in other species such as miniature pigs, alpacas, llamas, cattle, and goats.&lt;ref&gt;{{cite journal |title=Trochlear wedge sulcoplasty, tibial tuberosity transposition, and lateral imbrication for correction of a traumatic patellar luxation in a miniature companion pig: A case report and visual description |year=2020 |doi=10.3389/fvets.2020.567886 |pmid=33521073 |doi-access=free |last1=Høy-Petersen |first1=J. |last2=Smith |first2=J. S. |last3=Merkatoris |first3=P. T. |last4=Black |first4=K. E. |last5=Faivre |first5=C. M. |last6=Miles |first6=K. G. |last7=Tatarniuk |first7=D. M. |last8=Kraus |first8=K. H. |journal=Frontiers in Veterinary Science |volume=7 |article-number=567886 |pmc=7838352 }}&lt;/ref&gt;

==Causes==
Rarely, it can be caused by some form of [[blunt force trauma|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==
[[File:Patella Luxation coronar.png|thumb|MRI after luxation of the right patella: A bone bruise is at the medial surface of the patella (axial image) and in the corresponding surface of the lateral condyle of the femur (coronal). The medial retinaculum of the patella is at least partially disrupted.]]
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 &quot;loose knee&quot;, but this is not a medical term, and it is not correct to use it interchangeably with luxating patella.&lt;ref name=&quot;ofapatella&quot; /&gt;

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.&lt;ref name=&quot;ofapatella&quot; /&gt;

The four recognized diagnostic grades of patellar luxation include, in order of severity:&lt;ref name=&quot;ofapatella&quot;&gt;{{cite web | title = Patellar Luxation | publisher = [[Orthopedic Foundation for Animals]]  | url = http://www.offa.org/patluxinfo.html | format = text/html | access-date = 2007-09-04 |archive-url = https://web.archive.org/web/20070826115200/http://www.offa.org/patluxinfo.html |archive-date = 2007-08-26}}&lt;/ref&gt;

=== 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]] of the [[stifle joint]]. The patella remains luxated until it is manually reduced or when the animal extends the joint and derotates the [[tibia]] 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 [[Femur|femoral trochlear]] groove is shallow or absent, with displacement of the [[quadriceps]] muscle group in the direction of luxation.

==Treatment==
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.&lt;ref&gt;{{Cite web|url=http://vcahospitals.com/know-your-pet/luxating-patella-or-kneecap-in-dogs|title=Cruciate Ligament Rupture in Dogs|last=Ward, DVM|first=Ernest|website=VCA|language=en|access-date=2020-01-23}}&lt;/ref&gt;

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.

==In animal breeds==
Most cases of patellar luxation are medial, and this is frequently a congenital problem in toy- and miniature-breed dogs.&lt;ref&gt;{{cite journal |last1=Engdahl |first1=Karolina |last2=Bergström |first2=Annika |last3=Höglund |first3=Odd |last4=Hanson |first4=Jeanette |title=The epidemiology of patellar luxation in an insured Swedish dog population |journal=Preventive Veterinary Medicine |date=September 2023 |article-number=106034 |doi=10.1016/j.prevetmed.2023.106034 |url=https://www.sciencedirect.com/science/article/pii/S0167587723001988|doi-access=free }}&lt;/ref&gt; Breeds showing a predisposition for medial patellar luxation include miniature and [[poodle|toy Poodles]], [[Maltese (dog)|Maltese]], [[Jack Russell Terrier]]s, [[Yorkshire Terrier]]s, [[Pomeranian (dog)|Pomeranian]]s, [[Pekingese]], Patterdale Terriers, [[Chihuahua (dog)|Chihuahua]]s, [[Cavalier King Charles Spaniel]]s, [[Papillon (dog)|Papillon]]s, [[Boston Terrier]]s, [[Plummer Terrier]]s and [[Teddy Roosevelt Terrier]]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 (cat)|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.&lt;ref&gt;[http://www.vetspecialists.co.uk/06_Animal_Welfare/Orthopaedics/Patellar_Luxation.html Patellar Luxation, canine and feline (cat and dog) veterinary factsheets&lt;!-- Bot generated title --&gt;] {{webarchive|url=https://web.archive.org/web/20080427204435/http://www.vetspecialists.co.uk/06_Animal_Welfare/Orthopaedics/Patellar_Luxation.html |date=2008-04-27 }}&lt;/ref&gt;

==References==
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== External links ==
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|   ICD9           = {{ICD9|836.3}}, {{ICD9|836.4}} 
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{{Acquired deformities}}
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{{DEFAULTSORT:Luxating Patella}}
[[Category:Cat diseases]]
[[Category:Dog musculoskeletal disorders]]
[[Category:Patella]]