Sliding performance of unilateral external fixators for tibia.

Some unilateral external fixators have a sliding mechanism to achieve dynamic axial fixation. However, it has been reported that binding of this mechanism occurs during routine ambulation. The Hifixator, a unilateral external fixator, has been developed which has a new type of sliding mechanism. The mechanism of the Hifixator was tested by connecting it to a fractured bone model with pins, and applying dynamic axial loading. The conditions of connection between the pins and bone model were varied to simulate loosening of the pins. Two other external fixators commonly used for tibias, Orthofix and Monotube (blue), were tested for comparison. The amount of sliding motion of the Hifixator was maintained at more than 72% of the motion at the fracture site even when pins were loose and a torque of 4 N m was applied. The sliding mechanism of the Hifixator was shown to be more durable than those of the other fixators tested for conditions found in application to tibias.