Radiologic pelvic asymmetry in unilateral late-diagnosed developmental dysplasia of the hip.

Eighty-three cases of unilateral late-diagnosed (older than 4 months of age) developmental dysplasia of the hip (DDH) were studied to evaluate pelvic shape and innominate bone relationships in the initial anteroposterior radiograph. To be included, each initial radiograph had to have no lumbar pedicle rotation, lumbar scoliosis, gas shadows, or metallic protectors. Measurements were done using as reference a medial pelvic line, which divides the pelvis into two innominate bones. Lineal parameters were defined to assess pelvic radiologic shape; angular parameters defined the relationship between the ilium, ischium and pubis, and sacrum. Statistically significant differences were observed in most cases, and pelvis asymmetry was evident. The asymmetry was more obvious in cases in which the teardrop had a negative value and in low dislocations. Similar changes have been observed in experimental dislocation of the hip secondary to a triplane pelvic deformity. We suggest that similar alterations of pelvic shape occur in DDH, possibly secondary to growth disturbance in the triradiate cartilage.