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.