Exploration of femoral head coverage in screening developmental dysplasia of the hip in infants

PurposeTo investigate the relationship of femoral head coverage (FHC) with Graf's classification for diagnosis of developmental dysplasia of the hip (DDH) and its role in evaluating hip stability.MethodsA total of 4222 hips were screened ultrasonographically with Graf's and Harcke's methods. The stability of hips was analyzed using the difference between FHCs at neutral and flexion positions (FHC-D).Results(1) For the non-dislocated hips, the mean value of FHC at the neutral position was 59.4%, which was significantly greater than 55.0% of FHC at the flexion position (p<0.001). (2) FHC at the neutral position corresponding to Graf I, IIa/b, IIc, D, III, and IV was 63.04.7%, 57.0 +/- 5.2%, 49.5 +/- 5.5%, 37.7 +/- 3.7%, 30.2 +/- 12.7%, and 7.4 +/- 11.9%, respectively, and that at the flexion position was 59.0 +/- 4.4%, 50.7 +/- 9.4%, 35.2 +/- 5.2%, 30.8 +/- 1.3%, 23.4 +/- 10.7%, and 4.7 +/- 9.9%, respectively, showing a statistically significant difference between the two positions. (3) The AUC of FHC-D in evaluating the stability of hips was 0.972. When the threshold was 8.5%, the sensitivity, specificity, and accuracy of FHC-D in detecting hip instability were 89.0%, 93.0%, and 93.9%, respectively.Conclusions FHC can be used as a reference indicator for DDH classification. FHC at different positions corresponds to different reference values, and FHC-D can be used as a quantitative indicator for assessment of hip stability.