The intercostal muscles are a group of muscles that form a significant part of the chest wall. They are located within the intercostal spaces, which are the gaps between adjacent ribs. Their placement is integral to the structural integrity of the rib cage. These muscles work in concert with the diaphragm to facilitate the mechanical process of breathing and maintain the shape of the thoracic cavity.
Anatomy: Location and Types
The intercostal spaces house three distinct layers of muscle, arranged from the most superficial to the deepest. The outermost layer is the external intercostal muscle, whose fibers angle downward and forward. This layer extends from the back of the rib cage around to the point where the bony rib meets the cartilage near the front of the chest.
Beneath the external layer lies the internal intercostal muscle, with fibers running in the opposite direction—downward and backward. This fiber orientation is perpendicular to the external layer, providing a cross-hatch pattern that enhances the strength of the chest wall. The internal intercostals are found primarily from the breastbone toward the back, extending to the angle of the ribs.
The deepest layer is the innermost intercostal muscle, which often has a similar fiber direction to the internal layer. A space separates the internal and innermost layers, and this gap contains the intercostal neurovascular bundle. This bundle consists of the intercostal vein, artery, and nerve, which run along the underside of the rib for protection.
Primary Role in Respiration
The primary function of the intercostal muscle group is to alter the volume of the thoracic cavity, making them direct contributors to the process of ventilation. The external intercostals are the main muscles of inspiration, working alongside the diaphragm. When they contract, they pull the ribs upward and outward, which expands the chest cavity and decreases the pressure inside the lungs.
The internal and innermost intercostals perform the opposite action, primarily assisting with forced expiration. Their contraction pulls the ribs downward and inward, which decreases the size of the thoracic cavity and actively pushes air out of the lungs. Quiet, relaxed breathing out is normally a passive process that relies on the elastic recoil of the lungs and chest wall.
During quiet breathing, these muscles also serve an important function by stabilizing the rib cage. They prevent the spaces between the ribs from being sucked in or pushed out by the pressure changes that occur as the diaphragm moves up and down. This stability ensures that the breathing mechanics remain efficient, even when the body is in motion. The coordinated action of these opposing muscle groups allows for smooth and controlled expansion and contraction.
Common Causes of Intercostal Muscle Pain
Pain originating from the intercostal muscles or surrounding structures is a frequent cause of chest discomfort.
Muscle Strain
A common issue is muscle strain, which happens when the fibers are overstretched or torn due to sudden, forceful movements. Activities like heavy lifting, abrupt twisting of the torso, or repetitive motions in sports can cause this type of injury. Prolonged or severe coughing and sneezing fits are also known to cause strain because they involve powerful, sudden contractions of the chest wall muscles. Pain from a muscle strain is typically localized, feels sharp or pulling, and worsens noticeably with movement, deep breathing, or touching the affected area.
Costochondritis
Other causes of pain include costochondritis, which is inflammation of the cartilage that connects the ribs to the breastbone. While not a muscle issue itself, the pain is often confused with muscle pain because it is localized to the chest wall. This inflammation can result from physical strain, such as severe coughing, or may occur without a clear cause.
Intercostal Neuralgia
A distinct source of discomfort is intercostal neuralgia, which is pain related to the intercostal nerves that run through the muscle layers. This nerve pain is often described as burning, sharp, or stabbing, and it wraps around the chest and back along the path of the affected nerve. Causes of neuralgia can include nerve compression from an injury, trauma from a rib fracture, or irritation due to a viral infection like shingles.
It is important to seek medical attention for chest pain, especially if it is severe, follows a significant trauma, or is accompanied by symptoms like shortness of breath. A medical professional can properly distinguish between a simple muscle strain, a potentially more serious rib fracture, or nerve-related pain.