Posterior sacroiliac ligament

The posterior (a.k.a. dorsal) sacroiliac ligament (TA: ligamentum sacroiliacum posterius) is a very strong ligament important in stabilising the sacroiliac joint.

Gross anatomy

Some texts state that the posterior sacroiliac ligaments have two components; a more superior part, the short posterior sacroiliac ligament, which runs in an approximate mediolateral orientation between the first and second transverse tubercles of the dorsal sacral surface and the iliac tuberosity. More inferiorly, is the long posterior sacroiliac ligament which runs in a roughly inferosuperior orientation from the third transverse tubercle to the posterior superior iliac spine (PSIS) ^1-3,5-8.

Fibres of the posterior sacroiliac ligament partially blend with fibres of the sacrotuberous ligament ^3,7.

Function

The posterior sacroiliac ligaments are very strong ligaments acting as key supports to the sacroiliac joints by holding the sacrum firmly in place between the two ilia.  The larger interosseous sacroiliac ligaments may be even more important in stabilising these articulations. The anterior sacroiliac ligaments are much less important in holding the SI joints together ⁵.

Radiographic features

Ultrasound

Sonographic descriptions of the posterior sacroiliac ligaments, both short and long components, have demonstrated that the ligament is well seen with high-resolution transducers  ^9,10.

CT

CT is an invaluable imaging modality for evaluating the SI joints but is unable to visualise the sacroiliac ligaments of this joint ⁵.

MRI

The normal and injured posterior sacroiliac ligaments have been described in detail on MRI, both in anatomical and clinical studies ^4,5.