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Objectives and questions: Pedicle screw implantation is widely used in spinal surgery. Despite advancements in implant design and augmentation techniques, pedicle screw loosening remains a significant clinical challenge, often requiring revision surgery due to persistent pain and spinal instability. Common revision strategies include increasing screw diameter (upsizing), polymethylmethacrylate (PMMA) augmentation, or a combination of both. However, to date, no study has systematically evaluated the efficacy of these techniques under physiological conditions. The present cadaveric study investigated the most commonly used revision techniques in restoring pedicle screw anchorage.

Material and methods: Twenty-nine fresh-frozen vertebrae (L1-L5; BMD: 81.6±16.1 mg/cm³; age: 74.4±7.4 years) were instrumented using 6.2x45 mm monoaxial, cannulated and fenestrated pedicle screws. Screws were subjected to cyclic cranio-caudal loading with increasing load magnitude until screw loosening occurred. Loosened pedicle screws in group 1 (n=14) were revised using either 6.2mm PMMA-augmented screws or 8.2 mm non-augmented screws and in group 2 (n=15) with 7.2 mm PMMA-augmented or 7.2 mm non-augmented screws. The previous loading protocol was then repeated. During initial and revision loosening tests, load at failure and cycles until loosening were recorded. After failure, pull-out tests were performed to evaluate residual anchorage. Pairwise left-right comparisons were made in each vertebra within groups (Wilcoxon signed-rank test, paired-sample t-test).

Results: Load levels at loosening did not differ between the initial 6.2 mm screws in both groups (p>0.05). In group 1, both revision techniques resulted in significantly higher load levels compared to the initial screws (6 mm augmented: 260.4±112.9N to 350.7±140.4N, p=0.02; 8 mm non-augmented: 248.6±105.7 N to 311.8±115.7 N, p=0.005). In group 2, only the 7 mm augmented screws improved anchorage (287.3±90.0 N to 482.0±126.3 N, p<0.001) whereas the 7mm non-augmented screws did not (311.3±136.5 N to 295.3±127.9 N, p=0.57). The highest relative improvement was achieved by the 7 mm augmented screws with a mean of 175±39% of the initial screws. Pull-out force was significantly higher for augmented screws (group 1: 1368.1±402.0 N vs. 715.9±225.2 N, p<0.001; group 2: 1256.6±252.7 N vs. 717.1±274.2 N, p<0.001).

Discussion and conclusions: Increasing the screw diameter by only 1 mm without augmentation may restore the load-to-failure strength of the initial screw; however, this approach carries the risk of recurrent loosening. Among the available strategies to enhance screw anchorage in revision surgeries for loosened pedicle screws, both 2 mm screw upsizing and polymethylmethacrylate (PMMA) augmentation have demonstrated significant improvements in fixation strength. Notably, the combination of upsizing and PMMA augmentation has shown the most promising results and may offer superior anchorage compared to either technique alone.