Novel hook plate for radial semilunar lip facet fragment fixation: a finite element analysis

Abstract

Intra-articular fractures of the distal radius require anatomical reduction and stable fixation. When the fracture encompasses the articular facet of the bone, maintaining the reduction is challenging due to the fragment's size and high instability. While specific implants have been developed to fix this fragment, their effectives have been limited. This study evaluates the mechanical performance of a novel hook plate conceived to stabilize the small fragment of the semilunar facet of the radius in non-osteoporotic bones. A simulated lunate facet fracture was created in an adult radius in a virtual model, and a modification of a hook plate was developed using computer-aided design (CAD). Two groups were established for the finite element method (FEM) simulation: a control group (standard plate Medartis™ (Switzerland, A-5500.23) and an angled plate with hooks set at 60º, 90º and 120º. In the FEM simulation, an axial load of 100 N was applied in the Z-axis direction on the fragment. Fracture displacement along the Z axis was more pronounced in the control model (0.32 mm) and less in the angled models, ranging from 0.22 to 0.28 mm. Notably, the plate with a 90° angle showed a more effective reduction in fragment displacement. The distribution of stresses in the system showed the highest levels of stress in the control group (59.31 MPa), followed by the subgroup with a 60° angle (55.78 MPa).In the side view, the control model showed a higher concentration of stresses (59.74 MPa), while the model with a 90° angle showed a lower value of stresses (18.87 MPa). Critical stress regions were identified in the bolts of the control and 120° models (59.47 MPa and 57.64 MPa, respectively). However, in the 90° model, no critical regions were observed in the bolts, which showed lower stress values, reaching 26.33 MPa. In the bone, the greatest concentration of stress occurred in the region where the plate was anchored. Our results showed that the 90° hook plate had a superior mechanical performance in fixing simulate lunate facet fractures at the distal radius. This angle led to minor displacements and minimized stress concentrations in the hardware, thus contributing to enhance the stability of this specific fracture.

Keywords: Biomechanics; Distal radius; Finite Element Analysis; Novel hook plate; Volar marginal fractures.

Fig. 1

Different types of fracture fixations of the lunate lip facet. The top row represents the profile of the distal end of the radius, and the bottom row represents the front view of the bone. The control is represented by the standard plate and the other drawings represent the fixation with the hook plate with different angles

Fig. 2

Boundary conditions (100 N load on the fragment) and tetrahedral mesh in the distal radius with a tetrahedral mesh. The fragment (in purple) is fixed with a hook plate

Fig. 3

The displacement along the Z-axis of the models is displayed in side view, according to scale

Fig. 4

Displacements along the Z-axis with the different plates

Fig. 5

The von mises equivalent stress is illustrated for plates and screws, with the stress levels represented according to a scale. The arrows in the diagram point to the regions experiencing the highest levels of tension within various groups. Areas highlighted in red denote the zones of maximum stress concentration, whereas areas shaded in dark blue indicate the regions with the lowest stress concentration

Fig. 6

Von mises equivalent stress in plates and screws, the maximum values observed are shown in the graph

Fig. 7

Von mises equivalent stress in bone models without implants according to the scale. Arrows indicate the region of higher tension in the different groups

Fig. 8

Von mises equivalent stress in bone without implants. The maximum values are observed in the graph