Thoracolumbar Deformity Arthrodesis Stopping at L5: Fate of the L5-S1 Disc with a Minimum 5-Year Follow-Up

Purpose: Evaluate the fate of L5-S1 disc analyzing subsequent disc degeneration and associated risk factors for degeneration.

Methods: Thirty consecutive patients with an average age 45years(20-62yo)were fused from the thoracic spine to L5 and were evaluated at a mean follow-up of 8.7 years(5-15.5). Patients were evaluated preoperatively, postoperatively, and latest follow-up with radiograps and SRS scores. Disc degeneration utilizing validated radiographic Weiner grades. Grade 0-1 discs were "healthy" and grade 2-3 were degenerated. Patients with "healthy" discs preop that subsequently degenerated were designated subsequent advanced degeneration(SAD).

Results: 2/30 patients had preoperative advanced degeneration of the L5-S1 disc(Weiner Grade 2-3). 28/30 patients were assessed as "healthy discs" preop (Weiner Grade 0-1). By latest follow-up, subsequent advanced L5-S1 disc degeneration(SAD) developed in 19 of these 28 patients(68%) who had "healthy" discs. Younger age at the time of surgery is an associated risk factor for developing SAD(p=0.04). Preop sagittal balance was not significantly different between those patients that developed SAD and those who did not. 17/30 patients(57%) were noted to have sagittal imbalance >5cm at follow-up. At most recent follow-up the average sagittal imbalance in the SAD group was 72mm. In the "healthy" group it was 3mm (p=0.001). 6/30 patients(20%) were revised with extension to the sacrum. There was a trend toward inferior SRS pain scores at follow-up in SAD patients(avg. score-4.0 vs 3.2,p=0.08).

Conclusion: Advanced L5-S1 DDD developed in 68% of deformity patients after long fusions to L5 with 5-15 year follow-up. SAD frequently results in significant positive sagittal balance with minimum 5year follow-up.