Legg-Perthe's disease (LPD) occurs most frequently in dogs 5 to 8 months of age, with a reported range of 3 to 13 months. 1 It occurs primarily in small dogs, and has been reported in many small and toy breeds, including Italian greyhounds. Affected dogs are normal prior to the onset of the disease. Symptoms of LPD are lameness, and pain in the area of the affected hip. In some cases, the symptoms may be mild, and possibly go unnoticed. Upon examination, pain can be elicited by a skilled examiner by moving the hip in a variety of directions.

Definitive diagnosis is made by X-rays. As changes to bone occur slowly, X-rays taken early in the course of the disease may appear normal. Repeating the X-rays in 3 to 4 weeks will reveal the bony changes. A dog affected with LPD suffers a loss of blood supply to an area of the femur (thigh bone) known as the neck. Because the bone loses its blood supply, it dies. As a result of the loss of bone tissue, the neck of the femur collapses. The neck attaches the head of the femur to the body of the femur. When the neck collapses, the head of the femur is moved, and may also become deformed.

These changes are readily apparent in X-rays. The head of the femur is the "ball" which sits in the "socket" on the pelvis, making up the hip joint. Therefore, changes to the head result in disruption of function of the hip joint which causes the pain and lameness.

The term "avascular necrosis" means death of tissue due to lack of blood supply. In most dogs, only one hip is affected, and males and females are equally affected.(2) Why this loss of blood supply to the area occurs is not known. What is known however, is the genetic nature of the condition. The exact mode of inheritance of LPD has been debated among researchers. Pidduck et al.,(3)working with toy poodles, proposed a simple (autosomal) recessive mode of inheritance. Robinson,(4) working with data on West Highland white terriers, Yorkshire terriers, miniature poodles and pugs, also suggested an autosomal recessive.

In an effort to clarify the mode of inheritance, Vasseur et al.,(5) working with the Manchester terrier club, conducted a test breeding. Two affected individuals were bred, and all five resulting puppies were X-rayed monthly to check for signs of LPD. If the disease were inherited as a simple recessive in Manchester terriers, then the mating of two affected individuals should have produced 100% affected puppies. At the seven month radiographic examination, changes were noted in three of the puppies, and all three subsequently became lame. The two remaining puppies had no radiographic changes through nine months of age, and remained sound until 16 months when they were placed in homes.

This study indicates that either LPD has a multigenic (more than one gene) mode of inheritance in Manchester terriers, or that it is not completely expressed. That is, an animal may have the affected genes, but not show signs of the disease. Regardless of the exact mode of inheritance, statistical analysis of this and other studies reveals that LPD has a high degree of heritability.

Prevention of the disease is only possible through genetic means. Affected animals should not be bred. Breeding stock should have their hips X-rayed to insure that they are not affected with mild LPD, the symptoms of which went unnoticed during the dog's adolescence. Extreme caution should be used when considering breeding animals that have produced LPD, or have LPD affected littermates.

The Orthopedic Foundation of America (OFA) is a registry which examines X-rays of hips and certifies that they are normal. The address for the OFA is

Legg-Perthes, also called Legg-Calve-Perthes (LCP) disease, is a disease of the hip joints of small breeds of dogs. The head of the femur (the ball part of the ball and socket) begins to die and disintegrate. This causes limping, pain, and eventually arthritis. It usually appears between 6-12 months of age. It is treated surgically by removing the head of the femur and letting the muscles form a "false joint." It really does work. Veterinarians have begun to address the heritability of this disease, and it is generally agreed that although in very rare cases, the disease may be brought on by trauma, it is probably genetic. It has been well documented in terriers (Border Terrier, Lakeland Terrier, Jack Russell Terriers, Wheaten Terrier), and has been proven to be hereditary in some breeds such as the Wheaten Terrier. Bilateral cases (both hind legs affected) are not considered to be the result of trauma, and are accepted to be hereditary.