To evaluate long-term changes in sagittal plane of the lumbar spine in patients with anterior lumbar interbody fusion and pedicle instrumentation and to determine the influencing factors.

Eighty-seven patients underwent single level anterior lumbar interbody fusion with pedicle instrumentation. Each patient's disc space height and segmental sagittal angle was measured preoperatively, immediate postoperatively, and at the last follow-up.

Immediate postoperative radiographs demonstrated an average increase in disc space height of 2.8 mm. The follow-up radio-graphic evaluation showed an average decrease of 4.2 mm from the immediate postoperative period and 1.4 mm from the preoperative period. Sagittal angles of the preoperative, postoperative and follow-up period were 10.3 °, 14.2° and 10.4°, respectively. Decrease in disc space height correlated with patient's age and the amount of distraction by the operation.

Our data demonstrated that the change in the sagittal plane obtained by anterior lumbar interbody fusion with pedicle instrumentation is lost in the postoperative period. Most levels return to their original height or less. This finding suggests that a disc space distraction by this technique in elderly patients with kyphotic deformity is not reliable.