Finite Element Analysis of Protective Measures against Lateral Hinge Fractures in High-Tibial Osteotomy

Abstract

Background: Opening wedge high-tibial osteotomy (OWHTO) is widely used for correcting mechanical axis deviations and offloading the medial compartment in unicompartmental osteoarthritis. However, lateral hinge fractures (LHFs) pose a significant complication. This study investigates protective measures to mitigate these fractures, guided by prior observations of mechanical stress impact on LHFs.

Purpose: The study aims to assess the effectiveness of different protective measures, specifically the use of varying sizes of Kirchner wires and drill holes, in reducing the incidence of LHFs during OWHTO. Study Design. The study employs a quantitative, comparative analysis using a finite element method (FEM) based on computed tomography (CT) scans.

Methods: Using CT-based FEM, the study compares the impact of different sizes of K-wires (1.6 mm, 2.0 mm, and 2.5 mm) and drill holes (3.2 mm and 4.5 mm) on the mechanical stresses around the hinge area in OWHTO. The models were created from a CT scan of a healthy 33-year-old male, focusing on the force required to open the osteotomy gap and the incidence of cracked shell elements.

Results: The study found that thicker K-wires increased the force required to open the osteotomy gap, whereas larger apical holes decreased it. The 4.5 mm apical hole model demonstrated significantly fewer cracks compared to the 2.0 mm K-wire model, with no significant difference observed compared to the 2.5 mm K-wire model. Models using a 1.6 mm K-wire or a 3.2 mm drill hole did not significantly reduce cracks compared to the base model.

Conclusions: The findings suggest that a 4.5 mm drill hole may be more effective in reducing the risk of LHFs compared to thinner diameter K-wires or smaller apical holes. Both a 2.5 mm K-wire and a 4.5 mm drill hole reduce the number of cracked elements, but the 4.5 mm drill hole also significantly decreases the average and maximum principal stresses as well as the average tensile strength ratio at the hinge area. These findings may be important for surgical planning, particularly in cases requiring increased osteotomy distraction.

Figure 1

(a) Density (mg/mm³) and (b) Young's modulus (MPa) of the tibia model after conversion of CT values through Keyak's formula.

Figure 2

Models used in the study. (a) Base uniplanar opening wedge HTO model (b) 3.2 mm apical hole model (c) 4.5 mm apical hole model (d) 1.6 mm K-wire model (e) 2.0 mm K-wire model (f) 2.5 mm K-wire.

Figure 3

Loading (area around the tip of the red arrow) and boundary conditions (2 mm of proximal tibia from the joint line) are shown. The red arrow represents the direction of the tangential distractive force at the osteotomy site.

Figure 4

(a) Force required to open the osteotomy site vs. gap. (b) Maximum principal stress vs. gap. (c) Average principal stress vs. gap. (d) Tensile strength ratio vs. gap.

Figure 5

Anteroposterior and lateral views of a model. Note that the surface cracks do not cover join on the lateral side, representing to an osteotomy without hinge fracture.