Objective
To develop a pedicle screw for posterior spinal fixation using this long fiber carbon fiber reinforced plastic (CFRP) technology and evaluate its strength and radiolucency compared with titanium (Ti)-alloy screws.
Methods
In this preclinical study, the shear strength, torsional strength, loosening resistance, and image evaluation of long fiber type CFRP pedicle screws and Ti-alloy screws were compared. A series of tests was conducted for future clinical-use approval.
Results
The long fiber type CFRP pedicle screw (mean±standard deviation: 11,377.7±245.1 N) had superior shear strength compared to the Ti-alloy pedicle screw (10,300.3±249.7 N). The long fiber type CFRP pedicle screw (4.4±0.5 Nm) had inferior torsional strength compared to the Ti-alloy pedicle screw (22.4±0.6 Nm), although it could withstand twice the maximum load applied during surgery, suggesting that this will not be a clinical concern. In terms of loosening resistance, maximum torque values of the long fiber type CFRP pedicle screw and Ti-alloy pedicle screw were 0.99±0.08 and 0.75±0.05 Nm, respectively. The long fiber type CFRP pedicle screw was significantly more resistant to loosening than the Ti-alloy pedicle screw. Moreover, artifacts in the radiographic images were smaller than those observed for the Ti alloy. Biosafety and magnetic resonance safety tests also yielded satisfactory results, supporting approval of the long fiber CFRP pedicle screws for clinical use.
Conclusion
Compared to existing Ti-alloy screws, the long fiber type CFRP pedicle screw with innovative manufacturing technology has sufficient performance for clinical use, and its use may make spinal surgery safer and more effective.

Objective
Our study aimed to compare the posterior interposition technique against the posterolateral transosseous technique in the same cadaver specimens.
Methods
Computer and cadaver models of 2 fixation techniques were developed. The computer model was constructed to analyze bone volume removed during implant placement and the bony surface area available for fusion. The cadaver model included quasi-static multidirectional bending flexibility and dynamic fatigue loading. Relative motions between the sacrum and ilium were measured intact, after joint destabilization, after fixation with direct-posterior and posterolateral techniques, and after 18,500 cycles of fatigue loading. Relative positions between each implant and the sacrum and ilium were measured after fixation and fatigue loading to ascertain the quality of the bone-implant interface. The 2 techniques were randomized to the left and right sacroiliac joints of the same cadavers.
Results
The posterior interposition technique removed less bone volume and facilitated a larger surface area available for bony fusion. Posterior interposition significantly reduced the nutation/counternutation motion of the sacroiliac joint (42% ± 8%) and reduced it more than the posterolateral transosseous technique (14% ± 4%). Upon fatigue loading, the posterior interposition implant maintained the bone-implant interface across all specimens, while the posterolateral transosseous implant migrated or subsided in 20%–50% of specimens.
Conclusion
Posterior interposition fixation of the sacroiliac joint reduces joint motion. The amount of fixation from the posterior technique is superior and more durable than the amount of fixation achieved by the posterolateral technique.