What exactly are the "complications" that occur with tear trough implants?

I have been researching ways to fill the hollow under my eyes after an overly-aggressive lower bleph. It seems to me that implants would be ideal--they are permanent unlike fillers, and more consistent than fat grafting (some doctors swear by it, but others seem very wary of it... what gives?!). Anyway, I keep reading that tear trough implants almost always have complications and often end up requiring removal. Is this true, and if so, what exactly are the complications? Thanks!