MRI scans were obtained before surgery and the AP and lateral plain radiographs were obtained before surgery, immediately after surgery, at 6 weeks, 3 months, and 6 months after surgery and the last follow-up. Flexion-extension lateral views were also obtained from 3 months after surgery. The anterior segmental height (ASH), posterior segmental height (PSH) (Fig. 1A ) and cage distance (CD: the distance from the anterior edge of the upper vertebra to the anterior margin of the cage) (Fig. 1B ) were measured on the radiographs. The ratio of the AP diameter at the middle of the upper vertebral body on the radiographs to that on the MRI scans was used to correct for the magnification difference of each image (Fig. 1C ). The ASH and PSH values were used to assess the anterior/posterior intraoperative distraction and the anterior/posterior subsidence. The ASH/PSH was measured as the distance between the anterior/posterior margin of the upper end plate of the upper vertebra and the anterior/posterior margin of the lower end plate of the lower vertebra. The anterior/posterior intraoperative distraction was calculated as a difference in the ASH/PSH between before surgery and immediately after surgery. Anterior/posterior subsidence was defined as ≥ a 2 mm (minor subsidence) or 3 mm (major subsidence) reduction in the ASH/PSH between immediately after surgery and the last follow-up. The patients with ≥ 2 mm subsidence were classified as the subsidence group.
Segmental lordosis was measured using Cobb's method to assess the sagittal alignment (Fig. 1D ). The increase in lordosis from before surgery to immediately after surgery and the decrease in lordosis from immediately after surgery to the last follow-up were recorded.
Nonunion was defined as the appearance of segmental instability with ≥ 2 mm widening of the interspinous distance on the flexion-extension lateral views at the last follow-up.
Radiological assessments were performed by an independent orthopedic surgeon on two occasions with using two PACS digital software systems: a Marosis 5.0 PACS viewer (Marotech, Seoul, Korea) and an Impax CS 5000 (Agfa-Gevaert, Mortsel, Belgium).
Segmental lordosis was measured using Cobb's method to assess the sagittal alignment (
Nonunion was defined as the appearance of segmental instability with ≥ 2 mm widening of the interspinous distance on the flexion-extension lateral views at the last follow-up.
Radiological assessments were performed by an independent orthopedic surgeon on two occasions with using two PACS digital software systems: a Marosis 5.0 PACS viewer (Marotech, Seoul, Korea) and an Impax CS 5000 (Agfa-Gevaert, Mortsel, Belgium).
