Analysis of sacro-iliac joint screw fixation: does quality of reduction and screw orientation influence joint stability? A biomechanical study.

Abstract

Treatment of posterior pelvic ring injuries is frequently associated with pain or/and high mortality rates. Percutaneous sacro-iliac (SI) screw fixation has proved to be one of the methods of choice, providing minimal operative time, blood loss and wound-related morbidity. However, fixation failures due to secondary fracture dislocation or screw backing out have been reported. There is a little knowledge regarding the impact of varying screw orientation and quality of reduction on the fixation strength. The purpose of the present study was biomechanical investigation of joint stability after SI screw fixation and its dependence on quality of reduction and screw orientation. Thirty-two artificial hemi-pelvices were assigned to four study groups and simulated SI dislocations were fixed with two SI screws in oblique or transverse screw orientation and anatomical or non-anatomical reduction in group A (oblique/anatomical), B (transverse/anatomical), C (oblique/non-anatomical) and D (transverse/non-anatomical). Mechanical testing was performed under progressively increasing cyclic axial loading until fixation failure. SI joint movements were captured via optical motion tracking. Fixation performance was statistically evaluated at a level of significance p = 0.05. The highest cycles to failure were observed in group A (14038 ± 1057), followed by B (13909 ± 1217), D (6936 ± 1654) and C (6706 ± 1295). Groups A and B revealed significantly longer endurance than C and D (p ≤ 0.01). Different screw orientations in the presented model do not influence substantially SI joint stability. However, anatomical reduction is not only mandatory to restore a malalignment, but also to increase the SI screw fixation strength and prevent fixation failures.