The intervertebral disc has an important role in the spinal biomechanics. The influence of lumbar discectomy on the disc space height is still uncleared. This study was performed to evaluate the long term influence of lumbar discectomy on intervertebral disc space height.

The author analysed the disc space height in 25 patients who had performed open discectomy for the disc herniation at least two years age. The height was compared with that of unoperated disc and evaluated the role of discectomy in the change of disc space height.

The decrease of disc space height was 3.3mm in average. The loss of anterior height was 4.1mm and that of posterior height was 2.5mm. This discrepancy was statistically significant(p<0.05). Although the difference of disc height loss in each disc space was not significant. the loss in L4-5 disc space was greater than that of other disc space.

These data suggest that lumbar discectomy accelerate the loss of disc height and influence the process of vertebral degeneration by change of spinal biomechanics in long term period.

In order to evaluate clinical significance of MR signal change within vertebral body marrow, we investigated the relationship between signal change of marrow and duration of low back pain, hight of disc, segmental hypermobility, disc degeneration and degree of disc herniation.

We reviewed retrospectively simple radiograph, flexion-extension dynamic radiograph and MR images of the lumber spines(L3-S1) of 100 patients, who underwent discectomy at Ewha Womans University Mokdong Hospital from September 1993 to October 1996.

1) There were Modic type 2 changes in 36 patients of 100 patients(36%) and in 52 segments of 300 segments(17.3%). 2) Average was older in the group with signal change in marrow than in that without signal change. 3) Signal change of vertebral body marrow was not significantly related to duration of low back pain. 4) Decreased disc heght was more frequently found in segments with signal change in marrow than in those without signal chagne. 5) Modic type 2 changes was not related to lumbar segmental hypermobility. 6) Degeneration of disc was more frequently found in segments with signal change in marrow than in those without signal change. 7) Signal change of vertebral body marrow was not directly related to degree of disc herniation.

Signal change of vertebral body marrow in MRI was significantly related to age, disc height and degree of disc degeneration, and it suggests that the marrow change can be induced by response of vertebral body to the changed mechanical environment, which is due to long-standing disc degeneration.