Crepitus is a medical term to describe the sound and sensation created when two rough surfaces in the human body come into contact - for example, in osteoarthritis (where the cartilage around joints has eroded away, and joints grind against one another), or when the ends of two broken bones rub together. The term can also be used when describing the sounds produced by conditions such as emphysema. Crepitus is often loud enough to be heard by the human ear, although a stethoscope may be needed to detect incidences caused by respiratory diseases.