DEVELOPMENTAL DYSPLASIA OF THE HIP (DDH)

 

Developmental dysplasia of the hip (DDH) is one of the most common musculoskeletal problems in newborns. It results from an abnormal relationship of the femoral head to the acetabulum. The reported incidence of DDH varies between 1.5 and 20 per 1000 births, with a clear female predominance (M:F ratio ~1:8). DDH usually occurs from ligamentous laxity and abnormal position in utero. For some reason, the left hip is said to be more frequently affected. One-third of cases are affected bilaterally.

Ultrasound is the modality of choice for imaging assessment of DDH in the infant (<6 months) prior to ossification of the proximal femoral epiphysis. A lineair, high frequency probe is used and the focus is set at the acetabular edge. Once there is a significant ossification then x-ray examination is required.

The Graf classification of hip dysplasia is mainly based on the morphology of the iliac bone, where we look at the shape of the acetabulum, the bony and cartilaginous acetabular rim, labrum and position of the femoral head, and also look at the coverage of the femoral head by the cartilage of the acetabulum and the labrum.

The alpha-angle, which is a measurement of the bony roof of the acetabulum, mainly determines the hip type. The normal value is greater than or equal to 60º. Note that up to the age of 3 months (13 weeks) an alpha angle below 60 degrees is acceptable.

The beta angle is formed by the vertical cortex of the ilium and the triangular labral fibrocartilage. The normal value is less than 77º but is only useful in assessing immature hips when combined with the alpha angle, to differentiate between type Ia and Ib (both normal hips) and between type IIc and type D.

Bony coverage represents the percentage of the femoral epiphysis covered by the acetabular roof. A value of >50% is considered normal.

Treatment varies from Pavlik bracing to surgical reduction and osteotomies depending on the age of the patient and the degree of dysplasia.

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