The first half of 2018 has been a pretty good one across the board for most, but not all, U.S. healthcare stocks. The sector-tracking iShares U.S. Healthcare ETF (NYSEMKT: IYH) is up 7.1% in 2018, without any help from a couple of troubled drugmakers and a dental equipment specialist that you're probably more familiar with than you think.While there were plenty of smaller biotechs that imploded this year, most of those start-ups, at their peak, were worth less than a Lebron James contract.