The problem of instability of reduction of congenital dislocation and congenital subluxation of the hip has been studied. The basic cause of this instability is the abnormal direction in which the entire acetabulum faces. An operation, innominate osteotomy, has been designed to correct the abnormal direction of the entire acetabulum

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in children more than eighteen months old. The principle of innominate osteotomy is redirection of the acetabulum so that the reduced dislocation or subluxation, which was stable previously only in the position of abduction and flexion, is rendered stable in the functional position of weight-bearing.

The advantages of innominate osteotomy are:

1. Correction of the abnormal direction in which the entire acetabulum faces

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produces immediate stability of reduction in the functional position of weight-bearing without altering the congruity of the acetabulum or decreasing its capacity.

2. After innominate osteotomy, the area of articular cartilage of the femoral head and acetabulum in contact in the functional position of weight-bearing is increased considerably because the femoral head is covered better by the acetabulum. As a result, the pressure of weight-bearing is distributed over a larger area of articular cartilage. It is suggested that this may be an important. factor in helping

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to prevent the degenerative changes in articular cartilage with subsequent function of the joint.

3. Both reduction and stability are provided by a single operative procedure.

4. The stability of reduction permits early resumption of function of the hip, thereby avoiding the undesirable effects as well as the hardships of prolonged immobilization.

5. Early weight-bearing on a completely reduced and completely stable hip seems to provide the best possible stimulus for subsequent normal development of both femoral head and acetabulum.

Since the development of innominate osteotomy in 1957, in our experience the results have been especially encouraging.