Avascular necrosis of the femoral head in congenital dislocations of the hip, even in the time of sonography, is a danger we are afraid of, but we know how to avoid it. (Fig.1).

If a too high pressure after birth is put on the cartilage of the femoral head by a too increased abduction and 90° flexion in the cast of Lorenz (Fig.2) or after Lange (Fig.3) a position of too much abduction and internal rotation without flexion ...

... or by high pressure in a too decreased narrow entrance of the joint (Fig. 4), ...

... then the circulation of the blood in the high number of little blood vessels in the soft cartilage of the femoral head is limited. Here, however, a strong nucleus of the femoral head is to be seen (Fig. 5).

In necrosis there is a different decay, partially or fully. Tab.1. shows our degrees.(Fig. 6).

It was noted that Graf's type of hip 3b had the highest rate of 12.5%, type 3a 4.4%, type 4 5.0%. The other types had ony very little rates.

When we checked the dislocation degrees, which we introduced in our research group, the peak was found at 14.7% at grade 3. Then the nucleus of the femoral head or its center corresponds to Graf's grade 3 of dislocation standing in the vicinity of the upper acetabular rim. At grade 4 however necrosis was not found. Probably these hips were reduced by operation.

Let us look at such cases in arthrographies. Here we see Graf's type 3 at both sides (Fig. 7).

In the sonography we find a slight density probably of cartilage. However, here we have already a femoral  nucleus, which appears earlier in sonography than in roentgenography (Fig. 8).

In the reduced position of the right hip, we see the femoral head beneath the upper labrum, but the buttom of the joint is filled by a large Lig. capitis and lower labrum (Fig. 9). Probably the transverse ligament is also narrowing the entrance of he acetabulum.

The later x-ray controlles showed no necroses of the head of the femur, but very tender acetabular nuclei (Fig. 10).

And here is another type 3 hip (Fig. 11).

In the position of reposition the soft issues are still blocking a deep reduction (Fig. 12).

4 months later - what is that? A strong femoral nucleus has made his way deep into the acetabulum (Fig. 13). A dangerous undertaking.

Now let us see the development when there is a similar joint without a femoral nucleus. This hip seems to be the type 3 of Graf (Fig. 14).

The arthrography shows the reduction in a narrow entrance of the acetabulum between upper labrum plus transverse ligament and the lower labrum (Fig. 15). A femoral head nucleus is still missing.

In the following time a severe osteonecrosis was seen including the metaphysis (Fig. 16).

And this was the pitiful result at the age of 15 years (Fig. 17).

And here, the contrary, when a femoral nucleus is present (Fig. 18). Then, even in this severely displaced typ 3 hip joints with femoral nuclei, there was no osteonecrosis.

Here we see an arthrography in the mean position of the joint (Fig. 19).

In the position for reduction, at the right, the femoral head is placed very well beneath the cartilaginous acetabular roof and relatively close, but not fully, to the bottom (Fig. 20).

At the age of 5 1/2 years the x-ray presents a regular development of the hips (Fig. 21).

1984 we have already pointed out that osteonecrosis of the femoral head will develop, when the femoral nucleus is missing or delayed and the femoral head is opposed with difficulties at reduction into the acetabular fossa.

The diameter size of the acetabular fossa is important, as you see in the table above.

Also the distance to the bottom of the acetabular fossa is of much influence, as you see in this table.

The same findings are important in Grafs type 4 of the hips (Fig. 22).

The femoral head forms its way into the fossa acetabuli (Fig. 23), ...

... but the limitation of blood supply is seen at the left (Fig. 24).

This is another severely dislocated type 4 hip (Fig. 25).

Here the labrum is pushed into the acetabulum (Fig. 26). This joint also has only a very low depth. Here an open reduction is necessary.

In these joints osteonecrosis developed in 31%, as the last line of statistics shows, when conservative treatment was applied and open reduction avoided.

This is a picture of 2 hip joints, where the treatment of dysplasia leads to a good result, when a plastercast in squatting position after appearing of the femoral nucleus is applied in the first year of life. In the second year of life and later at this degree of dysplasia we had to add an (Fig. 27) acetabuloplasty (Fig. 27). Otherwise a residual dysplasia would remain.

Here we see again a hip joint, where the femoral head in neutral position is in good contact with the acetabular bottom, but the acetabulum is still in a steep position, which we call hip dysplasia (Fig. 28).

And here we see the exact deep reposition as it should be (Fig. 29).