Articulated external fixation of pilon fractures: the effects on ankle joint kinematics

The effect of the Orthofix articulated ankle external fixator on ankle and subtalar joint kinematics and fracture fragment motion was investigated in fresh cadaver specimens using biplanar radiographic analysis. The kinematic testing was performed for the normal ankle (i.e., no fixation) and for three alternate fixator hinge orientations. The fixator applications simulated a horizontal ankle axis (the current clinically preferred orientation), an axis coincident with a previously defined approximate ankle axis, and an axis located using a mechanical axis finder. The horizontal fixator application significantly disturbed normal ankle kinematics. Aligning the fixator hinge with an approximate ankle axis caused significant distortion of motion about only two of six possible rotational axes. Aligning the fixator hinge with the (specimen-specific) ankle axis determined by the axis finder most closely matched the motion of the normal ankle. For pilon fractures simulated by a transverse osteotomy, there appeared to be no physiologically significant fracture fragment motions, regardless of fracture stability or fixator orientation.