From the archive of our institution,
we selected several ultrasound images illustrating the different imaging findings of DDH.
The ultrasound technique is reviewed.
There are three different techniques that can be used for sonographic evaluation of the hip:
- Two of them are based on morphological criteria,
the static techniques of Graf and Morin,
and the other is based on a dynamic evaluation,
Harcke's dynamic technique.
- The hip joints should be evaluated with a linear,
high frequency probe,
with frequencies between 5 MHz and 7.5 MHz.
The two static techniques,
Graf's and Morin's,
evaluate acetabular morphology in a coronal plane.
The child should be placed in lateral decubitus position with the hips flexed at 30º-45º (Fig. 3).
In the correct normal plane we will see the rectified wing of the iliac bone,
the triradiate cartilage,
the cartilaginous head of the femur and the acetabular labrum.
When we identify these structures in the same image,
we know that we are on the correct plane to perform the necessary measures for the evaluation of the hip (Fig. 4).
When there is displacement of the femoral head,
usually anterior and lateral,
it may not appear in the standard plane.
After the correct plan is obtained,
the alpha and beta angles (Graf’s technique) or the percentage of coverage of the femoral head by the bony acetabulum (Morin’s technique) are measured (Fig. 5 and Fig. 6).
- In the former one,
the hip is classified into four main types based on the age of the child,
the values of the angles obtained and the characteristics of acetabular hyaline cartilage (Table 1).
- In the latter one,
the hip is classified as abnormal,
undetermined or normal,
depending on the percentage of femoral head coverage obtained (Table 2).
Graf´s Technique:
The Graf´s alpha angle is measured in the coronal plane and is defined as the angle formed between the vertical cortex of the ilium and the acetabular roof,
indicating the degree of acetabular roof coverage (Fig. 7).
An α angle less than 60° is abnormal and reflects a shallow acetabulum.
The beta angle is formed by a line through the vertical ilium and the cartilaginous acetabular labrum (Fig. 7).
With superolateral femoral head displacement,
the labrum is elevated,
thereby increasing the beta angle.
Graf´s ß angle greater than 55° is abnormal.
In clinical practice,
the different categories of Graf´s classification can be grouped in three hip types:
- Normal hip: Type I hips are normal and require no treatment.
The alpha angle is greater than 60 degrees (Fig. 7).
- Immature hip: Type IIa hips.
These patients require no treatment,
and there is a small risk of delayed DDH.
Follow-up is recommended to confirm normal development (Fig. 8).
- Abnormal hip: Types IIb,
IIc,
D,
III,
and IV hips (Fig. 9,
Fig. 10,
Fig. 11,
Fig. 12 and Fig. 13,
respectively).
Represent progressive abnormal hips with frank subluxation in types III and IV.
Alpha angle is <50 degrees in types IIc and D and <43 degrees in types III and IV.
Morin´s Technique:
A normally positioned femoral head is more than 50% covered by the acetabulum (Fig. 14 and Fig. 15).
DDH results in a shallow acetabulum and decreased coverage of the femoral head (Fig. 16,
Fig. 17,
Fig. 18,
Fig. 19 and Fig. 20).
Harcke´s Technique:
The Harcke’s dynamic technique uses images of the coronal plane with the hip in rest and of the transverse planes with the hip flexed,
in rest and subjected to stress maneuvers (controlled application of force with posterior direction to the femoral head,
with the femur in flexion and adduction).
This technique is based on the positional relationship between the femoral head and the acetabulum and on hip stability,
classifying the hip joints as normal,
sub-luxated or displaced.
It is the most subjective and the least used technique in Europe,
not being performed in our institution.
It will not be explored here.