Background Many studies have reported that minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) provides satisfactory treatment comparable to other fusion methods. However, in the case of MI-TLIF, there are concerns about the long-term outcome compared to conventional bilateral PLIF due to the small amount of disc removal and the lack of autogenous bone graft. Long-term follow-up studies are still lacking as most of the previous reports have follow-up periods of up to 5 years. Methods Thirty patients who underwent MI-TLIF were followed up for > 10 years (mean, 11.1 years). Interbody fusion rates were determined using a modified Bridwell grading system. Adjacent segment disease (ASD) was defined as radiological adjacent segment degeneration (R-ASDeg) as seen on plain X-rays; reoperated adjacent segment disease referred to the subsequent need for revision surgery. Clinical outcomes after surgery were assessed based on back and leg pain as well as the Oswestry disability index (ODI). Results The overall radiological fusion rate, at the 1-, 5-, and 10-year follow-up was 77.1%, 91.4%, and 94.3%, respectively. The incidence of R-ASDeg 1, 5, and 10 years after surgery was 6.7%, 16.7%, and 43.3% at the proximal adjacent segment and 4.8%, 14.3%, and 28.6% at the distal adjacent segment, respectively. R-ASDeg at either the proximal or distal segment was determined in 50.0% of the patients 10 years postoperatively. All clinical parameters improved significantly during follow-up, although the ODI and the visual analog scale (VAS) for leg pain at the 10-year follow-up were significantly worse in the R-ASDeg group than in the other patients ( P = 0.009, P = 0.040). Conclusion MI-TLIF improved both clinical and radiological outcomes, and the improvements were maintained for up to 10 years after surgery. However, R-ASDeg developed in up to 50% of the patients within 10 years, and both leg pain on the VAS and the ODI were worse in patients with R-ASDeg.

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Background To evaluate the accuracy of percutaneous pedicle screw (PPS) insertion in degenerative lumbar disease treated with minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) and to analyze risk factors and long-term clinical outcomes of screw violation. Methods Sixty-two consecutive patients (262 screws) were included. Based on postoperative computed tomography (CT) axial images, a PPS that perforated out of the pedicle was classified into a violation group, while screws surrounded by pedicular cortical bone were classified into a correct group. A logistic regression model was used for risk factor analysis of violation. We also observed the long-term clinical outcomes using the Oswestry disability index and visual analog scale. Results Of the 262 screws, 14 (5.3%) were considered to be violated (10 medial violations and 4 lateral violations). All violations of S1 and L5 were in the medial direction. In contrast, entire violations of L4 were always lateral and of the 2 violations of L3, one was lateral and the other was medial. There were no cases of superior or inferior violation. The mean pedicle convergence angle (CA) was significantly higher in the violation group (mean ± standard deviation, 27.0° ± 6.2°) than in the correct group (21.7° ± 5.4°). There were no significant differences according to vertebral rotational angle, body mass index, bone mineral density, and surgical timing (learning curve) between the two groups. Logistic regression analyses demonstrated that a high CA was a significant risk factor for pedicle wall violation ( p = 0.002). There were no significant differences in clinical or radiographic results between the two groups in 60 patients who were followed up for more than 1 year and in 40 patients who were followed up for more than 5 years. There were 2 patients who required reoperation to replace a screw due to leg pain. Conclusions With PPS insertion during MI-TLIF, the rate of pedicle violation was 5.3% (14/262). An understanding of the anatomical characteristics of each vertebra and the unique structures of the patient is essential to prevent pedicle violations. Even in the violation group, PPS fixation was found to be a safe and useful procedure with successful long-term radiographic and clinical outcomes.

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