Letter to “Effect of Baseline Adjacent Segment Degeneration on Clinical Outcomes After Lumbar Fusion”

Dear Editor,

We read with great interest the article by Toivonen et al on the impact of preoperative adjacent segment degeneration on long-term outcomes following lumbar spine fusion. ¹ The authors provide valuable insights into the role of end-stage degenerative segments, suggesting that these segments, when devoid of stenosis, may be safely excluded from fusion constructs. While the study is commendable for its robust methodology and long-term follow-up, we would like to raise several points for further discussion and consideration.

First, the finding that end-stage degeneration (CIS >10) is associated with lower reoperation rates and better functional outcomes compared to intermediate degeneration (CIS 7-10) is intriguing. The authors suggest that the natural collapse of motion segments in end-stage degeneration may stabilize the spine and reduce pain. However, this raises a clinical question: should surgeons actively avoid fusing end-stage segments even when mild stenosis is present? While the study excluded stenotic segments, in real-world practice, mild stenosis is often encountered in end-stage degeneration. Could such cases still benefit from exclusion, or would this increase the risk of postoperative complications such as residual radiculopathy?

Second, the authors report that postoperative sagittal alignment, including PI-LL mismatch, did not significantly influence long-term functional outcomes. While this finding is consistent with prior studies in degenerative populations, ² it contrasts with the established importance of sagittal balance in deformity surgery. ³ This discrepancy underscores the need for a more tailored approach to sagittal alignment in degenerative spine disorders. For instance, should surgeons prioritize achieving optimal sagittal alignment only in patients with severe preoperative imbalance, or is it sufficient to focus on localized decompression and stabilization in most degenerative cases?

Third, the study relies on the CIS as a measure of degeneration is a strength, as it integrates multiple radiographic and MRI parameters. However, the clinical applicability of CIS in routine practice may be limited by its complexity. Simplified scoring systems, such as the Pfirrmann classification, are more commonly used but lack the resolution to differentiate advanced degeneration. ⁴ Could a streamlined version of CIS be developed to balance accuracy and practicality, thereby facilitating its adoption in clinical settings?

Finally, the authors concluded that end-stage degenerative segments can be safely excluded from fusion constructs is compelling but warrants caution. While the study demonstrates favorable outcomes in this cohort, it is important to consider patient-specific factors such as activity level, comorbidities, and overall spinal alignment. For example, in younger, more active patients, excluding end-stage segments might predispose them to future degeneration and instability.

In conclusion, Toivonen et al provide valuable evidence supporting the selective exclusion of end-stage degenerative segments in lumbar fusion surgery.