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Posterior Sacroiliac Ligaments

ligamenta sacroiliaca posteriora

The posterior sacroiliac ligaments are the strongest ligaments in the human body by tensile strength, forming the posterior tension band of the pelvic ring and resisting sacral nutation under body weight loading. They fail completely in vertical shear pelvic injuries, producing the catastrophic posterior ring instability with hemipelvis displacement requiring urgent fixation.

Region: Pelvis & Hip

Anatomical Data

Origin, Insertion & Supply

Origin	Posterior iliac crest and PSIS
Insertion	Posterior sacrum at S1 through S4 level

Biomechanics

Function & Actions

Actions	Strongest pelvic ligaments — resist sacral nutation and superior-inferior displacement; provide the posterior pelvic tension band

Clinical Relevance

Clinical Notes

Posterior SI ligament disruption in vertical shear injuries produces superior hemipelvis displacement visible on AP pelvis radiograph. Posterior ring stabilisation using iliosacral screws percutaneously placed into the sacral ala is the current gold standard, supplemented by anterior ring fixation of the symphysis.

Pathology

Common Injuries & Conditions

Vertical Shear Pelvic Instability

Complete posterior SI ligament disruption producing superior hemipelvis displacement requiring urgent posterior iliosacral screw fixation.