The sternum, often called the breastbone, is the long, flat bone in the center of the chest that connects the ribs via cartilage. Many people experience an audible “pop” or “click” from this area when performing stretches or movements that expand the chest. While the sensation can be startling, a sternum popping sound without other symptoms is usually a normal mechanical event. Understanding the mechanics of joint noises and chest wall anatomy clarifies why this happens during stretching.
The Science Behind Joint Sounds
Joint sounds, including those from the sternum, generally result from two physiological phenomena. The most common explanation for a sharp, sudden sound is cavitation, which involves synovial fluid, a viscous liquid that lubricates joint surfaces.
When a joint is stretched, separating the surfaces causes a rapid decrease in pressure within the joint capsule. This sudden drop forces dissolved gases, primarily carbon dioxide and nitrogen, to rapidly come out of solution. The instantaneous formation or subsequent collapse of this temporary gas bubble generates the distinct popping sound.
A secondary cause of joint sounds is the movement of soft tissues like tendons or ligaments. As the body moves, a tendon may momentarily catch or snap over underlying bone or cartilage. This tension and release creates a reproducible clicking or snapping noise as the structure returns to its normal position. These mechanical sounds are often more subtle than the sound produced by cavitation.
Anatomical Origins of Sternum Popping
The popping sensation near the sternum originates from movement within the small, flexible joints of the chest wall. The sternum is a series of articulations that permit the chest to expand and contract during breathing and movement. The two most common sources for this audible release are the costosternal and sternoclavicular joints.
The costosternal joints are where the ribs connect to the sternum through flexible costal cartilage. These joints allow for slight gliding and movement as the chest expands during a deep breath or stretch. When stretching the chest, a minor shift or momentary misalignment of the rib’s cartilage against the sternum can occur. This results in a popping sound as the joint surfaces separate and realign.
The sternoclavicular joints, located at the top of the breastbone, connect the collarbones (clavicles) to the manubrium, the upper part of the sternum. These joints are the only direct skeletal connection between the arm and the trunk of the body. Stretching the arms or shoulders exerts forces on the clavicle, causing a slight mechanical shift in the sternoclavicular joint that may lead to an audible click or pop.
Associated Symptoms Requiring Medical Attention
While a sternum pop during stretching is typically a harmless mechanical occurrence, certain accompanying symptoms suggest an underlying issue requiring professional evaluation. The presence of pain that is sharp, persistent, or worsens with movement is a clear indication to consult a healthcare provider. Pain suggests the mechanical event is irritating surrounding tissues or that joint surfaces are not moving smoothly.
Any visible swelling, localized tenderness, or warmth around the sternum or rib joints should also prompt a medical consultation. These symptoms can indicate inflammation, potentially pointing toward conditions such as costochondritis or a less common inflammatory disorder like Tietze syndrome. Inflammation suggests a more significant structural irritation than a simple mechanical sound.
If the popping sensation is accompanied by joint instability or a sense that the joint is “giving way,” medical attention is appropriate. Popping that began immediately following trauma or an accident, or is associated with difficulty breathing or chest tightness, should be evaluated urgently. These symptoms may suggest a more serious injury, such as a sternal fracture or a joint subluxation.