T10-pelvic angle as a newly introduced sagittal parameter: a validation study in terms of pelvic tilt restoration, proximal junctional kyphosis, and clinical outcomes in adult spinal deformity surgery

Purpose: This study aims to validate the usefulness of T10-pelvic angle (T10PA) in predicting pelvic tilt (PT) restoration, proximal junctional kyphosis (PJK) development, and clinical outcomes after adult spinal deformity (ASD) surgery. Methods: This retrospective study included 213 ASD patients who underwent fusion from the lower thoracic spine (T9 or T10) to the pelvis. T10PA was measured on 6-week postoperative radiographs as the angle between the center of T10 and the hip center, and from the hip center to the midpoint of the S1 upper endplate. Patients were classified into three groups based on pelvic incidence (PI)- and age-adjusted normative T10PA: undercorrection (offset > + 3.5°), matched correction (± 3.5°), and overcorrection (< − 3.5°). At 2 years postoperatively, outcome including pelvic non-response (PNR), PJK, and clinical results—visual analogue scale (VAS) for back pain, Oswestry Disability Index (ODI), Scoliosis Research Society-22 (SRS-22), and patient satisfaction—were compared among groups. Results: The cohort included 192 females (90.1%) with a mean age of 70.1 years. PNR was significantly more frequent in the undercorrection group (P = 0.027), while PJK was more common in the overcorrection group (P = 0.011). The matched correction group showed superior outcomes in ODI (P = 0.030), SRS-22 (P = 0.018), and patient satisfaction score (P < 0.001). Conclusions: T10PA undercorrection was associated with higher PNR and overcorrection with increased PJK. Matched correction yielded the best clinical outcomes. Therefore, optimal T10PA alignment may serve as an effective strategy to reduce both PNR and PJK while improving outcomes in ASD surgery.