The first time John Johnson's artificial hip squeaked, he was bending down to pick up a pine cone in his yard in Thomasville, Georgia. Johnson looked up, expecting to find an animal nearby. Susan O'Toole, a nutritionist at Montefiore Medical Center in New York, who first squeaked going up stairs after getting home from her hip-replacement surgery in 2005, said she thought the banister she was gripping needed repair. And Edward Heary, an apprentice appraiser in Hatboro, Pennsylvania, said clients sometimes look with embarrassment or concern at their floorboards when he walks though their homes. As those three patients -...