Magnetic resonance imaging after reduction for congenital dislocation of the hip.

BACKGROUND: Reliable concentric reduction of the femoral head and subsequent retention in a centred position are indispensable preconditions for the remodelling of the acetabulum in developmental dysplasia of the hip (DDH) and to prevent damage to the hip joint, i.e. avascular necrosis. The objective of this study is to evaluate the necessity of verifying the reduced position of the articulation in the plaster cast.

METHOD: MRI was carried out in 15 infants with 21 unstable hip joints after reduction under arthrographic control and fixation in a plaster cast in the 'human' position with the hips flexed above 90 degrees and abducted to 50 degrees or 60 degrees. When the reduction was found to be inadequate-the hip still partially or completely dislocated-the plaster cast was removed, reduction repeated, a new cast applied, and MRI carried out again.

RESULTS: After primary reduction, 1 of 21 hips was dislocated, and 2 showed unsatisfactory reduction. Three hip joints out of 21 (14.3%) were not fixed in the plaster cast in the optimal centred position.

CONCLUSION: In view of the number of inadequate reductions in plaster casts, we recommend verifying the position of the hip joint by MRI. This MRI documentation should be established as a standard examination post-reduction.