The sternum, or breastbone, is the long, flat bone in the center of the chest. It protects the heart and lungs, connecting to the ribs via flexible cartilage. While a “crack” or “pop” sensation is possible, a true fracture rarely occurs without significant force. The noise experienced is typically related to joint movement, not the bone breaking.
Mechanisms of a True Sternal Fracture
A sternal fracture requires substantial, direct force to the anterior chest wall. The most common mechanism is high-impact blunt force trauma, such as a motor vehicle collision. In these accidents, the chest often strikes the steering wheel or is subjected to rapid deceleration, concentrating immense pressure on the breastbone.
While preventing catastrophic injuries, shoulder seatbelts can focus deceleration forces directly onto the sternum, increasing the incidence of this specific fracture. Because the sternum is robust, its fracture signals that a powerful force has been transmitted through the chest cavity. Therefore, a sternal fracture is rarely an isolated injury, often occurring in conjunction with other thoracic trauma.
The sternum’s proximity to vital structures, including the heart, major blood vessels, and lungs, makes this injury high risk. A significant concern is blunt cardiac injury, or myocardial contusion, where the heart muscle is bruised by the impact. Fractures can also be associated with serious spinal injuries.
In rare cases, a fracture can occur without a single traumatic event. These stress or insufficiency fractures are typically seen in individuals with underlying conditions like severe osteoporosis or kyphosis, which weakens the bone structure. Repetitive, strenuous activities, such as weightlifting or golfing, can also lead to these uncommon stress fractures.
Common Causes of Sternal Popping and Clicking
The sensation of the sternum “cracking” or “popping” is caused by the movement of cartilage and joints in the chest wall. The sternum connects to the first seven pairs of ribs through costal cartilage, forming the sternocostal joints. These joints can produce audible sounds through normal movement.
One common explanation for the noise is cavitation, which is the release of gas bubbles within the joint fluid, similar to cracking knuckles. This phenomenon is often painless and occurs during deep stretches or certain torso movements. The cartilage itself can also be the source of the sound, as it may shift slightly when the chest wall moves during breathing or twisting.
Inflammation of the cartilage that joins the ribs to the sternum is a frequent cause of sternal discomfort and occasional popping, known as costochondritis. This condition causes localized chest pain and tenderness. A related, but rarer, inflammatory condition is Tietze syndrome, which involves noticeable swelling on the chest wall.
Movement or instability in the sternoclavicular joint, where the collarbone meets the top of the sternum, can also result in a clicking sound. Muscle tension from poor posture, physical activity, or even severe anxiety can create strain on the chest wall muscles. When these tight muscles suddenly spasm or release, they can momentarily shift the joints and produce a crackling sound known as crepitus.
When to Seek Emergency Medical Attention
Any pain or sound following an accident or trauma warrants a medical evaluation due to the risk of associated internal injuries. Immediate emergency attention is necessary if the chest pain is severe, sharp, or rapidly worsening. Pain that increases significantly with deep breathing, coughing, or sneezing is a common symptom of a sternal fracture and should be a cause for concern.
Other red flag symptoms require prompt medical assessment:
- Difficulty breathing or shortness of breath, which can indicate damage to the lungs or a flail chest injury.
- Visible signs like bruising, swelling, or a noticeable deformity or tender lump over the breastbone.
- Pain that radiates to the jaw, arm, or back, suggesting a potential cardiac issue.
To accurately diagnose a sternal injury, physicians rely on imaging studies, since a simple physical examination may not reveal a small fracture. While a lateral chest X-ray is often the initial step, a Computed Tomography (CT) scan is the preferred diagnostic tool. The CT scan provides a detailed view of the sternum and detects associated internal injuries. Electrocardiograms (ECGs) and blood tests for troponin levels are also used to rule out potential damage to the heart muscle.