Results in axial pullout tests in three groups (n = 8, means ± SD).

CPS, PMMA-PS and EPS indicate conventional pedicle screw, polymethylmethacrylate-augmented pedicle screw and expansive pedicle screw, respectively. Fmax and E indicate the maximum pullout strength and energy-to-failure, respectively.
*Compared with CPS group at the same study period, p<0.05; # Compared with PMMA-PS group at the same study period, p>0.05; & Compared with 6-week in the same group, p>0.05; Δ Compared with 6-week in the same group, p<0.05.