Behavior of an external fixation frame incorporating an angular separation of the fixator pins. A finite element approach.

A finite element model has been developed to simulate the deformation that occurs at the fracture site of an externally fixed bone as a result of applied bending, compression, and torsional loads. The pin configuration in this model is constructed to allow an angular separation of the fixator pins. The mechanical effect of this angular separation and of the distribution of the pins along the fixator bar is examined. The model shows that an angular separation of the pins provides a more symmetric deformation of the fracture site when a bending load is applied in different directions to the bone and thereby protects a fracture from excessive movement in any direction. The torsional stability of an external fixation frame is considerably increased by incorporating an angular separation of the pins. The model also shows that the most stable configuration for the fixator uses a wide separation of the pins along the fixator bar.