Sternocostal joints

Diagram of the sternocostal joints

The sternocostal joints are the articulations between the sternum and the costal cartilages of the ribs. These joints play a crucial role in the mechanics of breathing by allowing the thoracic cage to expand and contract.

Anatomy

The sternocostal joints are classified into two types: the first sternocostal joint and the second to seventh sternocostal joints.

First Sternocostal Joint

The first sternocostal joint is a primary cartilaginous joint, also known as a synchondrosis. It is formed by the articulation of the first costal cartilage with the manubrium of the sternum. This joint is unique because it is immovable, providing stability to the upper part of the thoracic cage.

Second to Seventh Sternocostal Joints

The second to seventh sternocostal joints are synovial plane joints. These joints are formed by the articulation of the costal cartilages of the second to seventh ribs with the lateral border of the sternum. Each of these joints is surrounded by a thin, fibrous capsule lined with synovial membrane, allowing for slight gliding movements.

Ligaments

Several ligaments support the sternocostal joints, providing stability and limiting excessive movement.

• Radiate Sternocostal Ligaments: These ligaments radiate from the costal cartilages to the anterior and posterior surfaces of the sternum, reinforcing the joint capsule.
• Intra-articular Sternocostal Ligament: Present in the second sternocostal joint, this ligament divides the joint into two cavities.

Function

The primary function of the sternocostal joints is to facilitate the movement of the thoracic cage during respiration. The slight gliding movements allowed by the synovial joints enable the ribs to elevate and depress, increasing and decreasing the volume of the thoracic cavity, respectively.

Clinical Significance

Disorders of the sternocostal joints can lead to pain and restricted movement. Conditions such as costochondritis, an inflammation of the costal cartilage, can cause significant discomfort and are often mistaken for cardiac pain due to their location.

Related Pages

• Rib
• Sternum
• Costal cartilage
• Thoracic cage
• Respiration