Final answer:
The uterosacral ligament is the structure that joins the sacrum to each side of the uterus, playing an important role in stabilizing the uterus' position.
Step-by-step explanation:
The ligament that joins the sacrum to each side of the uterus is known as the uterosacral ligament. This ligament serves a crucial role in stabilizing the position of the uterus by connecting the cervix, which is the lower part of the uterus, to the sacrum. The uterosacral ligament forms part of the network of ligaments that help maintain the orientation of the uterus within the abdominopelvic cavity, which also includes the broad ligament and the round ligament.
While the sacrum is also supported by ligaments such as the anterior and posterior sacroiliac ligaments, sacrospinous ligament, and sacrotuberous ligament, these are primarily concerned with supporting the pelvic structure rather than the uterus. The uterosacral ligament is particularly significant in terms of anchoring the uterus to the pelvic wall, thereby providing posterior support to the uterus.