Mode-Specific Association Between Tri-Cortical Pedicle Screws and Proximal Junctional Kyphosis in Adult Spinal Deformity

Study Design. Retrospective propensity score–matched cohort study. Objective. To evaluate the association between tri-cortical pedicle screw (TPS) fixation and radiographic proximal junctional kyphosis (PJK) after adult spinal deformity (ASD) surgery and to explore mode-specific associations. Summary of Background Data. PJK is common after long-segment fusion for ASD. Binary PJK endpoints may overlook heterogeneous PJK modes. The mode-specific association of TPS fixation remains uncertain. Methods. Adults undergoing long-segment posterior fusion with a lower thoracic upper instrumented vertebra (T9-T12) and at least 2 years of follow-up were retrospectively identified. Patients were categorized according to TPS use at the upper instrumented vertebra. Propensity score matching was performed to address baseline differences. The primary outcome was radiographic PJK, defined as a ≥10-degree increase in proximal junctional angle from the immediate postoperative radiograph. PJK modes were classified using a published system. Overall and mode-specific associations were evaluated using LASSO-selected and adjusted logistic regression, bias-reduced multinomial regression, and E-value sensitivity analysis. Results. Of 304 eligible patients, 189 received conventional pedicle screw fixation and 115 received TPS fixation. Propensity score matching generated 110 pairs. In the matched cohort, radiographic PJK occurred in 8.2% of the TPS group and 27.3% of the Control group ( P <0.001). TPS fixation was associated with lower PJK odds in the LASSO-selected model (OR, 0.36, 95% CI, 0.14-0.87, P =0.028). Type 2 PJK occurred in 10 Control patients and in no TPS patients. Type 1 and combined Type 3-4 PJK showed no significant association with TPS. The E-value for the point estimate was 5.00. Conclusions. TPS fixation was associated with a lower incidence of radiographic PJK after ASD surgery. Mode-specific analysis suggested fewer Type 2 PJK events with TPS fixation, supporting mode-specific radiographic assessment and further evaluation of TPS as a proximal fixation strategy. Level of Evidence. Level III.