Shares of Medical Properties Trust (MPW 2.53%) have defied the market downdraft this year. The real estate investment trust (REIT) has rallied about 35%, significantly outperforming the roughly 10% decline in the S&P 500. That's a welcome turn for investors, given the stock's struggles in recent years. Even with that big rally, shares of the healthcare REIT still offer a compelling dividend yield of more than 6%. Here's a look at whether it still has more upside ahead.What drove this year's rally?The past f ...