A new biomechanical study has compared two common sacroiliac (SI) joint fixation designs and found that a fully threaded screw may offer substantially stronger anchorage than a non‑threaded triangular titanium implant under pullout testing. The work focuses on how implant geometry and surface design affect axial pullout strength, a key factor in resisting loosening along the implant’s long axis.

What the researchers tested

The study evaluated a non‑threaded triangular titanium implant (TTI), similar to the long‑used iFuse design, against a fully threaded sacroiliac screw (TS) from Sacrix in a controlled biomechanical setup. Using standardized polyurethane foam blocks to simulate bone, the team applied static axial pullout tests and measured the force required to extract each implant.

Key findings in pullout strength

The fully threaded Sacrix screw showed a dramatic increase in pullout strength compared with the non‑threaded triangular implant, with mean values reported at roughly 815 N for the screw versus about 200 N for the triangular device—approximately a threefold difference. While the threaded screw demonstrated higher absolute strength, its results showed somewhat greater variability than the triangular implant, suggesting that performance may be more sensitive to local bone conditions or test nuances.

Why this matters for SI fusion

Stronger pullout performance implies better resistance to axial loosening, especially in compromised bone, and may translate into lower risk of implant migration or failure over time. The authors suggest that fully threaded designs should be seriously considered for SIJ fusion when robust anchoring is a priority, while noting that clinical outcomes still depend on factors beyond pullout strength alone, including bone quality, surgical technique, and fusion biology.

Read in Detail Here:  A comparative biomechanical study of a non-threaded triangular titanium implant versus a fully threaded screw: assessing pullout strength of two sacroiliac joint fixation implant designs