Dislocation of the sternum, or breastbone, is possible but exceptionally rare. The sternum is a flat, protected bone at the center of the chest, requiring a tremendous amount of force to separate its joints. Any sternal dislocation indicates a high-energy impact, requiring doctors to prioritize investigating potential damage to underlying internal structures.
Understanding the Sternum’s Joints
The sternum is composed of three parts that articulate with other bones, forming joints where dislocation can occur. The most common site is the sternoclavicular (SC) joint, where the clavicle (collarbone) meets the upper part of the sternum (manubrium). This joint relies heavily on strong ligaments for stability, making it the most susceptible to separation under extreme stress.
A less frequent area for dislocation is the manubriosternal joint, located between the manubrium and the main body of the sternum. This junction is reinforced by cartilage and offers very little motion, making its dislocation extremely uncommon and almost always the result of severe trauma.
Common Causes of Dislocation
Sternal joint dislocation requires substantial blunt force delivered directly to the chest or indirectly through the shoulder. The most frequent cause is high-speed motor vehicle accidents, where the chest impacts the steering wheel or is compressed by a seatbelt. This force often overcomes the strong ligamentous support of the joints.
Severe injuries sustained during contact sports, such as football or hockey, can also cause dislocation. This happens either from a direct blow to the chest or, more commonly, from an indirect force transmitted when falling onto an outstretched hand or the shoulder tip. This indirect force drives the shoulder inward, leveraging the clavicle against the sternum and causing separation.
Dislocations are classified by the direction of displacement. An anterior dislocation, where the bone is pushed forward, is more common. A posterior dislocation, where the bone is pushed backward, is a greater concern because the bone fragment can compress or damage major blood vessels, the trachea, or the esophagus, which lie directly behind the sternum.
Recognizing the Signs of Injury
A sternal joint dislocation causes immediate, severe pain localized to the center of the chest near the breastbone or collarbone. Pain is often exacerbated by movements like raising the arm, deep breathing, or coughing. With an anterior dislocation, a visible deformity, such as a lump or prominence, is often noticeable at the injury site.
A posterior dislocation may not present with an obvious lump. Instead, it can cause symptoms related to compression of underlying structures, including difficulty breathing, hoarseness, or a sensation of throat constriction. Diagnosis typically begins with a physical examination but requires imaging. A Computed Tomography (CT) scan is the preferred method to clearly visualize the dislocation, its direction, and rule out damage to the heart, lungs, and major blood vessels.
Treatment and Recovery
Treatment for a sternal joint dislocation depends on the specific joint and the direction of displacement. For less severe, non-displaced injuries or stable anterior dislocations, conservative management is used. This focuses on rest, immobilization with a sling, and pain management. This approach allows the ligaments and joint capsule to heal naturally over several weeks.
If the dislocation is acute, unstable, or posterior, a reduction procedure is required to reposition the bone. A closed reduction involves manually guiding the bone back into place without surgery, which is sometimes successful for anterior dislocations. However, an open reduction and internal fixation (ORIF) is often necessary for unstable or posterior dislocations. Surgery helps reduce the risk of internal damage and ensures the joint is securely stabilized. Following reduction, the joint is immobilized, and a recovery period of two to eight weeks is common before activity can gradually resume.