Sydney Rucker, BS, Medical University of South Carolina College of Medicine, Charleston, SC.
Adrienne Kelly, MD, FRCSC, Orthopaedic Surgeon, Sault Area Hospital, Assistant Professor, Northern Ontario School of Medicine, Sault Ste Marie, ON.
David W. Polly, MD, Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, MN, USA.
Robert J. Ferdon, MS, Department of Orthopaedics and Physical Medicine, Medical University of South Carolina, Charleston, SC, University of South Carolina School of Medicine, Columbia, SC.
Robert A. Ravinsky, MDCM, MPH, FRCSC, Department of Orthopaedics and Physical Medicine, Medical University of South Carolina, Charleston, SC.

Abstract
Mechanical dysfunction of the sacroiliac joint (SIJ) is an often overlooked, but a common cause of low back pain in the North American adult population. The diagnosis is primarily clinical and requires the exclusion of other potential etiologies of low back pain (LBP). A number of non-surgical treatment options are available for patients with this pathological entity. In cases of persistent, severe SIJ pain refractory to non-operative measures, SIJ fusion may be considered as a surgical intervention.
Key Words: sacroiliitis, sacroiliac dysfunction, sacroiliac joint (SIJ), low back pain (LBP), gluteal pain, SI joint fusion, percutaneous SI joint fixation.

Introduction
Although the etiologies are diverse and heterogeneous, low back pain (LBP) remains a leading source of morbidity in North America and a major financial burden on the healthcare system.¹ A common cause of LBP is the sacroiliac joint (SIJ), increasingly recognized as a major source of LBP and disability.² SIJ pain can be severely debilitating, leading to substantial functional impairment and diminished quality of life. Studies show that patients with SIJ dysfunction have a quality of life equivalent to those with advanced hip and knee arthritis and worse than those with chronic obstructive pulmonary disease or mild heart failure.²

The notion that the SIJ is a common pain generator is not new but the joint’s relevance as a target of both conservative and surgical treatments has waxed and waned over the last several decades. Nevertheless, a growing body of literature has resulted in improved knowledge of the anatomy, physiology, mechanics and pathology of this previously nebulous part of the musculoskeletal system. Improved understanding of SIJ anatomy and biomechanics has allowed for the development of evidence-based treatment pathways and effective treatment modalities for this condition.

In this review article we aim to provide clear guidance for appropriate identification, clinical and radiographic evaluation of mechanical SIJ dysfunction and provide a framework for treatment of this pathological entity in the primary care setting.

Epidemiology
SIJ dysfunction is a known contributor to LBP, accounting for approximately 15-30% of LBP cases in the outpatient setting.^3-7 Several primary risk factors for mechanical SIJ dysfunction have been identified: 1) multigravida females with a prior history of vaginal birth (likely due in part to the increased levels of estrogen or relaxin during the third trimester of pregnancy resulting in increased ligamentous laxity and trauma to the pelvic floor and SIJ ligaments during childbirth.8-9), 2) a prior history of high-energy pelvic trauma or iliac crest bone grafting, because of the extent of the associated soft tissue injury which can result in pathological motion at this joint.10), 3) a prior history of lumbosacral fusion, particularly multilevel lumbar fusion is a known risk factor for development of secondary mechanical SIJ dysfunction; the causal mechanism is analogous to that of adjacent segment disease, as several previously mobile segments in the lumbar spine and lumbosacral junction are immobilized, stress transferred to the SIJ substantially increases and results in subsequent degeneration. SIJ pain as a secondary source of discomfort following lumbar fusion is exceedingly common, with studies indicating between 34-43% of patients develop SIJ-related pain postoperatively.^11-14 Apart from these risk factors, many cases are idiopathic (see Table 1).