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

OBJECTIVE

To predict bone and medial meniscal stresses and contact pressures in an equine stifle with a medial femoral condyle (MFC) intact or with a 2-cm subchondral bone void, under varying degrees of internal femoral rotation (IFR).

STUDY DESIGN

Finite element model (FEM) of a cadaveric equine stifle loaded to 8000 N.

METHODS

The FEM was constructed from computed tomography (CT) of the right, extended stifle of a yearling. The CT image was segmented into relevant anatomic structures and meshed into 4-node tetrahedrons. Bone material properties were assigned according to Hounsfield units, soft tissue properties were estimated from published data, and the model was loaded to 8000 N in 155° extension.

RESULTS

The main stresses found in the intact MFC were in compression, with very small areas of shear and tension. Adding a 2-cm MFC void increased peak compression stress by 25%, shear by 50%, and tension by 200%. An MFC void also increased tension and shear placed on the medial meniscus by 30%. Under load, IFR of 2.5° and 5° increased MFC peak stresses 8%-21%.

CONCLUSION

A 2-cm MFC void in an equine stifle FEM increased stress in the bone and meniscus. Internal femoral rotation slightly increased predicted bone stress.

CLINICAL SIGNIFICANCE

Increases in bone and meniscal stress predicted in an MFC with a void provide evidence to understand the persistence of voids and mechanism of damage to the medial meniscus.