Reduction and fixation capabilities of different plate designs for pubic symphysis disruption: a biomechanical comparison.

BACKGROUND: Typical stabilisation of pelvic open book injuries consists in plate fixation of the symphysis, leading to many different plate designs and procedures that have evolved. However, implant loosening and development of chronic instability are still evident and represent major complications after plate fixation of the symphysis. The aim of this study was to analyse reduction and fixation capabilities of different classical plate techniques with dynamic compression (DC), prebending or modern interlocking screws.
METHODS: Compression injuries (OTA B1.1) were simulated on synthetic composite pelvises. Sensor films placed in the disrupted symphysis allowed assessment of reduction and compression forces, as well as contact characteristics by implants at defined time points under static non loaded conditions. The commercially available steel plates used in our study differed in curved design, prebending and DC- or locking screw capabilities, as narrow large fragment (4.5) or small fragment plates (3.5).
RESULTS: DC procedure clearly increased the compressive force in the symphysis and improved the reduction by enhanced contact areas. These effects were preserved to the end of the experiments only when the plates were prebended (10°). Anatomically contoured and prebended 3.5 plates had a similar effect, but the contact area was even more pronounced. Best results were observed using the "3.5 symphyseal plate" with DC-effect medially and locking screws laterally. Purely interlocking screw plates by themselves allowed an optimal contact area, yet failed to preserve the initial compressive reduction force.
CONCLUSIONS: The experimental results suggest a biomechanical advantage in using prebended plates for symphysis fixation compared to non-bended plates. Best results with regard to compression and increased contact area can be achieved by anatomically contoured plates with combined DC and locking screw capabilities. These findings are of special interest in pelvic surgery for choosing the right implant in severe displacements, obese patients and symphysiodesis techniques.