Combining the Michigan State University disc classification with the surgical corridor to anticipate perioperative technical events in single-level lumbar discectomy: A two-center cohort study

Background The Michigan State University (MSU) classification characterizes lumbar disc herniation by size and axial location but does not consider the operative corridor. This study describes an MSU-surgical corridor grade that integrates disc morphology with corridor accessibility and evaluates its association with perioperative technical events. Methods This retrospective two-center cohort study included 219 patients who underwent single-level lumbar discectomy. Cases were assigned to 3 grades according to the MSU disc size, location and the selected surgical corridor. The primary outcome was a composite event comprising prolonged operative time, extended bony work, incidental dural tear, and residual disc fragment requiring immediate revision. Secondary outcomes were minimal clinically important difference (MCID) achievement for leg pain, back pain, and Oswestry Disability Index (ODI)․ Multivariable logistic regression‚ receiver operating characteristic analysis‚ and sensitivity analyses were performed․ Results Composite events occurred in 18.8% of Grade 1, 45.4% of Grade 2, and 61.5% of Grade 3 cases (P < 0.001). Compared with Grade 1, adjusted event odds were higher for Grade 2 (odds ratio, 3.79; 95% confidence interval, 1.92–7.50) and Grade 3 (odds ratio, 7.39; 95% confidence interval, 2.76–19.79). The adjusted model showed moderate apparent discrimination (area under the curve, 0.731; 95% confidence interval, 0.661–0.802). Findings were consistent in microscopic and endoscopic sensitivity analyses. Conclusion The MSU-surgical corridor grade was independently associated with perioperative technical events and operative difficulty during single-level lumbar discectomy. The grade may improve preoperative technical risk stratification and operative planning․