Researchers studied the association between pedicle screw fixation strength and bone mineral density in regard to various transverse screw insertion angles, according to an article published by Spine Deformity.
The study used ASTM F543 as a reference. Researchers conducted pullout tests with an Instron mechanical testing machine of a posterior fixation construct, which resembled two pedicle screws connected between at a distance of 40 mm.
Here are four observations:
1. The study resulted in a linear regression with two independent variables of "Y = −354.8812 + 91.8102 × X1 − 6.8747 × X2 (X1 = density [pcf], X2 = angle [degrees])," according to the study.
2. Researchers found a correlation coefficient of 0.95 for all experimental data.
3. Researchers concluded the "pedicle screw insertion angle and bone density are critical to pullout strength."
4. In osteoporotic bone, the insertion angle impacts pullout strength, minimally.