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Postoperative T10 Tilt at Two Weeks as an Early Prognostic Marker for Proximal Junctional Kyphosis and Failure After Adult Spinal Deformity Surgery

This study demonstrates that two-week postoperative T10 tilt is an independent prognostic marker for proximal junctional kyphosis and failure in adult spinal deformity patients with an upper instrumented vertebra at T9 or T10, offering modest predictive value comparable to or slightly better than L1 pelvic angle for early risk assessment.

Original authors: Jae Heouk Choi, Dong Seok Kim, Jin S. Yeom, Sang-Min Park, Ohsang Kwon, Ho-Joong Kim

Published 2026-07-07

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CC BY 4.0

Original authors: Jae Heouk Choi, Dong Seok Kim, Jin S. Yeom, Sang-Min Park, Ohsang Kwon, Ho-Joong Kim

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your spine is a long, flexible tower built to hold up your body. When doctors fix a crooked tower (a condition called Adult Spinal Deformity), they often use metal rods and screws to straighten it. They usually anchor the top of this new, rigid structure at a specific point in the upper back, around the 9th or 10th rib bone (T9 or T10).

The big worry after this surgery is Proximal Junctional Kyphosis (PJK). Think of this like a "hinge failure." Because the bottom part of the tower is now rigid and fused, the top part (where the metal ends) has to take all the bending stress. Over time, this stress can cause the vertebrae right above the metal to crack, the screws to pull out, or the spine to bend backward again. This is a painful complication that often requires a second, major surgery.

The Problem:
Doctors usually wait months to see if this hinge failure is happening. By the time they see it on an X-ray, the damage might already be significant. The researchers wanted to find a way to spot the trouble early, right after the patient wakes up and starts walking again.

The Solution (The "T10 Tilt"):
The team looked at a specific measurement taken just two weeks after surgery. They measured the T10 Tilt.

The Analogy: Imagine the patient is standing up. Draw a straight line from their hip bone up to the center of that 10th rib bone (T10). Now, measure the angle of that line compared to a perfectly vertical plumb line.
What it means: If that line is leaning too far backward (a high T10 tilt), it means the patient's body is still trying to compensate for the surgery by tilting their pelvis backward. Because the spine is now fused from T10 down to the pelvis, this backward tilt puts extra strain on the top of the metal rod.

What the Study Found:
The researchers looked at 210 patients who had this specific type of surgery. They checked their T10 tilt two weeks after the operation and then watched them for a year to see who developed the "hinge failure."

The Early Warning: Patients who ended up with complications had a significantly higher T10 tilt at the two-week mark than those who didn't.
The "Slippery Slope": It wasn't just a "yes or no" thing. The higher the tilt angle, the higher the chance of trouble. If the tilt was 5 degrees, the risk was low (about 20%). If the tilt was 20 degrees, the risk jumped to about 50%.
Better than the Old Way: They compared this new measurement to an older method called "L1 Pelvic Angle." The T10 tilt was slightly better at predicting trouble, though the difference wasn't huge.
It's Not Just the Hips: They checked if the tilt was just a reflection of the patient's pelvic position. It wasn't. Even after accounting for how the pelvis was tilted, the T10 angle still predicted the risk. This means the measurement tells you something specific about how the surgical construct is sitting, not just how the patient is standing.

The Bottom Line:
This study suggests that measuring the T10 Tilt two weeks after surgery is like checking the foundation of a building right after construction. If the angle is too steep, it's an early warning sign that the top of the spine is under too much stress and might fail later.

Important Caveats:

It's a Clue, Not a Crystal Ball: The study calls this a "modest" predictor. It's not a perfect crystal ball that says "This patient will definitely fail." Instead, it's one piece of a puzzle. Doctors should use it as one input along with other factors to decide who needs extra monitoring.
It's Early: The study only looked at patients two weeks post-op. It doesn't tell us if changing the treatment because of this measurement will stop the failure, only that the measurement is associated with the risk.

In short, if a patient's spine is leaning back too much two weeks after surgery, they are on a "high-risk trajectory" for future complications, and doctors should keep a very close eye on them.

Technical Summary: Postoperative T10 Tilt as an Early Prognostic Marker for Proximal Junctional Complications

Problem Statement
Proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) represent significant mechanical complications following adult spinal deformity (ASD) surgery, particularly in constructs extending to the pelvis with the upper instrumented vertebra (UIV) at T9 or T10. While junctional changes often begin within weeks post-surgery, current risk identification relies on established risk factors that do not fully capture the interplay between global pelvic position and construct orientation. Existing measures often characterize local geometry without reflecting the patient's residual compensatory posture. There is a clinical need for early, readily available prognostic markers at the routine 2-week postoperative visit to identify patients on a trajectory toward complications before they become radiographically manifest months later.

