LC2 screws may significantly increase fixation stability when compared with plate osteosynthesis in type IIIa fragility fractures of the pelvis: A biomechanical comparison study.

Abstract

Fragility fractures of the pelvis (FFP) from low-energy trauma are increasingly frequent in older patients. FFP type IIIa, with displaced posterior ilium fracture, usually needs surgical treatment and its optimal fixation technique is unclear. Here, construct stiffness and failure load after fixation of an FFP type IIIa with anterior plate osteosynthesis (PO) with an additional lateral compression 2 (LC2) screw, was compared with PO alone under weight-bearing conditions. Twelve artificial left hemipelvises with simulated FFP type IIIa fractures were assigned into the PO (for fixation with an anteriorly fixed 3.5-mm plate) or PO with a 7.3-mm fully threaded antegrade LC2 screw (POLC2) groups (n = 6 per group). All specimens underwent ramped loading (at 18 N/s) from 20 N (preload) to 200 N, followed by progressively increasing cyclic testing at 2 Hz until failure, performed at 0.05 N/cycle on a servohydraulic material test system. Relative displacements and bone fragment angles were monitored using motion tracking. Initial stiffness (N/mm) did not differ significantly in the PO vs POLC2 group (139.8 ± 31.7 vs 140.1 ± 27.0). After 5000 cycles, dynamic stiffness was significantly higher in the POLC2 group than in the PO group (199.0 ± 20.4 vs 163.8 ± 25.2, p = 0.041) while fracture displacement, torsional fracture displacement, and gap angle were significantly increased in the PO group than in the POLC2 group (p < 0.0001). Cycles to failure and load to failure were higher in the POLC2 group (6922 ± 1133 and 892.2 ± 113.3 N, respectively) when compared with the PO group (4979 ± 943 and 697.9 ± 94.3 N, respectively) (p = 0.015). Compared with plate osteosynthesis alone in an FFP type IIIa model, antegrade LC2 screw augmentation demonstrated significantly increased stability against axial and torsional loading. The combined plate-LC2 screw construct might be an ideal fixation option for posterior iliac fracture of FFP, safely allowing early weight bearing and rehabilitation.