Serial changes in signal intensities of the adjacent discs on T2-weighted sagittal images after surgical treatment of cervical spondylosis: Anterior interbody fusion versus expansive laminoplasty

Background. There have been many reports about newly developed degenerative changes in the adjacent segments after anterior interbody fusion. It is a controversial issue whether the adjacent-segment disease in patients treate d by anterior interbody fusion is the result of progressive cervical spondy losis at the adjacent levels or is caused by the arthrodesis. The aim of th is study is to clarify the difference in postoperative effect on the adjace nt segments between anterior interbody fusion and expansive laminoplasty. Method. This study included 14 patients who underwent pre- and postoperativ e MR images at 6 and 12 months. Seven patients underwent cervical interbody fusion and the other 7 patients underwent expansive laminoplasty. Disc deg eneration was evaluated semiquantitatively by calculating the degenerative index (DI) that is a ratio of the intensity in the disc to that in the uppe r cervical cord. Findings. In the anterior interbody fusion group, the adjacent disc intensi ties decreased within 12 months (F = 20.42; P < 0.01). The pre-operative me an DI was 0.59 +/- 0.16. The post-operative mean DIs were 0.56 +/- 0.16 at 6 months and 0.47 +/- 0.16 at 12 months. In the expansive laminoplasty grou p, the signal intensities of both the adjacent discs and the discs within t he range of laminoplasty had no serial changes during the same period (F = 2.67; P = 0.09 and F = 0.15; P = 0.87 respectively). Interpretation. Anterior interbody fusion had a significant influence on th e adjacent discs even as soon as 12 months after surgery, but laminoplasty had no influence on them during the same period.