your surgeon should be asking you that. The fact you are in the field and have no clue about templatimg/ligament balancing besides the fact you think they are stretched out enough to use 18mm polys…. I rarely use more then an 11mm for nasty 20-30 degree varus/valgus deformities. Did you go to training? What are they teaching these days? Insane your asking this on CP and even more insane your in the field in cases with little knowledge of what to do. Stay off CP for advice, go sit in some cases with reps who have been around awhile and ask questions and take notes. NO WAY IN HELL SHOULD YOU USE A 18MM POLY IN A TOTAL KNEE. If you find yourself there ask what the hell happened and how could have this been avoided, have that conversation with your surgeon, if he still has any trust in anything you say.