The effect of osteochondral fragment loss on maximal tibiotalar articular stress in posterior malleolus fractures: A finite element study

Introduction

Posterior malleolus fractures are frequently associated with varying degrees of comminution. This comminution often leads to osteochondral fragment loss from the posterior articular surface of the tibial plafond. The purpose of this study is to use finite element modeling to determine whether osteochondral defects at the posterior malleolus fracture interface significantly influence tibiotalar contact stress.

Methods

3D models of 10 randomly selected patients were created of the tibia and talus from CT scans. A layer of cartilage was added to simulate contact at the tibiotalar joint. Different circular osteochondral defects were modeled at the fracture interface 3 mm, 5 mm, 10 mm in diameter. Two sizes of fractures were modelled (5 mm and 10 mm), from the posterior-most point on the articular tibial surface. Models with fractures and without osteochondral defects, were tested as controls. Models were loaded in finite element software under single-leg-stance at average body weight. Scenarios were repeated for maximal dorsiflexion and plantarflexion. Differences between the sizes of osteochondral defects across different fracture sizes for each ankle range of motion scenario were determined.

Results

No significant differences in maximum articular contact stresses were observed between different sized osteochondral defect sizes in the 5 mm fracture size and ankle range of motion scenarios. However, significant differences in maximum articular contact stresses were observed between different sized osteochondral defect sizes with 10 mm fracture sizes. These differences were observed in neutral and dorsiflexion, but not in plantarflexion.

Conclusion

Larger posterior malleolus fractures with osteochondral defects, when loaded with the ankle in neutral and dorsiflexion, resulted in larger tibiotalar articular stresses.