* LPSL = long posterior sacroiliac ligament
In many patients with non-specific low back pain or peripartum pelvic pain, pain is experienced in the region in which the long dorsal sacroiliac ligament is located (3,1).
25 sides of the pelvis from 16 cadavers were studied by McGrath et al (2005) revealed that
1. LPSL is penetrated by the lateral branches of the dorsal sacral rami of predominantly S3 & and S2. Only in few cases LPSL is innervated by S4 and rarely by S1.
2. Some of the penetrating lateral branches give off nerve fibres that disappear within the LPSL ligament.
These findings provide an anatomical basis for the notion that the LPSL is a potential pain generator in the posterior sacroiliac region.
Same researcher McGrath et al in 2009 (2) reported few more interesting aspects of LPSL & it’s anatomical relationships
1. The LPSL was observed to have proximal and distal regions of osseous attachment.
2. Between these regions of attachment the middle LPSL was observed as a convergence of three layers: the erectores spinae aponeurosis, the 'deep fascial layer' and the gluteal aponeurosis.
3. Deep to the 'deep fascial layer' a layer of adipose and loose connective tissue was observed. Lateral branches of the dorsal sacral rami were identified within this layer.
This study further indicate that there is a morphological basis for the proposal that putative sacroiliac joint pain may be due to an entrapment neuropathy of the lateral branches of the dorsal sacral rami at the middle long posterior sacroiliac ligament.
Vleeming et al in 1996 reported LPSL has
1. Close anatomical relations with the erector spinae muscle, the posterior layer of the thoracolumbar fascia, and a specific part of the sacrotuberous ligament (tuberoiliac ligament).
2. Functionally, it is an important link between legs, spine, and arms.
3. The LPSL is tensed when the sacroiliac joints are counternutated and slackened when nutated (ventral rotation of the sacrum relative to the iliac bones). The reverse holds for the sacrotuberous ligament. Slackening of the long dorsal sacroiliac ligament can be counterbalanced by both the sacrotuberous ligament and the erector muscle.
Pain localized within the boundaries of the long ligament could indicate among other things a spinal condition with sustained counternutation of the sacroiliac joints. In diagnosing patients with non-specific low back pain or peripartum pelvic pain, the long dorsal sacroiliac ligament should not be neglected. Even in cases of arthrodesis of the sacroiliac joints, tension in the long ligament can still be altered by different structures.
1. McGrath MC et al; Surg Radiol Anat. 2005 Nov;27(4):327-30. Epub 2005 Nov 9.
2. McGrath C et al; Joint Bone Spine. 2009 Jan;76(1):57-62. Epub 2008 Sep 25.
3. Vleeming A et al; Spine (Phila Pa 1976). 1996 Mar 1;21(5):556-62.