What Is Crepitus?

What's That Crackling Sound?

Knee pain and crepitus.
Nisian Hughes/The Image Bank/Getty Images

Crepitus is defined as a crackling or grating feeling or sound under the skin, usually in the joint or around the lungs. Essentially, it is a sound coupled with a sensation. The term "crepitus" is derived from the Latin, meaning "rattling or creaking."

Crepitus and Joint Conditions

In soft tissues, crepitus is often due to gas, most often air, that has abnormally penetrated and infiltrated an area. The palpable (i.e., readily seen, heard, or felt) crunching or grating sensation, when present, is generated with movement or motion.

Crepitation can also occur when roughened articular (joint) surfaces or extra-articular (other than joint) surfaces are rubbed together via active or passive motion. There may be pain or discomfort associated with crepitus, but that is not always the case -- crepitus can occur without pain.

In a joint, crepitus can be indicative of cartilage wear. For example, when crepitus is detected in the patellofemoral, tibial, or femoral condyles around the knee, degenerative changes would likely be evident arthroscopically.  Crepitus also can occur with chronic inflammatory types of arthritis. In such cases, there is roughening of the opposing surfaces of joints due to erosion and the presence of granulation of tissue. Crepitus is also a symptom associated with rotator cuff tears.

When cartilage within a joint completely erodes or is worn away, the result is bone-on-bone. The sound of crepitus, which is associated with a joint that has become bone-on-bone, typically is a high frequency, audible, palpable squeak.

Crepitus must be differentiated from cracking and popping sounds that may be associated with the shifting of ligaments and tendons over bone surfaces as movement occurs. The shifting of ligaments and tendons over bone is not necessarily associated with arthritis. It occurs with normal movement of a normal joint, too.

Another distinctive characteristic worthy of mention -- with scleroderma, there is a distinct, coarse, creaking crepitus that is palpable and audible over the tendon sheaths upon movement.

Crepitus and Lung Conditions

Crepitus also is used to describe sounds produced by the lungs in certain conditions, such as interstitial lung disease. In such cases, crepitus may be loud enough to be heard with the human ear. Sometimes, a stethoscope is necessary to hear the crepitus associated with lung conditions.

The Bottom Line

While we now understand what crepitus is, within the diagnostic process, crepitus is just one clue and not a very distinctive one. Several conditions and disease processes can be associated with crepitus. The diagnostician must look deeper, utilizing imaging and lab tests, to identify the underlying condition.    

Sources:

Osteoarthritis: Diagnosis and Medical/Surgical Management. Fourth edition. Chapter 7 - Osteoarthritis: Clinical Presentations. Hooper and Moskowitz. Wolters Kluwer | Lippincott Williams & Wilkins. 2007.

Kelley's Textbook of Rheumatology. Ninth edition. Elsevier. Chapter 40 - History and Physical Examination of the Musculoskeletal System. Davis, Moder, and Hunder.

Rotator Cuff Tears. OrthoInfo.org. AAOS.
http://orthoinfo.aaos.org/PDFs/A00064.pdf

Online Etymology Dictionary. Crepitus.
http://www.etymonline.com/index.php?term=crepitus

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