Confirmation of the reduction and containment of the femoral head with CT or MRI scans in DDH: The need for repeated scans

The accuracy of reduction of the femoral head in the acetabulum after the application of plaster casts in open and closed reduction was retrospectively assessed by means of CT or MRI scan in 59 patients and 67 hips. Scanning after the first plaster application showed that the position was not maintained in the hip spica in 1 out of 37 patients (3%), who had undergone open reduction, and 8 out of 30 (27%), who had undergone closed reduction. All hips shown to be reduced and contained at the time of the first scan, and held in a spica remained reduced on subsequent scans. This study shows that the hip is vulnerable to redisplacement, especially after closed reduction, but stabilises after the first 6 to 8 weeks in plaster. This suggests therefore that repeating the scan after each plaster change was not necessary, and that resources could be conserved. This study has also shown that all the 113 CT scans clearly defined the anatomy but 6 out of the 33 MRI scans were blurred and needed repeating.