Coronal Compensation Mechanism of Pelvic Obliquity in Patients With Developmental Dysplasia of the Hip

STUDY DESIGN: Descriptive retrospective study. OBJECTIVE: DDH is a common lower limb deformity. It has been reported that this deformity can change the sagittal alignment of spine and pelvis. Sacral obliquity (SO) and iliac obliquity (IO) have been proven simple and reliable pelvic-lower limb coronal parameters to evaluate the coronal balance of the pelvis. To study the spine-pelvic coronal compensation mechanism of pelvic obliquity in patients with developmental dysplasia of the hip (DDH). METHODS: We collected the data of 110 patients with DDH in our hospital from January 2009 to December 2019, who underwent total hip arthroplasty. We used ICC (Intraclass correlation coefficient) to test the reliability of the measurement result of SO and IO in patients with DDH. A paired t-test was used for the statistical analysis. RESULTS: The intra observer reliability of IO and SO was 0.965 and 0.875 respectively, and the inter observer reliability of IO and SO was 0.887 and 0.889 respectively. The sacroiliac joint and spine can compensate for pelvic obliquity in patients with DDH. We classified the compensatory mechanism into 3 types according to the different imaging performances. CONCLUSIONS: The sacroiliac joint has a considerable compensatory ability to ensure coronal balance. We clarified and classified the compensatory mechanism of pelvic obliquity into 3 types. We differentiated the pelvic obliquity in patients with DDH and in those with scoliosis, which is clinical significant to understand the process of development of the disease.