Comparative study of the Orthofix and Pittsburgh frames for external fixation of unstable pelvic ring fractures.

We compared the mechanical performance of the Orthofix pelvic external fixator with that of the Pittsburgh triangular frame (PTF) on eight fresh-frozen cadaver pelves with experimentally created Malgaigne (double-vertical) fracture/dislocations. The pelves were quasi-statically loaded in longitudinal compression and loss of reduction (i.e., failure) was defined as 1.5 cm of diastasis at either of the fracture/dislocation sites. The Orthofix frame-pelvis complex (four 6-mm half-pins) was comparable to the PTF-pelvis complex (eight 5-mm half-pins) in terms of load to failure and overall stiffness, but was 4-7 times stiffer at lower load levels. Both frame-and-pin complexes deformed moderately at the pin-bone interface, but, while the PTF also showed moderate displacement between frame components, the Orthofix had almost no frame intercomponent motion.