Stability of pedicle screws after kyphoplasty augmentation: an experimental study to compare transpedicular screw fixation in soft and cured kyphoplasty cement

OBJECTIVE: The goal of this cadaver study was to compare the stability of pedicle screws after implantation in soft or cured kyphoplasty cement. METHODS: Pedicle screws were inserted in a total of 30 thoracolumbar vertebrae of 10 different human specimens: 10 screws were implanted in nonaugmented vertebrae (group 1), each 10 screws were placed in soft (group 2) and cured (group 3) cement. Pedicle screws were than evaluated for biomechanical axial pullout resistance. RESULTS: Mean axial pullout strength was 232 N (range 60-600 N) in group 1, 452 N (range 60-1125 N) in group 2 and 367 N (range 112-840 N) in group 3. The paired Student t-test demonstrated a significant difference between pullout strength of groups 1 and 2 (P = 0.0300). Between pullout strength of groups 1 and 3 and between groups 2 and 3 no significant difference was seen. CONCLUSION: We achieved a 1.9 times higher pullout strength with kyphoplasty augmentation of osteoporotic vertebrae compared with the pullout strength of nonaugmented vertebrae. Implantation of pedicle screws in cured cement is a sufficient method. With this method we found a 1.6 times higher pullout strength then in nonaugmented vertebrae.