Frozen shoulder is a painful and disabling condition affecting the ligaments that form the shoulder joint capsule. Patients experience severe stiffening of their affected shoulder which can last for several years, interfering with activities of daily life. Frozen shoulder is a unique musculoskeletal disease as it unusually resolves spontaneously over time. This distinguishes the condition from most fibrotic (scarring) diseases that are progressive and irreversible, for example knee arthrofibrosis affecting the ligaments comprising the knee capsule after joint replacement.
Writing in Nature Communications, senior author Professor Stephanie Dakin, Versus Arthritis Career Development Fellow, and the team at Nuffield Departments of Orthopaedics, Rheumatology and Musculoskeletal Sciences (NDORMS) studied tissues collected from frozen shoulder patients undergoing surgery to improve their shoulder mobility. Stephanie explained: ‘We purposefully studied tissues from patients with advanced-stage frozen shoulder to understand how the condition ultimately resolves. Using cutting-edge technologies, we identified that the shoulder capsule is predominantly comprised of fibroblasts (the major cell types that form ligaments) and macrophages, a type of immune cell. We discovered that distinct populations of macrophages in the shoulder capsule are enriched to resolve inflammation. We performed experiments using patient-derived cells, revealing that crosstalk between these resolving macrophages and fibroblasts reduced inflammation and promoted tissue remodelling, providing us with cellular evidence of how frozen shoulder resolves.’