So what is it about unilateral that prevents the FE?
50% less fat globules get reamed out of the bone canal, and subsequently your body's mechanism for dissolving these fat globules is faster/more efficient. This decreases your chances of fat globules getting dislodged in your lungs, brain or brain stem. Even by very very rare chance, fat embolism syndrome does occur in unilateral lengthening, it will also most likely have low incidence of mortality due to less fat globules that are dislodged or are in your blood stream
Look at how many unilateral deformity corrections/leg length discrepancy surgeries are done around the united states and the incidence of fat embolism syndrome and compare that to the ~2% chance from cosmetic bilateral femoral lengthening.
It should also be noted that femurs have higher chance of getting fat embolism than tibias. Dr. Paley has never seen a fat embolism syndrome from bilateral tibia lengthening. Also research papers have shown that femurs trauma has a higher incidence of FES than tibias. Bilateral internal tibias should be generally safe when it comes to fat embolism syndrome if anyone is considering that. However internal tibias can cause permanent knee pain due to the rod going through the knee joint.
Thus, my own research has shown that external tibias are the safest and least invasive form of lengthening, although recovery will take longer and must wear frames for long time. Also I can only advise a max of 5 cm for tibias due to biomechanical and proportion issues. And if you want to do internal lengthening, you should do unilateral femurs.