While the exact cause behind the sharp cracking noise from joints is not known, it is believed that joints may snap or pop due to the release of gases dissolved in the synovial fluid. As the bones pull apart when you stretch, the connective tissue capsule surrounding the joint also stretches. This is followed by a decrease in the pressure of the synovial fluid, which causes the gases dissolved in the fluid to form bubbles. Crepitus is the medical term used for the crackling sound that can be heard when these bubbles burst. It is believed that such sounds might also be heard when a tendon snaps over a joint or the ligaments are stretched rapidly. Though cracking noises are often heard from the knuckles, knees, neck, or back, some people experience popping in their sternum while stretching. If the noise is not accompanied by pain or other symptoms, it's nor really a cause of serious concern. Popping of the Sternum The sternum, which is commonly referred to as the breastbone, is a T-shaped bone that is located at the center of the chest. It is divided into the manubrium, gladiolus, and the xiphoid process. The manubrium attaches to the first two pairs of the true ribs, meeting the gladiolus at an angle (sternal angle). The lower part of the sternum is a cartilaginous extension that is known as the xiploid process. The sternoclavicular joint is the articulation between the clavicle (collarbone), manubrium, and the first costal cartilage (cartilage connecting the sternum and the ends of the rib). Many people feel that cracking their joints (knuckles, back, or knees) releases stress and provides relief. Some people feel that the feeling of pressure in the chest resolves when the sternum pops back into place with a physical maneuver. When Should You Consult a Doctor Do consult a doctor, if these cracking noises are accompanied by swelling, tightness in the chest, and pain. It must be noted that the area below the sternal angle is more susceptible to fractures. Here are some medical conditions that might be associated with a popping sternum. Trauma to the Chest Blunt trauma to the chest can cause the sternum to develop cracks. Trauma to the chest can occur in the event of a hard blow to the chest, car accident where the chest slams against the steering wheel, or a fall. Osteoarthritis, which is a degenerative disease which is characterized by the inflammation of the cartilage in the joints, can make one susceptible to fractures. When the ends of the broken bone rub against each other, popping or clicking sounds might be heard. Ligament Injuries Though a small section of the sternoclavicular joint is actually attached to the sternum, it is supported by strong ligaments. Sternoclavicular injuries are quite rare, but rapid stretching of these ligaments or a severe injury can cause the joint to become unstable. Under such circumstances, the joint could pop. At times, the joint might be stable, but the intra-articular disc ligament may get injured. Strain due to lifting heavy objects can also lead to subluxation or dislocation of the sternomanubrial joint. At times, the sternum might be pushed posterior to the manubrium in the event of hyperflexion of the thoracic spine. Costochondritis Costochondritis, which is a condition that is characterized by the inflammation at the junction of the rib and costal cartilage, could be a contributing factor. Severe coughing, trauma to the chest, upper respiratory tract infections, or strain could lead to costochondritis. Tietze's syndrome is a similar condition, which can be differentiated from costochondritis due to the presence of swelling of the costal cartilage. Sternal Instability Persistent pain in the sternum and clicking/grinding noises could occur in the event of sternal instability. Also referred to as sternal non-union, sternal instability is used with reference to a sternum that does not heal after trauma or surgery. Cases of sternal instability have been reported in case of people who have undergone coronary artery bypass grafting, wherein median sternotomy is followed. On a concluding note, popping of joints should not be looked upon as a serious problem, unless it is accompanied by pain or discomfort. Physical examination and imaging tests can help doctors diagnose if popping is linked to any injury or joint problem. Once the underlying cause is identified, doctors can recommend suitable treatment options to stabilize the joint and speed up the healing process. Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.