Ultrasound hip evaluation in achondroplasia.

BACKGROUND: During the period from 1985 to 2006, 22 children (44 hips) affected by achondroplasia were ultrasonographically evaluated.

METHODS: The patients' age at examination ranged from 7 days to 29 months. The hip ultrasound (US) examination was performed, according to Graf's method, using a Siemens Sonoline sonogram with linear 5.0- and 7.5-MHz probes. In all the hips, the alpha angle was impossible to be measured because the medial margin of the ilium was not ultrasonographically detectable. The ultrasonographic findings included the following: configuration of the acetabular bony rim, configuration of the acetabular roof, echogenicity of the head and acetabular cartilage, bony coverage percentage of the femoral head according to Morin et al, beta angle according to Graf, dynamic hip instability, and presence of the proximal femoral ossific nucleus.

RESULTS: All hips had a sharp acetabular bony rim, a horizontal acetabular roof, thickened acetabular cartilage, and normal echogenicity. The femoral head was well centered and deeply contained in the acetabular fossa. The mean coverage was 86.7% (range: 78%-90%) and showed progressively larger values with increasing age. The mean value of the beta angle was 20 degrees (range: 8 degrees-38 degrees). The value of the beta angle tended to decrease as age increased. No difference was observed between the right and the left hip in both measurements. All hips were stable. The ossific nucleus was present in 5 children.

CONCLUSIONS: The characteristic findings in hip ultrasonography in children with achondroplasia can aid in its early diagnosis because ultrasound can anatomically detect the altered development of the achondroplastic acetabulum.