• Christopher McGrath, Helen Nicholson, and Peter Hurst.
• Otago University Department of Anatomy and Structural Biology, Dunedin, New Zealand. christopher.mcgrath@anatomy.otago.ac.nz
• Joint Bone Spine. 2009 Jan 1; 76 (1): 57-62.

ObjectivesTo investigate the morphology of the long posterior sacroiliac ligament (LPSL) and its potential relationship to adjacent structures in the posterior sacroiliac region, and to consider any possible functional anatomical implications that may arise.MethodsFour large cadaveric tissue blocks of the posterior sacroiliac region were utilised in this qualitative histological study. The blocks underwent demineralisation in ethyl-diamine-tetra-acetic acid (EDTA). The end-point was determined radiographically. The demineralised tissue blocks were subsequently processed and a base sledge microtome used to section the blocks. Sequential sections were stained with Harris haematoxylin and alcoholic eosin (H&E) and mounted on glass slides prior to viewing under a light microscope.ResultsThe LPSL was observed to have proximal and distal regions of osseous attachment. Between these regions of attachment the middle LPSL was observed as a confluence of three layers: the erectores spinae aponeurosis, the 'deep fascial layer' and the gluteal aponeurosis. 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.ConclusionsThe middle long posterior ligament appears to provide a pathway for the lateral branches of the dorsal sacral rami between the posterior sacral region and the gluteal region. This histological study provides 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 long posterior sacroiliac ligament.

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