The sound can be created when two rough surfaces in an organism's body come into contact—for example, in osteoarthritis or rheumatoid arthritis when the cartilage around joints erodes and the surfaces in the joint grind against one another, or when the two fractured surfaces of the broken bones rub together.<unk>  is a common sign of bone fracture.<unk>  can easily be created and observed by exerting a small amount of force on a joint, thus 'cracking it'. This is caused by bubbles of nitrogen forming in the synovial fluid bursting. Almost every joint in the body can be 'cracked' in this way, but the joints which require the least amount of effort include the hallux, knuckles and neck joints. In soft tissues,<unk>  can be produced when gas is introduced into an area where it is normally not present. The term can also be used when describing the sounds produced by lung conditions such as interstitial lung disease—these are also referred to as "rales".<unk>  is often loud enough to be heard by the human ear, although a stethoscope may be needed to detect instances caused by respiratory diseases. In times of poor surgical practice, post-surgical complications involved anaerobic infection by Clostridium perfringens strains, which can cause gas gangrene in tissues, also giving rise to<unk> . Subcutaneous<unk>  (or surgical emphysema) is a crackling sound resulting from subcutaneous emphysema, or air trapped in the subcutaneous tissues.
Crepitus
Linitis plastica
Arcus senilis
Oral galvanism
Nevus anemicus
Steatopygia
Pellagra
Trichostasis spinulosa