Abstract / Summary
Study Design Retrospective cohort study. Objectives To determine whether thoracic compensation (TC) assessed against the deformity burden is associated with proximal junctional kyphosis (PJK) after lower thoracic fusion for adult spinal deformity (ASD). Methods We reviewed 343 patients fused from T9-L1 to the sacrum or pelvis with a pelvic incidence (PI) minus lumbar lordosis (LL) mismatch above 20°. Expected thoracic kyphosis (TK) was derived from the PI-LL mismatch using published equations, and a measured TK below it defined TC. PJK was defined as a proximal junctional angle of 20° or more, or revision, within two years. Multivariable logistic regression adjusted for patient, operative, and radiographic covariates including two measures of correction adequacy. Results PJK occurred in 60 of 124 patients (48.4%) without TC and 68 of 219 (31.1%) with TC (P = 0.002). Correction was equivalent for PI-LL, the L1 pelvic angle (L1PA), and pelvic tilt, yet the TC present group restored more TK (19.1° vs. 11.0°) while reaching a lower postoperative value (21.5° vs. 33.7°, both P < 0.001). TC remained associated with a lower risk of PJK after adjustment (odds ratio 0.431, 95% CI 0.261-0.713, P = 0.001), consistently across eight prespecified subgroups. Relative to TC without overcorrection, the odds ratio reached 3.41 (95% CI 1.37-8.46) when TC was absent and the L1PA offset indicated overcorrection. Conclusions TC assessed against the deformity burden was associated with a lower risk of PJK despite a larger reciprocal increase in TK. Risk was highest when TC was absent and lordosis overcorrected.