Mechanical complications in adult deformity surgery: behavioral patterns

Mechanical complications after adult deformity surgery are typically considered as a composite variable. This study aims to differentiate their characteristics and analyze their behavioral patterns based on time-to-onset and predisposing factors.

This retrospective observational study analyzed patients from a prospective multicenter database. Operated patients were analyzed for proximal junctional kyphosis (PJK), proximal junctional failure (PJF), pseudarthrosis (PA), rod breakage (RB), and no complications. Kaplan-Meier survival analysis and multivariate Cox regression models encompassing clinical, biological, radiographic, and surgical parameters were utilized to identify complication-related factors.

Among 1,505 patients analyzed, 260 (17.3%) developed mechanical complications: PJK (65), PJF (43), PA (56), and RB (96). Similar time-to-event patterns were observed for PJK and PJF (Log-Rank test p = 0.446) (160 days [Q1 = 72; Q3 = 492]), and PA and RB (Log-Rank test p = 0.782) (695 days [Q1 = 371; Q3 = 1059]), clustering them in pairs. Proximal junctional problems (PJK/PJF) and failure of fusion (PA/RB) demonstrated different survival curves (Log-Rank test p < 0.001). Multivariate models associated (p < 0.05) proximal junctional problems with age (OR = 1.039), SF36-PCS (OR = 0.963), number of instrumented levels (OR = 1.123), and immediate postoperative alignment (Relative Lumbar Lordosis [OR = 1.025] and Relative Spinopelvic Alignment [OR = 1.064]). Failure of fusion occurrence was associated (p < 0.05) with number of instrumented levels (OR = 1.127) and 1-year postoperative: age (OR = 1.017), body mass index (OR = 1.044), SF36-PCS (OR = 0.975) and Relative Spinopelvic Alignment (OR = 1.034).

Time-to-onset differed between proximal junctional problems and failure of fusion, and predisposing factors overlap. Nevertheless, the former was associated with immediate postoperative lumbar and global sagittal misalignment, the latter with mid-term biological factors and global sagittal misalignment.