The acetabular teardrop and ultrasonography of the hip.

The acetabular teardrop is an important tool for the diagnosis of acetabular dysplasia. Since it was first described by Köhler its widespread use has not become established due to the relative subjectivity in classification of the types. The acetabular teardrop angle (ATA) is proposed for this purpose, and to show the teardrop's direct relation to acetabular development by correlating it with hip ultrasonography results. Patients (51 male, 53 female) included in this study received hip ultrasonography and concomitant pelvic radiography. In the 296 hips, alpha and beta angles were measured from ultrasonography, whilst the acetabular index (AI), ATA, teardrop distance and the transverse diameter of the most upper, most widened part of the teardrop were measured from the radiographs. The enlarged, and triangle-shaped teardrop is seen later than normal ones, and the triangle-shaped-teardrop hips have a higher AI than the normal hips. The ATA is in good correlation with the widest diameter, showing this to be a reliable tool for describing the teardrop. The ATA also has a positive correlation with the beta angle denoting its significance to acetabular development. High-risk babies should be followed-up primarily with ultrasonography wherever possible. The AI from radiographs and the acetabular teardrop may be used as a helper tools in decision-making, with the guides of the ATA and the transverse diameter of the most upper, most widened part of the teardrop, as proposed in this study.