Biomechanical comparison of augmented versus non-augmented sacroiliac screws in a novel hemi-pelvis test model

Abstract

Operative treatment of sacral insufficiency fractures is frequently being complicated by osteopenic bone properties. Cement augmentation of implanted sacroiliac screws may lead to superior construct stability and prevent mechanical complications. A novel hemi-pelvis test model with dissected symphysis was developed. Five fresh-frozen cadaveric pelvises were vertically osteotomized at the sacrum on both sides and fixed with sacroiliac screws in both corridors of the first sacral vertebral body. One side was randomly augmented with bone cement. Cyclic testing consisting of torsional loading (±2.5 Nm) combined with progressively increasing axial loading (+50 N compression, -10 N traction, ±0,01 N/cycle) was performed until failure; simulated physiological loads derived from inverse dynamic calculations. The fixation was analyzed fluoroscopically quantifying screw migrations and assessing failure mechanisms. Failure modes were cut-out, pull-out, screw-out, and washer penetration. Motion at fracture site was analyzed via optical motion tracking. Unscrewing was provoked four times with non-augmented and twice with augmented screws. When focusing on the sacral region only, cement augmentation significantly improved screw fixation in terms of increased number of cycles to failure (p = 0.043). However, when considering overall construct stability, there was no significant difference between augmented and non-augmented state due to washer penetration at the iliac bone. The generated hemi-pelvis model was found to be valid due to the reproduction of the clinically observed failure mode (unscrewing). Unscrewing was not fully prevented by cement augmentation. Augmentation effects stability at the screw tip, but particularly in porotic bone, failure may shift to the next weak point. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1485-1493, 2017.

Comparative Study of Percutaneous Sacroiliac Screw with or without TiRobot Assistance for Treating Pelvic Posterior Ring Fractures

“…The Advantages of TiRobot Over Traditional Surgical Techniques Biomechanical studies confirmed that the stability of the anterior and posterior pelvic rings accounted for 40% and 60% [27][28][29][30] . The stability of the posterior pelvic ring is maintained by the sacroiliac joint complex, which is composed of the bilateral ilium, the sacrum, the sacroiliac joint, and the surrounding ligaments; it also plays an important role in the stability of the pelvic ring 21 .…”

Biomechanics of Osteoporotic Fracture Fixation

“…Placement of two iliosacral screws achieves higher biomechanical stability than just one, and, similarly, longer screws achieve a higher stability than shorter ones [86,87]. Clinically, screws often fail by loosening or unscrewing [85] due to reduced bone quality [81] which can be effectively addressed by using cannulated screws and bone cement to augment the fixation site [88,89]. Bone cement is also an option for isolated and incomplete compression fractures [83] in which the cement is injected via a needle accessing the sacrum via the sacrum ala.…”

Minimal Invasive Surgical Treatment of Fragility Fractures of the Pelvis

“…Special care should be taken to avoid cement leakage into the sacral canal, the neuroforamina or through the anterior sacral cortex. Biomechanical studies have shown that stability of iliosacral screw fixation in FFP is significantly higher with cement augmentation than without (44,45). Clinical experience is still small, but results are promising (42,43).…”