Figure 5

The measured and predicted pullout strength of six pedicle screws. One standard deviation is used as the error bar of the experimental data. The 0.5 value of the equivalent diameter ratio is used in calculating the Chapman's and Lin's formulae. It is obvious that the predicted pullout strength of each screw using the new formula was closer to those under testing, while the calculated data from the Chapman's formula were very variable and could not match the experimental data.