RF30#180
Rapid Fire
A Regression-based Equation for Postoperative Spontaneous Correction of the Unfused Proximal Thoracic Curve in Lenke Type 1 and Type 2 Adolescent Idiopathic Scoliosis
Masayoshi Iwamae, Shinji Takahashi, MD, PhD, Yuki Kinoshita, MD, Minori Kato, MD, PhD, Hiromitsu Toyoda, MD, PhD, Akinobu Suzuki, MD, PhD, Koji Tamai, MD, PhD, Yuta Sawada, MD, PhD, Yuki Okamura, MD, Yuto Kobayashi, MD, Masato Uematsu, MD, Hiroshi Taniwaki, MD, Masashi Tsujino, MD, Hiroaki Nakamura, MD, PhD, Hidetomi Terai, MD, PhD
Department of Orthopaedic Surgery, Osaka Metropolitan University Graduate School of Medicine
Study Design: Retrospective cohort study. Objectives: To identify radiographic parameters associated with the final follow-up (FFU) T1–UIV angle and to develop and validate a regression-based equation for predicting the FFU T1–UIV angle in adolescent idiopathic scoliosis (AIS).
Summary of Background Data: Shoulder imbalance after posterior spinal fusion (PSF) for AIS remains a clinical concern and is associated with postoperative T1 tilt. Although UIV tilt can be surgically adjusted, control of T1 tilt is challenging because postoperative behavior of the unfused proximal thoracic curve (T1–UIV angle) is unpredictable.
Methods: Ninety-seven consecutive AIS patients (Lenke types 1 and 2) who underwent PSF were analyzed. T1 tilt, UIV tilt, and the T1–UIV angle were measured preoperatively, intraoperatively (post-correction), postoperatively at 1 week, and at FFU. Factors associated with the FFU T1–UIV angle were evaluated using multiple linear regression based on predefined preoperative and surgically adjustable variables, and a regression-based equation was derived. Predictive performance was assessed using a separate internal validation cohort.
Results: UIV tilt remained stable from intraoperative correction through FFU (p = 0.619). Multivariate analysis identified the preoperative T1–UIV angle (B = 0.61, p < 0.001) and preoperative UIV tilt (B = 0.08, p = 0.030) as independent factors associated with the FFU T1–UIV angle. The regression-based equation was defined as: FFU T1–UIV angle = 1.2 + 0.61 × (preoperative T1–UIV angle) + (preoperative UIV tilt / 12). The model demonstrated good internal validity (mean absolute error = 2.06°, adjusted R² = 0.694). Predicted T1 tilt, expressed as intraoperative UIV tilt + predicted FFU T1-UIV angle, was significantly associated with FFU radiographic shoulder height (r = 0.517, p < 0.001).
Conclusions: This regression-based equation provides a practical intraoperative reference for UIV tilt adjustment and may help reduce postoperative shoulder imbalance.
