Objective:

Changes in indirect decompression using lateral lumbar interbody fusion (LLIF) were classified into three clusters based on cluster analysis. We investigated cage variables and position to assess the effects of single-level LLIF on indirect decompression.

Methods:

Cluster analysis was used to classify patients into three groups based on the change in the axial cross-sectional spinal canal area (ΔCSA): group 1 with slight postoperative indirect decompression (n = 35); group 2 with average indirect decompression (n = 19); and group 3 with marked indirect decompression (n = 13). Preoperative and immediately postoperative imaging data were compared between groups.

Results:

Postoperative segmental lordosis, anterior, posterior, and average disc height increased significantly in each group, but the differences between groups were not significant. Cage length (p = 0.251) and cage height (p = 0.709) did not differ, but cage position differed significantly between groups (p < 0.05). ΔCSA correlated significantly with cage position for all 67 levels (r = 0.411, p < 0.01), but this association was not significant in group 2 (r = - 0.367, p = 0.122) or group 3 (r = - 0.005, p = 0.986). ΔCSA correlated with cage height in group 2 (r = 0.645, p < 0.01) and with cage width in group 3 (r = 0.644, p < 0.05).

Conclusions:

The cluster analysis results suggest that placing the cage in the posterior position might be effective for expanding the CSA, but other factors, such as cage height or width, may also influence the sufficiency of LLIF.