Fri., 10/5/12 Basic Science, PAPER #55, 1:46 pm OTA-2012
Comparison of Standard Iliosacral Screw Fixation to Transsacral Locked Screw Fixation in a Type C Zone II Pelvic Fracture Model With Residual Fracture Site Separation
Sean A. Tabaie, MD; Gary Bledsoe, PhD; Berton R. Moed, MD;
Saint Louis University School of Medicine, Saint Louis, Missouri, USA
Purpose: Iliosacral screw fixation into the first sacral body is a preferred method for pelvic ring fixation. However, this construct has been shown to be clinically unreliable for the percutaneous fixation of unstable Type C zone II vertically oriented sacral fractures with residual fracture site separation. The purpose of this study was to biomechanically compare a locked transsacral construct versus the standard iliosacral construct in a Type C zone II sacral fracture model.
Methods: A Type C pelvic ring injury was created in 10 cadaver pelves by performing vertical osteotomies through zone II of the sacrum and the ipsilateral pubic rami. The sacrum was then reduced maintaining a 2-mm fracture gap. Five specimens were fixed using two 7.0-mm iliosacral screws into the S1 body; the other five were fixed using one 7.0-mm iliosacral screw and one 7.0-mm transsacral screw exiting the contralateral ilium with a nut placed on its end, creating a locked construct. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. Vertical displacements at 25,000, 50,000, 75,000, and 100,000 cycles and failure force were recorded for each pelvis. The differences between the two groups were compared using the Mann-Whitney U test.
Results: The mean displacements at 25,000, 50,000, 75,000, and 100,000 cycles and force to failure for the iliosacral group were 5.1 mm, 9.6 mm, 15.5 mm, 19.7 mm and 825 N respectively. Comparatively, the values for the transsacral group were 3.6 mm, 5.5 mm, 10.2 mm, 15.5 mm and 1056 N. The locked transsacral construct performed significantly better than the iliosacral construct at all four measurement points (P = 0.009) and in force to failure (P = 0.02).
Conclusion: Fixation of unstable Type C zone II sacral fractures using the combination of an iliosacral screw and a locked transsacral screw resists deformation and withstands a greater force to failure as compared to fixation with two standard iliosacral screws. This locked transsacral construct may prove advantageous, especially when a percutaneous technique is used for a Type C zone II vertically oriented sacral fracture injury pattern, which can result in residual fracture site separation.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.