Upper instrumented vertebra pedicle screw loosening following adult spinal deformity surgery: incidence and outcome analysis

Abstract

Objective: Surgical correction of adult spinal deformity (ASD) is associated with a high rate of hardware complication that can be challenging to predict. Hardware integrity and alignment after surgery are typically followed with standing radiography, where pedicle screw loosening may be incidentally identified but the clinical significance of which is often unclear. This study aimed to identify the incidence and implications of pedicle screw loosening at the upper instrumented vertebra (UIV) after surgical correction of ASD.

Methods: A single-institution retrospective analysis was performed on a cohort of 217 patients who underwent long-segment fusion with pelvic fixation for correction of ASD between September 2013 and November 2021. Cases with a minimum 1-year follow-up were included. UIV pedicle screws were graded on radiographs for evidence of loosening with a 0- to 3-point scale: 0, no loosening; 1, lucency within screw threads; 2, lucency around screw threads; and 3, screw dislodgment/backout. Need for hardware revision surgery was assessed as the primary outcome. Patient-reported outcome measures (PROMIS and Oswestry Disability Index scores) were assessed as secondary outcomes among the patients with available scores.

Results: Low-grade UIV screw loosening (grade 1) was identified in 37 patients (17.1%), and high-grade UIV loosening (grade 2 or 3) was identified in 23 patients (10.6%). Low-grade UIV loosening was not associated with eventual need for hardware revision (OR 0.52, 95% CI 0.17-1.61, p = 0.258); however, high-grade loosening was associated with increased odds of hardware revision (OR 5.17, 95% CI 1.74-15.36, p = 0.003), including specifically surgery for correction of proximal junctional kyphosis (OR 5.73, 95% CI 1.27-25.95, p = 0.024). Among patients with PROMIS T-scores, those requiring hardware revision reported worse Pain Interference (65.0 ± 5.1 vs 59.6 ± 7.7, p = 0.001) and Physical Function (33.3 ± 5.6 vs 37.4 ± 7.4; p = 0.011). Patients with high-grade UIV loosening reported higher Oswestry Disability Index scores than those without high-grade loosening (grade 0 or 1), although this failed to reach statistical significance (44.0 ± 8.5 vs 33.7 ± 18.5, p = 0.101).

Conclusions: Grade 1 UIV pedicle screw loosening may represent a benign incidental finding, whereas high-grade loosening is associated with significantly increased odds of hardware revision surgery. High-grade loosening may also be associated with worse patient-reported disability. The authors' findings suggest that while low-grade UIV loosening may often be managed expectantly, identification of high-grade UIV pedicle screw loosening on follow-up imaging warrants increased attention and continued surveillance.

Keywords: pedicle screw; proximal junctional kyphosis; scoliosis; spine deformity.