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The Grades of Patellar Luxation in Dogs

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Knowing the grades of patellar luxation in dogs is helpful considering that it allows a classification system considering that not all patellar luxation are the same and there can be several levels of severity. The grades of patellar luxation in dogs are typically determined by physical examination on how mobile the dog's knee cap is relative to the groove at the base of the femur. Veterinarian Dr. Ivana shares information about luxating patella in dogs along with the various grades of patellar luxation in dogs.

Luxating patella, Hellerhoff, wikipedia

Luxating patella, Hellerhoff, wikipedia

Patellar Luxation in Dogs

Patellar luxation is the most common cause of hind leg lameness in small and toy dog breeds. Small and toy dog breeds such as Yorkshire Terrier, Maltese, Chihuahua, Bichon Frise and French Poodle are dogs that are genetically predisposed to patellar luxation.

Patellar luxation, also known as luxating patella or "trick knee," is an inherited condition that varies in severity. Namely, dogs are born with slightly rotated tibias (tibial torsion), which leads to a slackness in the knee ligaments. This defect allows the dog's kneecap to slip off inward. It therefore simply dislocates, moving out of its normal location.

Usually, there is no pain associated with the kneecap slipping, but once it has come off, the leg no longer supports weight normally. An affected dog continues walking or running as if nothing has happened, but hops along not bearing weight on the affected hind leg. If the kneecap spontaneously slips back, which often happens, the leg then again functions normally and the dog resumes running normally.

Owners will therefore report these signs to their veterinarian. Based on these signs, vets will suspect patellar luxation and will proceed to an orthopedic examination. This examination will include palpating and manipulating the dog's legs and evaluating how mobile the dog's knee cap is relative to the groove at the base of the femur. With this examination, it is possible grading the level of patellar luxation.

There are several grading methods, but the most commonly used grading system is the Putnam/Singleton grading system.

The Grades of Patellar Luxation in Dogs 

Based on the severity of the luxation, the condition is categorized in different grades:

  • Grade I (least severe) – patellar luxation grade I is when the vet can manually luxate the patella but the patella returns to its normal position once released. A small dog with patellar luxation grade I can live its entire life without showing any clinical signs and without developing arthritis.
  • Grade II – patellar luxation grade II is when the patella can be luxated either with manual manipulation or stifle flexion and it remains luxated until manual replacement occurs or until a stifle extension repositions it.
  • Grade III – patellar luxation grade III is when the patella is continually luxated, and even if manually replaced, it spontaneously re-luxates once the manual pressure is removed.
  • Grade IV (most severe) – patellar luxation grade IV is when the patella is permanently luxated and cannot be manually repositioned. A dog with patellar luxation grade III or IV has decreased quality of life and requires prompt veterinary attention.

What are some patellar luxation long-term consequences? Whether or not the dog will experience long-term consequences depends on two main factors: 1) The grade of luxation – as stated patellar luxations are graded from grade I to grade IV based on the severity and 2) whether both legs are equally affected – roughly 50 percent of affected dogs have both knees luxating, however the grade of luxation may differ.

Nevertheless, patellar luxation is a condition that predisposes the knee to a plethora of injuries. The most common and frequently reported is a torn cruciate ligament. In fact, according to statistics, between 15 and 20 percent of dogs with patellar luxation will have their cranial cruciate ligament ruptured at some point.

Over time, since the patellar luxation causes alteration of the weight bearing stress on the leg, changes in the shin, thigh and hip bones are likely to be expected. As the dog grows older, arthritic changes will occur and eventually lead to chronic joint pain and decreased mobility.

There are consequences for delayed treatment in some cases. Severe cases of patellar luxation (grade III and grade IV) can cause skeletal abnormalities if left untreated. The most frequently observed skeletal abnormalities include bowing of the tibia and femur. Therefore, as with any other health problem, early treatment not only prevents potential complications but it also ensures better treatment outcome.

Treatment For Patellar Luxation in Dogs

The treatments of patellar luxation can be classified as surgical and non-surgical. Which approach should be chosen depends on the grade of luxation. Generally speaking, patellar luxation grade I is treated with non-surgical methods. Patellar luxation grade II is also treated non-surgically, unless there are significant clinical signs that warrant surgical repair. Patellar luxations grade III and grade IV are almost exclusively treated surgically.

The non-surgical treatment of patellar luxation is based on 4 principles:

  • Body weight management
  • Exercise modification
  • Physiotherapy (hydrotherapy)
  • Medication (pain killers and anti-inflammatories).

It should be noted that the above mentioned principles can also be used for short-term management of dogs who are waiting surgical correction.

Surgical treatment of patellar luxation is advisable for all dogs experiencing either intermittent or permanent lameness. The surgical correction of a luxating patella is complex and requires soft tissue reconstruction as well as bone reshaping.

Generally speaking, the surgical repair involves 3 steps:

  1. Transplanting or moving the point of attachment of the patellar ligament to the shin bone to its proper position
  2. Deepening the femoral groove to ensure the patella will stay in its anatomically correct position
  3. Tightening the capsule around the joint to prevent future luxation of the patella.

The prognosis for dogs with surgically corrected luxating patella is based on two main factors: the timing of the surgery and the grade of luxation. If the surgery is performed before any long-term consequences develop, the prognosis is excellent and the dog will regain full use of the affected leg.

On the flip side, if there are arthritic changes, the surgery will correct the luxating problem, but the arthritis is likely to progress. Because of the progression of the arthritis, the dog will experience intermittent pain in the affected leg. As for the grade of luxation, generally speaking, the higher the grade the more likely it is for the condition to reoccur after surgery.

Managing Dogs with Surgically Corrected Luxating Patella

To control the pain and discomfort associated with the surgical correction, prescription anti-inflammatories and pain killers should be used. With proper pain and inflammation management, the recovery period is smooth and rapid. To ensure better outcome, the vet will advise a six- week rest.

On the long-run, to slow down the progression of arthritis, the vet will suggest using certain joint supplements and special diets formulated for improving joint health. For overweight dogs, weight reduction is of imperative importance. Last but not least, special exercise regimens should be implemented. The exact exercise regimen is individually tailored and determined by your trusted vet.

Photo credits: Luxating patella, Hellerhoff, wikipedia CC BY-SA 3.0

About the Author 

Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.

ivana crnec

She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.

Ivana’s research has been published in international journals, and she regularly attends international veterinary conferences.

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