A Finite Element Analysis of Fracture Obliquity on the Stability of Tension Band Wiring in the Treatment of Olecranon Fractures

Introduction: Tension band wiring (TBW) is a common form of fixation for olecranon fractures which occur commonly in the elderly. More unstable, oblique fractures are thought to not do as well and the more expensive plate fixation is preferred. This study aims to elucidate the limits for which simple olecranon fractures can be safely fixed using a tension band wire construct.

Methods: An anonymised, CT scan of the right upper limb of a middle aged male was used to create a 3D model of the ulna using MIMICS (v19.0, Materialise, Belgium). This was subsequently exported to SOLIDWORKS (Dassault Systèmes, France) for modelling of the TBW construct and creation of fracture lines at the midpoint of the olecranon at 90, 75, 60 and 45 degrees to the long axis of the ulna. Finite element analysis was carried out using ABAQUS. The model was constrained proximally, and increasing axial loads of 50N, 250N and 500N was applied distally. Displacement was measured in the X, Y and Z axis for nodes placed along the fracture line.

Results: A total of 36 analysis was carried out with ABAQUS. At axial loads of 50, 250 and 500N, the tension band wire construct demonstrated good stability with minimal displacement in all axis at all fracture angles. There was a trend towards increased fracture displacement with greater loads. There was an increase in fracture displacement associated with decreasing fracture angle, most markedly at fracture angle below 60 degrees. At 500N of axial loading, net displacement was 0.000000183mm for the 90° fracture, 0.0043mm for 75° fracture, 0.0096mm for 60° fracture and 0.0132mm for 45° fracture.

Conclusion: The tension band wire appears to be stable at loads up to 500N at fracture angles ranging from 45 to 90 degrees to the ulna shaft. It may be prudent to avoid early loading of more oblique fractures to prevent risk of displacement.