lengthening done on tibias and around 10% of the length will almost result in no lifelong sideeffects given it was done with a surgeon who knew what he was doing. however there will be 1 side effect stated by ppl who did ll decades ago, ezily getting tired. The amount of work you could do with the new leg would be less than before and it will get tired more easily unless you build up alot of strength in gym for years.