Ligaments of Pelvis

Inherent stability of the pelvis is provided by ligaments. The 3 groups of ligaments are:

1. Sacrum to Pelvis:

Sacroiliac ligamentous complex: is divided into posterior (short and long) and anterior ligaments. Posterior ligaments provide most of the stability.

Sacrotuberous ligament: runs from the posterolateral aspect of the sacrum and the dorsal aspect of the posterior iliac spine to the ischial tuberosity.

Sacrospinous ligament: is triangular, running from the lateral margins of the sacrum and coccyx and inserting on the ischial spine.

2. Pubis to pubis: Symphyseal ligaments

3. Lumbar spine to pelvic ring: Provides additional stability

Iliolumbar ligaments: originate from the L4 and L5 transverse processes and insert on the posterior iliac crest.

Lumbosacral ligaments: originate from the transverse process of L5 to the ala of the sacrum.

Transversely placed ligaments: resist rotational forces

1. Anterior sacroiliac ligament
2. Short posterior sacroiliac ligament
3. Iliolumbar ligament
4. Sacrospinous ligament

Vertically placed ligaments: resist vertical shear forces

1. Long posterior sacroiliac ligament
2. Sacrotuberous ligament
3. Lateral lumbosacral ligament

Injured ligaments of the pelvis determine relative contributions to pelvic stability:

• Symphysis alone: pubic diastasis <2.5 cm
• Symphysis and sacrospinous ligaments: >2.5 cm of pubic diastasis (rotationally unstable)
• Symphysis, sacrospinous, sacrotuberous, and posterior sacroiliac: unstable vertically, posteriorly, and rotationally