Young pugs affected with Legg-Perthes usually have normal growth and development during the first three months of life. The disease starts when the blood supply to the head of the femur (thigh bone) decreases. The inadequate blood supply can cause the bone to deteriorate which eventually dies off. When this happens, the bone making up the head of the femur becomes malformed and the cartilage which covers the femoral head becomes cracked and deformed. The hip joint becomes malformed and there is a high probability of secondary arthritis setting in causing pain and lameness.

Although the deterioration of the structures of the hip joint starts when the puppy is around three months old, the effect, particularly the pain and lameness can be felt when the puppy is six to ten months of age. Aside from limping, a puppy suffering from Legg-Perthes is often irritable and constantly chews at the region of the affected flank. Lameness is usually progressive until the dog will stop putting weight on the affected limb. When this happens, the affected leg becomes stiff and the muscles will become atrophied as a result of disuse.

Pain can be induced when the dog moves its hip particularly when the affected limb is manipulated by extending it backward and also to the side. When the limb is manipulated on its range of motion, one can feel crepitus or a feeling of crunchiness on the affected hip joint.

It has been observed that more than 90% of dogs suffering from Legg-Perthes have only one hip affected.

To prevent painful complications surgery is the best remedy for dogs suffering from Legg-Perthes. Surgery involves the removal of the diseased femoral head and neck excision. There is a high success rate and the prognosis is quite good provided that rehabilitation is done after surgery.

In some cases, conservative treatment that involves strict cage confinement and rest coupled with regular physical therapy can only be successful if the femoral head has not yet started to erode and still snuggly fits inside the socket of the hip joint.