MRI evaluation of hip containment and congruency after closed reduction in congenital hip dislocation

Background: Developmental dysplasia of the hip is the most common congenital skeletal disease. In its most severe form - dislocation - the treatment is directed at reducing the hip and establishing normal congruency between the femoral head and the acetabulum. Closed reduction with casting is a common primary treatment, where reduction is confirmed by magnetic resonance imaging (MRI). Objective: This study analyses anatomical aspects depicted on MRI after closed reduction to identify disparities in the growth behaviour of dislocated hips. Materials and methods: In 38 patients MRI after closed reduction was available for analysis. After exclusion of children with underlying diseases or syndromes, MRIs of 28 children were evaluated with respect to head coverage index, acetabular head index and sphericity. The results were compared to the stable opposite sides. Results: Twenty-two stable and 27 initially unstable hips were available for further analysis. The head coverage index as well as the acetabular head index of the unstable hips was significantly smaller than that of the stable hips. The sphericity score of the dislocated femoral heads was significantly lower than that of the stable ones. Conclusion: Dislocated hips showed significantly lower values for all of the evaluated parameters concerning congruency and containment. MRI is not only useful to confirm successful reduction but may also help to predict outcome by evaluating following dislocation.