Biomechanical comparison of different acetabular plate systems and constructs--the role of an infra-acetabular screw placement and use of locking plates.

Abstract

The aim of this study was the direct comparison of the static fixation strength of two common plate systems: MPS (Matta Pelvic System) and LPPS (Low Profile Plate System). Furthermore the role of a modified screw placement with addressing the infra-acetabular corridor and the use of locking screws were evaluated. Custom made anterior column fractures in artificial SYNBONE pelves were fixed with different acetabular plates (group I: MPS, group II: LPPS none locking and group III: LPPS locking). Each pelvis was tested twice, with the additionally placed infra-acetabular lag screw [+] first, followed by a repeated measurement without the infra-acetabular screw [-]. Six pelves per group were tested under static loading with six cycles up to 800N, each. The fracture displacement was measured in the weight bearing dome using an ultrasound based Zebris-3D-Motion Analyzer. The MPS-plate had a less fixation strength compared to the LPPS-plate (mean±SD of maximum fracture displacement [mm] in group I vs. group II=0.63±0.02 vs. 0.37±0.02, p<0.05). The locking feature did not increase the fracture fixation strength (mean±SD of maximum fracture displacement [mm] in group II vs. group III: 0.37±0.02 vs. 0.37±0.03; ns). The infra-acetabular screw significantly reduces the maximum fracture displacement in all groups, independent of the plate systems ([Delta%] in group I=50; group II=63 and group III=40; p<0.05 each). The LPPS-plate performed superior fixation strength for anterior column fractures compared to the MPS-plate. The locking plate modality did not reduce the maximum fracture displacement, whereas the additional infra-acetabular screw placement actually doubles the fracture fixation strength independent of the used plate system.