Objectives:

To compare radiographic parameters at adjacent segments between before and after MIS-TLIF and to assess relationships of radiographic changes between adjacent segments and fused level.

Methods:

Forty-four patients who underwent MIS-TLIF at L4/5 level were examined. The radiographic parameters at adjacent segments (L3/4 and L5/S1), including dural sac area (DSA), sagittal spinal AP diameter (SAPD), ligamentum flavum area (LFA), ligamentum flavum thickness (LFT), foraminal height (FH), disc height (DH), segmental angle (SA), and lumbar lordosis (LL) were reviewed. The clinical parameters were also reviewed.

Results:

Post-operative DSA significantly increased in upper (mean change 8.05 mm², P<0.001), and lower (14.08 mm²; P<0.001) adjacent segments. Significant increases in SAPD were seen in both upper (0.85 mm; P<0.001), and lower (0.66 mm; P<0.001) adjacent segments. LFT significantly decreased in lower adjacent segments (-0.37 mm; P=0.006). For every 1-mm increase in FDH, lower SAPD increased 0.22 mm (P=0.04), and lower SA increased 0.91° (P=0.04). For every 1° increase in FSA, lower DSA increased 1.25 mm² (P=0.03), and lower SAPD increased 0.12 mm (P=0.003). 6- and 12-month post-operative VAS of back and leg significantly decreased compared to pre-operative period (mean change -5.98, -6.05; P<0.001 for back and -6.86, -6.89; P<0.001 for leg).

Conclusion:

Performing MIS-TLIF at the symptomatic index level does not worsen canal dimension of the asymptomatic adjacent segments in short-term period. In contrast, there might be a possibility to improve canal dimension at the adjacent segments by changing disc height or lordosis at the fused level via adjusting size and position of interbody cage.