1. Legg-Perthes disease is an affection of the head and neck of the femur which runs a cyclical course. The first, or degenerative. phase of the cycle extends through a period of approximately a year and a half. The second, or regenerative, phase requires two to three years for its completion. Adequate treatment by prolonged non-weight-bearing shortens the cycle, and absence of such treatment prolongs it.

2. The etiology is as yet unproved. The age incidence, in the author's cases, has been between three and eleven years and 85 percent. have been boys (just the reverse of the sex incidence of congenital dislocation). Tuberculin reactions have been consistently negative, and the blood sedimentation rate has been normal.

3. The usual symptoms are limp, and pain which is more commonly felt at the knee. The disease is often far advanced at the onset of symptoms.

4. The physical signs are limitation of motion (particularly of rotation) and a slight, but definite, firm thickening of the hip. Occasionally there is slight wasting of the muscles of the thigh.

5. The pathological process is essentially one of aseptic necrosis of the neck and head of the femur which is succeeded by a physiological process of repair.

6. The necrosis is always evident in the metaphysis, and the study of early cases indicates that here is the primary location of the disease. Necrosis of the head follows, and the primary area in the head corresponds exactly to the primary area in the metaphysis. As the disease spreads in the metaphysis, corresponding changes occur in the remainder of the head.

7. Healing occurs first in the metaphysis and later in the head. The corresponding part in each which was the first to show evidence of necrosis is the first to repair.

8. These observations indicate that the disease is essentially one which produces a progressive destruction of the blood supply through the metaphysis and the epiphyseal plate of cartilage, and that the changes which occur in the head are secondary to those in the neck.

9. The deformities that arise in the head and the neck are due to a mechanical crushing of the necrotic tissue caused by weight-bearing and muscle pull. Deformity of the acetabulum is dependent upon the altered shape and position of the head.

10. Treatment by rest in bed with Buck's extension leads to such complete restoration that in the final result it is difficult to detect any deformity of head, neck, and acetabulum.