Pet Library

Luxating Patella (Dislocated Kneecap)

The patella, or kneecap, should be located in the center of the knee joint. The term “luxating” means out of place or dislocated. Therefore, a luxating patella is a kneecap that moves out of its normal location.

Contributing Factors

The muscles of the thigh attach, directly or indirectly, to the top of the kneecap. There is a ligament, the patellar ligament, running from the bottom of the kneecap to a point on the tibia just below the knee joint. When the thigh muscles contract, the force is transmitted through the patella and through the patellar ligament to the point on the top of the tibia. This results in extension (straightening) of the knee. The patella stays in the center of the leg because the point of attachment of the patellar ligament is on the midline and because the patella slides in a groove on the lower end of the femur (the long bone which fits between the knee and the hip).

Prevalence

Patellar luxation is most common in small toy breeds of dogs.

Causes/Transmission

The patella luxates when the point of attachment of the patellar ligament is not on the midline of the tibia. It is almost always located too far medial (toward the midline of the body). As the thigh muscles contract, the force is pulled medial. After several months or years of this abnormal movement, the inner side of the groove in the femur wears down. Once the side of the groove wears down, the patella is then free to dislocate. When this occurs, the dog has difficulty bearing weight on the leg. It may learn to kick the leg and snap the patella back into its normal location. However, because the side of the groove is gone, it dislocates again easily.

Clinical Signs

Some dogs can tolerate this problem for many years, some for all of their lives. However, this weakness in the knee predisposes the knee to other injuries, especially torn cruciate ligaments. Also, arthritic changes may take place in the joint and make it painful.

Diagnosis

Luxating patellae can be detected with a routine orthopedic examination of the knee joint and X-rays.

Therapy

A luxating patella can be repaired surgically by relocating the point of attachment of the patellar ligament and by deepening the groove in the femur. This should be done if your dog has a persistent lameness or if other knee injuries occur secondary to the luxating patella.

Prognosis

Surgical repair is generally very successful. The prognosis is more favorable when the luxation is not severe or if repair occurs before arthritis develops.

Addison’s Disease (Hypoadrenocorticism)

Addison’s disease is also known as hypoadrenocorticism. It is a disease that results from the reduction of corticosteroid secretion from the adrenal gland. The adrenal gland is a small gland located near the kidney that secretes several different substances to help regulate normal body function. Some of the most important products it secretes are glucocorticoids and mineralocorticoids. Addison’s is difficult to recognize initially, but once diagnosed can be successfully treated.

Glucocorticoids and Mineralocorticoids
Glucocorticoids, such as cortisol, have an effect on sugar, fat, and protein metabolism. They are partially responsible for the flight or fight response during stressful periods. Mineralocorticoids, such as aldosterone, have an influence on the electrolytes sodium and potassium in the body. They help regulate these electrolytes, particularly in stressful situations. When the adrenal gland stops functioning, these hormones are not produced and the metabolism and electrolyte balance of the animal becomes unbalanced.

Who gets Addison’s and what are the symptoms?
Addison’s is primarily a disease of young to middle-aged female dogs, but can affect any dog of any age or sex. Some of the more common symptoms are lethargy, anorexia, vomiting, and muscle weakness. The other presentation for this disease is an episode called an “Addisonian crisis”. In this scenario, the animal collapses in a state of shock due to an imbalance of electrolytes and metabolism during a period of stress. This episode may be the first time the owner suspects disease, and may be fatal if not treated promptly.

What causes the adrenal glands to stop producing corticoids?
The most common is destruction of the adrenal glands by the body, an ‘immune mediated destruction’. Other causes can be infections in the gland from fungal diseases or through other means such as infarcts, tumors, or amyloidosis of the gland. Another cause of Addison’s can be the failure of the pituitary gland to secrete adrenocorticotropic hormone (ACTH), a hormone that stimulates the adrenal gland to work. Failure of the pituitary gland or hypothalamus is usually a result of a tumor, inflammation, or injury.

How is hypoadrenocorticism diagnosed?
Diagnosis is confirmed by a blood test called ACTH stimulation test. To perform the test, the dog is given an injection of the adrenal stimulating hormone ACTH. A normal dog will respond by having an increase in blood cortisol. If a dog with Addison’s disease is given ACTH, the dog will not have an increase in blood cortisol and the diagnosis of Addison’s disease is confirmed. The test is not always accurate, however, and the veterinarian may recommend a secondary test called a Low Dose Dexamethasone Test (LDD), or refer for an ultrasound to try and evaluate the adrenal glands directly.

How is it treated?

Treatment involves replacing the missing glucocorticoids (steroids) or mineralocorticoids. The steroids are replaced with daily oral pills of Prednisone. The mineralocorticoids are usually replaced by injections of DOCP. The injections have to be given on a very regular schedule for the rest of the dog’s life – depending on the dog, every 24-29 days. While the schedule is being determined, the veterinarian will have to regularly check the Sodium/Potassium (NA/K) ratio to assure close control of this potentially fatal disease.