Abstract
Osteoporosis is one of the most challenging diseases facing orthopedic surgery. Implants may exhibit poor bone retention due to the decreased density of osteoporotic bone, leading to mechanical failure. Our study aimed to design a pedicle screw for vertebral implantation that exhibited pullout strengths that were higher than the current industry standard screw. We created three prototypes to address pullout failure with varying numbers of helices and one design that was a two-part hybrid (triple helix and pedicle screw). Each screw was subjected to pull-out testing in foam blocks (n=3). Ultimate pull-out load, ultimate extension, and screw removal energy were determined based on testing results. Based on the results, the two-part assembly demonstrated significantly improved pull-out strength to 102.76 ± 2.52 N (P > 0.0002), ultimate extension to 8.787 ± 0.242 (P > 0.002), and screw removal energy of 2.37 ± 0.03 kJ (P > 0.0003) vs 1.66 ± .08 kJ in the control screw, and the other two screw designs. It is noteworthy that the flexible and stiff helix designs by themselves did not exhibit improved performance, but when combined into a dual-threaded screw the helix features improved performance. The results for the two-part design suggested that there is utility in this design or variations thereof for improving screw-to-bone retention in osteoporotic patients.
