Finite element analysis and a pilot study of different fixation constructs for Danis-Weber A and B lateral malleolus fractures

Abstract

Background: Displaced lateral malleolus fractures are typically stabilised through open reduction and internal fixation. The biomechanically and clinically efficacy of locking plates and lag screws, particularly in Weber A and B distal fibular fractures remains a subject of contention. This study examines two locking plate designs for lateral malleolus fractures, evaluating their performance with and without interfragmentary screws using finite element models.

Methods: Utilising CT images of a healthy adult male volunteer, a three-dimensional finite element model was constructed. The Fibula-specific Flank Multiaxial Locking Anatomic Plate (FMLP) and the Conventional Locking Plate (CLP) were subjected to stabilisation, both with and without an interfragmentary screw, mimicking the Danis-Weber A and B lateral malleolus oblique fracture fixation. Loads of 140 N and 70 N, equivalent to 20% of the body weight, were applied to simulate the single-leg and two-leg standing conditions in the axial direction. The von Mises stress (VMS) distributions and element displacements were subsequently analyzed.

Results: In the Danis-Weber A fracture model group, the FMLP with an interfragmentary screw fixation exhibited the lowest peak VMS values: 51.9 MPa in the fibula, 89.0 MPa in the plate, and 61.3 MPa in the screws for simulating single-leg conditions. Under two-leg standing conditions, these peak VMS values decreased to 25.9 MPa in the fibula, 44.5 MPa in the plate, and 30.6 MPa in the screws, respectively. Furthermore, the overall structural peak displacements during single-leg standing for both Weber-A and B fractures with different implants ranged from 1.61 to 2.54 mm. While standing on two feet, the ranged was from 0.80 to 1.27 mm. An interfragmentary screw at the oblique fracture site resulted in reduced the peak value of VMS in the fibula, plate, screws, consequently decreased the overall structural displacement for FMLP and CLP fixation in lateral malleolus fractures.

Conclusions: The current finite element analysis (FEA) demonstrates that FMLP exhibits superior mechanical characteristics in Danis-Weber A and B lateral malleolus fractures compared to CLP. The inclusion of an interfragmentary screw, combined with locking plate design, enhances stability for simple oblique distal fibular fractures. The FMLP presents itself as potential as an alternative for lateral malleolus fractures from a biomechanical perspective. Nevertheless, further verification of these results is imperative through subsequent clinical studies.

Keywords: Ankle fracture; Fibular fracture; Finite element; Fracture fixation; Osteosynthesis.

Fig. 1

A schematic illustrating the Fibular Medial Locking Plate (FMLP) applied to the distal fibula. A Lateral view; B Front view

Fig. 2

Various geometric models for internal fixation were developed for lateral malleolus fractures of Danis-Weber A and B types. A1: FMLP for the type A fracture model. A2: FMLP with an interfragmentary screw for the type A fracture model. A3: Conventional Locking Plate (CLP) for the A fracture model. A4: CLP with an interfragmentary screw for the type A fracture model. B1: FMLP for Danis-Weber type B fracture. B2: FMLP with an interfragmentary screw for the type B fracture. B3: CLP for the type B fracture. B4: CLP with an interfragmentary screw for the type B fracture

Fig. 3

Boundary conditions of fibula fixation (A1 as an example)

Fig. 4

Von Mises Stress (VMS) distribution varied among different fracture types (Danis-Weber A and B) and fixation/implant methods (FMLP, CLP with or without an interfragmentary screw) in the position of one foot. A1: FMLP fo the type A fracture model. A2: FMLP plus an interfragmentary screw for the type A fracture model. A3: CLP for the type A fracture model. A4: CLP plus an interfragmentary screw for the type A fracture model. B1: FMLP only for the type B fracture. B2: FMLP plus an interfragmentary screw for the type B fracture. B3: CLP only for the type B fracture. B4: CLP plus an interfragmentary screw for the type B fracture. a. VMS distribution cloud diagram of the overall structure and fibula. b. VMS distribution cloud diagram of plate, screws, and interfragmentary screw

Fig. 5

Von Mises Stress (VMS) distribution varies concerning different fracture types (Danis-Weber A and B) and fixation/implant methods (FMLP, CLP with or without interfragmentary screw) in the two-foot standing position. A1: FMLP for the type A fracture model. A2: FMLP plus an interfragmentary screw for the type A fracture model. A3: CLP for the type A fracture model. A4: CLP plus an interfragmentary screw for the type A fracture model. B1: FMLP only for the type B fracture. B2: FMLP plus an interfragmentary screw for the type B fracture. B3: CLP only for the type B fracture. B4: CLP plus an interfragmentary screw for the type B fracture. a. VMS distribution cloud diagram of the overall structure and fibula. b. VMS distribution cloud diagram of plate, screws, and interfragmentary screw

Fig. 6

PeakVon Mises Stress (VMS) varies among different model groups representing Fibular Medial Locking Plate (FMLP), Conventional Locking Plate (CLP), with or without an interfragmentary screw for the fixation of Danis-Weber A and B fractures in the one-footed standing position

Fig. 7

Peak Von Mises Stress (VMS) varies among different model groups representing FMLP, CLP, with or without an interfragmentary screw for the fixation of Danis-Weber A and B fractures during the two-leg standing position

Fig. 8

Stress peaks and the displacement relative increment (%) of the distal fibula fractures are observed with different internal fixation groups during one-footed standing position

Fig. 9

Changes in the overall structural displacemenare evident in various model groups, including FMLP, CLP, with or without an interfragmentary screw, for the fixation of Danis-Weber A and B fractures during one-leg standing position

Fig. 10

Changes in fracture displacement are observed among different model groups, including FMLP, CLP, with or without an interfragmentary screw, for the fixation of Danis-Weber A and B fractures during two-leg standing position