Objective: Determine if herniation morphology based on the Michigan State University Classification is associated with differences in (1) patient-reported outcome measures (or (2) surgical outcomes after a microdiscectomy.
Methods: Adult patients undergoing single-level microdiscectomy between 2014 and 2021 were identified. Demographics and surgical characteristics were collected through a query search and manual chart review. The Michigan State University classification, which assesses disc herniation laterality (zone A was central, zone B/C was lateral) and degree of extrusion into the central canal (grade 1 was up to 50% of the distance to the intra-facet line, grade >1 was beyond this line), was identified on preoperative MRIs. patient-reported outcome measures were collected at preoperative, 3-month, and 1-year postoperative time points.
Results: Of 233 patients, 84 had zone A versus 149 zone B/C herniations while 76 had grade 1 disc extrusion and 157 had >1 grade. There was no difference in surgical outcomes between groups (P > 0.05). Patients with extrusion grade >1 were found to have lower Physical Component Score at baseline. On bivariate and multivariable logistic regression analysis, extrusion grade >1 was a significant independent predictor of greater improvement in Physical Component Score at three months (estimate = 7.957; CI: 4.443-11.471, P < 0.001), but not at 1 year.
Conclusions: Although all patients were found to improve after microdiscectomy, patients with disc herniations extending further posteriorly reported lower preoperative physical function but experienced significantly greater improvement three months after surgery. However, improvement in Visual Analog Scale Leg and back, ODI, and MCS at three and twelve months was unrelated to laterality or depth of disc herniation.
Keywords: Classification; Disc herniation; Lumbar spine; Microdiscectomy; Outcomes; Patient-reported outcomes.
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