Analysing plate fixation of a comminuted fracture of the proximal ulna in relation to the elbow joint: a finite element study

Abstract

This study investigated the biomechanical behavior of four different screw configurations used to fix comminuted proximal ulna fractures with a locking compression plate (LCP), via a detailed finite element model based on realistic anatomical geometry. The model incorporated realistic anatomical geometry including both cortical and cancellous bone, soft tissue constraints, and loading conditions representing the physiological self-weight of the forearm, with the humerus fixed at its proximal end. The stress distribution on the plate, strain intensity within the bone tissue, and interfragmentary motion (IFM) between fracture fragments were evaluated for each configuration. The results indicate that all the tested configurations provide adequate stability under normal loading conditions, with no risk of material failure. However, excessive stress concentrations were observed in specific screw regions depending on the configuration, particularly when proximal screws anchoring the olecranon (e.g. screws 2 and 3 in Variant 3) were omitted. Strain analysis revealed moderate physiological bone loading across variants, whereas IFM assessment highlighted the importance of securing the coronoid and apical fragments to prevent compromised healing. These findings suggest that a specific reductions in osteosynthetic material, such as omitting certain diaphyseal screws while maintaining crucial olecranon and coronoid fixation, may provide sufficient fracture stabilisation under the modelled conditions, potentially minimising implant-related complications. This modelling approach offers a valuable tool for preclinical assessment of osteosynthesis strategies and supports future comparative research on fixation methods with varying biomechanical properties.

Keywords: Elbow joint; Finite element analysis; Interfragmentary motion; Locking compression plate; Olecranon fracture; Proximal ulna comminuted fracture.

Fig. 1

Analysing fracture of the ulna (left side– Model of the elbow joint with comminuted fracture; right side– CT image of the comminuted ulna)

Fig. 2

Complete model of geometry with detail of cartilages models

Fig. 3

The ulna with the position of the screws and visualisation of the fragment edges

Fig. 4

All variants of screws with plate (missing screws coloured red). Variant 1 includes all fixation screws. Variant 2 omits the middle bicortical screw from the distal fragment (screw 7, as per Table 1). Variant 3 omits the screws that anchor the proximal fragment of the olecranon (screws 2 and 3, as per Table 1). Variant 4 is configured like Variant 2 (omitting screw 7) but additionally omits the screw that holds the coronoid fragment in place (screw 5, as per Table 1)

Fig. 5

Visualisation of loads and constraints for the computational model (red line– fixed, blue point– mass 2.7 kg)

Fig. 6

Visualisation positions of tendons for muscles and ligaments via the element LINK180 (blue lines– ligaments; red lines– muscles) with example of the tendon connection markings on the bone model

Fig. 7

Proximal part of the ulna model with marked frictional and fixed areas

Fig. 8

Model of geometry– used sub-models and visualisation of the sub-model mesh

Fig. 9

Workflow of the methodology

Fig. 10

Distribution of von Mises stress for all the variants (focused areas have the highest equivalent stress distribution)

Fig. 11

The von Mises stress distribution with sub-modelling results with its local maximum in each variant

Fig. 12

Strain intensity on each fragment on the fracture planes for each variant

Fig. 13

Olecranon fracture– IFM of fragment A

Fig. 14

Coronoid fracture– IFM of fragment B

Fig. 15

IFM of fragment C