If you're hearing a snapping or popping sound when you stretch your rib cage, it is most likely your breast bone or sternum popping. Your first seven ribs are connected to your sternum and held in place by ligaments and cushioned by cartilage, all of which move together when you stretch.
According to Drs. Michael Roizen and Mehmet Oz on Cleveland.com, it is usually quite difficult to identify the exact cause of popping joints, also known as crepitus, but a number of possible causes exist, most of which are not serious and generally don't require treatment.
Joints often pop during movement as gas is released. Most of the time, joint popping is normal and does not cause pain. Consult a doctor if you have pain with rib cage popping or difficulty breathing.
Normal Bone Movement and Popping
Your ligaments connect to your rib bones and control the range of movement within your joints. If these connective tissues become tight — for example, through weightlifting exercises such as the bench press — they will move less smoothly over the bones in your joints. As a result, they might grate or snap over your rib joints when you stretch, making a popping noise as they move into the new position.
Slipping Rib Syndrome
An injury to your chest can place additional pressure on the muscles in your chest and your rib joints, which can ultimately lead to rib cage popping. It can also damage your ligaments and tendons, which may cause subluxation — or bone slipping — in the joints.
This occurs when the connective tissues are unable to adequately support your rib joints through their normal range of movement during a stretch, causing a condition called slipping rib syndrome, according to Medical News Today. Instead, the injured ligaments or tendons snap out of position and can make a popping sound as they do so.
Joint Gas Bubbles
The joints in your rib cage are cushioned by cartilage, which is covered in a membrane of synovial fluid. This substance helps the bones move smoothly within the joint, and is made up of a number or of different gases.
When you stretch your ribs and chest beyond their normal range of movement, the joint expands and the pressure changes within the fluid, according to The Joint Chiropractic. This causes bubbles to form and, when they burst, you might notice your chest pops when stretching.
Cartilage and Inflammation
Two conditions can cause cartilage inflammation in your ribs: costochondritis and Tietze's syndrome. Both are brought on by repeated physical strain, such as persistent coughing or vomiting. However, costochondritis can also result from a chest infection, including after chest or heart surgery.
Cartilage inflammation can mean your rib joints move less freely and the bones may grate or snap over the affected cartilage as you move or stretch. If you believe either of these conditions are the cause of your ribs popping, or your rib popping interferes with your ability to breath easily, you should see a doctor immediately.