Sacroiliac Joint Ligaments and Sacroiliac Pain: A Case–Control Study on Micro- and Ultrastructural Findings on Morphologic Alterations

Background: The sacroiliac joint (SIJ) is a common source of low back pain. SIJ pain has shown to have negative impact on patients’ quality of life. Although clinically there is an increasing interest to treat SIJ-related pain both conservatively and surgically, the underlying mechanisms related to pathology in that region are poorly understood. One hypothesis is that the SIJ ligaments are structurally altered in SIJ pain. Objectives: The given study investigated patient cases with different pain durations undergoing posterior distraction arthrodesis of the SIJ, with subsequent micro- and ultrastructural assessment of the interosseous and posterior SIJ ligaments compared with autopsy controls without known history of low back pain. Study Design: Case–control study. Morphologic-pathological analysis of tissue samples obtained during surgery with controls from legal medicine. Setting: Rural hospital setting in Halberstadt, Germany. Methods: SIJ ligaments were removed from 6 patients undergoing SIJ arthrodesis for histological and ultrastructural assessment in scanning and transmission electron microscopy, and compared with 6 controls without known history of SIJ pathology. Results: A number of alterations were observed in the ligaments of patients with SIJ, namely ligament disruption, collagen loosening and coiling, vascularization, and hemorrhage. In some areas, these changes were observed in proximity to healthy (structurally unaltered and intact tissues), indicative of a potential disease progression. Comparison to controls yielded a significant correlation between SIJ pathology and the level of collagen degeneration (φ ≥ 0.82; P < 0.001). Limitations: Small sample size, method of tissue removal from patients may have influenced tissue integrity. Conclusions: The combined clinical, histological, and ultrastructural analysis provided, to our knowledge, first-time evidence of morphologic SIJ ligament alteration of a nontraumatic and noninflammatory cause. Further research is necessary to elucidate these structural changes and to substantiate pain duration and patient-history-dependent changes at the ligaments of the posterior pelvis