Legg-Perthes disease has many names: Legg-Calve-Perthes disease, aseptic necrosis of the femoral head and avascular necrosis of the femoral head. This is a disease that causes lameness of the hip joint in young, small breed dogs.
Toy breeds or terriers 5-8 months old are most commonly affected.
The condition arises when there is an interruption in blood supply to the head of the femur, which is the "ball" portion of the hip's "ball and socket joint." Portion of the boney tissues begin to degenerate and the associated cartilage that lines the hip joint collapses.
This results in a painful, poorly-fitting hip joint. Initially, the dog will show pain and lameness. As the lameness continues and the dog favors the leg, the muscles of the hip and thigh region will begin to shrink and atrophy from lack of use. Legg-Perthes disease usually involves only one hip but approximately 1 out of every 6 - 8 cases will involve both hips. While trauma to the hip can occasionally be the cause of the disruption in blood supply, most cases are thought to be genetically determined.

Legg-Perthes Disease
Radiograph of normal canine pelvis and hips

Legg-Perthes Disease
Radiograph of the hips of a young toy poodle with Legg Perthes Disease. Note the irregular shape of the femoral head ("ball" portion of the "ball and socket" joint of the hip) on the right side of the picture.

Clinical Signs
Lameness is the most common sign and usually gradual onset over 2-3 months. Most patients are able to bear weight, but will sometimes carry the affected leg. Some owners describe these dogs crying out when they stretch the limb or try to bear weight. Atrophy of the affected leg is apparent in chronic cases.

Diagnosis of this condition requires radiographs of the hips. In the early stages of the disease, the normal density of the bone in the femoral head may be diminished.
With time, the top surface of the femoral head will become flattened and misshapen as the cartilage and underlying bone collapses.

Treating Legg-Perthes disease inevitably involves surgery. Anti-inflammatory and pain relieving medications can ease the pain, but almost never resolve the problem. The best solution is a surgical procedure called a femoral head and neck ostectomy (FHO). The FHO involves surgical removal of the diseased femoral head and neck that is the source of the pain. Removing the femoral head and neck does not interfere with the major supporting muscles in the hind leg. After removal, the body forms a "false joint" consisting of a cushion of scar tissue between the cut edge and the hip socket. The result, especially in small to medium size dogs, is a pain-free return to good function of the leg in the vast majority of cases.
Post-operative monitoring of the patient is especially important to ensure they begin to use the surgically repaired leg as soon as possible. Most dogs will begin to bear weight within the first 1 to 2 weeks after surgery. This schedule can be delayed if there has been significant muscle weakening leading up to the surgery. A course of post-operative physiotherapy exercises will help to strengthen the muscles. The best physiotherapy is walking and running the dog as soon as possible after surgery to strengthen the muscles. Potential complications can arise if post operative exercise is limited and can result in poor limb function.
Prognosis is good to excellent for full recovery in most cases

Case of the month
Patient is an 8 month old male intact Chihuahua that presented for intermittent limping over 4 days. Physical exam was unremarkable. Patient did not demonstrate any lameness in the examination room or pain on palpation of the hind limbs. The patient was sent home with 4 days of anti-inflammatory tablets and instructed to return for a recheck exam and radiographs if symptoms continued once finished with medication. The patient returned 4 months later for limping on the right hind limb. The owners noted the patient initially responded to medical management, but intermittent limping continued after finishing medication. The patient then fell down the stairs a few weeks after the initial appointment and limping was considerably worse thereafter. On physical exam patient was unable to bear weight on the right hind limb. muscle atrophy of the right hind limbs was also apparent. Radiographs of the pelvis revealed significant degeneration of the right femoral head. The patient was then referred for orthopedic consult. Femoral head ostectomy was performed 1 week later. Patient has done very well post operatively and doing great.