FIG 5. Correlation plot of gain (the wedge angle reduction)versus loss (original wedge angle) after vertebroplasty. There is a trend toward higher gain in cases with more original loss. Most cases of the "gas" group are in the right upper quadrant, whereas most cases of the "non-gas" group are in the left lower quadrant, suggesting that the gas group had larger wedge angle before vertebroplasty and more wedge angle reduction after vertebroplasty. After linear regression analysis, the slope for the "gas" group (0.61) is significantly larger than that for the "non-gas" group (0.24), again confirming the wedge angle reduction effect was more obvious in the "gas" group.

FIG 6. Correlation plot of the gain from percutaneous vertebroplasty versus the loss from fracture for the anterior border of collapsed vertebral bodies. There is a trend toward higher gain in cases with more original loss. Most cases of the "gas" group are in the right upper quadrant, whereas most cases of the "non-gas" group are in the left lower quadrant, suggesting the gas group had larger initial loss of height before vertebroplasty and more gain after vertebrolasty. The regression line for the "gas" group is higher than the "non-gas" group, which confirms again that the vertebroplasty resulted in better height restoration at the anterior border of the collapsed body in the "gas" group.