Long-term Follow-up Motion Analysis of ACD Versus ACDA

Cinematographic recordings will be made. Participants are seated on a crutch, adjustable in height, with their neck, shoulders and head free. Before recordings are made, participants will be instructed to perform the prescribed flexion and extension movement in about 10 seconds with 7 frames per second. Participants are placed on the crutch with their shoulder's perpendicular to the image intensifier to obtain sagittal images from the occiput till C7. As soon as the recording is started, the participant is instructed to move his head in the sagittal plane from maximal extension to maximal flexion, without moving the upper part of the body. It is important that the participants shoulders are kept as low as possible while making the recordings to ensure that all the cervical vertebrae are visible. The movement of the cervical spine should be as fluent as possible to prevent for sudden large rotations and translations between consecutive frames.