RADIOLOGIC PELVIC ASYMMETRY IN UNILATERAL LATE-DIAGNOSED DEVELOPMENTAL DYSPLASIA OF THE HIP

Eighty-three cases of unilateral late-diagnosed (older than 4 months o f age) developmental dysplasia of the hip (DDH) were studied to evalua te pelvic shape and innominate bone relationships in the initial anter oposterior radiograph. To be included, each initial radiograph had to have no lumbar pedicle rotation, lumbar scoliosis, gas shadows, or met allic protectors. Measurements were done using as reference a medial p elvic line, which divides the pelvis into two innominate bones. Lineal parameters were defined to assess pelvic radiologic shape; angular pa rameters defined the relationship between the ilium, ischium and pubis , and sacrum. Statistically significant differences were observed in m ost cases, and pelvis asymmetry was evident. The asymmetry was more ob vious in cases in which the teardrop had a negative value and in low d islocations. Similar changes have been observed in experimental disloc ation of the hip secondary to a triplane pelvic deformity. We suggest that similar alterations of pelvic shape occur in DDH, possibly second ary to growth disturbance in the triradiate cartilage.