Influence of flexible fixation for open book injury after pelvic trauma--a biomechanical study.
BACKGROUND
Implant loosening is frequently detected after fixation of open book injuries. Though many authors do not see this as a complication, it is often the reason for hardware removal or reinstrumentation in the case of remaining instability. We hypothesized that the flexibility of the implant has an influence on loosening and thus on failure of the construct.


METHODS
We used 6 fresh-frozen pelvic specimens and tested them with our recently introduced test setup for two-leg alternate loading. We subjected them to a non-destructive quasi-static test in the intact condition followed by a non-destructive cyclic test under axial sinusoidal loading with progressive amplitude. Afterwards we simulated an open book injury and performed fixation with three different configurations of a modular fixation system (1-, 2- or 4-rod configuration) in randomized order. Subsequently, the specimens were subjected to 3 cyclic tests with the same loading protocol as previously defined. Finally, each construct was cyclically tested to failure keeping the final rod configuration.


RESULTS
We detected significantly greater mobility after 1-rod-fixation and no significant differences after 2-rod or 4-rod-fixation compared to the intact symphysis condition. In the destructive test series the 4-rod-fixation failed first followed by the 1-rod-fixation. The 2-rod-fixation sustained almost 3 times as many load cycles prior to failure as the 4-rod-fixation, whereas the 1-rod-fixation sustained twice as many cycles as the 4-rod-fixation.


CONCLUSIONS
In conclusion, flexible fixation of the ruptured pubic symphysis in human specimens shows superior behavior with respect to load bearing capacity and ability to withstand cyclic loading compared to stiff constructs.
BG Trauma Center, Eberhard Karls University, Schnarrenbergstrasse 95, D-72076 Tuebingen, Germany. Electronic address: fabian.stuby@uni-tuebingen.de.
Fabian M
FM
Stuby
BG Trauma Center, Eberhard Karls University, Schnarrenbergstrasse 95, D-72076 Tuebingen, Germany. Electronic address: sdoebele@bgu-tuebingen.de.
Stefan
S
Doebele
AO Research Institute Davos, Clavadelerstrasse 8, CH-7270 Davos, Switzerland. Electronic address: yash.agarwal@aofoundation.org.
Yash
Y
Agarwal
AO Research Institute Davos, Clavadelerstrasse 8, CH-7270 Davos, Switzerland. Electronic address: markus.windolf@aofoundation.org.
Markus
M
Windolf
AO Research Institute Davos, Clavadelerstrasse 8, CH-7270 Davos, Switzerland. Electronic address: boyko.gueorguiev@aofoundation.org.
Boyko
B
Gueorguiev
BG Trauma Center, Eberhard Karls University, Schnarrenbergstrasse 95, D-72076 Tuebingen, Germany. Electronic address: gochs@bgu-tuebingen.de.
Bjoern Gunnar
BG
Ochs
D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D001860:Bone Plates; D002102:Cadaver; D005260:Female; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery; D007866:Leg; D008023:Ligaments, Articular / Q000293:injuries / Q000601:surgery; D008297:Male; D009068:Movement; D011474:Prosthesis Design; D011631:Pubic Symphysis / Q000293:injuries* / Q000601:surgery; D012421:Rupture / Q000503:physiopathology / Q000601:surgery; D012446:Sacroiliac Joint / Q000293:injuries / Q000601:surgery; D016474:Weight-Bearing
Biomechanics; Flexible fixation; Implant loosening; Open book; Pelvic ring