Michael Frank ran his finger down his medical bill, studying the charges and pausing in disbelief. The numbers didn’t make sense. His recovery from a partial hip replacement had been difficult. He’d iced and elevated his leg for weeks. He’d pushed his 49-year-old body, limping and wincing, through more than a dozen physical therapy sessions. The last thing he needed was a botched bill. His December 2015 surgery to replace the ball in his left hip joint at NYU Langone Medical Center in New York City had been routine.