[Primary (idiopathic) shoulder stiffness : Definition, disease progression, epidemiology and etiology]

Shoulder stiffness is characterized by restriction of the active and passive movement of the glenohumeral joint. The stiffness is ultimately caused by fibrosis and the resulting contracture of the glenohumeral joint capsule and its ligaments; however, the term stiff shoulder is only a descriptive umbrella term that must be further defined as the course of the disease and the recommended treatment are decisively influenced by the cause of the shoulder stiffness. Primary shoulder stiffness, also known as idiopathic shoulder stiffness or "frozen shoulder", must be distinguished from various forms of secondary shoulder stiffness and often occurs in three stages, which can all last for several months to years: the initial "freezing phase", followed by a "frozen phase" and finally a "thawing phase". Although primary shoulder stiffness is a frequent pathological alteration with an prevalence of 2-5% in the general population, the exact etiology remains largely unknown; however, there is consensus throughout the literature that certain systemic pathologies, such as diabetes mellitus are associated with a higher incidence of primary shoulder stiffness.