A quantitative study of intervertebral disc morphologic changes following plasma-mediated percutaneous discectomy

Abstract

Objective: To quantitatively evaluate interval magnetic resonance imaging (MRI) changes in disc morphology following plasma-mediated percutaneous discectomy. Design/Setting: A retrospective comparison of pretreatment and posttreatment MRIs at a single university spine clinic. Subjects: From a group of 60 consecutively treated patients, 15 met the study inclusion and exclusion criteria. All had either failed treatment or had other clinical reasons for a posttreatment MRI. Methods: Two independent physicians electronically measured disc protrusion size and disc height at the treatment discs and adjacent discs on pre- and posttreatment MRI scans. Additionally, images were compared for gross anatomic changes including disc degeneration by Pfirrman classification, new disc herniations, high intensity zone (HIZ), vertebral endplate changes, post-contrast enhancement, and changes in segmental alignment. Pearson r correlation was used to determine interobserver reliability between the two physicians' MRI measurements. Paired t-tests were calculated for comparisons of pre- and posttreatment MRI measurements, and an ANOVA was performed for comparison of pre- to posttreatment changes in disc height measurements at treatment levels relative to adjacent levels. Results: Correlation was high for measurement of disc height change (r=0.89; P<0.0001) and good for anteroposterior protrusion size change (r=0.51; P=0.0512). Disc height at treated discs demonstrated a small but statistically significant mean interval reduction of 0.48mm (P=0.0018). This remained significant when compared with the adjacent control discs (P<0.0001). Pretreatment mean disc protrusion size (4.74mm; range 3.75-6.55mm) did not differ significantly (P=0.1145) from posttreatment protrusion size (4.42mm; range 2.55-7.95mm). Gross anatomic changes at treatment levels included reduced disc protrusion size (N=6), enlarged protrusion (N=3), resolution of HIZ (N=3), and improvement in endplate signal changes (N=1). Also, 11/15 posttreatment MRIs included post-contrast images that showed epidural fibrosis (N=1), rim enhancement (N=2), and enhancement of the posterior annulus (N=4). Conclusions: Based on MRI examinations, subtle anatomic changes may occur following plasma-mediated percutaneous discectomy. Further study is required to determine the clinical relevance of these changes.