Objective: To compare radiographic parameters at adjacent segments before and after minimally invasive transforaminal lumbar interbody fusion and assess relationships of radiographic changes between adjacent segments and fused level.
Methods: Study participants included 44 patients who underwent minimally invasive transforaminal lumbar interbody fusion at L4-5 level. Radiographic parameters at adjacent segments (L3-4 and L5-S1) and clinical parameters were reviewed.
Results: Postoperative dural sac area 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 upper (0.85 mm, P < 0.001) and lower (0.66 mm, P < 0.001) adjacent segments. Ligamentum flavum thickness significantly decreased in lower adjacent segments (-0.37 mm, P = 0.006). For every 1-mm increase in fused level disc height, lower SAPD increased 0.22 mm (P = 0.04), and lower segmental angle increased 0.91° (P = 0.04). For every 1° increase in fused level segmental angle, lower dural sac area increased 1.25 mm2 (P = 0.03), and lower SAPD increased 0.12 mm (P = 0.003). The 6- and 12-month postoperative visual analog scale back and leg scores significantly decreased compared with preoperatively (back: mean change -5.98 and -6.05, P < 0.001; leg: -6.86 and -6.89, P < 0.001).
Conclusions: Performing minimally invasive transforaminal lumbar interbody fusion at the symptomatic index level does not worsen canal dimension of asymptomatic adjacent segments during short-term follow-up. It might be possible to improve canal dimension at adjacent segments by changing disc height or lordosis at the fused level via adjusting size and position of the interbody cage.
Keywords: Adjacent segment; Canal dimension; Dura sac area; MIS-TLIF; Minimally invasive.
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