Methodology
This retrospective cohort study analyzed 210 patients who underwent posterior corrective ASD surgery with a UIV at T9 or T10 and fusion to the pelvis between 2020 and 2025. The study utilized standing whole-body biplanar slot-scanning (EOS) radiographs taken at two weeks postoperatively.

Primary Predictor: T10 tilt, defined as the angle between the line connecting the hip center and the T10 vertebral body centroid and the vertical axis. This parameter captures both the sagittal orientation of the distal thoracic construct and residual pelvic retroversion.
Comparators: The study compared T10 tilt against the L1 pelvic angle (L1 PA) and standard spinopelvic parameters (e.g., pelvic tilt [PT], sagittal vertical axis [SVA]).
Outcomes: Three outcomes were assessed at 6 or 12 months (or within 1 year for PJF):
1. Glattes PJK: $\Delta$ PJA $\ge$ 10° and absolute PJA $\ge$ 10°.
2. Strict PJK: $\Delta$ PJA $\ge$ 20° and absolute PJA $\ge$ 20°.
3. PJF/Revision: Vertebral fracture, implant failure, neurological deficit, or revision surgery within 1 year.
Statistical Analysis: Discriminative performance was evaluated using Receiver Operating Characteristic (ROC) analysis and Area Under the Curve (AUC). T10 tilt was compared to L1 PA using the paired DeLong test. Multivariable logistic regression adjusted for eight established risk factors (age, sex, BMI, preoperative PI-LL mismatch, 2-week PT, 2-week SVA, and femoral neck BMD) to assess independence.

Key Results

Incidence: Glattes PJK occurred in 37.6% (79/210), strict PJK in 13.8% (29/210), and PJF/revision in 11.0% (23/210).
Discriminative Performance: 2-week T10 tilt demonstrated modest but significant discrimination for all outcomes:
- Glattes PJK: AUC 0.644 ( $p < 0.001$ ).
- Strict PJK: AUC 0.691 ( $p < 0.001$ ).
- PJF/Revision: AUC 0.693 ( $p < 0.001$ ).
- Predicted probability of complications increased continuously with higher T10 tilt values (e.g., rising from ~20% at 5° to ~50% at 20° for Glattes PJK).
Comparison with L1 PA: T10 tilt showed numerically higher AUCs than L1 PA across all outcomes (differences ranging from +0.060 to +0.114), though these differences did not reach statistical significance in the paired DeLong test. Notably, L1 PA was only statistically significant for the strict PJK definition, whereas T10 tilt was significant for all three.
Independence from Pelvic Tilt: While T10 tilt was moderately correlated with 2-week pelvic tilt (PT) ( $r = 0.565$ ), PT alone did not significantly discriminate any outcome. In multivariable models, T10 tilt remained an independent predictor of all outcomes (e.g., adjusted OR 1.182 for Glattes PJK per degree increase, $p < 0.001$ ), whereas PT alone lost significance.
Multivariable Analysis: After adjusting for covariates, T10 tilt was independently associated with the primary outcome (Glattes PJK) and, in exploratory models, with strict PJK and PJF/revision.

Significance and Claims
The authors conclude that 2-week postoperative T10 tilt is independently associated with subsequent PJK and PJF in ASD patients with UIV at T9 or T10. The paper positions T10 tilt not as a standalone predictor, but as a valuable "early prognostic marker" and a readily obtainable input for multiparameter risk assessment.

Key claims regarding the significance of the findings include:

Early Identification: T10 tilt allows for risk stratification at the routine 2-week visit, identifying patients on a trajectory toward complications months before formal diagnosis.
Mechanistic Insight: Unlike T10 pelvic angle (T10PA), which is fixed once the pelvis and T10 are fused, T10 tilt (referenced to the vertical) captures residual pelvic retroversion in non-compensators, offering informational advantages regarding the mechanical demand at the proximal construct endpoint.
Clinical Utility: As T10 tilt is derived from standing radiographs already acquired at the 2-week follow-up, it can be integrated into risk assessment without additional cost or radiation exposure.
Modest but Continuous Risk: The study emphasizes that the discriminative performance is modest for a single parameter, reflecting early risk identification rather than causal prediction, but the continuous rise in probability with increasing tilt values supports its utility in a broader risk model.

The authors acknowledge limitations, including the retrospective single-center design, the lack of formal reliability assessment, and the exploratory nature of secondary outcome models due to low events-per-variable ratios. They note that the causal direction (whether T10 tilt is a mechanical driver or an early manifestation of incipient PJK) remains to be established.

Technical Summary: Postoperative T10 Tilt as an Early Prognostic Marker for Proximal Junctional Complications

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