The authors describe the operative principles of the C.D. device reviewing implantable material (rods and hooks, screws and transverse system). The principles of this surgical approach (2 rods) which offers the possible distraction and contraction where necessary, are described. Good derotation is achieved and a strong and stable square support device enabling the patient to be got out of bed rapidly without any need for post-operative support. The post-operative care is extremely easy and a rapid return to school activity is possible.