Fig. 2

Serial radiographs of a representative case underwent contiguous two-level (C4/5 and C5/6) cervical disc arthroplasty. The series showed the sagittal area loss of middle vertebra. The changes in middle vertebral body profile are highlighted, with a yellow outline indicating the reference profile of 1-week post-operative and red outlines indicating the profile of each follow-up thereafter. a Pre-operative lateral radiograph of the cervical spine; b 1-week post-operative lateral radiograph showed cervical disc arthroplasty at C4/5 and C5/6 levels; c Early follow-up lateral radiograph showed moderate ABL at the anterior part of middle vertebral body; d and e Late follow-up lateral radiographs showed no obvious progress of anterior bone loss, but high-class heterotopic ossification developed at the posterior edge of caudal endplate. Sagittal area of C5 (follow-up time): 181mm² (1 week), 172mm² (6 months), 178mm² (48 months), 179mm² (84 months)