Knee effusion, sometimes called water on the knee, occurs when excess fluid accumulates in or around the knee joint. Common causes include arthritis and injury to the ligaments or meniscus, which is cartilage in the knee.
CTS is common in pregnancy and can occur in 31% to 62% of people who are pregnant. Researchers aren’t sure why CTS is so common in pregnancy. They speculate that pregnancy-related hormones might contribute to increased swelling throughout the body.