Pullout Strength after Expandable Polymethylmethacrylate Transpedicular Screw Augmentation for Pedicle Screw Loosening

Objective : Pedicle screw fixation for spine arthrodesis is a useful procedure for the treatment of spinal disorders. However, instrument failure often occurs, and pedicle screw loosening is the initial step of a range of complications. The authors recently used a modified transpedicular polymethylmethacrylate (PMMA) screw augmentation technique to overcome pedicle screw loosening. Here, they report on the laboratory testing of pedicle screws inserted using this modified technique. Methods : To evaluate pullout strengths three cadaveric spinal columns were used. Three pedicle screw insertion methods were utilized to compare pullout strength; the three methods used were; control (C), traditional transpedicular PMMA augmentation technique (T), and the modified transpedicular augmentation technique (M). After control screws had been pulled out, loosening with instrument was made. Screw augmentations were executed and screw pullout strength was rechecked. Results : Pedicle screws augmented using the modified technique for pedicle screw loosening had higher pullout strengths than the control ($1106.2{\pm}458.0N$ vs. $741.2{\pm}269.5N$; p=0.001). Traditional transpedicular augmentation achieved a mean pullout strength similar to that of the control group ($657.5{\pm}172.3N$ vs. $724.5{\pm}234.4N$; p=0.537). The modified technique had higher strength than the traditional PMMA augmentation technique ($1070.8{\pm}358.6N$ vs. $652.2{\pm}185.5N$; p=0.023). Conclusion : The modified PMMA transpedicular screw augmentation technique is a straightforward, effective surgical procedure for treating pedicle screw loosening, and exhibits greater pullout strength than traditional PMMA transpedicular augmentation. However, long-term clinical evaluation is required.