Frozen Shoulder as a Systemic Immunometabolic Disorder: The Roles of Estrogen, Thyroid Dysfunction, Endothelial Health, Lifestyle, and Clinical Implications

Frozen shoulder (FS), traditionally regarded as an idiopathic musculoskeletal disorder characterized by pain, stiffness, and capsular fibrosis, is increasingly recognized as the clinical manifestation of systemic endocrine, metabolic, vascular, and immunological dysfunctions. This narrative review reframes FS within a broader neuro–endocrine–immunometabolic model, emphasizing the central role of estrogen deficiency, resistance, and receptor-level disruption, together with their interactions with thyroid dysfunction, endothelial health, and lifestyle-related low-grade inflammation (LGI). Evidence from epidemiological, clinical, and mechanistic studies shows that estrogen signaling failure weakens anti-inflammatory, antifibrotic, and antioxidant defenses, predisposing peri- and postmenopausal women to more severe FS phenotypes. Thyroid dysfunction, particularly hypothyroidism, further contributes to fibrosis and pain sensitization. Endothelial dysfunction—driven by poor diet, advanced glycation end-products (AGEs), and oxidative stress—impairs vascular integrity and promotes local microvascular inflammation. In parallel, lifestyle factors such as sedentarism, circadian misalignment, psychosocial stress, and environmental exposures sustain systemic LGI and hormonal resistance. Together, these interconnected mechanisms suggest that FS is not merely a localized joint pathology but a systemic disorder requiring integrative clinical strategies that combine orthopedic management with endocrine evaluation, metabolic monitoring, dietary interventions, circadian health, and stress regulation. In addition, this review outlines specific clinical implications, highlighting how an integrative, personalized approach that targets hormonal, metabolic, vascular, and lifestyle dimensions may improve pain, function, and long-term prognosis in FS. This paradigm shift underscores the need for future research to focus on stratified patient profiling and interventional trials targeting hormonal, vascular, and lifestyle axes to improve outcomes, particularly in women who remain disproportionately affected by FS.