Application of "safety belt sign" in the treatment of developmental dysplasia of the hip in children aged under 2 years

Objective To evaluate the clinical value and feasibility of belt of arthrography in the treatment of developmental dysplasia of the hip (DDH) in children aged under 2 years. Methods Between July 2013 and July 2017, retrospective reviews of clinical and radiographic data were reviewed for 75 DDH children (84 hips). Their age range was 3 to 20 (12.5±5.7) months and the follow-up period 3 to 48 (20.8±14) months.According to the Bowen’s criteria, intra-operative arthrographs were qualitatively evaluated and divided into 3 groups, group A (n=39, 45 hips) managed by closed reduction, group B (n=29, 31 hips) by simple open reduction and group C (n=8, 8 hips) by simple open reduction after failed reduction. Safety belt refers to a filling defect zone of vertical femoral neck around femoral head of a dislocated hip on arthrography.And safety belt sign ratio is defined as the ratio between perpendicular distance d from center of belt to the upper medial edge diameter of safety belt sign and femoral head diameter D. Femoral head coverage rate h/D was also determined where h is vertical distance between medial femoral head edge and the farthest point on P line.We compared the inter-group differences in d/D and h/D.Intra-class correlation coefficient (ICC) was used for testing consistency while receiver operating characteristic curve for assessing the sensitivity, specificity and cutoff points of d/D and h/D.We also assessed for persistent belt after open reduction in group C. Results Statistically significant inter-group differences existed in d/D and h/D (P 0.75) demonstrated an excellent inter-group consistency.The maximal area under the curve of d/D and h/D on the ROC curves of groups A and B were 0.876 and 0.846 respectively.A sensitivity of 84.8%, a specificity of 87.3% and a cutoff value of 0.485 of d/D were obtained.Six cases (75%) in group C had belt after reduction. Conclusions Safety belt of intraoperative arthrography may be used as a parameter for preoperatively diagnosing DDH in children aged under 2 years.When d/D ratio surpasses 0.500, closed reduction is more feasible and successful.