Increasing neuroforaminal volume by anterior interbody distraction in degenerative lumbar spine.

STUDY DESIGN

This study quantified changes in the size of the stenotic neuroforamen in degenerative lumbar spines. The volume and area of the neuroforamen were measured before and after the application of anterior distraction using the BAK interbody fusion system.

OBJECTIVE

To quantitatively assess the neuroforaminal area and volume when the BAK interbody fusion system is applied to lumbar spines with neuroforaminal stenosis.

SUMMARY OF BACKGROUND DATA

The spatial relationship between the nerve root and the osseous and nonosseous elements of the neuroforamen is clinically important. Few studies have focused on changes in neuroforaminal size in the lumbar spine after anterior interbody distraction. No previous study has assessed the neuroforaminal volume.

METHODS

The BAK instrumentation system was applied anteriorly at L4-L5 and L5-S1 intervertebral discs in nine degenerative cadaver lumbar spines. The neuroforaminal volumes of L4-L5 and L5-S1 were measured from silicon molds taken of the neuroforamen. In addition, computed tomography and circular blunt probes were used to determine the neuroforaminal areas. The disc height was recorded from lateral radiographs.

RESULTS

After the BAK instrumentation, the volume of the neuroforamen increased significantly--by 22.9% for L4-L5 and 21.5% for L5-S1. The posterior disc height increased by 37.1% at L4-L5 and 45.1% at L5-S1. The neuroforaminal areas significantly increased--by 29.0% at L4-L5 and 33.8% at L5-S1. There was good correlation between the volume and the posterior disc height (R2 = 0.50) and the volume and the area of the narrowest portion of neuroforamen (R2 = 0.56).

CONCLUSIONS

The results indicated that anterior systems such as the BAK system, which increase disc heights, can significantly increase neuroforaminal volume and area, providing adequate space for the nerve root and improving neuroforaminal stenosis.