Spine surgeons frequently face a critical operative dilemma when planning arthrodesis for adult spinal deformity and degenerative disc disease. Deciding on the optimal lumbar fusion stopping level represents one of the most debated topics in modern reconstructive spinal surgery. Historically, surgical dogma suggested that terminating a long lumbar construct at the upper lumbar spine, particularly at L1, dramatically elevates mechanical stress. Consequently, surgeons often crossed the thoracolumbar junction into the lower thoracic spine, aiming for T10, T11, or T12 to prevent rapid junctional breakdown. However, crossing into the thoracic cage increases surgical invasiveness, blood loss, operative duration, and overall perioperative morbidity.

The Thoracolumbar Junction Dilemma in Spinal Arthrodesis

The transition between the rigid thoracic cage and the mobile lumbar lordosis creates significant biomechanical forces. Because the thoracolumbar junction experiences substantial rotational and shear stress, terminating instrumentation at L1 has long raised concerns regarding proximal junctional failure and adjacent segment pathology. Therefore, many practitioners routinely extended instrumented constructs to T10 or T11 to achieve superior biomechanical anchorage. Nevertheless, this traditional assumption lacks robust, long-term comparative validation from large registries. Extending fusion unnecessarily exposes frail or elderly patients to greater tissue disruption and longer recovery times. Consequently, contemporary spine specialists increasingly seek clear clinical evidence to justify whether extending fusions across the thoracolumbar junction truly reduces revision surgeries.

Methodology and Cohort Profile for Lumbar Fusion Stopping Level

To investigate whether this longstanding surgical principle holds true, investigators conducted a rigorous retrospective cohort study utilizing data from an integrated healthcare system registry. They examined adult patients undergoing primary lumbar fusion for degenerative disc disease or adult lumbar deformity. Specifically, the study analyzed the comparative impact of selecting a lumbar fusion stopping level at L1 versus extending the construct proximally to T10, T11, or T12. The final study cohort included 227 patients whose fusions stopped at L1 and 228 patients whose constructs terminated at T10, T11, or T12. The overall cohort demonstrated a mean age of 68.4 years and an extensive mean follow-up period of 6.3 years. Furthermore, investigators applied propensity score-weighted Cox proportional hazards regression models to balance baseline confounders while evaluating reoperation risks.

Operative Adjacent Segment Disease Rates and Comparison

The primary clinical outcome centered on reoperations required for symptomatic adjacent segment disease, termed operative adjacent segment disease. When analyzing constructs ending caudally at L5, researchers observed no statistically significant difference in operative adjacent segment disease between fusions stopping at L1 versus those terminating at T10, T11, or T12. Similarly, for constructs terminating caudally at S1, terminating at L1 did not significantly increase revision risk compared to thoracic termination. In addition, subgroup analyses evaluated both short-segment constructs terminating at L3 through L5 and long-segment constructs terminating at L5, S1, or the ilium. Across these configurations, stopping at L1 demonstrated statistically comparable hazard rates for revision surgery relative to extending instrumentation into the thoracic spine. Therefore, the data suggest that proximal extension does not inherently protect patients from adjacent breakdown requiring surgical revision.

Nonunion Reoperation Risks Across Fusion Constructs

In addition to junctional degeneration, pseudarthrosis represents a major indication for revision spinal surgery. Long-segment fusions crossing multiple motion segments face substantial strain, which may impair solid bony consolidation. In this registry cohort, researchers evaluated the incidence of reoperations performed specifically for symptomatic nonunion across different construct lengths. When analyzing long-segment fusions, the propensity score-weighted models demonstrated no statistical difference in operative nonunion between constructs terminating at L1 and those extending to T10, T11, or T12. Consequently, crossing the thoracolumbar junction did not provide measurable protection against mechanical pseudarthrosis. Furthermore, terminating at L1 preserved thoracic motion segments without compromising the rate of successful arthrodesis. These findings provide compelling objective evidence that upper lumbar termination does not inherently elevate nonunion failure rates.

Clinical Implications for Reconstructive Spine Surgery

These findings offer practical insights for spine surgeons, orthopedic specialists, and neurosurgeons managing complex degenerative lumbar disorders. Historically, surgeons frequently extended fusion to T10 out of abundance of caution, accepting higher surgical morbidity to avoid proximal junctional reoperations. However, the comparable revision rates demonstrated in this long-term cohort challenge the routine necessity of this practice. By terminating stable constructs at L1 when appropriate, surgeons can preserve native thoracolumbar kinematics and reduce muscular dissection. Furthermore, minimizing construct length reduces implant costs, operative time, intraoperative hemorrhage, and hospital length of stay. Nonetheless, clinicians must still carefully evaluate regional alignment parameters, bone mineral density, and sagittal balance when individualizing upper instrumented vertebra selection.

Future Directions and Individualized Surgical Planning

Although this study provides substantial real-world evidence against routinely crossing the thoracolumbar junction, individualized decision-making remains paramount. The authors emphasize that further prospective studies must evaluate whether these findings remain uniform across specific caudal endpoints, particularly constructs ending at L2, L3, L4, or those incorporating pelvic fixation with iliac screws. In addition, future investigations should correlate patient-reported outcome measures, functional recovery scores, and radiographic sagittal vertical axis correction with reoperation endpoints. In conclusion, surgeons should avoid dogmatic construct extensions and instead tailor the upper instrumented vertebra to patient-specific anatomical and biomechanical requirements.

Frequently Asked Questions

What was the main objective of this lumbar fusion study?

The study aimed to evaluate whether stopping primary lumbar fusions at L1 versus extending instrumentation to T10, T11, or T12 alters reoperation risks for adjacent segment disease or symptomatic nonunion among adult patients with degenerative spinal disorders over long-term follow-up.

Did stopping at L1 increase reoperation rates for adjacent segment disease?

No, the propensity score-weighted analysis revealed no statistically significant differences in reoperation rates for adjacent segment disease between constructs stopping at L1 and those extending to T10, T11, or T12, across both short-segment and long-segment fusion cohorts.

How did nonunion revision rates compare between the two proximal levels?

For long-segment lumbar fusions, the study demonstrated no statistically significant difference in reoperations for nonunion between constructs terminating at L1 and those crossing the thoracolumbar junction to T10 through T12, showing comparable structural durability between the surgical approaches.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. Clinical decisions should always be made by qualified healthcare professionals based on individual patient assessments and established surgical indications. Refer to the latest local and national guidelines for clinical practice.

References

Guppy KH et al. Incidence Rates and Risks for Reoperations for Nonunion and Adjacent Level Disease: Stopping at L1 Versus T10/T11/12. Spine (Phila Pa 1976). 2025 Sep 15. doi: 10.1097/BRS.0000000000005257. PMID: 39840471.

Bridwell KH et al. Selection of the Upper Instrumented Vertebra for Adult Lumbar and Lumbosacral Deformity: Is Stopping at L1 or L2 Safe? Spine (Phila Pa 1976). 2013;38(10):809-816.

Kim YJ et al. Proximal Junctional Kyphosis in Adult Spinal Deformity After Long-Segment Instrumentation and Fusion to the Sacrum. Spine (Phila Pa 1976). 2005;30(18):2084-2090.