noun
sacroiliac joint
Anatomical term for the joint between the sacrum and the ilium.
仙腸関節の痛みは腰痛の原因の一つです。
Pain in the sacroiliac joint is one cause of lower back pain.
Compound of 仙 (sen, 'sacrum'), 腸 (chō, 'intestine', here used in the anatomical sense of 'ilium'), and 関節 (kansetsu, 'joint'). The derivation is straightforward from the kanji components.