The Ideal Cage Position for Achieving Both Indirect Neural Decompression and Segmental Angle Restoration in Lateral Lumbar Interbody Fusion (LLIF).

STUDY DESIGN

A prospective radiographic analysis.

OBJECTIVE

To assess the ideal cage position for lateral lumbar interbody fusion (LLIF) together.

SUMMARY OF BACKGROUND DATA

Achieving both indirect decompression and restoration of the segmental angle (SA) appear to be contrary to one another because the anteriorly located cage might be advantageous for restoring the SA, and posteriorly located cage might be favorable for achieving the indirect decompression effect. Little has been known about the significance of cage position in LLIF.

METHODS

Forty-one patients who underwent LLIF followed by percutaneous pedicle screw fixation for 94 levels were evaluated. Postoperative plain radiographs and magnetic resonance images were obtained 3 days after surgery. The cage position was determined by the anterior, middle, and posterior portions. The anterior and posterior disk heights, SA, cross-sectional area of the thecal sac (CSA), and the foraminal area (FA) were compared according to the cage position.

RESULTS

The cage was placed in the anterior area for 31 levels and middle for 63 levels. The cage height was 13.0±1.3 degrees. The increases in anterior disk height and SA were significantly greater in the anterior group (9.1 mm, 6.1 degrees) than those of the middle group (6.7 mm, 2.4 degrees). Posterior disk height increased by a mean of 4.5 mm, but its change did not differ according to the cage position. CSA and FA increased by 36.5% and 69.6%, respectively. There were no significant differences in the CSA and FA increases with respect to the cage position. Regression analysis showed that the increase of SA was affected by cage position, but the increase ratios of CSA and FA were not affected.

CONCLUSIONS

The cage position within the anterior 1/3 of disk space is better for achieving the restoration of the SA without compromising the indirect neural decompression, if the height of cage is large enough.