Dynamic trapezoid external fixation: Enhancing temporary stability in unstable pelvic ring fractures.

Background: Unstable pelvic fractures often require emergency temporary external fixation before definitive management by internal fixation. The objective of this study was to improve the stability of the posterior arc of the pelvic ring during the placement of a temporary external fixator.

Hypothesis: Did a temporary pelvic external fixator with dual bars (compression and distraction) enhances posterior pelvic stability by increasing posterior compression?

Materials and method: Four supracetabular fixation setups, including a "dynamic trapezoid external fixator" (a supra-acetabular external fixation construct featuring two connecting rods, one in compression and the other in distraction), were tested on foam pelvis models with simulated sacroiliac disjunction. Each configuration was also tested with a supra-acetabular pin partially or fully inserted into the SA corridor. Stability was assessed using a biomechanical model through reproducible cranial and lateral traction force applied to the iliac tuberosity under a 20N load to identify the most effective temporary pelvic ring stabilization method. Each measurement was repeated 10 times per configuration. Student's t-test and two-way analysis of variance (ANOVA) was used to compare the different models.

Results: Sacroiliac displacement under vertical and lateral forces was measured for each configuration. Fully inserted supra-acetabular pins significantly reduced displacement compared to half insertion (p < 0.001). The "dynamic" construct exhibited the lowest displacement across all configurations (mean 2.9 ± 0.9 mm under lateral force; 1.8 ± 0.3 mm under vertical force). Compared to other constructs, it was significantly associated with superior stability (p < 0.005). ANOVA confirmed the effects of construct type (p < 0.0001) and SA pin length (p < 0.0001) on displacement, with the "dynamic" construct and full pin insertion yielding the best outcomes.

Conclusion: Our study demonstrates that a dynamic trapezoidal supra-acetabular external fixator, with rods in compression and distraction, enhances resistance to vertical and horizontal displacement of SI joint compared to other construct. Though not fully replicating in vivo conditions, this model supports a streamlined approach to temporary pelvic stabilization.

Level of evidence: V; In Vitro Research.