Introduction: Spinal fusion as a treatment for degenerative disc disease is controversial. Prior authors have identified various MRI findings as being pain generators, which might help guide patient selection for lumbar fusion procedures. These findings have included disc desiccation, disc contour, high-intensity zone annular disruption, the presence of Modic endplate changes, and disc space collapse. The purpose of this study is to investigate which MRI findings in patients with degenerative disc disease predict clinical improvement with lumbar fusion.
Methods: A single-center surgical database of patients undergoing lumbar fusion was reviewed for patients whose indication for fusion surgery was primary disc pathology. We identified 51 patients (71 disc levels) who had completed 2-year prospectively collected outcomes questionnaires and had preoperative MRIs available for review. NRS (0-10) back and leg pain, Oswestry Disability Index (ODI) and SF-36 Physical Composite Summary scores were obtained preoperatively and at 1- and 2-year follow-up. MRIs were reviewed by three fellowship-trained spine surgeons who were asked to grade them for the following five characteristics: (a) disc desiccation, (b) disc contour, (c) presence of a high-intensity zone (HIZ) annular tear, (d) presence of Modic endplate changes and (e) disc height. Two-year outcome measures were compared to MRI findings to identify which findings correlated with improvement in outcome scores.
Results: Statistically significant improvements were noted in back pain, leg pain, SF-36 PCS and ODI in the group overall. Disc desiccation, disc contour, presence of an HIZ lesion, and the presence of Modic endplate changes did not correlate with 2-year outcomes. Disc height was correlated with 2-year change in outcome measures. Discs with preoperative height less than 5 mm demonstrated a 23.4 point ODI improvement compared to 9.2 points for discs >7 mm. Similarly, SF-36 PCS improved 9.5 points in discs <5 mm compared to 0.7 in discs greater than 7 mm. Discs between 5 and 7 mm demonstrated intermediate levels of improvement.
Conclusions: Several commonly utilized MRI criteria proposed as indications for lumbar fusion do not seem to correlate with 2-year improvement in clinical outcomes. Discs which are narrowed and collapsed, preoperatively, demonstrate better improvement at 2 years postoperatively as compared to discs which have maintained disc height. Significant disc space collapse may represent a subset of "degenerative disc disease" which responds more favorably to treatment with fusion.