Patella Luxation

Patella luxation

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 Terriers, Yorkshire Terriers, Pomeranians, Pekingese, patterdale terrier, Chihuahuas, Cavalier King Charles Spaniels, Papillons, Boston 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, it is generally agreed that a defect in hind limb conformation is the underlying cause.

Causes

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

Diagnosis is made through palpation of the knee, to see if it slips inside the joint more than would normally be expected. Often a dog-owner may be told his 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, there may be no symptoms or only mild ones, such as intermittent limping in the rear leg. X-Rays can determine how serious the condition is. More extreme cases can result in severe lameness. Osteoarthritis typically develops secondarily. There are four diagnostic grades of patellar luxation, each more severe than the previous:

• Grade I - the patella can be manually luxated but is reduced (returns to the normal position) when released
• 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 - 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 in reluxation of the patella
• Grade IV - the patella is permanently luxated and cannot be manually repositioned. There may be up to 90¼ of rotation of the proximal tibial plateau. The femoral trochlear groove is shallow or absent, and there is displacement of the quadriceps muscle group in the direction of luxation.