Early postoperative L1 pelvic angle and T10 pelvic angle as predictors of proximal junctional kyphosis in adult spinal deformity.

BACKGROUND

Excessive posterior inclination of the thoracolumbar spine increases stress concentration at the upper instrumented vertebra (UIV) and adjacent motion segments, potentially accelerating junctional collapse or kyphotic failure. This study evaluated whether early postoperative regional parameters - specifically T10 pelvic angle (T10PA) and L1 pelvic angle (L1PA) - predict the development of proximal junctional kyphosis (PJK) following long-segment fusion for adult spinal deformity (ASD).

METHODS

A retrospective review of 100 patients undergoing long-segment posterior fusion to the pelvis with a minimum 2-year radiographic follow-up was performed. Radiographs from approximately 6 weeks postoperatively were analyzed for T10PA and L1PA, categorized as under-corrected (UC), functionally corrected (FC), or over-corrected (OC) using established patient-specific targets.

RESULTS

Global and regional alignment parameters improved significantly postoperatively. T10PA overcorrection was associated with a markedly higher PJK rate (66.7%) compared to functional correction (24.5%) or under-correction (28.6%; p < 0.001). Over-corrected cohorts exhibited exaggerated lumbar lordosis and negative PI--LL mismatch. L1PA overcorrection alone did not significantly predict PJK (40.0%, p = 0.47). Patients with concordant functional correction (FC/FC) had the lowest PJK incidence (9.3%), whereas concordant overcorrection (OC/OC) carried the highest risk (63.3%, p < 0.001).

CONCLUSION

Early postoperative overcorrection of thoracolumbar alignment, reflected by T10PA, is a powerful predictor of PJK. T10PA may serve as a practical, construct-specific alignment target to minimize overcorrection and reduce junctional complications.