Distinct Recovery Patterns After Transforaminal Lumbar Interbody Fusion: Comparing Minimally Invasive and Open Approaches Using Mixed-Effects Segmented Regression

OBJECTIVE: While minimally invasive-transforaminal lumbar interbody fusion (MIS-TLIF) has shown superiority in key clinical metrics over the open approach, evidence regarding patient-reported outcomes remains limited. This study compared postoperative recovery trajectories and symptomatic improvement phases between MIS and open TLIF. METHODS: This retrospective review included patients who underwent single-level MIS or open TLIF. Oswestry Disability Index (ODI) and Numerical Rating Scale (NRS) for back and leg pain were collected preoperatively and postoperatively. Segmented regression analysis with mixed-effects modeling, allowing for identification of distinct recovery phases, compared symptomatic trends between approaches. RESULTS: Of 324 patients (268 MIS, 56 open), baseline demographics were similar except for greater preoperative leg pain in the MIS group (NRS: 6.0 vs. 5.0, p = 0.027). A segmented regression model identified 4 ODI recovery phases: postoperative disability phase (PDP, day 0 to 13), early improvement phase (day 13 to 28), late improvement phase (day 28 to 110), and plateau phase (later than day 110). The MIS group exhibited significantly lower disability exacerbation during PDP (β = 0.93 vs. 1.42 points per day, p = 0.008). Additionally, the plateau of NRS back occurred significantly earlier in the MIS group than in the open group (MIS, 26.7 ± 2.6 days vs. open, 51.7 ± 6.6 days, p < 0.001). CONCLUSION: MIS-TLIF resulted in lower postoperative disability during the first 2 weeks compared to the open approach. Furthermore, low back pain achieved an earlier plateau in back pain by about 4 weeks in the MIS approach.