Bone maturation of MRI residual developmental dysplasia of the hip with discrepancy between osseous and cartilaginous acetabular index.

Quality of spontaneous amelioration of residual developmental dysplasia of the hip (DDH) is nowadays not possible to predict. Normal age-related values of the osseous acetabular index (OAI), cartilaginous acetabular index and labral acetabular index have been established on MRI. In this study, MRI of dysplastic hips has been evaluated, and further osseous acetabular maturation was followed-up over time on pelvic radiography to find a correlation between MRI findings and radiological evolution. This is a retrospective single-centre study. Children with DDH who had a pelvic MRI between February 2007 and June 2014 were included. AI was measured for osseous (OAI), cartilaginous (cartilaginous acetabular index) and labral (labral acetabular index) values on MRI. OAI was thereafter recorded on each available radiograph during follow-up. A total of 20 hips were included. The mean age at MRI diagnosis was 3.55 years. Two types of DDH were observed: harmonious dysplasia, associated with an osseous and cartilaginous defect (group A, n = 14), and divergent dysplasia, associated with an osseous defect but with sufficient cartilaginous coverage (group B, n = 6). The mean age at final radiological follow-up was 7.6 and 8.3 years (P = 0.7408), respectively. In group A, four (28.6%) children older than 6 years had an OAI of less than 18°, whereas only two (33.3%) children older than 6 years had an OAI less than 18° in group B (P = 0.0117). This study shows that, in one-third of cases, divergent dysplasia leads to a spontaneous recovery. MRI should be used early to accurately diagnose and follow-up DDH cases and allow surgeons to justify the required surgical treatment. Level of Evidence: IV.