Abstract
Background: Sacroiliitis, as the inflammation of sacroiliac joints (SIJ), is a central feature of axial spondyloarthritis. Nonetheless, its occurrence in women without inflammatory rheumatic disease, particularly in relation to cyclic hormonal fluctuations, remains poorly understood. Thus, this review evaluated data on the influence of relaxin, estradiol, and other sex steroids on SIJ biomechanics, extracellular matrix integrity, and bone marrow edema (BME). Accordingly, a hypothesis was proposed suggesting that the premenstrual hormonal milieu may induce transient sacroiliitis in a subset of women, especially those with hyperandrogenic conditions, including polycystic ovary syndrome or idiopathic hirsutism.
Methods: PubMed and related databases were searched to identify studies addressing SIJ MRI findings in women, hormonal regulation of pelvic ligaments, molecular pathways of connective-tissue remodeling, and endocrine abnormalities in hyperandrogenic states. Human, animal, biomechanical, and imaging studies were synthesized qualitatively.
Results: MRI investigations in pregnancy and postpartum demonstrated a high prevalence of SIJ BME, with 58–80% of women affected in early postpartum months. Although many cases met ASAS criteria for sacroiliitis, erosions were rare, and progression to structural damage was limited, indicating a non-inflammatory, hormonally driven mechanism. Relaxin and estradiol induced collagen breakdown, increased ligamentous laxity, and activated matrix metalloproteinases. Evidence from other joints revealed that cyclic relaxin peaks can produce micro-instability and chronic microtrauma.
Conclusion: It is hypothesized that the cyclical elevations of relaxin and estradiol, especially during the late luteal phase, may transiently remodel SIJ-associated connective tissues, provoking BME or subclinical sacroiliitis. Hyperandrogenic women may be particularly vulnerable due to altered sex hormone receptor profiles, increased inflammatory tone, and pelvic biomechanical variations. Prospective studies combining hormonal assays, serial MRI, and inflammatory biomarkers are essential to verify this proposed premenstrual, hormone-sensitive sacroiliitis phenotype.