A biomechanical study comparing minimally invasive anterior pelvic ring fixation techniques to external fixation

Introduction: INFIX and Pelvic Bridge are two new minimally invasive surgical techniques for unstable pelvic ring injuries, and they have demonstrated early clinical success in small, single-center case-series. The primary objective of this study is to gather evidence speaking to the biomechanical stability of internal bridging methods relative to external fixation, with the expectation of biomechanical equivalence. Methods: Ten human cadaveric pelvic specimens were dissected free of all skin, fat, organs, and musculature and were prepared with a partially unstable pelvic ring injury (OTA/AO 61-B). The specimens were randomized to two groups and were repaired and tested with anterior pelvic external fixation (APEF) and INFIX sequentially, or APEF and Pelvic Bridge sequentially. Testing was performed with each specimen mounted onto a servo-hydraulic testing frame with axial compression applied to the superior base of the sacrum under five axial loading/unloading sinusoidal cycles between 10 N and 1000 N at 0.1 Hz. Relative translational motion and rotation across the osteotomy site was reported as our primary outcome measures. Outcome measures were further analyzed using a Wilcoxon signed-rank test to determine differences between non-parametric data sets with significance defined as a p value < 0.05. Results: We found no statistical difference in translation (p = 0.237, 0.228) or rotation (p = 0.278, 0.873) at the fracture site when comparing both new constructs to external fixation. Under the imposed loading protocol, no episodes of implant failure or failure at the bone-implant interface occurred. Discussion: Our study provides the biomechanical foundation necessary to support future clinical trial implementation for pelvic fracture patients. While biomechanical stability of these newer, subcutaneous techniques is equivalent to APEF, the surgeon must take into account their technical abilities and knowledge of pelvic anatomy, patient-specific factors including body habitus, and the potential complications associated with each implant and the ability to avoid them.