Mechanical and biological factors associated with screw loosening and adjacent segment disease after cement-augmented pedicle screw fixation in osteoporotic patients

Screw loosening and adjacent segment disease (ASD) remain important complications following cement-augmented pedicle screw fixation in osteoporotic patients. Although cement augmentation increases fixation strength, the associations of cement-related parameters with screw loosening and ASD remain controversial. This study aimed to examine patient- and cement-related factors associated with screw loosening and ASD in osteoporotic patients who underwent cement-augmented spinal fixation. This retrospective study included 92 osteoporotic patients (530 pedicle screws) who underwent cement-augmented pedicle screw fixation for degenerative lumbar or thoracolumbar pathology between 2018 and 2022, with a minimum follow-up of 2 years. Demographic characteristics, surgical variables, cement parameters, and radiographic outcomes were analyzed. Screw loosening and ASD were evaluated using postoperative computed tomography (CT) and clinical follow-up. Logistic regression analyses were used to estimate associations with these complications. Screw loosening and ASD occurred in 17 (18.5%) and 19 (20.7%) patients, respectively. Greater cement volume was associated with lower loosening rates in unadjusted analyses but was not independently associated with loosening in the multivariable analysis. Structural severity, reflected by the osteoporotic fracture (OF) score, was the only variable independently associated with screw loosening (adjusted OR 1.60 per point increase, 95% CI 1.25–2.15; p < 0.001), although this association was sensitive to the exclusion of seven thoracolumbar-extending constructs (adjusted OR 1.50 per point increase, 95% CI 1.00–2.35; p = 0.049). High-viscosity cement was associated with lower cement leakage rates. In contrast, male sex and fusion status were independently associated with ASD, whereas cement volume and cement viscosity were not associated with ASD in the univariate analysis. In this exploratory cohort, structural severity, as reflected by the OF score, was associated with screw loosening, whereas ASD was associated with fusion status and male sex. These exploratory associations require prospective validation before they can inform surgical planning in osteoporotic spine surgery.