Association between early sonographic findings and acetabular index at the age of 6 months: a prospective observational study

BACKGROUND: This study investigated the association between early Graf classification and femoral head coverage (FHC) with the acetabular index (AI) at the age of 6 months. METHODS: A prospective observational study was conducted between 2017–2018. Patients requiring Pavlik harness treatment and patients with syndromic dislocation or neurogenic dislocation were excluded. In total, 169 newborns with the first ultrasound performed at the mean age of 12.3 (0–15) days, the second ultrasound performed at the mean age of 3.2 (2.5–4.1) months, and the AI measured at the age of 6.6 (4.3–7.1) months were enrolled. The correlation between the AI and first and second alpha angles and FHC measurements, and the correlation of dysplasia in early ultrasound with dysplasia in the AI were analyzed. RESULTS: At the first ultrasound, only the FHC (P = .02) demonstrated a significant negative correlation with the AI. At the second ultrasound, both the alpha angle (P < .01) and FHC (P < .01) demonstrated a significant negative correlation with the AI. With the AI as a reference, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were found to be 77%, 7%, 5%, and 81%, respectively, for the first Graf; 91%, 37%, 9%, and 98%, respectively, for the first FHC measurement; 82%, 90%, 35%, and 99%, respectively, for the second Graf; and 95%, 97%, 68% and 99%, respectively, for the second FHC measurement. CONCLUSIONS: FHC and alpha angle exhibited significant negative correlations with the AI at six months, both ultrasound parameters may have the potential to predict AI in DDH screening. Compared to the ultrasound measurements taken at 2 weeks, Graf and FHC at 3 months demonstrated superior sensitivity, specificity, PPV, and NPV to detect abnormal AI. The best timing to perform ultrasound examination may need further research.