Purpose:

To analyse the progression of disc degeneration in distal unfused lumbar segments in post-operative Adolescent Idiopathic Scoliosis (AIS) patients; and to evaluate pre-operative and post-operative radiological parameters associated with progressive disc degeneration.

Methods:

A retrospective study of patients, who underwent surgery for AIS between 2006 and 2013 at a tertiary-care spine hospital, was conducted. Only patients aged between 11 and 18 years, who underwent deformity correction surgery with pedicle screw-only constructs, minimum of 6.5 year follow-up, and complete radiological data, and were included. On plain radiographs, coronal cobb’s angle (CCA), apical translation, lower instrumented vertebra tilt (LIV tilt), LIV-Sacral angle, and sagittal spinal and pelvic parameters were measured. Disc degeneration was assessed on Magnetic Resonance Imaging (MRI) using Pfirrmann’s grading. Total endplate score (TEPS) and facet degeneration (by Fujiwara’s grading) were also measured. Based on the difference in progression of disc degeneration, patients were classified as Pfirrmann’s grade static (PGS) and Pfirrmann’s grade progressive (PGP) groups. Comparison of all pre- and post-operative parameters was made between PGS and PGP groups, and statistically analyzed. Functional evaluation was performed using SRS-22 score.

Results:

A total of 58 patients were finally included. The mean follow-up was 9.1 years. 43 (74.1%) and 15 (25.9%) patients were classified under PGS and PGP groups, respectively. Among the15 patients in PGP group, selected LIV was L4 in 8, L3 in 3, L1 in 3, and L2 in 1. Among them, 11 patients (73.3%) progressed from grade 1 to grade 2. In the remaining 4 (26.6%), Pfirrmann’s grade progressed to ≥ 3. The progression of disc degeneration did not correlate with age or sex distribution (p = 0.3), pre-operative and post-operative TEP scores (p = 032), pre-operative disc or facet degeneration (p = 0.52), number of unfused spinal segments (p = 0.56), pre-operative or post-operative coronal (p = 0.42), or sagittal spinal (p = 0.27) or pelvic parameters (p = 0.14). The final functional outcome (SRS-22) was not significantly different between PGS and PGP groups (p = 0.67).

Conclusion:

74% of AIS patients demonstrated no signs of progressive disc degeneration at an average follow-up of 9.1 years. 26% (15/58) of AIS patients demonstrated progressive disc degeneration, among whom, degeneration progressed by only 1 Pfirrmann’s grade in 74% (11/15). In the remaining four patients, disc degeneration progressed to Pfirrmann’s grades 3 or greater. There was no correlation between higher grades of disc degeneration and lower instrumented vertebra (LIV) or functional outcomes scores (SRS-22).