Clinical and biomechanical aspects of external fixation of the pelvis

Objective. The aim was to evaluate the mechanical stability of several traditional and modern external fixators in unstable pelvic ring disruption. Design. In a laboratory study external and internal fixation techniques were tested in seven fresh and five embalmed human pelves with a disruption of the pubic symphysis and one sacroiliac joint (type C1.2 injury according to the Tile-AO classification). Background. Stability provided by external fixation depends upon many factors, with the residual pelvic stability being the most important. Methods. Simulating a single-leg stance, the load was applied quasi-statically to the acetabulum of the unstable hemipelvis. Device failure was defined as displacement >10 mm either at the symphysis pubis or the sacroiliac joint. Results. The frame with the highest failure load (fresh versus embalmed specimens) was the Egbers configuration with the AO fixator (analysis of variance; P < 0.05). Failure was noted at 114.9 N versus 129.5 N. Augmentation of the Mono-Tube by additional internal posterior osteosynthesis gave the following results: sacral bars 325.4 N versus 217.8 N, plate fixation 294.3 N versus 215.8 N, lag screws 338.4 N versus 215.8 N. Failure loads of hybrid fixation of the Orthofix were as follows: sacral bars 257.9 N versus 213.9 N, plate fixation 333.5 N versus 245.3 N, lag screws 397.3 N versus 280.6 N. The differences between the two fixators were not statistically significant. Conclusions. No single external frame provided sufficient stability. The addition of a posterior internal fixation significantly increased failure loads and controlled the weight-bearing pelvic elements.