Dynamic ultrasonography in neonatal hip instability and acetabular dysplasia

Abstract

The clinical hip examination, although highly sensitive in expert hands in detecting neonatal hip instability, can lead to considerable overtreatment. Ultrasound is increasingly being used to complement the clinical examination in assessing neonatal hip instability and acetabular dysplasia, often leading to increased treatment rate. Several different ultrasound methods are in use.

In this thesis a new dynamic ultrasound method was tested using a special examination table with transducer fixing device allowing one person to perform clinical hip examination with use of the Barlow/Palmén method with simultaneous ultrasonographic visualisation.

An examination table was constructed and tested by examining 57 infants of varying ages between 1 day and 10 months (paper 1). An upper feasible limit of about three months of age was established. The hip joint was easily visualized, and the femoral head and the acetabulum were kept in the field of view during the stress test, allowing measurements of the amount of hip instability to be made.

In order to compare the dynamic ultrasound method with clinical hip examination, 1072 hips (536 infants) were examined at a mean age of 12 days (paper 2). The inclusion criteria were risk factors for DDH, clinical signs of hip instability or ambiguous clinical findings. Use of subjective dynamic ultrasound evaluation led to a reduction in calculated treatment rate from 0.85% to 0.49% as compared to the clinical examination.

To investigate the relationship between neonatal hip morphology and stability, two methods of testing hip stability, the present dynamic ultrasound method and the clinical hip examination, were compared with a static ultrasound method, the Graf method (paper 3). Acetabular morphology correlated better to stability as assessed by dynamic ultrasound than to the clinical examination results, with Cohen´s kappa = 0.381 and 0.199 respectively. Of the hips that were dysplastic by the Graf method, 97% were unstable or dislocatable by subjective dynamic ultrasound evaluation. Of the hips that were unstable or dislocatable by subjective dynamic ultrasound evaluation, 21% had normal acetabular morphology according to the Graf method and 56% were immature.

Two methods of evaluating the anterior dynamic ultrasound examination were compared (paper 4). A subjective evaluation made during the examination and an objective evaluation made later on by making measurements of the femoral head movement based on recorded loops. The results were also compared with clinical hip examination and Graf´s ultrasound method. 498 infants (996 hips) with risk factors for DDH, clinical signs of hip instability or ambiguous clinical findings were examined at a mean age of 12 days. An upper normal limit of hip laxity in this age group of 3 mm absolute value and 20% relative to the femoral head diameter was established. Use of objective dynamic ultrasound evaluation with a threshold value of 20% resulted in a reduction of abnormal hips by 63% as compared to the clinical examination and by 45% as compared to the subjective dynamic ultrasound evaluation.