A Systematic Review of the Normal Sacroiliac Joint Anatomy and Adjacent Tissues for Pain Physicians

Background: The sacroiliac joint (SIJ) forms a complex joint and has shown to be underappreciatedin its involvement with lower back pain. Research efforts have intensified on SIJ anatomy andbiomechanics because of its predisposing position to pain and dysfunction in individuals sufferingfrom lower back discomfort. Previous work has focused on SIJ anatomy including bone and jointstructure, innervation, as well as biomechanics and the treatment of SIJ pain. However, to date, noreview exists describing the range of ‘normal’ anatomic features of the SIJ.Objectives: To describe the normal appearance of the SIJ and adjacent tissues, as opposed to‘abnormal’ conditions involving SIJ morphology. It will also identify key areas that require further studybecause of lacking information or disagreement.Study Design: A systematic literature review.Setting: The research took place at the University of Otago, New Zealand. All published research on‘normal SIJ anatomy’ available from MEDLINE, OVID, Scopus, Web of Science, PubMed, and ScienceDirect were included, available until December 2018, in English, French, and German. Subject areasincluded bony landmarks, joint type, bone morphology, ligamentous attachments, muscular andfascial relationships, blood supply, fatty infiltration, and morphologic variation.Methods: Articles met the selection criteria if they contained specific information on SIJ anatomy,including bone morphology and architecture, ligaments, muscle attachments, innervation, vasculature,and the presence of fat. Biomechanics and kinematics related keywords were used as the literature oftencouples these with the anatomy. Keywords of individual articles were named as ‘structures of interest.’Results: A total of 88 primary and 101 secondary articles were identified in the time frame from1851 to 2018. Primary articles provided quantitative data and detailed anatomic descriptions.Secondary articles did not focus specifically on the anatomy of the SIJ. Although research appearedto be in general agreement on bony landmarks, joint type, myofascial attachments, vasculature,and innervation of the SIJ, there was only part consensus on ligament attachments and cartilagestructure. Information regarding bone density of the articulating surfaces of the SIJ is lacking. Despiteits potential clinical significance, fatty infiltration within the joint lacks research to date.Limitations: Only the given databases were used for the initial search. Keyword combinations usedfor this review may not have been inclusive of all articles relevant to the SIJ. Work in languages otherthan the ones listed or work that is not available via the internet may be missing.Conclusions: This study provides an overview of normal SIJ structures, including allneuromusculoskeletal elements related to the joint. There is a lack of knowledge on the SIJ ligamentswarranting further investigation. Furthermore, there are discrepancies in relation to the nomenclature,layers, attachment sites, and on the topographical relationships between ligamentous tissues andnerves. Subsequent studies on the quantification of fat and bone density in the SIJ have beensuggested. These could be useful radiologic parameters to assess the condition of the joint clinically.This review may provide insight into the clinical signs and abnormal biomechanical features of thejoint for the purposes of treating SIJ pain.Key words: Bone density, bony landmarks, fat infiltration, innervation, ligaments morphology,muscles, sacroiliac joint, vasculature