Ankylosing spondylitis (AS) is a chronic inflammatory disease primarily affecting the spine and sacroiliac joints, but it also has significant effects on the rib joints and lungs. The disease causes inflammation where ligaments and tendons attach to bones, leading to pain, stiffness, and eventually fusion of the spine. When AS involves the rib joints and lungs, it can severely impact breathing and lung function.
The rib cage expands and contracts with each breath, allowing the lungs to fill with air. This movement depends on the flexibility of the joints between the ribs and the spine, as well as the elasticity of the chest wall. In AS, inflammation can affect these rib joints, particularly the costovertebral and costosternal joints, causing them to become stiff and less mobile. Over time, this stiffness reduces the ability of the ribs to expand during inhalation, limiting chest expansion and lung inflation.
As the disease progresses, the spine itself may fuse in a fixed, curved position (kyphosis), which further restricts the chest cavity. This spinal fusion combined with stiffened rib joints leads to a mechanically restricted thoracic cage. The chest cannot expand fully, so lung volumes decrease, resulting in a restrictive pattern of lung impairment. This means that although the lungs themselves may be healthy, they cannot fully inflate because the chest wall is too rigid.
In addition to mechanical restriction, AS can cause inflammation and scarring in the lung tissue itself. This scarring, or fibrosis, reduces lung elasticity and impairs gas exchange, making breathing even more difficult. The combination of chest wall rigidity and lung tissue damage can lead to symptoms such as shortness of breath, reduced exercise tolerance, and an increased risk of lung infections.
The reduced lung capacity in AS patients is often measured by pulmonary function tests, which show decreased forced vital capacity (FVC) and total lung capacity (TLC). These changes correlate with the severity of spinal deformity and rib joint involvement. Some studies report that between 18% and 57% of people with AS develop restrictive lung disease due to these factors.
Because the lungs are compromised, people with AS may find it harder to recover from respiratory infections. The inflammation and fibrosis can also increase vulnerability to infections like pneumonia. Therefore, protecting lung health is crucial for people with AS, including avoiding smoking and getting vaccinated against common respiratory infections.
Breathing exercises and physical therapy play an important role in managing lung and rib joint involvement in AS. Deep breathing exercises help maintain chest expansion and prevent further loss of rib cage mobility. Regular physical activity, especially exercises that promote spinal and chest flexibility, can reduce stiffness and improve lung function. Maintaining good posture and preventing spinal fusion through early treatment also help preserve chest wall movement.
Medications used to treat AS, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and biologics like TNF inhibitors, reduce inflammation and may slow the progression of joint damage and lung involvement. Early diagnosis and consistent treatment are key to preventing severe complications affecting the ribs and lungs.
In summary, ankylosing spondylitis affects the lung and rib joints by causing inflammation and stiffness in the joints that connect the ribs to the spine, leading to reduced chest expansion. Spinal fusion further restricts the thoracic cage, resulting in decreased lung volumes and restrictive lung disease. Lung tissue inflammation and scarring may also occur, compounding breathing difficulties. Managing these effects involves medication, physical therapy, breathing exercises, and lifestyle measures to protect lung health and maintain chest mobility.