Stiffness of the locking compression plate as an external fixator for treating distal tibial fractures: a biomechanics study

Abstract

Background: Locking compress plate, as external fixator, is an attractive technique for distal tibial fracture treatment. But it still remains unclear whether the external LCP has sufficient stiffness. Thus, the present study aims to make a comprehensive evaluation of the stiffness of external locking compress plate when it is used as an external fixator in distal tibial fractures treatment.

Methods: Composite tibia was used to simulate distal tibia fracture (Orthopedic Trauma Association type 43 A3 fracture). The fractures were stabilized with medial distal tibial locking compress plates (LCP group), medial distal tibial locking compress plates with 30-mm plate-bone distances (EF-tibia group), and medial distal femur locking compress plates with 30-mm plate-bone distances (EF-femur group). Stiffness of each configuration was measured under axial compression loading and in axial torsion loading directions. Compression stiffness and torsional rigidity were compared across different groups.

Results: Compared with LCP group, (1) EF-tibia group showed significantly lower (p < 0.001) compression stiffness and torsional rigidity; (2) EF-femur group showed significantly lower (p < 0.001) compression stiffness, but significantly higher (p < 0.001) torsional rigidity.

Conclusions: The results indicated that locking compress plate as an external fixator was flexible, and the distal femur locking compress plate was preferred over the distal tibial locking compress plate to be an external fixator in distal tibia fracture treatment.

Keywords: Biomechanics; External fixation; Fracture; Locking compression plate; Tibia.

Fig. 1

Examples of different models of specimen. The tibia in the external fixation (EF)-femur model (a) was plated on the medial aspect using an ure titanium 5-mm 9 + 7-hole LCP (medial distal femur plate, Kanghui), with a distance of 30-mm between the surface of the tibia to the lower surface of the plate. Standard, pure titanium 5-mm cortical screws were used in proximal slot nos. 1, 2, 4, and 7, as well as in distal slot nos. 10, 11, 12, and 13. The tibia in the EF-tibia model (b) was was plated on the medial aspect using a pure titanium 3.5-mm 9 + 10-hole LCP, with a distance of 30-mm between the surface of the tibia to the lower surface of the plate. Standard, pure titanium 3.5-mm cortical screws were used in proximal slot nos. 1, 2, 5, and 8, as well as in distal slot nos. 12, 13, 16, 17, and 18. The tibia in the LCP model (c) was plated on the medial aspect using a standard, pure titanium 3.5-mm 9 + 10-hole LCP, with standard, pure titanium 3.5-mm cortical screws used in proximal slot nos. 1, 2, 5, and 8, as well as in distal slot nos. 12, 13, 16, 17, and 18

Fig. 2

Load deformation curves in different models. The group-level load deformation curves of samples in EF-femur, LCP, and EF-tibia models were obtained in the axial compression and torsion rigid tests. The deformation curves were plotted in black line for EF-femur model, in red line for LCP model, and in green line for EF-tibia model. Panel a: x-axis, deformation (mm); y-axis, load (N). Panel b: x-axis, rotational deformity (deg); y-axis, toque (Nm)

Fig. 3

Comparison of compression stiffness and torsional rigidity in different models. Values of compression stiffness and torsional rigidity are displayed in black, grey, and white bars for LCP, EF-femur, and EF-tibia models respectively. Asterisk **** indicates a significant difference (p < 0.0001) between models