Crepitation is a medical term describing a distinct crackling, grating, or popping sensation or sound that occurs in the body. It is not a disease itself but a descriptive quality healthcare providers use to diagnose underlying issues. The sound may be audible or only felt as a palpable vibration when the affected area is touched. Crepitation can arise from different body systems, including joints, lungs, and skin, with causes and implications varying by location.
Crepitation in Joints
Joint crepitation, often called crepitus, is the most common form and is experienced as a clicking, cracking, or grinding noise during movement. It frequently occurs in the knees, shoulders, hips, and neck, but can affect any joint. Joint crepitus is categorized into two main mechanical causes: the popping of gas bubbles and the friction between rough surfaces.
The familiar sound of “cracking” knuckles is typically due to cavitation. This occurs when a joint is stretched, causing a rapid pressure change in the synovial fluid. The pressure drop causes tiny gas bubbles, primarily nitrogen and carbon dioxide, to form and rapidly collapse, producing the distinct popping sound. This type of crepitus is usually painless and harmless.
The more concerning cause is the friction of irregular surfaces rubbing together. Degraded cartilage, often from conditions like osteoarthritis, can expose the underlying bone, leading to a gritty, grinding sensation. This mechanical grating indicates wear within the joint space. When this sound is accompanied by pain, swelling, or limited mobility, it signals potential joint damage.
Crepitation in Lungs
In the lungs, crepitation is referred to as “crackles” and is heard by a healthcare provider using a stethoscope. These sounds are discontinuous, nonmusical, and brief, often likened to Velcro being slowly torn apart. Crackles are caused by the sudden opening of small, collapsed airways and alveoli that have been stuck closed by fluid or exudate.
Crackles are classified into two types based on their acoustic characteristics: fine and coarse. Fine crackles are short, high-pitched sounds that typically occur in late inspiration. Their presence often suggests conditions affecting the small air sacs, such as pulmonary edema or interstitial lung disease. Coarse crackles are louder, lower-pitched, and last longer, sounding more like a bubbling or rattling. These sounds are usually generated in larger airways and may indicate conditions involving excess secretions, like chronic bronchitis or pneumonia.
Crepitation in Skin
Crepitation in the skin is known as subcutaneous crepitus or subcutaneous emphysema. It is caused by air trapped within the subcutaneous tissue beneath the skin. When this area is pressed, it produces a unique crackling sensation, often described as feeling like pressing on “Rice Krispies” or bubble wrap. The air accumulation causes a smooth bulging of the skin, most commonly in the chest, neck, or face.
This trapped air typically originates from a tear or rupture in the respiratory system, allowing air to escape into surrounding soft tissues. Common causes include chest trauma, such as a collapsed lung (pneumothorax) or rib fractures, or a tear in the airway. Subcutaneous crepitus can also result from high-pressure mechanical ventilation or certain medical procedures. Its presence is a sign of a serious underlying injury that requires prompt attention.
When to Consult a Healthcare Professional
Crepitation alone is not always a sign of a serious medical problem, but its presentation alongside other symptoms signals a need for professional evaluation. For joint crepitus, the presence of accompanying pain, swelling, warmth, or a reduction in the joint’s range of motion should prompt a consultation. Painful grinding sounds, particularly in weight-bearing joints, may indicate joint damage that requires management.
Crepitation originating from the lungs, heard as crackles, is never considered normal and warrants immediate medical assessment. If the sound is accompanied by shortness of breath, fever, chest pain, or a persistent cough, it could signal conditions like pneumonia or heart failure. Subcutaneous crepitus also requires immediate attention, especially if it appears suddenly after an injury or trauma, as it can indicate a life-threatening air leak.