Ah, the humble flip-flop. Unglamorous in essence, often constructed of rubber and plastic, and costing just a couple bucks (unless you're springing for an exorbitant designer version or this $18K pair ), they're ideal for poolside wear or sandy situations. Designer Christian Louboutin is actually a huge fan of 'em . But they're mired in controversy when it comes to being worn while running around the city ( Jennifer Aniston doesn't seem to mind , nor does Kristen Wiig ). Now, there's a new concern associated with the oft-debated footwear: Injuries, as Lena Dunham kindly brought to our attention on Instagram last night.We're not just talking about garden-variety strap chafing or inadequate arch support. Dunham ended up in a Lenox Hill hospital after stumbling over her shoes. "But seriously I tripped over my flip-flop," Dunham captioned the shot of herself looking pretty peeved and, well, flopped on a hospital bed. The snapshot shows her accompanied by a stethoscope and hospital gown to ominously underscore where one could end up simply by donning flip-flops. X-rays revealed it was a "just a stupid sprain" and Dunham said she left the ER "intact but for my pride."So, wherever you stand on the mingling of flip-flops and dirty streets, there's clearly a more pressing paranoia now involved with wearing the divisive sandals than just the potential for, oh, deadly staph infections and such.