Learning Curve of MIS-TLIF using 22 mm-tubular Retractor in Degenerative Spondylolisthesis (Grade 1-2) - A Review over 100 Cases

Objective To evaluate the learning curve of MIS-TLIF in degenerative spondylolisthesis with understanding of problems and challenges faced during initial cases. Methods After taken approval from institutional review board, first 109 patients who underwent MIS-TLIF for singlelevel low-grade degenerative spondylolisthesis between 2010 to 2015 were evaluated. First 100 cases that formed the study cohort at final follow-up were arranged sequentially in order of date of operation and then grouped in four quartiles. Comprehensive data which included demographics, clinical parameters, surgical parameters, peri-operative incidents (dural tear, technical issues like guide-wire migration, tube docking problems) and complications were assessed. Results Median operative time, median blood loss and median radiation exposure gradually decreased as the series progressed, however, showed statistically significant difference between Q1 and Q2 with no significant difference between later quartiles. There was a significant decline in postoperative VAS and ODI scores in all quartiles, however, there was no statistically significant difference in their values on comparison between quartiles. Guide-wire migration, dural tear and tube docking related problems, pedicle screw perforation significantly reduced after 1st quartile. Conclusion MIS-TLIF is safe and effective means of treating lumbar spondylolisthesis. The learning curve is achieved between 1st and 2nd quartile (25th to 50th cases). Familiarity with instrumentation, preoperative anatomical planning, better coordination with surgical team and hands-on tissue-training are keys to reduce the learning curve.