S2AI revision surgery - biomechanical evaluation of increased screw diameters

This cadaveric study investigated whether, during revision surgery for S2 ala ilium (S2AI) screws, the choice of 11.5 mm diameter screws is superior to 10.5 mm screws in terms of biomechanical stability. The secondary goal was to determine whether increasing the diameter of the revision screws provided adequate stability.

9.5 mm diameter S2AI screws were subjected to cyclic mechanical vertical loading until failure (loosening > 5 mm) occurred. A revision using a 10.5- or 11.5-mm diameter screw was performed, and the described vertical loading was applied again. The force in Newtons (N) until failure was assessed and subjected to matched-pair analysis.

10.5 mm screws demonstrated greater stability (mean + 41.9 N) compared to the 9.5 mm screws (p = 0.0205). 11.5 mm screws also demonstrated greater stability (mean + 53.9 N) compared to the 9.5 mm screws (p = 0.0242). Comparison of both 10.5 mm and 11.5 mm revision screw options showed no significant difference in absolute increase of stability (p = 0.6004). Similarly, there was no significant difference in the relative increase in stability, measured as fold change (p = 0.4052).

Revision surgery with both screws demonstrated noteworthy enhancement in stability. However, the choice between 10.5 mm and 11.5 mm screws for optimal revision stability appears inconsequential. This suggests that factors beyond the screw diameter may play a crucial role in the stability of revision screws.