• Jonathan M Vigdorchik, Amanda O Esquivel, Xin Jin, King H Yang, and Rahul Vaidya.
• Orthopaedic Surgery, Detroit Medical Center, 4D4 University Health Center, Detroit Receiving Hospital, Wayne State University, 4201 St. Antoine Blvd., Detroit, MI 48201, USA. JVigdorchik@gmail.com
• Int Orthop. 2013 Jul 1; 37 (7): 1341-6.

PurposeThe purpose of this study was to evaluate the biomechanical stability and compressive forces across the sacroiliac (SI) joint of an anterior internal fixator compared to the femoral distractor and external fixator for vertically unstable pelvic fractures.MethodsFive composite pelvises with a simulated APC type III injury fixed with a femoral distractor, external fixator, or anterior internal fixator were tested. A pressure-sensitive film (Tekscan) was placed in the disrupted SI joint recording the magnitude of force. Then, in a single-leg stance model (Instron machine), a load was applied through the sacrum. We recorded displacement at the pubic symphysis and SI joint using high-speed video. Peak load and displacement were measured, and axial stiffness was calculated. Values were compared using a Student's t-test (p < 0.05).ResultsThe SI joint was compressed significantly (p < 0.001) more using the anterior internal fixator (18.9 N) and femoral distractor (18.6 N) than the two-pin external fixator (2.5 N). There was no significant difference between the anterior internal fixator and the femoral distractor in displacement at the SI joint. The pubic symphysis displaced less with the femoral distractor than the anterior internal fixator (5.5 mm vs. 4.1 mm; p < 0.05).ConclusionsThe anterior pedicle screw internal fixator allows for indirect compression across the sacroiliac joint that is superior to two-pin external fixation and comparable to the femoral distractor. The anterior internal fixator may be an option for temporary anterior pelvic fixation in situations where external fixation or the femoral distractor have otherwise been used.

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