Spondylitis is a chronic inflammatory disease that affects the spine and sacroiliac joints, causing pain, stiffness, and fusion of the bones. It is caused by the immune system attacking the joints, resulting in inflammation and excessive bone growth. Common symptoms include back pain that worsens in the morning and with activity. Diagnosis involves blood tests, X-rays, and imaging to detect changes in the bones. While there is no cure, treatment focuses on reducing inflammation and pain through medications, physical therapy, exercise, and sometimes surgery.