In spring 2007, I went surfing. The weather was wild, the water was cold, and although it was exhilarating being thrown about in the waves, it was also chastening to feel so helpless pitting my relatively puny body against the churning tide.

At a certain point, turning one way but being propelled in the opposite direction by the sea, I felt a stab of pain in my left hip. I thought little of it then, though the next day I noticed a dragging sensation whenever I took a step. I shrugged this off as a minor injury, expecting it to settle down over time.