Here, I explore the anatomy of the pelvic ligaments, their structure, attachments, and how they mature through the decades of a person’s life.
Progression of Fusion
A complex fascial structure wraps the major bony structures of the pelvis. Like those osseous structures, the ligaments also evolve as we age. As a result, we have more boney pieces held together by cartilaginous plates that fuse as decades pass in the first two decades. Eventually, in our 4th or 5th decade, all of the pelvic joints, including the sacroiliac joint, fused into one large pelvic structure. These ligaments atrophy as the bones fuse.
In this illustration, for clarity, they are shown as very separate structures. However, in reality, they appear more like thickened sections woven together into a larger whole.
The sacroiliac ligament has three sections – anterior, interosseous, and posterior.
- The anterior section has mostly oblique fibers. They cross over the joint on the anterior surface near the 3rd sacral segment and seem
- to prevent anterior slippage.
- The posterior section is located in the deep depression between the ala of the sacrum and the PSIS. It has fibers that run almost laterally to connect the lateral posterior aspect of the upper two segments to the PSIS and the internal iliac crest. Shorter fibers in this area prevent the sacroiliac joint from flaring posteriorly. Longer fibers connect the 3rd and 4th sacral segments to the PSIS. These fibers are blended with the fibers of the thoracolumbar fascia and the lateral sacrotuberous ligament.
- The interosseous portion is the primary structure in this ligament for providing stability to the sacroiliac joint. It lies deep to the posterior section and forms the largest syndesmosis in the body.
The sacrotuberous ligament is attached broadly to the lateral aspect of the sacrum from the PSIS to the coccyx. The fibers converge and extend posteriorly to the ischial tuberosity. Fibers of this ligament pass over the ischial tuberosity to become the origin tendon of the biceps femoris.
The sacrospinous ligament (small or anterior sacrosciatic ligament) is a thin, triangular ligament attached by its apex to the ischial spine and medially, by its broad base, to the lateral margins of the sacrum and coccyx, as it fuses with the sacrotuberous ligament. Its main function is to prevent posterior rotation of the ilium with relation to the sacrum. However, the laxity of this ligament, along with the sacrotuberous ligament, allows posterior rotation to occur.
The iliolumbar ligament primarily connects the ilium’s crest to the transverse of the 5th lumbar and often the transverse of the fourth lumbar. It is part of a large web of connective tissue at the base of the spine. It has two major bands. The posterior band stabilizes L5 to prevent anterior shearing across the sacrum as the spine’s weight presses it down and forward. The anterior band stabilizes L5 and, when attached, L4 from side bending. This ligament is unique to animals that support their weight on their caudal limbs. In humans, it develops from fibers of the quadratus lumborum in adolescent years until about the time the os coxa fuses between 18 and 25. Unfortunately, it often starts to degenerate at about the same time as the sacroiliac joint fuses in the 40s.
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Tony Preston has a practice in Atlanta, Georgia, where he sees clients. He has written and taught about anatomy, trigger points, and cranial therapies since the mid-90s.
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