Impact of a void in the equine medial femoral condyle on bone stresses and peak contact pressures in a finite element model.

The study investigates the effects of a 2-cm subchondral bone void in the medial femoral condyle (MFC) of an equine stifle on bone stresses and contact pressures. This influence is examined under different degrees of internal femoral rotation using a finite element model (FEM) constructed from a computed tomography image of a young horse’s stifle.

FEM Construction and Experiment Design

• The finite element model (FEM) was developed from the computed tomography (CT) scan of a one-year-old horse’s stifle.
• This CT image was segmented into various anatomic components relevant to the research and then meshed into four-node tetrahedrons for accurate simulation.
• The FEM had material properties of bone designated based on Hounsfield units, which is a unit of measure used in CT imaging to define the radiodensity of tissues.
• The soft tissue properties were derived from previously published data.
• The model was then loaded with 8000 N (newtons) while in a 155° extension to simulate the physical conditions faced by the stifle.

Finding and Results

• The researchers noticed that most of the stress in an intact MFC was compressive, with minor areas subjected to shear and tension stresses.
• When the experiment introduced a 2-cm void in the MFC, there was a substantial increase in all forms of stress; peak compression stress increased by 25%, shear stress by 50%, and tensile stress by 200%.
• The void also resulted in an increase of 30% in the tension and shear stress acting on the medial meniscus, a crescent-shaped fibrocartilage positioned between the two joints formed by the femur and tibia.
• Additionally, an applied load with internal femoral rotation (IFR) of 2.5° and 5° saw an 8%-21% increase in peak MFC stresses.

Conclusion

• The presence of a 2-cm void in an equine stifle’s MFC, as simulated by the FEM, led to increased stress in both the bone and the medial meniscus.
• Even a slight Internal femoral rotation contributed to a rise in the predicted bone stress.
• The study implies that increased stresses on bones and medial meniscus might explain the lack of healing seen in MFV voids over time and shed light on possible mechanisms of medial meniscus damage.