Question: What is the difference between a uniplane external fixation system and multiplane external fixation system, and how do you code each type of application? Arizona Subscriber Answer: Generally, external fixation systems are devices made of metal rods, wires, and pins designed to provide stability to fractured leg bones. If there is a single metal rod (or fixator) on which the wires and pins are placed, it’s a uniplane fixation system. You should code this procedure with 20690 (Application of a uniplane (pins or wires in 1 plane), unilateral, external fixation system). If, on the other hand, the surgeon uses more than one metal rod (or fixator) to fix pins and wires, then it is a uniplane external fixation system, which you’d code with 20692 (Application of a multiplane (pins or wires in more than 1 plane), unilateral, external fixation system (eg, Ilizarov, Monticelli type)).