OTA 2005 Posters

Scientific Poster #57 Basic Science

Fixation of Vertically Unstable Pelvic Ring Injuries with a Locking Screw Construct: A Biomechanical Comparison to Iliosacral Screws

Catherine A. Humphrey, MD (n); Qi Liu, MS (n);

Thomas J. Ellis, MD (a-Zimmer Educational Grant, Synthes North America);

Oregon Health and Science University, Portland, Oregon, USA

Purpose: Vertically unstable sacral fractures have demonstrated high rates of chronic pain and malunion with early loss of reduction when treated with percutaneous iliosacral screw fixation. The purpose of this study was to compare a locked screw construct to a single iliosacral screw for fixation of a vertically unstable pelvic ring injury.

Methods: A biomechanical analysis was conducted using 10 cadaveric pelvic specimens. OTA type 61-C1.3a2c5 fractures were created. In group 1 the posterior injury was reduced and stabilized using a 2-hole locking plate with one solid 5.0-mm locking iliosacral screw and a second locking screw directed into zone 1 of the sacrum. The group 2 specimens were reduced and stabilized using a single cannulated 7.3-mm screw. The anterior ring was stabilized with a 6-hole 3.5-mm reconstruction plate in all testing specimens. Motion at the posterior fracture site was analyzed on a materials testing sSystem. Values for displacement in the 3 cardinal planes were recorded at 1,000 cycle intervals for 10,000 cycles per specimen. Macroscopic movement greater than 1 cm at any point during the testing was considered failure and testing was discontinued.

Results: The primary outcome measure was calculated as the resultant displacement in the three cardinal planes. The independent t-test was used for statistical comparison. The locked plate group had significantly less displacement (mean ± SD 2.04±0.92 mm) than the iliosacral group (mean ± SD 5.605±1.101 mm); P=0.003. All five specimens in group 1 completed 10,000 cycles of testing without gross failure. Two specimens in group 2 failed macroscopically during the first 1,000 cycles. Data from these specimens were not included in the analysis of displacement.

Conclusions/Significance: A low profile 2-hole locked plate construct reduces overall displacement of vertically unstable sacral fractures and has a tendency to prevent early catastrophic failure in this biomechanical model.